amiloride (Rx)

Brand and Other Names:Midamor
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Dosing & Uses


Dosage Forms & Strengths


  • 5mg

Congestive Heart Failure

5-10 mg/day PO qDay OR divided q12hr


5-10 mg/day PO qDay OR divided q12hr

Thiazide-Induced Hypokalemia

5-10 mg/day PO qDay OR divided q12hr

Renal Impairment

CrCl 10-50 mL/minute: 50% normal dose

CrCl <10 mL/minute: Not recommended

Overdose Management

May use normal saline for volume replacement

May use dopamine or norepinephrine to treat hypotension

Treat hyperkalemia with IV glucose (dextrose 25% in water) with rapid acting insulin with concurrent IV sodium bicarbonate and use oral or rectal solutions of kayexalate in sorbitol if needed

If dysrhythmia due to decreased K+ or Mg+ suspected replace aggressively

Discontinue treatment if no symptoms after 6hr

Other Information

Take with food

Monitor: Serum potassium

See also combo with hydrochlorothiazide

Other Indications & Uses

Off-label: cystic fibrosis, Li-induced polyuria

Dosage Forms & Strengths


  • 5mg

Hypertension (Off-label)

0.4-0.625 mg/kg/day PO; not to exceed 20 mg/day

5-10 mg/day PO qDay OR every other day

Maximum dosage limit: 20 mg PO qDay; 40 mg PO qDay has been used

Elderly patients may be more sensitive to the diuretic effects of the drug and are more likely to have age-associated renal dysfunction



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            Adverse Effects


            Hyperkalemia (10%)

            Anorexia (3-8%)

            Diarrhea (3-8%)

            Headache (3-8%)

            Nausea (3-8%)

            Vomiting (3-8%)

            Abdominal pain (<3%)

            Appetite changes (<3%)

            Constipation (<3%)

            Cough (<3%)

            Dizziness (<3%)

            Dyspnea (<3%)

            Encephalopathy (<3%)

            Fatigue (<3%)

            Gas pain (<3%)

            Impotence (<3%)

            Muscle cramps (<3%)

            Weakness (<3%)



            Black Box Warnings

            Like other potassium-conserving agents, amiloride may cause hyperkalemia (serum potassium levels greater than 5.5 mEq/L), which, if not corrected, is potentially fatal.

            Hyperkalemia occurs commonly (about 10%) when amiloride is used without a kaliuretic diuretic.

            This incidence is greater in patients with renal impairment, diabetes mellitus (with or without recognized renal insufficiency), and in elderly persons.

            When amiloride is used concomitantly with a thiazide diuretic in patients without these complications, the risk of hyperkalemia is reduced to about 1-2%. Monitoring serum potassium levels carefully in any patient receiving amiloride is essential, particularly when it is first introduced, at the time of diuretic dosage adjustments, and during any illness that could affect renal function.


            Hypersensitivity to amiloride

            Hyperkalemia (K+ >5.5 mEq/L [5.5 mmol/L])

            Concomitant use with K+-sparing diuretic, or K supplementation

            Impaired renal function (Scr >1.5 mg/dL [132.6 umol/L], or BUN >30 mg/dL [10.7 mmol/L]) diabetes



            • The risk of hyperkalemia may be increased when potassium-conserving agents, including amiloride hydrochloride are administered concomitantly with an angiotensin-converting enzyme inhibitor, an angiotensin II receptor antagonist, cyclosporine or tacrolimus
            • Warning signs or symptoms of hyperkalemia include paresthesias, muscular weakness, fatigue, flaccid paralysis of the extremities, bradycardia, shock, and ECG abnormalities; monitoring of the serum potassium level is essential because mild hyperkalemia is not usually associated with an abnormal ECG
            • When abnormal, the ECG in hyperkalemia is characterized primarily by tall, peaked T waves or elevations from previous tracings; there may also be lowering of the R wave and increased depth of the S wave, widening and even disappearance of the P wave, progressive widening of the QRS complex, prolongation of the PR interval, and ST depression
            • If hyperkalemia occurs the drug should be discontinued immediately; if serum potassium level exceeds 6.5 mEq per liter, active measures should be taken to reduce it; such measures include the intravenous administration of sodium bicarbonate solution or oral or parenteral glucose with a rapid-acting insulin preparation; if needed, a cation exchange resin such as sodium polystyrene sulfonate may be given orally or by enema; patients with persistent hyperkalemia may require dialysis

            Diabetes Mellitus

            • In diabetic patients, hyperkalemia has been reported with the use of all potassium-conserving diuretics, including amiloride hydrochloride, even in patients without evidence of diabetic nephropathy; therefore, amiloride should be avoided, if possible, in diabetic patients and, if it is used, serum electrolytes and renal function must be monitored frequently; amiloride should be discontinued at least 3 days before glucose tolerance testing

            Metabolic or Respiratory Acidosis

            • Antikaliuretic therapy should be instituted only with caution in severely ill patients in whom respiratory or metabolic acidosis may occur, such as patients with cardiopulmonary disease or poorly controlled diabetes
            • If therapy is administered to these patients, frequent monitoring of acid-base balance necessary; shifts in acid-base balance alter ratio of extracellular/intracellular potassium, and development of acidosis may be associated with rapid increases in serum potassium levels
            • In patients with renal disease, diuretics may precipitate azotemia; cumulative effects of the components of amiloride hydrochloride may develop in patients with impaired renal function; if renal impairment becomes evident discontinue therapy

            Drug interaction overview

            • In some patients, the administration of a non-steroidal anti-inflammatory agent can reduce the diuretic, natriuretic, and antihypertensive effects of loop and potassium-sparing diuretics
            • When amiloride and non-steroidal anti-inflammatory agents are used concomitantly, the patient should be observed closely to determine if the desired effect of the diuretic is obtained
            • Since indomethacin and potassium-sparing diuretics, including this product, may each be associated with increased serum potassium levels, the potential effects on potassium kinetics and renal function should be considered when these agents are administered concurrently

            Pregnancy & Lactation


            Teratogenicity studies in rabbits and mice given 20 and 25 times maximum human dose, respectively, revealed no evidence of harm to fetus, although studies showed that the drug crossed the placenta in modest amounts; reproduction studies in rats at 20 times the expected maximum daily dose for humans showed no evidence of impaired fertility

            At approximately 5 or more times the expected maximum daily dose for humans, some toxicity was seen in adult rats and rabbits and a decrease in rat pup growth and survival occurred


            Studies in rats have shown that amiloride is excreted in milk in concentrations higher than those found in blood, but it is not known whether amiloride hydrochloride is excreted in human milk

            Because of the potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother

            Pregnancy Categories

            A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA: Information not available.



            Mechanism of Action

            Exerts its potassium sparing effect through the inhibition of sodium reabsorption at the distal convoluted tubule, cortical collecting tubule and collecting duct; this decreases the net negative potential of the tubular lumen and reduces both potassium and hydrogen secretion and their subsequent excretion. This mechanism accounts in large part for the potassium sparing action of amiloride.

            Inhibits Na/K-ATPase, decreases Ca++, Mg++ and hydrogen excretion


            Half-Life: 6-9 hr

            Duration: 24 hr

            Onset: initial effect: 2-3 hr, max effect: 6-10 hr

            Peak Plasma Time: 3-4 hr

            Bioavailability: 30-90%

            Protein Bound: 23%

            Vd: 350-380 L

            Metabolism: NOT metabolized in the liver; no active metabolites


            • Urine: 50%
            • Feces: 40-50%




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            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
            3 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
            4 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            6 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            NC NOT COVERED – Drugs that are not covered by the plan.
            Code Definition
            PA Prior Authorization
            Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
            QL Quantity Limits
            Drugs that have quantity limits associated with each prescription. This restriction typically limits the quantity of the drug that will be covered.
            ST Step Therapy
            Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
            OR Other Restrictions
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            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.