Antibacterial drugs are derived from bacteria or molds or are synthesized de novo. Technically, “antibiotic” refers only to antimicrobials derived from bacteria or molds but is often (including in The Manual) used synonymously with “antibacterial drug.”

Antibiotics have many mechanisms of action, including inhibiting cell wall synthesis, activating enzymes that destroy the cell wall, increasing cell membrane permeability, and interfering with protein synthesis and nucleic acid metabolism.

Antibiotics sometimes interact with other drugs, raising or lowering serum levels of other drugs by increasing or decreasing their metabolism or by various other mechanisms (see Table 2: Bacteria and Antibacterial Drugs: Common Effects of Antibiotics on Other Drugs). The most clinically important interactions involve drugs with a low therapeutic ratio (ie, toxic levels are close to therapeutic levels). Also, other drugs can increase or decrease levels of antibiotics.

Many antibiotics are chemically related and are thus grouped into classes. Although drugs within each class share structural and functional similarities, they often have different pharmacology and spectra of activity.

Table 2
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Common Effects of Antibiotics on Other Drugs Drug Toxicity Enhanced By No Change With DigoxinSome Trade Names DIGITEK LANOXIN Click for Drug Monograph AzithromycinSome Trade Names ZITHROMAX Click for Drug Monograph ClarithromycinSome Trade Names BIAXIN Click for Drug Monograph DoxycyclineSome Trade Names PERIOSTAT VIBRAMYCIN Click for Drug Monograph ErythromycinSome Trade Names ERY-TAB ERYTHROCIN Click for Drug Monograph TetracyclineSome Trade Names ACHROMYCIN V TETRACYN TETREX Click for Drug Monograph TrimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph Aminoglycosides Cephalosporins ClindamycinSome Trade Names CLEOCIN Click for Drug Monograph Fluoroquinolones KetoconazoleSome Trade Names NIZORAL Click for Drug Monograph LinezolidSome Trade Names ZYVOX Click for Drug Monograph MetronidazoleSome Trade Names FLAGYL Click for Drug Monograph Penicillins Quinulpristine/dalfopristin Sulfonamides VancomycinSome Trade Names VANCOCIN Click for Drug Monograph PhenytoinSome Trade Names DILANTIN Click for Drug Monograph ChloramphenicolSome Trade Names CHLOROMYCETIN Click for Drug Monograph CiprofloxacinSome Trade Names CILOXAN CIPRO Click for Drug Monograph IsoniazidSome Trade Names INH NYDRAZID Click for Drug Monograph Macrolides (erythromycinSome Trade Names ERY-TAB ERYTHROCIN Click for Drug Monograph , clarithromycinSome Trade Names BIAXIN Click for Drug Monograph , dirithromycinSome Trade Names DYNABAC ) RifampinSome Trade Names RIFADIN RIMACTANE Click for Drug Monograph (decreased phenytoinSome Trade Names DILANTIN Click for Drug Monograph levels) Sulfonamides AzithromycinSome Trade Names ZITHROMAX Click for Drug Monograph Aminoglycosides Cephalosporins ClindamycinSome Trade Names CLEOCIN Click for Drug Monograph DoxycyclineSome Trade Names PERIOSTAT VIBRAMYCIN Click for Drug Monograph LinezolidSome Trade Names ZYVOX Click for Drug Monograph MetronidazoleSome Trade Names FLAGYL Click for Drug Monograph Penicillins Other fluoroquinolones Quinulpristine/dalfopristin TetracyclineSome Trade Names ACHROMYCIN V TETRACYN TETREX Click for Drug Monograph TrimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph VancomycinSome Trade Names VANCOCIN Click for Drug Monograph TheophyllineSome Trade Names ELIXOPHYLLIN THEO-DUR Click for Drug Monograph ClarithromycinSome Trade Names BIAXIN Click for Drug Monograph ErythromycinSome Trade Names ERY-TAB ERYTHROCIN Click for Drug Monograph Fluoroquinolones (ciprofloxacinSome Trade Names CILOXAN CIPRO Click for Drug Monograph ) RifampinSome Trade Names RIFADIN RIMACTANE Click for Drug Monograph (decreased theophyllineSome Trade Names ELIXOPHYLLIN THEO-DUR Click for Drug Monograph levels) Aminoglycosides AzithromycinSome Trade Names ZITHROMAX Click for Drug Monograph Cephalosporins ClindamycinSome Trade Names CLEOCIN Click for Drug Monograph DoxycyclineSome Trade Names PERIOSTAT VIBRAMYCIN Click for Drug Monograph LinezolidSome Trade Names ZYVOX Click for Drug Monograph MetronidazoleSome Trade Names FLAGYL Click for Drug Monograph Penicillins Quinulpristine/dalfopristin Sulfonamides TetracyclineSome Trade Names ACHROMYCIN V TETRACYN TETREX Click for Drug Monograph TrimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph VancomycinSome Trade Names VANCOCIN Click for Drug Monograph WarfarinSome Trade Names COUMADIN Click for Drug Monograph * Cefoperazone† CefotetanSome Trade Names CEFOTAN Click for Drug Monograph † ChloramphenicolSome Trade Names CHLOROMYCETIN Click for Drug Monograph ClarithromycinSome Trade Names BIAXIN Click for Drug Monograph DirithromycinSome Trade Names DYNABAC DoxycyclineSome Trade Names PERIOSTAT VIBRAMYCIN Click for Drug Monograph ErythromycinSome Trade Names ERY-TAB ERYTHROCIN Click for Drug Monograph Fluoroquinolones (ciprofloxacinSome Trade Names CILOXAN CIPRO Click for Drug Monograph , levofloxacinSome Trade Names IQUIX LEVAQUIN QUIXIN Click for Drug Monograph , ofloxacinSome Trade Names FLOXIN Click for Drug Monograph ) MetronidazoleSome Trade Names FLAGYL Click for Drug Monograph RifampinSome Trade Names RIFADIN RIMACTANE Click for Drug Monograph (decreased PT) Sulfonamides Aminoglycosides (IV) AzithromycinSome Trade Names ZITHROMAX Click for Drug Monograph Cephalosporins (some) ClindamycinSome Trade Names CLEOCIN Click for Drug Monograph DoxycyclineSome Trade Names PERIOSTAT VIBRAMYCIN Click for Drug Monograph LinezolidSome Trade Names ZYVOX Click for Drug Monograph Penicillins Quinulpristine/dalfopristin TetracyclineSome Trade Names ACHROMYCIN V TETRACYN TETREX Click for Drug Monograph TrimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph VancomycinSome Trade Names VANCOCIN Click for Drug Monograph *see Table 4: Pulmonary Embolism: Drug, Herbal Preparation, and Food Interactions With Warfarin. †These drugs interfere with vitamin K–dependent clotting factors and, when used with antiplatelet drugs and thrombolytics, may increase risk of bleeding.

Selection and Use of Antibiotics

Antibiotics should be used only if clinical or laboratory evidence suggests bacterial infection. Use for viral illness or undifferentiated fever is inappropriate, subjects patients to drug complications without any benefit, and contributes to bacterial resistance. Certain bacterial infections (eg, abscesses, infections with foreign bodies) require surgical intervention and do not respond to antibiotics alone.

Spectrum of activity: Cultures and antibiotic sensitivity testing are essential for selecting a drug for serious infections. However, treatment must often begin before culture results are available, necessitating selection according to the most likely pathogens (empiric antibiotic selection). Whether chosen according to culture results or not, drugs with the narrowest spectrum of activity that can control the infection should be used. For empiric treatment of serious infections that may involve any one of several pathogens (eg, fever in neutropenic patients) or that may be due to multiple pathogens (eg, polymicrobial anaerobic infection), a broad spectrum of activity is desirable. The most likely pathogens and their susceptibility to antibiotics vary according to geographic location (within cities or even within a hospital) and can change from month to month.

For serious infections, combinations of antibiotics are often necessary because multiple species of bacteria may be present or because combinations act synergistically against a single species of bacteria. Synergism is usually defined as a more rapid and complete bactericidal action from a combination of antibiotics than occurs with either antibiotic alone. A common example is a cell wall–active antibiotic (eg, a β-lactam, vancomycinSome Trade Names
VANCOCIN
Click for Drug Monograph
) plus an aminoglycoside.

Effectiveness: In vivo antibiotic effectiveness involves many factors, including

• Pharmacology (eg, absorption, distribution, concentration in fluids and tissues, protein binding, rate of metabolism or excretion)
• Pharmacodynamics (ie, the time course of antibacterial effects exerted by drug levels in blood and at the site of infection)
• Drug interactions or inhibiting substances
• Host defense mechanisms
• In vitro killing power but usually only if the site of infection (eg, in meningitis or endocarditis) is resistant to treatment or if systemic host defenses are weak (eg, in neutropenic or other immunocompromised patients)

Bactericidal drugs kill bacteria in vitro. Bacteriostatic drugs slow or stop in vitro bacterial growth. These definitions are not absolute; bacteriostatic drugs may kill some bacteria, and bactericidal drugs may not kill all of the bacteria in vitro. More precise quantitative methods identify the minimum in vitro concentration at which an antibiotic can inhibit growth (minimum inhibitory concentration, or MIC) or kill (minimum bactericidal concentration, or MBC).

The predominant determinant of bacteriologic response to antibiotics is the time that blood levels of the antibiotic exceed the MIC (time-dependence) or the peak blood level relative to MIC (concentration-dependence).

β-Lactams and vancomycinSome Trade Names
VANCOCIN
Click for Drug Monograph
exhibit time-dependent bactericidal activity. Increasing their concentration above the MIC does not increase their bactericidal activity, and their in vivo killing is generally slow. In addition, because there is no or very brief residual inhibition of bacterial growth after concentrations fall below the MIC (postantibiotic effect, or PAE), β-lactams and vancomycinSome Trade Names
VANCOCIN
Click for Drug Monograph
are most often effective when serum levels of free drug (drug not bound to serum protein) exceed the MIC for ≥ 50% of the time. Because ceftriaxoneSome Trade Names
ROCEPHIN
Click for Drug Monograph
has a long serum half-life, free serum levels exceed the MIC of very susceptible pathogens for the entire 24-h dosing interval. However, for β-lactams that have serum half-lives of ≤ 2 h, frequent dosing or continuous infusion is required. For vancomycinSome Trade Names
VANCOCIN
Click for Drug Monograph
, trough levels should be maintained at least at 10 to 15 μg/mL.

Aminoglycosides, fluoroquinolones, and daptomycinSome Trade Names
CUBICIN
Click for Drug Monograph
exhibit concentration-dependent bactericidal activity. Increasing their concentrations from levels slightly above the MIC to levels far above the MIC increases their rate of bactericidal activity and decreases the bacterial load. In addition, if concentrations exceed the MIC even briefly, aminoglycosides and fluoroquinolones have a PAE on residual bacteria; duration of PAE is also concentration-dependent. If PAEs are long, drug levels can be below the MIC for extended periods without loss of efficacy, allowing less frequent dosing. Consequently, aminoglycosides and fluoroquinolones are usually most effective as intermittent boluses that reach peak free serum levels ≥ 10 times the MIC of the bacteria.

Route: For many antibiotics, oral administration results in therapeutic blood levels nearly as rapidly as IV administration. However, IV administration is preferred in the following circumstances:

• Oral antibiotics cannot be tolerated (eg, because of vomiting).
• Oral antibiotics cannot be absorbed (eg, because of malabsorption after intestinal surgery).
• Intestinal motility is impaired (eg, because of opioid use).
• No oral formulation is available (eg, for aminoglycosides).
• Patients are critically ill, possibly impairing GI tract perfusion or making even the brief delay with oral administration detrimental.

Special populations: Doses and scheduling of antibiotics may need to be adjusted for the following:

• Infants
• The elderly
• Patients with renal failure (see Table 3: Bacteria and Antibacterial Drugs: Usual Doses of Commonly Prescribed Antibiotics)
• Patients with hepatic insufficiency (most commonly for cefoperazone, ceftriaxoneSome Trade Names
  ROCEPHIN
  Click for Drug Monograph
  , chloramphenicolSome Trade Names
  CHLOROMYCETIN
  Click for Drug Monograph
  , clindamycinSome Trade Names
  CLEOCIN
  Click for Drug Monograph
  , metronidazoleSome Trade Names
  FLAGYL
  Click for Drug Monograph
  , nafcillinSome Trade Names
  UNIPEN
  Click for Drug Monograph
  , rifabutinSome Trade Names
  MYCOBUTIN
  Click for Drug Monograph
  , and rifampinSome Trade Names
  RIFADIN
  RIMACTANE
  Click for Drug Monograph
  )

Pregnancy and breastfeeding affect choice of antibiotic. Penicillins, cephalosporins, and erythromycinSome Trade Names
ERY-TAB
ERYTHROCIN
Click for Drug Monograph
are among the safest antibiotics during pregnancy; tetracyclines are contraindicated. Most antibiotics reach sufficient concentrations in breast milk to affect a breastfed baby, sometimes contraindicating their use in women who are breastfeeding.

Table 3
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Usual Doses of Commonly Prescribed Antibiotics Drug Adult Dose Pediatric (Age > 1 mo) Dose Dose in Renal Failurea (CrCl < 10 mL/min) Oral Parenteral Serious Infections Oral Parenteral Aminoglycosides Amikacin N/A 15 mg/kg IV once/day or 7.5 mg/kg q 12 h 15 mg/kg IV once/day or 7.5 mg/kg IV q 12 h N/A 5–7.5 mg/kg IV q 12 h 1.5–2.5 mg/kg IV q 24–48 h Gentamicin N/A 5–7 mg/kg IV once/day or 1.7 mg/kg IV q 8 h 5–7 mg/kg IV once/day N/A 1–2.5 mg/kg IV q 8 h 0.34–0.51 mg/kg IV q 24–48 h For synergy with a cell wall–active antibiotic to treat enterococcal endocarditis caused by strains susceptible to gentamicinSome Trade Names GARAMYCIN Click for Drug Monograph N/A 1 mg/kg IV q 8 h N/A N/A 1 mg/kg IV q 8 h Infectious disease consultation required for dosage Dosage adjusted to achieve peak serum concentration of 3–4 μg/mL and trough concentration of < 1 μg/mL For streptococcal or Staphylococcus aureus endocarditis — 1 mg/kg IV q 8 h or 3 mg/kg IV once/day N/A N/A 1 mg/kg IV q 8 h or 3 mg/kg IV once/day N/A Neomycin For preoperative gut antisepsis (with erythromycinSome Trade Names ERY-TAB ERYTHROCIN Click for Drug Monograph and mechanical cleansing) 1 g for 3 doses (eg, at 1, 2, and 11 pm on the day before surgery) N/A N/A 15 mg/kg q 4 h for 2 days or 25 mg/kg at 1, 2, and 11 pm on the day before surgery N/A N/A For hepatic coma 1–3 g qid N/A N/A 0.6–1.75 g/m2 q 6 h or 0.4–1.2 g/m2 q 4 h N/A N/A Streptomycin For TB N/A 15 mg/kg IM q 24 h (maximum: 1.0 g/day) initially, then 1.0 g 2–3 times/wk N/A N/A 20–40 mg/kg IM once/day 7.5 mg/kg IM q 72–96 h (maximum: 1 g) For synergy with a cell wall–active antibiotic to treat enterococcal endocarditis N/A 7.5 mg/kg IM q 12 h N/A N/A N/A N/A Tobramycin N/A 5–7 mg/kg IVonce/day or 1.7 mg/kg IV q 8 h 5–7 mg/kg IV once/day or 1.7 mg/kg IV q 8 h N/A 1–2.5 mg/kg IV q 8 h 0.34–0.51 mg/kg IV q 24–48 h β-Lactams: Cephalosporins (1st generation) Cefadroxil 0.5–1 g q 12 h N/A N/A 15 mg/kg q 12 h N/A 0.5 g po q 36 h Cefazolin N/A 1–2 g IV q 8 h 2 g IV q 8 h N/A 16.6–33.3 mg/kg IV q 8 h 1–2 g IV q 24–48 h Cephalexin 0.25–0.5 g q 6 h N/A N/A 6.25–12.5 mg/kg q 6 h or 8.0–16 mg/kg q 8 h N/A 0.25–0.5 g po q 24–48 h β-Lactams: Cephalosporins (2nd generation) Cefaclor b 0.25–0.5 g q 8 h N/A N/A 10–20 mg/kg q 12 h or 6.6–13.3 mg/kg q 8 h N/A 0.5 g po q 12 h Cefotetan N/A 1–3 g IV q 12 h 2–3 g IV q 12 h N/A 20–40 mg/kg IV q 12 h 1–3 g IV q 48 h Cefoxitin N/A 1 g IV q 8 h to 2 g IV q 4 h 2 g IV q 4 h or 3 g IV q 6 h N/A 27–33 mg/kg IV q 8 h or, for severe infections, 25–40 mg/kg q 6 h 0.5–1.0 g IV q 24–48 h Cefprozil 0.25 g q 12 h or 0.5 g q 12–24 h N/A N/A 15 mg/kg q 12 h for otitis media N/A 0.25 g po q 12–24 h Cefuroxime 0.125–0.5 g q 12 h 0.75–1.5 g IV q 6–8 h 1.5 g IV q 6 h 10–15 mg/kg suspension q 12 h For older children: 125–250 mg tablets q 12 h 25–50 mg/kg IV q 8 h 0.25–0.5 g po q 24 h or 0.75 g IV q 24 h For meningitis — — 3 g IV q 8 h — 50–60 mg/kg IV q 6 h — β-Lactams: Cephalosporins (3rd generation) Cefoperazone N/A 1 g q 12 h to 2 g IV q 4 h 2 g IV q 4 h N/A 25–100 mg/kg IV q 12 h Same as adult dose Cefotaxime N/A 1 g q 12 h to 2 g IV q 4 h 2 g IV q 4 h N/A 8.3–33.3 mg/kg IV q 4 h or 16.6–66.6 mg/kg q 6 h 1–2 g IV q 24 h Cefpodoxime c 0.1–0.4 g q 12 h N/A N/A 5 mg/kg q 12 h N/A 0.1–0.4 g po q 24 h Ceftazidime N/A 1 g IV q 12 h to 2 g q 8 h 2 g IV q 8 h N/A 25–50 mg/kg IV q 8 h 0.5 g IV q 24–48 h Ceftibuten b 0.4 g q 24 h N/A N/A 9 mg/kg once/day N/A 0.1 g po q 24 h Ceftizoxime N/A 0.5 g IV q 12 h to 4 g IV q 8 h 4 g IV q 8 h N/A 50 mg/kg IV q 6–8 h 0.5 g IV q 24 h to 0.5–1 g IV q 48 h Ceftriaxone N/A 1–2 g IV q 24 h 2 g IV q 24 h N/A 50–75 mg/kg IV q 24 h or 25–37.5 mg/kg q 12 h Same as adult dose For meningitis N/A 2 g IV q 12 h 2 g IV q 12 h N/A 50 mg/kg IV q 12 h or 100 mg/kg q 24 h (not to exceed 4 g/day) Possibly a loading dose of 100 mg/kg IV (not to exceed 4 g) at the start of therapy 2 g IV q 12 h β-Lactams: Cephalosporin (4th generation) Cefepime N/A 1–2 g IV q 8–12 h 2 g IV q 8 h N/A 50 mg/kg IV q 8–12 h 0.25–1 g IV q 24 h β-Lactams: Penicillins Amoxicillin 0.25–0.5 g q 8 h or 0.875 g q 12 h N/A N/A 12.5–25 mg/kg q 12 h or 7–13 mg/kg q 8 h N/A 0.25–0.5 g po q 24 h For endocarditis prophylaxis 2 g for 1 dose N/A N/A 50 mg/kg 1 h before procedure N/A 2 g po for 1 dose Amoxicillin/clavulanate 0.25–0.5 g q 8 h or 0.875 g q 12 h N/A N/A If > 40 kg: Adult dose N/A 0.25–0.5 g po q 24 h Amoxicillin/clavulanate, ES-600 N/A N/A N/A 45 mg/kg q 12 h N/A N/A Amoxicillin/clavulanate, extended-release 2 g q 12 h N/A N/A N/A N/A N/A Ampicillin N/A 0.5–2.0 g IV q 4–6 h 2 g IV q 4 h N/A 25–50 mg/kg IV q 6 h 0.5–2.0 g IV q 12–24 h For meningitis N/A 2 g IV q 4 h 2 g IV q 4 h N/A 50–100 mg/kg IV q 6 h 2 g IV q 12 h Ampicillin/sulbactam (3 g = 2 g ampicillinSome Trade Names OMNIPEN PRINCIPEN Click for Drug Monograph + 1 g sulbactam) N/A 1.5–3.0 g IV q 6 h 3 g IV q 6 h N/A 25–50 mg/kg IV q 6 h 1.5–3.0 g IV q 24 h Dicloxacillin b 0.125–0.5 g q 6 h N/A N/A 3.125–6.25 mg/kg q 6 h N/A 0.125–0.5 g po q 6 h Nafcillin Rarely used 1–2 g IV q 4 h 2 g IV q 4 h N/A 12.5–25 mg/kg IV q 6 h or 8.3–33.3 mg/kg q 4 h 1–2 g IV q 4 h Oxacillin Rarely used 1–2 g IV q 4 h 2 g IV q 4 h N/A 12.5–25 mg/kg IV q 6 h or 8.3–33.3 mg/kg IV q 4 h 1–2 g IV q 4 h Penicillin G b 0.25–0.5 g q 6–12 h (penicillin V) 1–4 million units IV q 4–6 h 4 million units IV q 4 h Penicillin VK 6.25–12.5 mg/kg q 8 h 6,250–100,000 units/kg IV q 6 h or 4,166.6–66,666 units/kg IV q 4 h 0.5–2 million units IV q 4–6 h (maximum total daily dose: 6 million units/day) Penicillin G benzathine (Bicillin© L-A) For streptococcal pharyngitis N/A 1.2 million units IM for 1 dose N/A N/A 25,000–50,000 units/kg IM as a single dose or If < 27 kg: 300,000–600,000 units as a single dose or If ≥ 27 kg: 0.9 million units as a single dose 1.2 million units IM for 1 dose Prophylaxis for rheumatic fever N/A 1.2 million units IM q 3–4 wk N/A N/A 25,000–50,000 units/kg IM q 3–4 wk 1.2 million units IM q 3–4 wk For early syphilis N/A 2.4 million units IM for 1 dose N/A N/A 50,000 units/kg IM for 1 dose 2.4 million units IM for 1 dose For late syphilis (excluding neurosyphilis) N/A 2.4 million units IM/wk for 3 wk N/A N/A 50,000 units/kg IM in 3 doses 1 wk apart 2.4 million units IM for 1 dose Penicillin G procaine (IM only) N/A 0.3–0.6 million units IM q 12 h N/A N/A 25,000–50,000 units/kg IM q 24 h or 12,500–25,000 units/kg IM q 12 h 0.3 to 0.6 million units IM q 12 h Piperacillin (1.9 mEq Na/g) N/A 3 g IV q 4–6 h 3 g IV q 4 h N/A 50–75 mg/kg IV q 6 h or 33.3–50 mg/kg IV q 4 h 3–4 g IV q 12 h Piperacillin/tazobactam (2.25 g = 2.0 g piperacillinSome Trade Names PIPRACIL Click for Drug Monograph + 0.25 g tazobactam) N/A 3.375 g IV q 4–6 h 3.375 g IV q 4 h N/A 80 mg/kg IV q 8 h 2.25 g IV q 8 h to 4.5 g IV q 12 h Ticarcillin (5.2 mEq Na/g) N/A 3 g IV q 4–6 h 3 g IV q 4 h N/A If < 60 kg: 50 mg/kg IV q 4–6 h 1–2 g IV q 12 h Ticarcillin/clavulanate (3.1 g = 3 g ticarcillinSome Trade Names TICAR + 0.1 g clavulanic acid) N/A 3.1 g IV q 4–6 h 3.1 g IV q 4 h N/A If < 60 kg: 50 mg/kg IV (based on ticarcillinSome Trade Names TICAR component) q 4–6 h 2 g IV q 12 h Other β-lactams Aztreonam N/A 1–2 g IV q 6–12 h 2 g IV q 6 h N/A 30–40 mg/kg IV q 6–8 h 0.5 g IV q 8 h Ertapenem N/A 1 g IV q 24 h 1 g IV q 24 h N/A N/A 0.5 g IV q 24 h Imipenem N/A 0.5–1.0 g IV q 6 h 1 g IV q 6 h N/A For infants 4 wk to 3 mo: 25 mg/kg IV q 6 h For children > 3 mo: 15–25 mg/kg IV q 6 h 0.125–0.25 g IV q 12 h (may increase risk of seizures) Meropenem N/A 1.0 g IV q 8 h 1.0 g IV q 8 h N/A 20–40 mg/kg IV q 8 h 0.5 g IV q 24 h For meningitis — 40 mg/kg IV q 8 h 40 mg/kg IV q 8 h N/A — 20 mg/kg IV q 24 h Fluoroquinolonesd Ciprofloxacin 0.5–0.75 g q 12 h 0.2–0.4 g IV q 8–12 h 0.4 g IV q 8 h 10–15 mg/kg IV q 12 h (in select circumstances) 10–15 mg/kg IV q 12 h (in select circumstances) 0.5–0.75 g po q 24 h or 0.2–0.4 g IV q 24 h Extended-release for uncomplicated cystitis 0.5 g q 24 h for 3 days N/A N/A N/A N/A N/A Gemifloxacin 320 mg q 24 h N/A N/A N/A N/A 160 mg po q 24 h Levofloxacin 0.25–0.75 g q 24 h 0.25–0.75 IV g q 24 h 0.75 g IV q 24 h N/A N/A 0.25–0.5 g po or IV q 48 h Moxifloxacin 0.4 g q 24 h 0.4 g IV q 24 h 0.4 g IV q 24 h N/A N/A 0.4 g q 24 h po or IV Norfloxacin b 0.4 g q 12 h N/A N/A N/A N/A 0.4 g po q 24 h Ofloxacin 0.2–0.4 g q 12 h 0.4 g IV q 12 h 0.2–0.4 g IV q 12 h N/A N/A 0.1–0.2 g po or IV q 24 h Macrolides Azithromycin 0.5 g on day 1, then 0.25 g q 24 h for 4 days 0.5 g IV q 24 h 0.5 g IV q 24 h — N/A 0.5 g po on day 1, then 0.25 g po q 24 h for 4 days or 0.5 g IV q 24 h For nongonococcal cervicitis and urethritis 1 g for 1 dose N/A N/A N/A N/A N/A For traveler's diarrhea 1 g for 1dose N/A N/A 5–10 mg/kg for 1 dose N/A N/A For tonsillitis or pharyngitis N/A N/A N/A 12 mg/kg for 5 days N/A N/A For otitis media or community-acquired pneumonia N/A N/A N/A 10 mg/kg on day 1, then 5 mg/kg once/day on days 2–5 N/A N/A Clarithromycin 0.25–0.5 g q 12 h Extended-release: 1 g q 24 h N/A N/A 7.5 mg/kg q 12 h N/A 0.25–0.5 g po q 24 h Dirithromycin 0.5 g q 24 h N/A N/A N/A N/A 0.5 g po q 24 h Erythromycin base b 0.25–0.5 g q 6 h N/A N/A 10–16.6 mg/kg q 8 h or 7.5–12.5 mg/kg q 6 h N/A 0.25 g po q 6 h Lactobionate N/A 0.5–1 g IV q 6 h 1 g IV q 6 h N/A 3.75–5.0 mg/kg IV q 6 h 0.5 g IV q 6 h Gluceptate N/A 0.5–1 g IV q 6 h 1 g IV q 6 h N/A 3.75–5.0 mg/kg IV q 6 h 0.5 g IV q 6 h For GI preoperative bowel preparation 1 g for 3 doses N/A N/A 20 mg/kg for 3 doses N/A N/A Telithromycin 800 mg q 24 h N/A N/A N/A N/A 800 mg po q 24 h Sulfonamides and trimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph Sulfisoxazole 1.0 g q 6 h 25 mg/kg IV q 6 h (not available in US) N/A 30–37.5 mg/kg q 6 h or 20–25 mg/kg q 4 h N/A 1 g po q 12–24 h Sulfamethizole 0.5–1 g q 6–8 h N/A N/A 7.5–11.25 mg/kg q 6 h N/A N/A Sulfamethoxazole 1 g q 8–12 h N/A N/A 25–30 mg/kg q 12 h N/A 1 g po q 24 h Trimethoprim 0.1 g q 12 h or 0.2 g q 24 h N/A N/A 2 mg/kg q 12 h for 10 days for UTI N/A 0.1 g po q 24 h Trimethoprim/sulfamethoxazole e 0.16/0.8 g q 12 h 3–5 mg TMP/kg IV q 6–8 h 5 mg TMP/kg IV q 6 h 3–6 mg TMP/kg q 12 h 3–6 mg TMP/kg IV q 12 h (Not recommended if other alternatives are available) For Pneumocystis jirovecii pneumoniae 0.32/1.6 g q 8 h for 21 days 5 mg TMP/kg IV q 8 h for 21 days 5 mg TMP/kg IV q 6–8 h 5–6.6 mg TMP/kg q 8 h or 3.75–5 mg TMP/kg q 6 h 5–6.6 mg TMP/kg IV q 8 h or 3.75–5 mg TMP/kg IV q 6 h If essential, 5 mg TMP/kg IV q 24 h or 1.25 mg TMP/kg IV q 6 h Tetracyclines Doxycycline 0.1 g q 12 h 0.1 g IV q 12 h 0.1 mg IV q 12 h Age > 8 yr: 2–4 mg/kg q 24 h or 1–2 mg/kg q 12 h Age > 8 yr: 2–4 mg/kg IV q 24 h or 1–2 mg/kg IV q 12 h 0.1 g IV or po q 12 h Minocycline 0.1 g q 12 h 0.1 g IV q 12 h 0.1 g IV q 12 h N/A N/A 0.1 g IV or po q 12 h Tetracycline b 0.25–0.5 g q 6 h N/A N/A Age > 8 yr: 6.25–12.5 mg/kg q 6 h N/A DoxycyclineSome Trade Names PERIOSTAT VIBRAMYCIN Click for Drug Monograph used instead Tigecycline N/A 100 mg, then 50 mg (25 mg for severe hepatic dysfunction) IV q 12 hr Same as adult dose N/A N/A Same as adult dose Others Clindamycin 0.15–0.45 g q 6 h 0.6 g IV q 6 h to 0.9 IV g q 8 h 0.9 g IV q 8 h 2.6–6.6 mg/kg q 8 h or 2–5 mg/kg q 6 h 6.6–13.2 mg/kg IV q 8 h or 5–10 mg/kg IV q 6 h 0.15–0.45 g po q 6 h or 0.6–0.9 g IV q 6–8 h Chloramphenicol 0.25–1 g q 6 h 0.25–1.0 g IV q 6 h 1 g IV q 6 h N/A 12.5–18.75 mg/kg IV q 6 h 0.25–1.0 g IV q 6 h For meningitis N/A 12.5 mg/kg q 6 h (maximum: 4 g/day) 12.5 mg/kg IV q 6 h (maximum: 4 g/day) N/A 18.75–25 mg/kg IV q 6 h 12.5 mg/kg IV q 6 h (maximum: 4 g/day) Daptomycin N/A 4 mg/kg IV q 24 h 4 mg/kg IV q 24 h N/A N/A 4 mg/kg IV q 48 h Linezolid 0.6 g q 12 h 0.6 g IV q 12 h 0.6 g IV q 12 h 10 mg/kg q 8 h 10 mg/kg IV q 8 h 0.6 g IV or po q 12 h Metronidazole For anaerobic infection 7.5 mg/kg q 6 h (not to exceed 4 g/day) 7.5 mg/kg IV q 6 h (not to exceed 4 g/day) 7.5 mg/kg IV q 6 h (not to exceed 4 g/day) 7.5 mg/kg q 6 h 7.5 mg/kg IV q 6 h 3.75 mg/kg IV or po q 6 h (not to exceed 2 g/day) For trichomoniasis 2 g for 1 dose or 0.5 g q 12 h for 7 days N/A N/A N/A N/A N/A For Clostridium difficile–induced diarrhea (pseudomembranous colitis) 0.5 g q 6–8 h for 10–14 days 500 mg IV q 6–8 h 500 mg IV q 6 h 7.5 mg/kg q 8 h 7.5 mg/kg IV q 6 h 250 mg po or IV q 8 h For amebiasis 0.5–0.75 g q 8 h for 10 days followed by paromomycinSome Trade Names HUMATIN Click for Drug Monograph po 0.5 g q 8 h for 7 days 0.75 g IV q 8 h for 10 days followed by paromomycinSome Trade Names HUMATIN Click for Drug Monograph po 0.5 g q 8 h for 7 days 0.75 g IV q 8 h for 10 days followed by paromomycinSome Trade Names HUMATIN Click for Drug Monograph po 0.5 g q 8 h for 7 days 11.6–16.6 mg/kg q 8 h for 7–10 days 11.6–16.6 mg/kg IV q 8 h for 7–10 days N/A For giardiasis 0.25 g q 6–8 h for 5–7 days N/A N/A 5 mg/kg q 6–8 h for 5 days N/A N/A Nitrofurantoin macrocrystals 50–100 mg q 6 h N/A N/A 1.25–1.75 mg/kg q 6 h N/A Not recommended Nitrofurantoin monohydrate/macrocrystals 100 mg q 12 h N/A N/A N/A N/A N/A Quinupristin/dalfopristin N/A 7.5 mg/kg IV q 8–12 h 7.5 mg/kg IV q 8 h N/A 7.5 mg/kg IV q 12 h for complicated skin or skin structure infection or 7.5 mg/kg q 8 h for serious infections 7.5 mg/kg IV q 8–12 h Rifampin b For TB 0.6 g q 24 h 0.6 g IV q 24 h N/A 5–10 mg/kg q 12 h or 10–20 mg/kg q 24 h 10–20 mg/kg IV q 24 h 0.3–0.6 g IV or po q 24 h For meningococcal exposure 0.6 g q 12 h for 4 doses N/A N/A Age ≥ 1 mo: 10 mg/kg q 12 h for 2 days Age < 1 mo: 5 mg/kg q 12 h for 2 days N/A 0.6 g po q 12 h for 4 doses For Haemophilus influenzae exposure 20 mg/kg q 24 h for 4 days (not to exceed 600 mg q 24 h) N/A N/A 20 mg/kg q 24 h for 4 days Age < 1 mo: 10 mg/kg q 24 h for 4 days N/A 20 mg/kg q 24 h for 4 days (not to exceed 600 mg q 24 h) For staphylococcal infections (used with a penicillin, cephalosporin, or vancomycinSome Trade Names VANCOCIN Click for Drug Monograph ) 0.3 g q 8 h or 0.6–0.9 g q 24 h 0.3 g IV q 8 h or 0.6–0.9 g IV q 24 h 0.3 g IV q 8 h or 0.6–0.9 g IV q 24 h — — 0.3 g IV or po q 8 h or 0.6–0.9 g IV or po q 24 h Spectinomycin N/A 2 g IM for 1 dose N/A N/A N/A 2 g IM for 1 dose Vancomycin 125 mg q 6 h (only effective for C. difficile–induced diarrhea 15 mg/kg q 12 h (often 1 g q 12) 15 mg/kg IV q 12 h N/A 13 mg/kg IV q 8 h or 10 mg/kg q 6 h 0.5–1.0 g IV q wk For meningitis N/A 1 g IV q 8 h or 1.5 g IV q 12 hf 1 g IV q 8 h or 1.5 g IV q 12 h N/A 15 mg/kg IV q 6 h 15 mg/kg IV q wk aInitial loading dose should be equivalent to the usual dose for patients with normal renal function, followed by a dose adjusted for renal failure. Dosing adjustments of aminoglycosides should be assisted by measuring peak (drawn 1 h after the start of a 30-min IV infusion) and trough (drawn 30 min before next dose) serum levels. bRate or extent of absorption is decreased when the drug is taken with food. cDosage should not exceed that for adults. dThese drugs are generally avoided in children. eDose is based on TMP. fIn addition, intrathecal or intraventricular vancomycinSome Trade Names VANCOCIN Click for Drug Monograph 10–20 mg/day may be necessary, and dose may need to be adjusted to achieve trough CSF levels of 10–20 μg/mL. N/A = not applicable; TMP = trimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph . Usual Doses of Commonly Prescribed Antibiotics Drug Adult Dose Pediatric (Age > 1 mo) Dose Dose in Renal Failurea (CrCl < 10 mL/min) Oral Parenteral Serious Infections Oral Parenteral Aminoglycosides Amikacin N/A 15 mg/kg IV once/day or 7.5 mg/kg q 12 h 15 mg/kg IV once/day or 7.5 mg/kg IV q 12 h N/A 5–7.5 mg/kg IV q 12 h 1.5–2.5 mg/kg IV q 24–48 h Gentamicin N/A 5–7 mg/kg IV once/day or 1.7 mg/kg IV q 8 h 5–7 mg/kg IV once/day N/A 1–2.5 mg/kg IV q 8 h 0.34–0.51 mg/kg IV q 24–48 h For synergy with a cell wall–active antibiotic to treat enterococcal endocarditis caused by strains susceptible to gentamicinSome Trade Names GARAMYCIN Click for Drug Monograph N/A 1 mg/kg IV q 8 h N/A N/A 1 mg/kg IV q 8 h Infectious disease consultation required for dosage Dosage adjusted to achieve peak serum concentration of 3–4 μg/mL and trough concentration of < 1 μg/mL For streptococcal or Staphylococcus aureus endocarditis — 1 mg/kg IV q 8 h or 3 mg/kg IV once/day N/A N/A 1 mg/kg IV q 8 h or 3 mg/kg IV once/day N/A Neomycin For preoperative gut antisepsis (with erythromycinSome Trade Names ERY-TAB ERYTHROCIN Click for Drug Monograph and mechanical cleansing) 1 g for 3 doses (eg, at 1, 2, and 11 pm on the day before surgery) N/A N/A 15 mg/kg q 4 h for 2 days or 25 mg/kg at 1, 2, and 11 pm on the day before surgery N/A N/A For hepatic coma 1–3 g qid N/A N/A 0.6–1.75 g/m2 q 6 h or 0.4–1.2 g/m2 q 4 h N/A N/A Streptomycin For TB N/A 15 mg/kg IM q 24 h (maximum: 1.0 g/day) initially, then 1.0 g 2–3 times/wk N/A N/A 20–40 mg/kg IM once/day 7.5 mg/kg IM q 72–96 h (maximum: 1 g) For synergy with a cell wall–active antibiotic to treat enterococcal endocarditis N/A 7.5 mg/kg IM q 12 h N/A N/A N/A N/A Tobramycin N/A 5–7 mg/kg IVonce/day or 1.7 mg/kg IV q 8 h 5–7 mg/kg IV once/day or 1.7 mg/kg IV q 8 h N/A 1–2.5 mg/kg IV q 8 h 0.34–0.51 mg/kg IV q 24–48 h β-Lactams: Cephalosporins (1st generation) Cefadroxil 0.5–1 g q 12 h N/A N/A 15 mg/kg q 12 h N/A 0.5 g po q 36 h Cefazolin N/A 1–2 g IV q 8 h 2 g IV q 8 h N/A 16.6–33.3 mg/kg IV q 8 h 1–2 g IV q 24–48 h Cephalexin 0.25–0.5 g q 6 h N/A N/A 6.25–12.5 mg/kg q 6 h or 8.0–16 mg/kg q 8 h N/A 0.25–0.5 g po q 24–48 h β-Lactams: Cephalosporins (2nd generation) Cefaclor b 0.25–0.5 g q 8 h N/A N/A 10–20 mg/kg q 12 h or 6.6–13.3 mg/kg q 8 h N/A 0.5 g po q 12 h Cefotetan N/A 1–3 g IV q 12 h 2–3 g IV q 12 h N/A 20–40 mg/kg IV q 12 h 1–3 g IV q 48 h Cefoxitin N/A 1 g IV q 8 h to 2 g IV q 4 h 2 g IV q 4 h or 3 g IV q 6 h N/A 27–33 mg/kg IV q 8 h or, for severe infections, 25–40 mg/kg q 6 h 0.5–1.0 g IV q 24–48 h Cefprozil 0.25 g q 12 h or 0.5 g q 12–24 h N/A N/A 15 mg/kg q 12 h for otitis media N/A 0.25 g po q 12–24 h Cefuroxime 0.125–0.5 g q 12 h 0.75–1.5 g IV q 6–8 h 1.5 g IV q 6 h 10–15 mg/kg suspension q 12 h For older children: 125–250 mg tablets q 12 h 25–50 mg/kg IV q 8 h 0.25–0.5 g po q 24 h or 0.75 g IV q 24 h For meningitis — — 3 g IV q 8 h — 50–60 mg/kg IV q 6 h — β-Lactams: Cephalosporins (3rd generation) Cefoperazone N/A 1 g q 12 h to 2 g IV q 4 h 2 g IV q 4 h N/A 25–100 mg/kg IV q 12 h Same as adult dose Cefotaxime N/A 1 g q 12 h to 2 g IV q 4 h 2 g IV q 4 h N/A 8.3–33.3 mg/kg IV q 4 h or 16.6–66.6 mg/kg q 6 h 1–2 g IV q 24 h Cefpodoxime c 0.1–0.4 g q 12 h N/A N/A 5 mg/kg q 12 h N/A 0.1–0.4 g po q 24 h Ceftazidime N/A 1 g IV q 12 h to 2 g q 8 h 2 g IV q 8 h N/A 25–50 mg/kg IV q 8 h 0.5 g IV q 24–48 h Ceftibuten b 0.4 g q 24 h N/A N/A 9 mg/kg once/day N/A 0.1 g po q 24 h Ceftizoxime N/A 0.5 g IV q 12 h to 4 g IV q 8 h 4 g IV q 8 h N/A 50 mg/kg IV q 6–8 h 0.5 g IV q 24 h to 0.5–1 g IV q 48 h Ceftriaxone N/A 1–2 g IV q 24 h 2 g IV q 24 h N/A 50–75 mg/kg IV q 24 h or 25–37.5 mg/kg q 12 h Same as adult dose For meningitis N/A 2 g IV q 12 h 2 g IV q 12 h N/A 50 mg/kg IV q 12 h or 100 mg/kg q 24 h (not to exceed 4 g/day) Possibly a loading dose of 100 mg/kg IV (not to exceed 4 g) at the start of therapy 2 g IV q 12 h β-Lactams: Cephalosporin (4th generation) Cefepime N/A 1–2 g IV q 8–12 h 2 g IV q 8 h N/A 50 mg/kg IV q 8–12 h 0.25–1 g IV q 24 h β-Lactams: Penicillins Amoxicillin 0.25–0.5 g q 8 h or 0.875 g q 12 h N/A N/A 12.5–25 mg/kg q 12 h or 7–13 mg/kg q 8 h N/A 0.25–0.5 g po q 24 h For endocarditis prophylaxis 2 g for 1 dose N/A N/A 50 mg/kg 1 h before procedure N/A 2 g po for 1 dose Amoxicillin/clavulanate 0.25–0.5 g q 8 h or 0.875 g q 12 h N/A N/A If > 40 kg: Adult dose N/A 0.25–0.5 g po q 24 h Amoxicillin/clavulanate, ES-600 N/A N/A N/A 45 mg/kg q 12 h N/A N/A Amoxicillin/clavulanate, extended-release 2 g q 12 h N/A N/A N/A N/A N/A Ampicillin N/A 0.5–2.0 g IV q 4–6 h 2 g IV q 4 h N/A 25–50 mg/kg IV q 6 h 0.5–2.0 g IV q 12–24 h For meningitis N/A 2 g IV q 4 h 2 g IV q 4 h N/A 50–100 mg/kg IV q 6 h 2 g IV q 12 h Ampicillin/sulbactam (3 g = 2 g ampicillinSome Trade Names OMNIPEN PRINCIPEN Click for Drug Monograph + 1 g sulbactam) N/A 1.5–3.0 g IV q 6 h 3 g IV q 6 h N/A 25–50 mg/kg IV q 6 h 1.5–3.0 g IV q 24 h Dicloxacillin b 0.125–0.5 g q 6 h N/A N/A 3.125–6.25 mg/kg q 6 h N/A 0.125–0.5 g po q 6 h Nafcillin Rarely used 1–2 g IV q 4 h 2 g IV q 4 h N/A 12.5–25 mg/kg IV q 6 h or 8.3–33.3 mg/kg q 4 h 1–2 g IV q 4 h Oxacillin Rarely used 1–2 g IV q 4 h 2 g IV q 4 h N/A 12.5–25 mg/kg IV q 6 h or 8.3–33.3 mg/kg IV q 4 h 1–2 g IV q 4 h Penicillin G b 0.25–0.5 g q 6–12 h (penicillin V) 1–4 million units IV q 4–6 h 4 million units IV q 4 h Penicillin VK 6.25–12.5 mg/kg q 8 h 6,250–100,000 units/kg IV q 6 h or 4,166.6–66,666 units/kg IV q 4 h 0.5–2 million units IV q 4–6 h (maximum total daily dose: 6 million units/day) Penicillin G benzathine (Bicillin© L-A) For streptococcal pharyngitis N/A 1.2 million units IM for 1 dose N/A N/A 25,000–50,000 units/kg IM as a single dose or If < 27 kg: 300,000–600,000 units as a single dose or If ≥ 27 kg: 0.9 million units as a single dose 1.2 million units IM for 1 dose Prophylaxis for rheumatic fever N/A 1.2 million units IM q 3–4 wk N/A N/A 25,000–50,000 units/kg IM q 3–4 wk 1.2 million units IM q 3–4 wk For early syphilis N/A 2.4 million units IM for 1 dose N/A N/A 50,000 units/kg IM for 1 dose 2.4 million units IM for 1 dose For late syphilis (excluding neurosyphilis) N/A 2.4 million units IM/wk for 3 wk N/A N/A 50,000 units/kg IM in 3 doses 1 wk apart 2.4 million units IM for 1 dose Penicillin G procaine (IM only) N/A 0.3–0.6 million units IM q 12 h N/A N/A 25,000–50,000 units/kg IM q 24 h or 12,500–25,000 units/kg IM q 12 h 0.3 to 0.6 million units IM q 12 h Piperacillin (1.9 mEq Na/g) N/A 3 g IV q 4–6 h 3 g IV q 4 h N/A 50–75 mg/kg IV q 6 h or 33.3–50 mg/kg IV q 4 h 3–4 g IV q 12 h Piperacillin/tazobactam (2.25 g = 2.0 g piperacillinSome Trade Names PIPRACIL Click for Drug Monograph + 0.25 g tazobactam) N/A 3.375 g IV q 4–6 h 3.375 g IV q 4 h N/A 80 mg/kg IV q 8 h 2.25 g IV q 8 h to 4.5 g IV q 12 h Ticarcillin (5.2 mEq Na/g) N/A 3 g IV q 4–6 h 3 g IV q 4 h N/A If < 60 kg: 50 mg/kg IV q 4–6 h 1–2 g IV q 12 h Ticarcillin/clavulanate (3.1 g = 3 g ticarcillinSome Trade Names TICAR + 0.1 g clavulanic acid) N/A 3.1 g IV q 4–6 h 3.1 g IV q 4 h N/A If < 60 kg: 50 mg/kg IV (based on ticarcillinSome Trade Names TICAR component) q 4–6 h 2 g IV q 12 h Other β-lactams Aztreonam N/A 1–2 g IV q 6–12 h 2 g IV q 6 h N/A 30–40 mg/kg IV q 6–8 h 0.5 g IV q 8 h Ertapenem N/A 1 g IV q 24 h 1 g IV q 24 h N/A N/A 0.5 g IV q 24 h Imipenem N/A 0.5–1.0 g IV q 6 h 1 g IV q 6 h N/A For infants 4 wk to 3 mo: 25 mg/kg IV q 6 h For children > 3 mo: 15–25 mg/kg IV q 6 h 0.125–0.25 g IV q 12 h (may increase risk of seizures) Meropenem N/A 1.0 g IV q 8 h 1.0 g IV q 8 h N/A 20–40 mg/kg IV q 8 h 0.5 g IV q 24 h For meningitis — 40 mg/kg IV q 8 h 40 mg/kg IV q 8 h N/A — 20 mg/kg IV q 24 h Fluoroquinolonesd Ciprofloxacin 0.5–0.75 g q 12 h 0.2–0.4 g IV q 8–12 h 0.4 g IV q 8 h 10–15 mg/kg IV q 12 h (in select circumstances) 10–15 mg/kg IV q 12 h (in select circumstances) 0.5–0.75 g po q 24 h or 0.2–0.4 g IV q 24 h Extended-release for uncomplicated cystitis 0.5 g q 24 h for 3 days N/A N/A N/A N/A N/A Gemifloxacin 320 mg q 24 h N/A N/A N/A N/A 160 mg po q 24 h Levofloxacin 0.25–0.75 g q 24 h 0.25–0.75 IV g q 24 h 0.75 g IV q 24 h N/A N/A 0.25–0.5 g po or IV q 48 h Moxifloxacin 0.4 g q 24 h 0.4 g IV q 24 h 0.4 g IV q 24 h N/A N/A 0.4 g q 24 h po or IV Norfloxacin b 0.4 g q 12 h N/A N/A N/A N/A 0.4 g po q 24 h Ofloxacin 0.2–0.4 g q 12 h 0.4 g IV q 12 h 0.2–0.4 g IV q 12 h N/A N/A 0.1–0.2 g po or IV q 24 h Macrolides Azithromycin 0.5 g on day 1, then 0.25 g q 24 h for 4 days 0.5 g IV q 24 h 0.5 g IV q 24 h — N/A 0.5 g po on day 1, then 0.25 g po q 24 h for 4 days or 0.5 g IV q 24 h For nongonococcal cervicitis and urethritis 1 g for 1 dose N/A N/A N/A N/A N/A For traveler's diarrhea 1 g for 1dose N/A N/A 5–10 mg/kg for 1 dose N/A N/A For tonsillitis or pharyngitis N/A N/A N/A 12 mg/kg for 5 days N/A N/A For otitis media or community-acquired pneumonia N/A N/A N/A 10 mg/kg on day 1, then 5 mg/kg once/day on days 2–5 N/A N/A Clarithromycin 0.25–0.5 g q 12 h Extended-release: 1 g q 24 h N/A N/A 7.5 mg/kg q 12 h N/A 0.25–0.5 g po q 24 h Dirithromycin 0.5 g q 24 h N/A N/A N/A N/A 0.5 g po q 24 h Erythromycin base b 0.25–0.5 g q 6 h N/A N/A 10–16.6 mg/kg q 8 h or 7.5–12.5 mg/kg q 6 h N/A 0.25 g po q 6 h Lactobionate N/A 0.5–1 g IV q 6 h 1 g IV q 6 h N/A 3.75–5.0 mg/kg IV q 6 h 0.5 g IV q 6 h Gluceptate N/A 0.5–1 g IV q 6 h 1 g IV q 6 h N/A 3.75–5.0 mg/kg IV q 6 h 0.5 g IV q 6 h For GI preoperative bowel preparation 1 g for 3 doses N/A N/A 20 mg/kg for 3 doses N/A N/A Telithromycin 800 mg q 24 h N/A N/A N/A N/A 800 mg po q 24 h Sulfonamides and trimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph Sulfisoxazole 1.0 g q 6 h 25 mg/kg IV q 6 h (not available in US) N/A 30–37.5 mg/kg q 6 h or 20–25 mg/kg q 4 h N/A 1 g po q 12–24 h Sulfamethizole 0.5–1 g q 6–8 h N/A N/A 7.5–11.25 mg/kg q 6 h N/A N/A Sulfamethoxazole 1 g q 8–12 h N/A N/A 25–30 mg/kg q 12 h N/A 1 g po q 24 h Trimethoprim 0.1 g q 12 h or 0.2 g q 24 h N/A N/A 2 mg/kg q 12 h for 10 days for UTI N/A 0.1 g po q 24 h Trimethoprim/sulfamethoxazole e 0.16/0.8 g q 12 h 3–5 mg TMP/kg IV q 6–8 h 5 mg TMP/kg IV q 6 h 3–6 mg TMP/kg q 12 h 3–6 mg TMP/kg IV q 12 h (Not recommended if other alternatives are available) For Pneumocystis jirovecii pneumoniae 0.32/1.6 g q 8 h for 21 days 5 mg TMP/kg IV q 8 h for 21 days 5 mg TMP/kg IV q 6–8 h 5–6.6 mg TMP/kg q 8 h or 3.75–5 mg TMP/kg q 6 h 5–6.6 mg TMP/kg IV q 8 h or 3.75–5 mg TMP/kg IV q 6 h If essential, 5 mg TMP/kg IV q 24 h or 1.25 mg TMP/kg IV q 6 h Tetracyclines Doxycycline 0.1 g q 12 h 0.1 g IV q 12 h 0.1 mg IV q 12 h Age > 8 yr: 2–4 mg/kg q 24 h or 1–2 mg/kg q 12 h Age > 8 yr: 2–4 mg/kg IV q 24 h or 1–2 mg/kg IV q 12 h 0.1 g IV or po q 12 h Minocycline 0.1 g q 12 h 0.1 g IV q 12 h 0.1 g IV q 12 h N/A N/A 0.1 g IV or po q 12 h Tetracycline b 0.25–0.5 g q 6 h N/A N/A Age > 8 yr: 6.25–12.5 mg/kg q 6 h N/A DoxycyclineSome Trade Names PERIOSTAT VIBRAMYCIN Click for Drug Monograph used instead Tigecycline N/A 100 mg, then 50 mg (25 mg for severe hepatic dysfunction) IV q 12 hr Same as adult dose N/A N/A Same as adult dose Others Clindamycin 0.15–0.45 g q 6 h 0.6 g IV q 6 h to 0.9 IV g q 8 h 0.9 g IV q 8 h 2.6–6.6 mg/kg q 8 h or 2–5 mg/kg q 6 h 6.6–13.2 mg/kg IV q 8 h or 5–10 mg/kg IV q 6 h 0.15–0.45 g po q 6 h or 0.6–0.9 g IV q 6–8 h Chloramphenicol 0.25–1 g q 6 h 0.25–1.0 g IV q 6 h 1 g IV q 6 h N/A 12.5–18.75 mg/kg IV q 6 h 0.25–1.0 g IV q 6 h For meningitis N/A 12.5 mg/kg q 6 h (maximum: 4 g/day) 12.5 mg/kg IV q 6 h (maximum: 4 g/day) N/A 18.75–25 mg/kg IV q 6 h 12.5 mg/kg IV q 6 h (maximum: 4 g/day) Daptomycin N/A 4 mg/kg IV q 24 h 4 mg/kg IV q 24 h N/A N/A 4 mg/kg IV q 48 h Linezolid 0.6 g q 12 h 0.6 g IV q 12 h 0.6 g IV q 12 h 10 mg/kg q 8 h 10 mg/kg IV q 8 h 0.6 g IV or po q 12 h Metronidazole For anaerobic infection 7.5 mg/kg q 6 h (not to exceed 4 g/day) 7.5 mg/kg IV q 6 h (not to exceed 4 g/day) 7.5 mg/kg IV q 6 h (not to exceed 4 g/day) 7.5 mg/kg q 6 h 7.5 mg/kg IV q 6 h 3.75 mg/kg IV or po q 6 h (not to exceed 2 g/day) For trichomoniasis 2 g for 1 dose or 0.5 g q 12 h for 7 days N/A N/A N/A N/A N/A For Clostridium difficile–induced diarrhea (pseudomembranous colitis) 0.5 g q 6–8 h for 10–14 days 500 mg IV q 6–8 h 500 mg IV q 6 h 7.5 mg/kg q 8 h 7.5 mg/kg IV q 6 h 250 mg po or IV q 8 h For amebiasis 0.5–0.75 g q 8 h for 10 days followed by paromomycinSome Trade Names HUMATIN Click for Drug Monograph po 0.5 g q 8 h for 7 days 0.75 g IV q 8 h for 10 days followed by paromomycinSome Trade Names HUMATIN Click for Drug Monograph po 0.5 g q 8 h for 7 days 0.75 g IV q 8 h for 10 days followed by paromomycinSome Trade Names HUMATIN Click for Drug Monograph po 0.5 g q 8 h for 7 days 11.6–16.6 mg/kg q 8 h for 7–10 days 11.6–16.6 mg/kg IV q 8 h for 7–10 days N/A For giardiasis 0.25 g q 6–8 h for 5–7 days N/A N/A 5 mg/kg q 6–8 h for 5 days N/A N/A Nitrofurantoin macrocrystals 50–100 mg q 6 h N/A N/A 1.25–1.75 mg/kg q 6 h N/A Not recommended Nitrofurantoin monohydrate/macrocrystals 100 mg q 12 h N/A N/A N/A N/A N/A Quinupristin/dalfopristin N/A 7.5 mg/kg IV q 8–12 h 7.5 mg/kg IV q 8 h N/A 7.5 mg/kg IV q 12 h for complicated skin or skin structure infection or 7.5 mg/kg q 8 h for serious infections 7.5 mg/kg IV q 8–12 h Rifampin b For TB 0.6 g q 24 h 0.6 g IV q 24 h N/A 5–10 mg/kg q 12 h or 10–20 mg/kg q 24 h 10–20 mg/kg IV q 24 h 0.3–0.6 g IV or po q 24 h For meningococcal exposure 0.6 g q 12 h for 4 doses N/A N/A Age ≥ 1 mo: 10 mg/kg q 12 h for 2 days Age < 1 mo: 5 mg/kg q 12 h for 2 days N/A 0.6 g po q 12 h for 4 doses For Haemophilus influenzae exposure 20 mg/kg q 24 h for 4 days (not to exceed 600 mg q 24 h) N/A N/A 20 mg/kg q 24 h for 4 days Age < 1 mo: 10 mg/kg q 24 h for 4 days N/A 20 mg/kg q 24 h for 4 days (not to exceed 600 mg q 24 h) For staphylococcal infections (used with a penicillin, cephalosporin, or vancomycinSome Trade Names VANCOCIN Click for Drug Monograph ) 0.3 g q 8 h or 0.6–0.9 g q 24 h 0.3 g IV q 8 h or 0.6–0.9 g IV q 24 h 0.3 g IV q 8 h or 0.6–0.9 g IV q 24 h — — 0.3 g IV or po q 8 h or 0.6–0.9 g IV or po q 24 h Spectinomycin N/A 2 g IM for 1 dose N/A N/A N/A 2 g IM for 1 dose Vancomycin 125 mg q 6 h (only effective for C. difficile–induced diarrhea 15 mg/kg q 12 h (often 1 g q 12) 15 mg/kg IV q 12 h N/A 13 mg/kg IV q 8 h or 10 mg/kg q 6 h 0.5–1.0 g IV q wk For meningitis N/A 1 g IV q 8 h or 1.5 g IV q 12 hf 1 g IV q 8 h or 1.5 g IV q 12 h N/A 15 mg/kg IV q 6 h 15 mg/kg IV q wk aInitial loading dose should be equivalent to the usual dose for patients with normal renal function, followed by a dose adjusted for renal failure. Dosing adjustments of aminoglycosides should be assisted by measuring peak (drawn 1 h after the start of a 30-min IV infusion) and trough (drawn 30 min before next dose) serum levels. bRate or extent of absorption is decreased when the drug is taken with food. cDosage should not exceed that for adults. dThese drugs are generally avoided in children. eDose is based on TMP. fIn addition, intrathecal or intraventricular vancomycinSome Trade Names VANCOCIN Click for Drug Monograph 10–20 mg/day may be necessary, and dose may need to be adjusted to achieve trough CSF levels of 10–20 μg/mL. N/A = not applicable; TMP = trimethoprimSome Trade Names PROLOPRIM TRIMPEX Click for Drug Monograph .

Duration: Antibiotics should be continued until objective evidence of systemic infection (eg, fever, symptoms, abnormal laboratory findings) is absent for several days. For some infections (eg, endocarditis, TB, osteomyelitis), antibiotics are continued for weeks or months to prevent relapse.

Complications: Complications of antibiotic therapy include superinfection by nonsusceptible bacteria or fungi and cutaneous, renal, hematologic, and GI adverse effects. Adverse effects frequently require stopping the causative drug and substituting another antibiotic to which the bacteria are susceptible; sometimes, no alternatives exist.

Antibiotic Resistance

Resistance to an antibiotic may be inherent in a particular bacterial species or may be acquired through mutations or acquisition of genes for antibiotic resistance that are obtained from another organism. Different mechanisms for resistance are encoded by these genes (see Table 4: Bacteria and Antibacterial Drugs: Common Mechanisms of Antibiotic Resistance). Resistance genes can be transmitted between 2 bacterial cells by the following mechanisms:

• Transformation (uptake of naked DNA from another organism)
• Transduction (infection by a bacteriophage)
• Conjugation (exchange of genetic material in the form of either plasmids, which are pieces of independently replicating extrachromosomal DNA, or transposons, which are movable pieces of chromosomal DNA) Plasmids and transposons, which can rapidly disseminate resistance genes.

Antibiotic use preferentially eliminates nonresistant bacteria, increasing the proportion of resistant bacteria that remain. Antibiotic use has this effect not only on pathogenic bacteria but also on normal flora; resistant normal flora can become a reservoir for resistance genes that can spread to pathogens.

Table 4
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Common Mechanisms of Antibiotic Resistance Mechanism Example Decreased cell wall permeability Loss of outer membrane D2 porin in imipenem-resistant Pseudomonas aeruginosa Enzymatic inactivation Production of β-lactamases that inactivate penicillins in penicillin-resistant Staphylococcus aureus, Haemophilus influenzae, and Escherichia coli Production of aminoglycoside-inactivating enzymes in gentamicinSome Trade Names GARAMYCIN Click for Drug Monograph -resistant enterococci Changes in target Decreased affinity of penicillin-binding proteins for β-lactam antibiotics (eg, in Streptococcus pneumoniae with reduced penicillin sensitivity) Decreased affinity of methylated ribosomal RNA target for macrolides, clindamycinSome Trade Names CLEOCIN Click for Drug Monograph , and quinupristin in MLSB-resistant S. aureus Decreased affinity of altered cell wall precursor for vancomycinSome Trade Names VANCOCIN Click for Drug Monograph (eg, in Enterococcus faecium) Decreased affinity of DNA gyrase for fluoroquinolones in fluoroquinolone-resistant S. aureus Increased antibiotic efflux pump Increased efflux of tetracyclineSome Trade Names ACHROMYCIN V TETRACYN TETREX Click for Drug Monograph , macrolides, clindamycinSome Trade Names CLEOCIN Click for Drug Monograph , or fluoroquinolones (eg, in S. aureus) Bypass of antibiotic inhibition Development of bacterial mutants that can subsist on products (eg, thymidine) present in the environment, not just products synthesized within the bacteria (eg, in certain bacteria exposed to trimethoprim/sulfamethoxazoleSome Trade Names BACTRIM SEPTRA Click for Drug Monograph ) MLSB = macrolide, lincoside, streptogramin B.

Last full review/revision July 2009 by Matthew E. Levison, MD

Content last modified February 2012