MAXZIDE-25
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MAXZIDE-25 (MAXZIDE-25).
Maxzide-25 is a combination of hydrochlorothiazide, a thiazide diuretic that inhibits sodium and chloride reabsorption in the distal convoluted tubule, and triamterene, a potassium-sparing diuretic that inhibits sodium reabsorption in the collecting duct by blocking epithelial sodium channels.
| Metabolism | Hydrochlorothiazide: not extensively metabolized; Triamterene: metabolized primarily by CYP1A2 to hydroxytriamterene sulfate, an active metabolite. |
| Excretion | Renal: triamterene 80-85% (as metabolites, 5-10% unchanged), hydrochlorothiazide ≥95% unchanged via tubular secretion; biliary/fecal: minimal (<5% each). |
| Half-life | Triamterene: 2-4 hours (terminal half-life due to active metabolite hydroxylated triamterene, clinical effect persists 12-16 hours). Hydrochlorothiazide: 5.6-14.8 hours (mean 8.5 hours). |
| Protein binding | Triamterene: 55-67% (albumin). Hydrochlorothiazide: 40-68% (primarily albumin). |
| Volume of Distribution | Triamterene: 2.5-4.5 L/kg (extensive tissue distribution). Hydrochlorothiazide: 0.8-1.5 L/kg (primarily extracellular fluid). |
| Bioavailability | Oral: triamterene 50-60%, hydrochlorothiazide 65-75%; food may increase triamterene absorption. |
| Onset of Action | Oral: diuresis begins within 1-3 hours for both components. |
| Duration of Action | Diuretic effect lasts 12-16 hours for triamterene and 6-24 hours for hydrochlorothiazide; prolonged with renal impairment. |
1 tablet (triamterene 37.5 mg/hydrochlorothiazide 25 mg) orally once daily.
| Dosage form | TABLET |
| Renal impairment | Contraindicated if GFR <30 mL/min/1.73m2. For GFR 30-50 mL/min/1.73m2, use with caution and reduce dose to half tablet daily. Not recommended for GFR <30. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh class C). For Child-Pugh class A or B, use with caution and monitor electrolytes; no specific dose reduction established but consider starting at lowest dose. |
| Pediatric use | Safety and efficacy not established in pediatric patients. No standard dosing recommendations. |
| Geriatric use | Start at lowest dose (half tablet daily) and titrate slowly. Monitor renal function and electrolytes closely due to increased risk of hyperkalemia and hyponatremia. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MAXZIDE-25 (MAXZIDE-25).
| Breastfeeding | HCTZ excreted in breast milk in low concentrations (M/P ratio ~0.4-0.6). Triamterene: limited data; possibly excreted, but unknown. Use caution; may suppress lactation due to diuretic effect. Avoid use during breastfeeding unless essential. |
| Teratogenic Risk | First trimester: Hydrochlorothiazide (HCTZ) crosses placenta; association with congenital anomalies not definitively established, but theoretical risk of neural tube defects or cleft lip/palate due to folate antagonism. Triamterene: weak antifolate; limited human data, but potential risk additive. Second and third trimesters: Decreased placental perfusion; risk of fetal/neonatal jaundice, thrombocytopenia, electrolyte disturbances (hyponatremia, hypokalemia), and possible fetal growth restriction. |
■ FDA Black Box Warning
None
| Serious Effects |
["Anuria","Acute or chronic renal insufficiency (CrCl <10 mL/min)","Hyperkalemia (serum potassium >5.5 mEq/L)","Concurrent use of other potassium-sparing diuretics or potassium supplements","Hypersensitivity to hydrochlorothiazide, triamterene, or sulfonamides"]
| Precautions | ["Hyperkalemia: risk increased with renal impairment, diabetes, or concurrent use of ACE inhibitors, ARBs, NSAIDs, or potassium supplements.","Impaired renal function: monitor serum potassium and creatinine.","Electrolyte imbalances: hyponatremia, hypomagnesemia, hypochloremia.","Metabolic acidosis: may occur with triamterene.","Hypotension: especially with volume depletion.","Acute angle-closure glaucoma: rare with hydrochlorothiazide.","Sulfonamide cross-reactivity: hydrochlorothiazide may cause allergic reactions in sulfonamide-allergic patients.","Systemic lupus erythematosus exacerbation."] |
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| Fetal Monitoring | Maternal: Blood pressure, serum electrolytes (K, Na, Cl), BUN, creatinine, uric acid, glucose. Fetal: Ultrasound for growth assessment, amniotic fluid volume; neonatal monitoring for electrolyte imbalances, jaundice. |
| Fertility Effects | Data limited. No known direct impact on fertility. However, electrolyte imbalance or dehydration could theoretically affect ovulation. Triamterene may interfere with folate metabolism; folate supplementation recommended for women of childbearing age. |