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Pronunciation
(meth i kloe THYE a zide)
Generic Available (U.S.)
Yes
Index Terms
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Management of hypertension; adjunctive therapy of edema
Pregnancy Risk Factor
B
Pregnancy Considerations
Adverse events were not observed in animal reproduction studies. Thiazide diuretics cross the placenta and are found in cord blood. Maternal use may cause fetal or neonatal jaundice, thrombocytopenia, or other adverse events observed in adults. Use of thiazide diuretics during normal pregnancies is not appropriate; use may be considered when edema is due to pathologic causes (as in the nonpregnant patient); monitor.
Lactation
Excretion in breast milk unknown/not recommended
Breast-Feeding Considerations
Thiazide diuretics are found in breast milk.
Contraindications
Hypersensitivity to methyclothiazide or any component of the formulation, thiazides, or sulfonamide-derived drugs; anuria
Warnings/Precautions
Concerns related to adverse effects:
• Electrolyte disturbances: Hypokalemia, hypochloremic alkalosis, and hyponatremia can occur.
• Hypersensitivity reactions: Hypersensitivity reactions may occur.
• Photosensitivity: Photosensitization may occur.
• Sulfa allergy: Chemical similarities are present among sulfonamides, sulfonylureas, carbonic anhydrase inhibitors, thiazides, and loop diuretics (except ethacrynic acid). Use in patients with thiazide or sulfonamide allergy is specifically contraindicated in product labeling, however, a risk of cross-reaction exists in patients with allergy to any of these compounds; avoid use when previous reaction has been severe. Discontinue if signs of hypersensitivity are noted.
Disease-related concerns:
• Diabetes: Use with caution in patients with prediabetes or diabetes mellitus; may see a change in glucose control.
• Gout: In certain patients with a history of gout, a familial predisposition to gout, or chronic renal failure, gout can be precipitated.
• Hepatic impairment: Use with caution in patients with severe hepatic dysfunction; in cirrhosis, avoid electrolyte and acid/base imbalances that might lead to hepatic encephalopathy.
• Hypercalcemia: Thiazide diuretics may decrease renal calcium excretion; consider avoiding use in patients with hypercalcemia.
• Hypercholesterolemia: Use with caution in patients with moderate or high cholesterol concentrations; increased cholesterol and triglyceride levels have been reported with thiazides.
• Hypokalemia: Use with caution in patients with hypokalemia; correct before initiating therapy.
• Parathyroid disease: Thiazide diuretics reduce calcium excretion; pathologic changes in the parathyroid glands with hypercalcemia and hypophosphatemia have been observed with prolonged use.
• Renal impairment: Avoid in severe renal disease (ineffective). May precipitate azotemia; discontinue or consider withholding if renal impairment occurs.
• Systemic lupus erythematosus (SLE): Can cause SLE exacerbation or activation.
Adverse Reactions
Frequency not defined.
Cardiovascular: Necrotizing angiitis, orthostatic hypotension
Central nervous system: Dizziness, fever, headache, vertigo
Dermatologic: Photosensitivity, purpura, rash, Stevens-Johnson syndrome, urticaria
Endocrine & metabolic: Electrolyte imbalance, hypercalcemia, hyperglycemia, hyperuricemia, hypokalemia
Gastrointestinal: Anorexia, constipation, diarrhea, epigastric distress, gastric irritation, nausea, pancreatitis, sialadenitis, vomiting
Genitourinary: Glycosuria
Hematologic: Agranulocytosis, aplastic anemia, hemolytic anemia, leukopenia, thrombocytopenia
Hepatic: Jaundice
Neuromuscular & skeletal: Cramping, muscle spasm, paresthesias, restlessness, weakness
Ocular: Blurred vision (transient), xanthopsia
Respiratory: Pneumonitis, pulmonary edema, respiratory distress
Miscellaneous: Anaphylactic reactions
Metabolism/Transport Effects
None known.
Drug Interactions
ACE Inhibitors: Thiazide Diuretics may enhance the hypotensive effect of ACE Inhibitors. Specifically, postural hypotension which can accompany ACE Inhibitor initiation. Thiazide Diuretics may enhance the nephrotoxic effect of ACE Inhibitors. Risk C: Monitor therapy
Alcohol (Ethyl): May enhance the orthostatic hypotensive effect of Thiazide Diuretics. Risk C: Monitor therapy
Alfuzosin: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
Allopurinol: Thiazide Diuretics may enhance the potential for allergic or hypersensitivity reactions to Allopurinol. Thiazide Diuretics may increase the serum concentration of Allopurinol. Specifically, Thiazide Diuretics may increase the concentration of Oxypurinol, an active metabolite of Allopurinol. Risk C: Monitor therapy
Amifostine: Antihypertensives may enhance the hypotensive effect of Amifostine. Management: When amifostine is used at chemotherapy doses, antihypertensive medications should be withheld for 24 hours prior to amifostine administration. If antihypertensive therapy can not be withheld, amifostine should not be administered. Risk D: Consider therapy modification
Analgesics (Opioid): May enhance the orthostatic hypotensive effect of Thiazide Diuretics. Risk C: Monitor therapy
Antidiabetic Agents: Thiazide Diuretics may diminish the therapeutic effect of Antidiabetic Agents. Risk C: Monitor therapy
Antihypertensives: May enhance the hypotensive effect of other Antihypertensives. Risk C: Monitor therapy
Barbiturates: May enhance the orthostatic hypotensive effect of Thiazide Diuretics. Risk C: Monitor therapy
Beta2-Agonists: May enhance the hypokalemic effect of Thiazide Diuretics. Risk C: Monitor therapy
Bile Acid Sequestrants: May decrease the absorption of Thiazide Diuretics. The diuretic response is likewise decreased. Risk D: Consider therapy modification
Calcium Salts: Thiazide Diuretics may decrease the excretion of Calcium Salts. Continued concomitant use can also result in metabolic alkalosis. Risk C: Monitor therapy
CarBAMazepine: Thiazide Diuretics may enhance the adverse/toxic effect of CarBAMazepine. Specifically, there may be an increased risk for hyponatremia. Risk C: Monitor therapy
Corticosteroids (Orally Inhaled): May enhance the hypokalemic effect of Thiazide Diuretics. Risk C: Monitor therapy
Corticosteroids (Systemic): May enhance the hypokalemic effect of Thiazide Diuretics. Risk C: Monitor therapy
Dofetilide: Thiazide Diuretics may enhance the QTc-prolonging effect of Dofetilide. Thiazide Diuretics may increase the serum concentration of Dofetilide. Risk X: Avoid combination
Herbs (Hypertensive Properties): May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Herbs (Hypotensive Properties): May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
Hypotensive Agents: May enhance the adverse/toxic effect of other Hypotensive Agents. Risk C: Monitor therapy
Licorice: May enhance the hypokalemic effect of Thiazide Diuretics. Risk C: Monitor therapy
Lithium: Thiazide Diuretics may decrease the excretion of Lithium. Risk D: Consider therapy modification
MAO Inhibitors: May enhance the orthostatic hypotensive effect of Orthostatic Hypotension Producing Agents. Risk C: Monitor therapy
Methylphenidate: May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Nonsteroidal Anti-Inflammatory Agents: May diminish the therapeutic effect of Thiazide Diuretics. Risk C: Monitor therapy
OXcarbazepine: Thiazide Diuretics may enhance the adverse/toxic effect of OXcarbazepine. Specifically, there may be an increased risk for hyponatremia. Risk C: Monitor therapy
Pentoxifylline: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
Phosphodiesterase 5 Inhibitors: May enhance the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Porfimer: Photosensitizing Agents may enhance the photosensitizing effect of Porfimer. Risk C: Monitor therapy
Prostacyclin Analogues: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
RiTUXimab: Antihypertensives may enhance the hypotensive effect of RiTUXimab. Risk D: Consider therapy modification
Sodium Phosphates: Diuretics may enhance the nephrotoxic effect of Sodium Phosphates. Specifically, the risk of acute phosphate nephropathy may be enhanced. Management: Consider avoiding this combination by temporarily suspending treatment with diuretics, or seeking alternatives to oral sodium phosphate bowel preparation. If the combination cannot be avoided, hydrate adequately and monitor fluid and renal status. Risk D: Consider therapy modification
Topiramate: Thiazide Diuretics may enhance the hypokalemic effect of Topiramate. Thiazide Diuretics may increase the serum concentration of Topiramate. Management: Monitor for increased topiramate levels/adverse effects (e.g., hypokalemia) with initiation/dose increase of a thiazide diuretic. Closely monitor serum potassium concentrations with concomitant therapy. Topiramate dose reductions may be necessary. Risk D: Consider therapy modification
Toremifene: Thiazide Diuretics may enhance the hypercalcemic effect of Toremifene. Risk C: Monitor therapy
Vitamin D Analogs: Thiazide Diuretics may enhance the hypercalcemic effect of Vitamin D Analogs. Risk C: Monitor therapy
Yohimbine: May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Ethanol/Nutrition/Herb Interactions
Herb/Nutraceutical: Avoid dong quai if using for hypertension (has estrogenic activity). Avoid dong quai, St John's wort (may also cause photosensitization). Avoid ephedra, yohimbe, ginseng (may worsen hypertension). Avoid garlic (may have increased antihypertensive effect).
Storage
Store at controlled room temperature of 15°C to 30°C (59°F to 86°F). Protect from light.
Mechanism of Action
Inhibits sodium reabsorption in the distal tubules causing increased excretion of sodium and water, as well as, potassium and hydrogen ions
Pharmacodynamics/Kinetics
Onset of action: Diuresis: 2 hours
Peak effect: 6 hours
Duration: ~1 day
Excretion: Urine (as unchanged drug)
Dosage
Adults: Oral:
Edema: 2.5-10 mg/day
Hypertension: 2.5-5 mg/day; may add another antihypertensive if 5 mg is not adequate after a trial of 8-12 weeks of therapy
Administration: Oral
May be administered with food or milk. Take early in day to avoid nocturia. Take the last dose of multiple doses no later than 6 PM unless instructed otherwise.
Monitoring Parameters
Assess weight, I & O reports daily to determine fluid loss; blood pressure; serum electrolytes, BUN, creatinine
Dietary Considerations
May be taken with food or milk.
Patient Education
Take with meals. May take early in day to avoid nocturia. Include bananas or orange juice in daily diet, but do not take dietary supplements without advice or consultation of prescriber. Assess weight weekly and report weight gain. May cause dizziness or weakness. You may experience nausea, loss of appetite, or photosensitivity. Follow instructions for diet and lifestyle changes. Report weakness, skin rash, or swelling of extremities.
Geriatric Considerations
Methyclothiazide is not effective in patients with Clcr <30 mL/minute; therefore, it may not be useful in many elderly patients.
Cardiovascular Considerations
Thiazide diuretics are effective first-line therapeutic agents in the management of hypertension and have proven to be of benefit in terms of cardiovascular outcome. They may act synergistically to lower blood pressure when combined with an ACE inhibitor or beta-blocker. The initial concern about thiazide diuretic-induced hypokalemia, glucose intolerance, and lipid profiles does not appear to be of substantial clinical consequence in the treatment of hypertension. The benefits of this class of agents in the treatment of hypertension is established and compares well with other first-line therapeutic agents.
Diuretics are standard therapy for the management of edema in patients with heart failure.
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Orthostatic hypotension.
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Effects on Mental Status
May cause drowsiness
Mental Health: Effects on Psychiatric Treatment
May rarely cause agranulocytosis; use caution with clozapine and carbamazepine; may cause photosensitivity; use psychotropics with caution; may decrease lithium clearance resulting in an increase in serum lithium levels and potential lithium toxicity; monitor serum lithium levels
Nursing: Physical Assessment/Monitoring
Monitor positional blood pressure and fluid balance on a regular basis. Monitor for signs of hypokalemia. If used to treat CHF, monitor for signs of effectiveness.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Tablet, oral: 5 mg
Pricing: U.S. (www.drugstore.com)
Tablets (Methyclothiazide)
5 mg (30): $54.99
References
Chobanian AV, Bakris GL, Black HR, et al, “The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The JNC 7 Report,” JAMA, 2003, 289(19):2560-71.
International Brand Names
Lexi-Comp.com
Last full review/revision December 2011
Content last modified December 2011
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