HYDROCHLOROTHIAZIDE

Hydrochlorothiazide, USP is the 3,4-dihydro derivative of chlorothiazide. Its chemical name is 6-Chloro-3,4-dihydro-2 H -1,2,4-benzothiadiazine-7-sulfonamide 1,1-dioxide. Its molecular formula is C 7 H 8 ClN 3 O 4 S 2 ; its molecular weight is 297.74; and its structural formula is: It is a white, or practically white, crystalline powder which is slightly soluble in water, but freely soluble in sodium hydroxide solution. Hydrochlorothiazide is supplied as 12.5 mg capsules for oral use. Inactive ingredients : Black iron oxide, colloidal silicon dioxide, gelatin, magnesium stearate, microcrystalline cellulose, pregelatinized starch, sodium lauryl sulfate and titanium dioxide. FDA approved dissolution test specifications differ from USP. Structure of Hydrochlorothiazide

Hydrochlorothiazide capsules are indicated in the management of hypertension either as the sole therapeutic agent, or in combination with other antihypertensives. Unlike potassium sparing combination diuretic products, hydrochlorothiazide capsules may be used in those patients in whom the development of hyperkalemia cannot be risked, including patients taking ACE inhibitors. Usage in Pregnancy : The routine use of diuretics in an otherwise healthy woman 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 developed toxemia. Edema during pregnancy may arise from pathological causes or from the physiologic and mechanical consequences of pregnancy. Diuretics are indicated in pregnancy when edema is due to pathologic causes, just as they are in the absence of pregnancy. Dependent edema in pregnancy resulting from restriction of venous return by the expanded uterus is properly treated through elevation of the lower extremities and use of support hose; use of diuretics to lower intravascular volume in this case is illogical and unnecessary. There is hypervolemia during normal pregnancy which is harmful to neither the fetus nor the mother (in the absence of cardiovascular disease), but which is associated with edema, including generalized edema in the majority of pregnant women. If this edema produces discomfort, increased recumbency will often provide relief. In rare instances this edema may cause extreme discomfort which is not relieved by rest. In these cases a short course of diuretics may provide relief and may be appropriate.

For Control of Hypertension: The adult initial dose of hydrochlorothiazide capsules is one capsule given once daily whether given alone or in combination with other antihypertensives. Total daily doses greater than 50 mg are not recommended.

Hydrochlorothiazide capsules are contraindicated in patients with anuria. Hypersensitivity to this product or other sulfonamide derived drugs is also contraindicated.

The adverse reactions associated with hydrochlorothiazide have been shown to be dose related. In controlled clinical trials, the adverse events reported with doses of 12.5 mg hydrochlorothiazide once daily were comparable to placebo. The following adverse reactions have been reported for doses of hydrochlorothiazide 25 mg and greater 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, paresthesia, 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. Whenever adverse reactions are moderate or severe, thiazide dosage should be reduced or therapy withdrawn. Postmarketing Experience: The following adverse reaction has been identified during post-approval use of hydrochlorothiazide. Because the reaction is reported voluntarily from a population of uncertain size, it is not possible to reliably estimate the frequency or establish a causal relationship to drug exposure. 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 ≥50,000mg the risk increase was approximately 1 additional SCC case for every 6,700 patients per year.

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 - Cholestyramine and colestipol resins bind the hydrochlorothiazide and reduce its absorption from the gastrointestinal tract by up to 85 and 43 percent, respectively. Corticosteroid, 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 greatly increase the 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. When hydrochlorothiazide and non-steroidal anti-inflammatory agents are used concomitantly, the patients should be observed closely to determine if the desired effect of the diuretic is obtained. Drug/Laboratory Test Interactions - Thiazides should be discontinued before carrying out tests for parathyroid function (see PRECAUTIONS , General). Carcinogenesis, Mutagenesis, Impairment of Fertility: Two-year feeding studies in mice and rats conducted under the auspices of the National Toxicology Program (NTP) uncovered no evidence of a carcinogenic potential of hydrochlorothiazide in female mice (at doses of up to approximately 600 mg/kg/day) or in male and female rats (at doses of approximately 100 mg/kg/day). The NTP, however, found equivocal evidence for hepatocarcinogenicity in male mice. Hydrochlorothiazide was not genotoxic in vitro in the Ames mutagenicity assay of Salmonella typhimurium strains TA 98, TA 100, TA 1535, TA 1537, and TA 1538 and in the Chinese Hamster Ovary (CHO) test for chromosomal aberrations, or in vivo in assays using mouse germinal cell chromosomes, Chinese hamster bone marrow chromosomes, and the Drosophila sex-linked recessive lethal trait gene. Positive test results were obtained only in the in vitro CHO Sister Chromatid Exchange (clastogenicity) and in the Mouse Lymphoma Cell (mutagenicity) assays, using concentrations of hydrochlorothiazide from 43 to 1,300 mcg/mL, and in the Aspergillus nidulans non-disjunction assay at an unspecified concentration. Hydrochlorothiazide had no adverse effects on the fertility of mice and rats of either sex in studies wherein these species were exposed, via their diet, to doses of up to 100 and 4 mg/kg, respectively, prior to conception and throughout gestation.