ENDURON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ENDURON (ENDURON).
Thiazide diuretic that inhibits the sodium-chloride symporter in the distal convoluted tubule of the nephron, reducing sodium and chloride reabsorption and increasing water excretion.
| Metabolism | Primarily metabolized by cytochrome P450 enzymes; undergoes glucuronidation; elimination half-life approximately 2 hours. |
| Excretion | Primarily renal (approximately 50-70% as unchanged drug); biliary/fecal (15-30%); dose adjustment required in renal impairment (CrCl <30 mL/min). |
| Half-life | Terminal elimination half-life: 24-48 hours (mean 36 hours); prolonged in renal impairment or heart failure, allowing once-daily dosing. |
| Protein binding | Approximately 95-99% bound to albumin and plasma proteins. |
| Volume of Distribution | Apparent Vd: 3-5 L/kg (large due to extensive tissue binding, especially to erythrocytes and vascular smooth muscle). |
| Bioavailability | Oral: 40-60% (first-pass hepatic metabolism; food may reduce absorption). |
| Onset of Action | Oral: 2-3 hours after single dose; diuretic effect begins within 1-2 hours, peak at 4-6 hours; antihypertensive effect requires 1-2 weeks for full response. |
| Duration of Action | Diuretic effect: 12-24 hours (single dose); antihypertensive: 24 hours with once-daily dosing; sustained effect in chronic use due to long half-life. |
| Molecular Weight | 524.6 |
Oral, 2.5–5 mg once daily. Maximum dose 10 mg/day.
| Dosage form | TABLET |
| Renal impairment | CrCl <30 mL/min: avoid use. CrCl 30–60 mL/min: reduce dose by 50%. |
| Liver impairment | Child-Pugh B/C: contraindicated. Child-Pugh A: reduce dose by 50%. |
| Pediatric use | Weight-based: 0.05–0.1 mg/kg orally once daily. Maximum 5 mg/day. |
| Geriatric use | Initiate at 1.25 mg orally once daily; titrate cautiously due to increased risk of hypotension and electrolyte disturbances. |
| 1st trimester | Contraindicated due to risk of fetal hypotension, oligohydramnios, and renal impairment. |
| 2nd trimester | Contraindicated; may cause oligohydramnios, fetal renal dysfunction, and skull ossification defects. |
| 3rd trimester | Contraindicated; risk of neonatal hypotension, oligohydramnios, anuria, and hyperkalemia. |
Clinical note
Comprehensive clinical and safety monograph for ENDURON (ENDURON).
| Placental transfer | Crosses the placenta extensively in animal studies and humans; documented in cord blood and amniotic fluid. |
| Breastfeeding | Excreted into breast milk in low amounts; potential for adverse effects in nursing infants such as hypotension and electrolyte disturbances. Use caution, especially in neonates. |
| Lactation Rating |
■ FDA Black Box Warning
No FDA black box warnings.
| Serious Effects |
Hypersensitivity to ENDURON or any ACE inhibitorHistory of angioedema related to previous ACE inhibitor therapyPregnancy (second and third trimesters)Bilateral renal artery stenosisConcomitant use with aliskiren in patients with diabetes mellitus
| Precautions | Electrolyte imbalance (hypokalemia, hyponatremia, hypomagnesemia), Hyperuricemia and gout, Hyperglycemia and impaired glucose tolerance, Orthostatic hypotension, Systemic lupus erythematosus exacerbation |
| Food/Dietary | Avoid excessive salt intake to reduce hypertension. High-potassium foods (bananas, oranges, spinach) are not restricted unless on potassium supplements or with kidney disease. Limit alcohol. Grapefruit juice may increase effect; monitor blood pressure. |
Loading safety data…
| L3 - Moderately Safe |
| Teratogenic Risk | ENDURON (methylothiazide) is a thiazide diuretic. First trimester: Crosses placenta; theoretical risk of teratogenicity due to reduced placental perfusion, but no consistent human data; avoid if possible. Second/third trimester: May cause fetal electrolyte disturbances, icterus, thrombocytopenia; use only if clearly needed. Neonatal: Hypoglycemia, electrolyte imbalance, hypotension possible if used near term. |
| Fetal Monitoring | Monitor maternal serum electrolytes (Na, K, Cl), uric acid, glucose, renal function (BUN, Cr), blood pressure. Fetal: serial growth ultrasound (due to possible uteroplacental insufficiency) and non-stress test in third trimester if used. |
| Fertility Effects | No direct evidence of impaired fertility. Thiazides may cause hyperuricemia and glucose intolerance, but effect on ovulation or spermatogenesis not established. |
| Clinical Pearls | ENDURON (methylothiazide) is a thiazide diuretic. Monitor electrolytes, especially potassium and sodium. Can exacerbate gout and hyperglycemia. Avoid in severe renal impairment (CrCl <30 mL/min). May increase lithium levels. Start low and titrate to avoid hypotension. |
| Patient Advice | Take exactly as prescribed, usually once daily in the morning to avoid nighttime urination. · May cause dizziness or lightheadedness; avoid sudden standing up. · Report symptoms of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, excessive thirst. · Avoid alcohol and NSAIDs which can increase side effects. · Use sunscreen; this medication can increase sun sensitivity. · Do not stop suddenly; may need to taper under doctor guidance. |