MIDAMOR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MIDAMOR (MIDAMOR).
Amiloride is a potassium-sparing diuretic that blocks epithelial sodium channels (ENaC) in the distal convoluted tubule and collecting duct, reducing sodium reabsorption and potassium excretion.
| Metabolism | Amiloride is not metabolized in the liver; it is excreted unchanged primarily via the kidneys. |
| Excretion | Renal: 80-90% as unchanged drug; biliary/fecal: <5% |
| Half-life | Terminal half-life 6-9 hours; prolonged in renal impairment (up to 20 hours) and in heart failure |
| Protein binding | 40-50% bound to plasma proteins, primarily albumin |
| Volume of Distribution | 1-2 L/kg; indicates extensive tissue distribution |
| Bioavailability | Oral: 80-90%; intravenous: 100% |
| Onset of Action | Oral: 2-4 hours; intravenous: 15-30 minutes |
| Duration of Action | Oral: 12-24 hours; intravenous: 6-12 hours; duration extended with renal impairment |
5 mg orally once daily, increased to 10 mg if needed; maximum 20 mg/day.
| Dosage form | TABLET |
| Renal impairment | Contraindicated if eGFR <30 mL/min/1.73m². For eGFR 30-50, reduce dose to 2.5 mg daily and monitor potassium. |
| Liver impairment | Avoid in severe hepatic impairment (Child-Pugh C). For moderate impairment (Child-Pugh B), reduce dose to 2.5 mg daily. |
| Pediatric use | Not recommended for use in children <18 years due to lack of safety and efficacy data. |
| Geriatric use | Start at 2.5 mg daily; monitor potassium and renal function closely due to age-related decline in renal function and risk of hyperkalemia. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MIDAMOR (MIDAMOR).
| Breastfeeding | Amiloride (active ingredient in Midamor) is excreted into human milk in low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.3. The total daily infant dose via milk is estimated to be less than 1% of the maternal dose, which corresponds to <0.2 mg/kg/day. Risk to breastfeeding infant is considered minimal, but caution is advised, especially in premature or renally impaired infants, due to potential potassium-sparing diuretic effects. |
| Teratogenic Risk | FDA Pregnancy Category B. First trimester: No evidence of increased risk of major congenital malformations based on adequate human data. Second and third trimesters: No documented teratogenicity; however, use only if clearly needed due to potential maternal volume contraction and reduced placental perfusion. |
■ FDA Black Box Warning
Not applicable (no FDA black box warning).
| Serious Effects |
["Anuria","Acute or chronic renal insufficiency (eGFR <10-15 mL/min)","Pre-existing hyperkalemia (serum potassium >5.5 mEq/L)","Concomitant use of other potassium-sparing diuretics or potassium supplements (unless severe hypokalemia)","Hypersensitivity to amiloride or any component of the formulation"]
| Precautions | ["Hyperkalemia: risk increased with renal impairment, elderly, diabetes, or concomitant use of potassium supplements, ACE inhibitors, ARBs, NSAIDs, or other potassium-sparing diuretics","Electrolyte imbalances: hyponatremia, hypochloremia, hypercalcemia","Renal impairment: contraindicated in anuria, acute/chronic renal insufficiency (eGFR <10-15 mL/min)","Metabolic acidosis: may occur in patients with renal dysfunction or diabetes","Drug interactions: lithium toxicity risk; monitor serum potassium closely"] |
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| Fetal Monitoring | Monitor maternal renal function (serum creatinine, BUN), serum electrolytes (especially potassium and sodium), and blood pressure throughout pregnancy. Assess fetal growth via serial ultrasound (e.g., every 4-6 weeks) to rule out intrauterine growth restriction due to potential maternal volume depletion. Monitor for maternal hyperkalemia, particularly in combination with ACE inhibitors or ARBs. |
| Fertility Effects | No known adverse effects on male or female fertility in human studies. Animal reproductive studies show no impairment of fertility at clinically relevant doses. Theoretical concern of electrolyte disturbances affecting reproductive hormone function, but no clinical data support this. |