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Hydrochlorothiazide and Amiloride Hydrochloride

Tablets USP 50/5mg

Diuretic - Antihypertensive

PHARMACOLOGY: APO-AMILZIDE (hydrochlorothiazide and amiloride hydrochloride) is a diuretic/antihypertensive combining the potent natriuretic action of hydrochlorothiazide with the potassium conserving property of amiloride hydrochloride. The mild diuretic and antihypertensive actions of amiloride hydrochloride are additive to the natriuretic, diuretic and antihypertensive activity of the thiazide while minimizing the loss of potassium and lessening the likelihood of acid base imbalance. The onset of the diuretic action of APO-AMILZIDE is within 1 to 2 hours and this action appears to be sustained for approximately 24 hours.

Hydrochlorothiazide : Hydrochlorothiazide is a diuretic and antihypertensive agent. It affects the renal tubular mechanism of electrolyte reabsorption. Hydrochlorothiazide increases excretion of sodium and chloride in approximately equivalent amounts and may cause a simultaneous, usually minimal, loss of bicarbonate. Natriuresis is usually accompanied by some loss of potassium. The mechanism of the antihypertensive effect of thiazides may be related to the excretion and redistribution of body sodium. Hydrochlorothiazide usually does not decrease normal blood pressure. The onset of the diuretic action of hydrochlorothiazide occurs in 2 hours and the peak action in about 4 hours. Diuretic activity lasts about 6 to 12 hours. Hydrochlorothiazide is eliminated rapidly by the kidney.

Amiloride Hydrochloride : Amiloride hydrochloride is an antikaliuretic drug with mild natriuretic diuretic and antihypertensive activity. These activities may be additive to the effects of thiazides or other saluretic diuretic agents. The principal use of amiloride hydrochloride is to conserve potassium in selected patients receiving kaliuretic-diuretic agents. The action is not related to the level of aldosterone excretion. Amiloride hydrochloride is not an aldosterone antagonist. The drug acts directly on the distal portion of the nephron. Amiloride hydrochloride causes an increase in sodium excretion and a decrease in potassium and hydrogen ion excretion. Chloride excretion may remain unchanged or increase slowly with continued therapy. Approximately 50% of an oral dose is absorbed. Amiloride hydrochloride usually begins to act within 2 hours after an oral dose. Its effect on electrolyte excretion reaches a peak between 6 and 10 hours and lasts about 24 hours. Peak plasma levels are obtained in 3 to 4 hours and plasma half- life varies from 6 to 9 hours. Amiloride hydrochloride is not metabolized by the liver. About 50% of a 20mg dose amiloride hydrochloride is excreted unchanged in the urine and 40% is excreted in the stool within 72 hours. In clinical studies amiloride hydrochloride was found to have little effect on glomerular filtration rate or renal blood flow. Bioavailability studies were performed using normal human volunteers. The rate and extent of absorption after a single oral dose of 5mg amiloride and 50mg hydrochlorothiazide in the form of APO-AMILZIDE 5-50mg and Moduret 5-50mg was measured and compared. The results can be summarized as follows:

Amiloride HCI Moduret (SD*) Apo-Amilizide (SD*)
AUC 0-24 (ng-hr/ml) 62.5 (21.0) 66.8 (18.4)
Cmax (ng/ml) 6.0 (2.2) 6.7 (2.4)
Tmas (hrs) 3.8 (0.6) 3.3 (0.8)
t (hrs) 8.2 (2.5) 9.6 (3.8)
AUC 0-24 (ng-hr/ml) 1603 (414) 1654 (426)
Cmax (ng/ml) 235 (73) 242 (60)
Tmax (hrs) 2.3 (1.0) 2.4 (0.8)
t (hrs) 9.1 (3.3) 10.0 (5.6)
*SD - Standard Deviation    

INDICATIONS AND CLINICAL USES: Fixed-dose combination drugs are not indicated for initial therapy. Patients should be titrated on the individual drugs. If the fixed combination represents the dosage so determined, its use may be more convenient in patient management. If during maintenance therapy dosage adjustment is necessary, it is advisable to use the individual drugs. APO-AMILZIDE (hydrochlorothiazide and amiloride hydrochloride) is indicated in the maintenance therapy of: patients with hepatic cirrhosis with ascities and edema. Patients with edema of cardiac origin or with arterial hypertension who are hypokalemic or in whom maintenance of normal potassium levels is considered to be clinically important i.e., digitalized patients, patients in whom adequate dietary intake of potassium is not feasible or patients with cardiac arrhythmias. _: Amiloride hydrochloride used alone may provide satisfactory diuresis with diminished potassium loss and with a reduced risk of metabolic alkalosis. In resistant cases amiloride hydrochloride may be used with kaliuretic diuretic agents to help produce satisfactory diuretics, while maintaining a more balanced serum electrolyte pattern. As with all therapy for the ascites of hepatic cirrhosis, gradual weight loss and avoidance of electrolyte imbalance are the chief objectives (see PRECAUTIONS).

CONTRAINDICATIONS: Hyperkalemia : APO-AMILZIDE (hydrochlorothiazide and amiloride hydrochloride) should not be used in the presence of elevated serum potassium levels (see WARNINGS). Antikaliuretic Therapy or Potassium Salts : Other antikaliuretic agents and potassium supplements are contraindicated in patients receiving APO-AMILZIDE (such combination therapy is commonly associated with rapid increases in plasma potassium levels). Impaired Renal Function : Anuria, acute renal failure, severe or progressive renal disease and diabetic nephropathy are contraindications to the use of APO-AMILZIDE (see WARNINGS). Hypersensitivity : APO-AMILZIDE is contraindicated in patients who are hypersensitive to either component or to other sulfonamide derived drugs.

WARNINGS : Hvperkalemia: Hyperkalemia, i.e. serum potassium levels over 5.5mEq per litre, has been observed in some patients who received amiloride hydrochloride either alone or with diuretics. This has been noted particularly in elderly patients, in diabetic patients, and in hospitalized patients with hepatic cirrhosis or cardiac edema who had known renal impairment, were seriously ill, or were receiving vigorous diuretic therapy. Since fatalities have occurred in such patients, they should be monitored carefully for clinical, laboratory and electrocardiographic (ECG) evidence of hyperkalemia and for acidoses. Monitoring of the serum potassium level is important because hyperkalemia is not always associated with an abnormal ECG. Warning signs or symptoms of hyperkalemia include paresthesias, muscular weakness, fatigue, flaccid paralysis of the extremities, bradycardia, shock, and ECG abnormalities. 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 in patients taking APO-AMILZIDE (hydrochlorothiazide and amiloride hydrochloride), the drug should be discontinued immediately. If the serum potassium level exceeds 6.5mEq per litre, active measures should be taken to reduce it. Such measures include the intravenous administration of sodium bicarbonate solution or oral or parenteral. 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 commonly reported with the use of amiloride hydrochloride, particularly if they have chronic renal disease or pre-renal azotemia. Some deaths occurred in this last group of patients. Therefore, if therapy with amiloride hydrochloride is considered essential, the drug should be used with caution in diabetic or suspected diabetic patients and only after first determining the status of renal function. Careful monitoring of serum potassium levels is required throughout the therapy. One patient with poorly controlled diabetes mellitus who became severely hyperkalemia while on amiloride hydrochloride died following two repeated intravenous glucose tolerance tests. Therefore, amiloride hydrochloride should be discontinued at least 3 days before glucose tolerance testing. In diabetic patients, insulin requirements may be increased, decreased or unchanged due to the hydrochlorothiazide component. Diabetes mellitus which has been latent may become manifest during administration of thiazide diuretics. Metabolic or Respiratory Acidosis: Antikaliuretic therapy should be instituted only with caution in patients in whom respiratory or metabolic acidosis may occur, such as patients with cardiopulmonary disease or diabetes. If APO-AMILZIDE is given to these patients, frequent monitoring of acid base balance is necessary. Shifts in acid-base balance alter the ratio of extracellular/intracellular potassium, and the development of acidosis may be associated with rapid increases in serum potassium levels. Impaired Renal Function: Patients with impaired renal function other than those listed under CONTRA-INDICATIONS and who have BUN levels over 30mg per 100ml, serum creatinine levels over 1.5mg per 100ml, or blood urea values over 60mg per 100ml, should not receive the drug without careful, frequent monitoring of serum electrolyte, creatinine and BUN levels. Potassium retention associated with the use of APO-AMILZIDE is accentuated in the presence of renal impairment and may result in the rapid development of hyperkalemia. Prolongation of amiloride hydrochloride excretion was observed in patients with renal impairment.

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