HYDROCHLOROTHIAZIDE

Hydrochlorothiazide is a diuretic and antihypertensive. It is the 3,4-dihydro derivative of chlorothiazide. It is chemically designated as 6-chloro-3,4-dihydro-2 H -1,2,4-benzothiadiazine-7-sulfonamide 1,1-dioxide and it has the following structural formula: Hydrochloro­thiazide USP is a white, or practically white, crystalline powder which is slightly soluble in water, but freely soluble in sodium hydroxide solution. Each tablet for oral administration contains 25 mg or 50 mg hydrochlorothiazide USP. In addition, each tablet contains the following inactive ingredients: dibasic calcium phosphate, lactose monohydrate, pregelatinized starch, FD&C yellow No.6 lake, corn starch, colloidal silicon dioxide, and magnesium stearate. Chemical Structure

Hydrochlorothiazide tablets, USP are indicated as adjunctive therapy in edema associated with congestive heart failure, hepatic cirrhosis, and corticosteroid and estrogen therapy. Hydrochlorothiazide tablets, USP have also been found useful in edema due to various forms of renal dysfunction such as nephrotic syndrome, acute glomerulonephritis, and chronic renal failure. Hydrochlorothiazide tablets, USP are indicated in the management of hypertension either as the sole therapeutic agent or to enhance the effectiveness of other antihypertensive drugs in the more severe forms of hypertension. Use in Pregnancy Routine use of diuretics during normal pregnancy is inappropriate and exposes mother and fetus to unnecessary hazard. Diuretics do not prevent development of toxemia of pregnancy and there is no satisfactory evidence that they are useful in the treatment of toxemia. Edema during pregnancy may arise from pathologic causes or from the physiologic and mechanical consequences of pregnancy. Thiazides are indicated in pregnancy when edema is due to pathologic causes, just as they are in the absence of pregnancy (see PRECAUTIONS, Pregnancy ). Dependent edema in pregnan­cy, resulting from restriction of venous return by the gravid uterus, is properly treated through elevation of the lower extremities and use of support stockings. Use of diuretics to lower intravascular volume in this instance is illogical and unneces­sary. During normal pregnancy there is hypervolemia which is not harmful to the fetus or the mother in the absence of cardiovascular disease. However, it may be associated with edema, rarely generalized edema. If such edema causes discomfort, in­creased recumbency will often provide relief. Rarely this edema may cause extreme discomfort which is not relieved by rest. In these instances, a short course of diuretic therapy may provide relief and be appropriate.

Therapy should be individualized according to patient response. Use the smallest dosage necessary to achieve the required response. Adults For Edema The usual adult dosage is 25 mg to 100 mg daily as a single or divided dose. Many patients with edema respond to intermittent therapy, i.e., administration on alternate days or on 3 to 5 days each week. With an intermittent schedule, excessive response and the resulting undesirable electrolyte imbalance are less likely to occur. For Control of Hypertension The usual initial dose in adults is 25 mg daily given as a single dose. The dose may be increased to 50 mg daily, given as a single or two divided doses. Doses above 50 mg are often associated with marked reductions in serum potassium (see also PRECAUTIONS ). Patients usually do not require doses in excess of 50 mg of hydrochlorothiazide daily when used concomitantly with other antihypertensive agents. Infants and Children For Diuresis and for Control of Hypertension The usual pediatric dosage is 0.5 mg to 1 mg per pound (1 to 2 mg/kg) per day in single or two divided doses, not to exceed 37.5 mg per day in infants up to 2 years of age or 100 mg per day in children 2 to 12 years of age. In infants less than 6 months of age, doses up to 1.5 mg per pound (3 mg/kg) per day in two divided doses may be required. (See PRECAUTIONS, Pediatric Use .)

Anuria. Hypersensitivity to this product or to other sulfonamide-derived drugs.

The following adverse reactions have been reported and, within each category, are listed in the order of decreasing severity. Body as a Whole Weakness. Cardiovascular Hypotension including orthostatic hypotension (may be aggravated by alcohol, barbiturates, narcotics or antihypertensive drugs). Digestive Pancreatitis, jaundice (intrahepatic cholestatic jaundice), diarrhea, vomiting, sialadenitis, cramping, constipation, gastric irritation, nausea, anorexia. Hematologic Aplastic anemia, agranulocytosis, leukopenia, hemolytic anemia, thrombocytopenia. Hypersensitivity Anaphylactic reactions, necrotizing angiitis (vasculitis and cutaneous vasculitis), respiratory distress including pneumonitis and pulmonary edema, photosensitivity, fever, urticaria, rash, purpura. Metabolic Electrolyte imbalance (see PRECAUTIONS ), hyperglycemia, glycosuria, hyperuricemia. Musculoskeletal Muscle spasm. Nervous System/Psychiatric Vertigo, paresthesias, dizziness, headache, restlessness. Renal Renal failure, renal dysfunction, interstitial nephritis (see WARNINGS ). Skin Erythema multiforme including Stevens-Johnson syndrome, exfoliative dermatitis including toxic epidermal necrolysis, alopecia. Special Senses Transient blurred vision, xanthopsia. Urogenital Impotence. Non-melanoma Skin Cancer Hydrochlorothiazide is associated with an increased risk of non-melanoma skin cancer. In a study conducted in the Sentinel System, increased risk was predominantly for squamous cell carcinoma (SCC) and in white patients taking large cumulative doses. The increased risk for SCC in the overall population was approximately 1 additional case per 16,000 patients per year, and for white patients taking a cumulative dose of ≥50,000 mg the risk increase was approximately 1 additional SCC case for every 6,700 patients per year. Whenever adverse reactions are moderate or severe, thiazide dosage should be reduced or therapy withdrawn.

When given concurrently the following drugs may interact with thiazide diuretics. Alcohol, Barbiturates, or Narcotics Potentiation of orthostatic hypotension may occur. Antidiabetic Drugs (Oral Agents and Insulin) Dosage adjustment of the antidiabetic drug may be required. Other Antihypertensive Drugs Additive effect or potentiation. Cholestyramine and Colestipol Resins Absorption of hydrochlorothiazide is impaired in the presence of anionic exchange resins. Single doses of either cholestyramine or colestipol resins bind the hydrochlorothiazide and reduce its absorption from the gastrointestinal tract by up to 85% and 43%, respectively. Corticosteroids, ACTH Intensified electrolyte depletion, particularly hypokalemia. Pressor Amines (e.g., Norepinephrine) Possible decreased response to pressor amines but not sufficient to preclude their use. Skeletal Muscle Relaxants, Nondepolarizing (e.g., Tubocurarine) Possible increased responsiveness to the muscle relaxant. Lithium Generally should not be given with diuretics. Diuretic agents reduce the renal clear­ance of lithium and add a high risk of lithium tox­icity. Refer to the package insert for lithium preparations before use of such preparations with hydrochloro­thiazide. Non-Steroidal Anti-Inflammatory Drugs In some patients, the administration of a non-steroidal anti-inflammatory agent can reduce the diuretic, natriuretic, and antihypertensive effects of loop, potassium-sparing and thiazide diuretics. Therefore, when hydrochlorothiazide 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.