Penicillins

Penicillin G–like drugs (including penicillin V) are primarily used against

A minority of gram-negative bacilli are also susceptible to large parenteral doses of penicillin G. Most staphylococci, most Neisseria gonorrhoeae, many anaerobic gram-negative bacilli, and about 30% of Haemophilus influenzae are resistant.

Penicillin G is the drug of choice for syphilis Syphilis Syphilis is caused by the spirochete Treponema pallidum and is characterized by 3 sequential clinical, symptomatic stages separated by periods of asymptomatic latent infection. Common... read more , for certain clostridial infections Overview of Anaerobic Bacteria Bacteria can be classified by their need and tolerance for oxygen: Facultative: Grow aerobically or anaerobically in the presence or absence of oxygen Microaerophilic: Require a low oxygen concentration... read more , and, with gentamicin, for endocarditis Infective Endocarditis Infective endocarditis is infection of the endocardium, usually with bacteria (commonly, streptococci or staphylococci) or fungi. It may cause fever, heart murmurs, petechiae, anemia, embolic... read more due to susceptible enterococci.

Benzathine penicillin G is a long-acting formulation that is available as

Of the 3 products, only pure benzathine penicillin is recommended for treating syphilis and preventing rheumatic fever Rheumatic Fever Rheumatic fever is a nonsuppurative, acute inflammatory complication of group A streptococcal pharyngeal infection, causing combinations of arthritis, carditis, subcutaneous nodules, erythema... read more . Pure benzathine penicillin and the mixture of equal amounts are indicated for treating upper respiratory infections and skin and soft-tissue infections Overview of Bacterial Skin Infections Bacterial skin infections can be classified as skin and soft tissue infections (SSTI) and acute bacterial skin and skin structure infections (ABSSSI). SSTI include Carbuncles Ecthyma Erythrasma... read more caused by susceptible streptococci.

These drugs are more active against

The addition of a beta-lactamase inhibitor (clavulanate or sulbactam) allows use against methicillin-sensitive staphylococci Staphylococcal Infections Staphylococci are gram-positive aerobic organisms. Staphylococcus aureus is the most pathogenic; it typically causes skin infections and sometimes pneumonia, endocarditis, and osteomyelitis... read more , H. influenzae, Moraxella catarrhalis Moraxella catarrhalis Infection Moraxella catarrhalis is a gram-negative cocci that causes ear and upper and lower respiratory infections. M. catarrhalis is also known as Branhamella catarrhalis. M... read more , Bacteroides Mixed Anaerobic Infections Anaerobes can infect normal hosts and hosts with compromised resistance or damaged tissues. Mixed anaerobic infections can include both single anaerobic species or multiple anaerobic species... read more species, E. coli, and K. pneumoniae Klebsiella, Enterobacter, and Serratia Infections The gram-negative bacteria Klebsiella, Enterobacter, and Serratia are closely related normal intestinal flora that rarely cause disease in normal hosts. Diagnosis is by... read more .

Ampicillin is indicated primarily for infections typically caused by susceptible gram-negative bacteria:

These drugs (dicloxacillin, nafcillin, cloxacillin, flucloxacillin, and oxacillin) are used primarily for

These drugs are also used to treat some Streptococcus pneumoniae, group A streptococcal, and methicillin-sensitive coagulase-negative staphylococcal infections.

Piperacillin and piperacillin/tazobactam have activity against

The addition of a beta-lactamase inhibitor enhances activity against beta-lactamase–producing methicillin-sensitive S. aureus, E. coli, K. pneumoniae, H. influenzae, and gram-negative anaerobic bacilli but not against gram-negative bacilli that produce AmpC beta-lactamase or KPC and may only partially inhibit ESBL produced by some K. pneumoniae, E. coli, and other Enterobacterales. Broad-spectrum penicillins exhibit synergy with aminoglycosides and are usually used with this class to treat P. aeruginosa infections.

Most adverse effects are hypersensitivity reactions:

Most patients who report an allergic reaction to penicillin do not react to subsequent exposure to penicillin. Although small, risk of an allergic reaction is about 10 times higher for patients who have had a previous allergic reaction. Many patients report adverse reactions to penicillin that are not truly allergic (eg, gastrointestinal adverse effects, nonspecific symptoms).

If patients have a vague or inconsistent history of penicillin allergy and taking alternative antibiotics is not effective or convenient, skin testing Skin testing Drug hypersensitivity is an immune-mediated reaction to a drug. Symptoms range from mild to severe and include rash, anaphylaxis, and serum sickness. Diagnosis is clinical; skin testing is occasionally... read more may be done. Desensitization Desensitization Drug hypersensitivity is an immune-mediated reaction to a drug. Symptoms range from mild to severe and include rash, anaphylaxis, and serum sickness. Diagnosis is clinical; skin testing is occasionally... read more may be attempted in patients with a positive skin test if there is no alternative to a penicillin-type drug. However, patients with a history of anaphylaxis to penicillin should not be given other penicillins or any beta-lactam with similar side chains (including for skin testing), except in very rare circumstances when no substitute can be found and the drug can be given under supervision in a controlled environment. In such cases, special precautions and desensitization regimens are required.

Rashes occur more often with ampicillin and amoxicillin than with other penicillins. Patients with infectious mononucleosis often develop a nonallergic rash, typically maculopapular, usually beginning between days 4 and 7 of treatment.

Penicillins can also cause

Leukopenia seems to occur most often with nafcillin. Any penicillin used in very high IV doses can interfere with platelet function and cause bleeding.

Other adverse effects include pain at the IM injection site, thrombophlebitis when the same site is used repeatedly for IV injection, and, with oral formulations, gastrointestinal disturbances.

Ticarcillin and carbenicillin in high doses may cause sodium overload, especially in patients with heart or kidney failure, because both are disodium salts. Ticarcillin and carbenicillin can also cause hypokalemic metabolic alkalosis because the large amount of nonabsorbable anion presented to the distal tubules alters H+ ion excretion and secondarily results in potassium loss.