Hydrochlorothiazide, a sulfonamide, can cause an idiosyncratic reaction, resulting in acute transient myopia and acute angle-closure glaucoma. Symptoms include acute onset of decreased visual acuity or ocular pain and typically occur within hours to weeks of drug initiation. Untreated acute angle-closure glaucoma can lead to permanent vision loss. The primary treatment is to discontinue hydrochlorothiazide as rapidly as possible. Prompt medical or surgical treatments may need to be considered if the intraocular pressure remains uncontrolled. Risk factors for developing acute angle-closure glaucoma may include a history of sulfonamide or penicillin allergy.
Electrolyte and Fluid Balance Status
Although the probability of developing hypokalemia is reduced with bisoprolol fumarate and hydrochlorothiazide because of the very low dose of HCTZ employed, periodic determination of serum electrolytes should be performed, and patients should be observed for signs of fluid or electrolyte disturbances, i.e., hyponatremia, hypochloremic alkalosis, hypokalemia and hypomagnesemia. Thiazides have been shown to increase the urinary excretion of magnesium; this may result in hypomagnesemia.
Warning signs or symptoms of fluid and electrolyte imbalance include dryness of mouth, thirst, weakness, lethargy, drowsiness, restlessness, muscle pains or cramps, muscular fatigue, hypotension, oliguria, tachycardia, and gastrointestinal disturbances such as nausea and vomiting.
Hypokalemia may develop, especially with brisk diuresis when severe cirrhosis is present, during concomitant use of corticosteroids or adrenocorticotropic hormone (ACTH) or after prolonged therapy. Interference with adequate oral electrolyte intake will also contribute to hypokalemia. Hypokalemia and hypomagnesemia can provoke ventricular arrhythmias or sensitize or exaggerate the response of the heart to the toxic effects of digitalis. Hypokalemia may be avoided or treated by potassium supplementation or increased intake of potassium-rich foods.
Dilutional hyponatremia may occur in edematous patients in hot weather; appropriate therapy is water restriction rather than salt administration, except in rare instances when the hyponatremia is life threatening. In actual salt depletion, appropriate replacement is the therapy of choice.
Calcium excretion is decreased by thiazides, and pathologic changes in the parathyroid glands, with hypercalcemia and hypophosphatemia, have been observed in a few patients on prolonged thiazide therapy.
Hyperuricemia or acute gout may be precipitated in certain patients receiving thiazide diuretics. Bisoprolol fumarate, alone or in combination with HCTZ, has been associated with increases in uric acid; however, in U.S. clinical trials, the incidence of treatment-related increases in uric acid was higher during therapy with HCTZ 25 mg (25%) than with B/H 6.25 mg (10%). Because of the very low dose of HCTZ employed, hyperuricemia may be less likely with bisoprolol fumarate and hydrochlorothiazide.
Bisoprolol fumarate and hydrochlorothiazide may potentiate the action of other antihypertensive agents used concomitantly. Bisoprolol fumarate and hydrochlorothiazide should not be combined with other beta-blocking agents. Patients receiving catecholamine-depleting drugs, such as reserpine or guanethidine, should be closely monitored because the added beta-adrenergic blocking action of bisoprolol fumarate may produce excessive reduction of sympathetic activity. In patients receiving concurrent therapy with clonidine, if therapy is to be discontinued, it is suggested that bisoprolol fumarate and hydrochlorothiazide be discontinued for several days before the withdrawal of clonidine.
Bisoprolol fumarate and hydrochlorothiazide should be used with caution when myocardial depressants or inhibitors of AV conduction, such as certain calcium antagonists (particularly of the phenylalkylamine [verapamil] and benzothiazepine [diltiazem] classes), or antiarrhythmic agents, such as disopyramide, are used concurrently.
Both digitalis glycosides and beta-blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia.
Pharmacokinetic studies document no clinically relevant interactions with other agents given concomitantly, including thiazide diuretics and cimetidine. There was no effect of bisoprolol fumarate on prothrombin times in patients on stable doses of warfarin.
Risk of Anaphylactic Reaction
While taking beta-blockers, patients with a history of severe anaphylactic reaction to a variety of allergens may be more reactive to repeated challenge, either accidental, diagnostic, or therapeutic. Such patients may be unresponsive to the usual doses of epinephrine used to treat allergic reactions.
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 cholestyramine and colestipol resins bind the hydrochlorothiazide and reduce its absorption in the gastrointestinal tract by up to 85 percent and 43 percent, 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 bisoprolol fumarate and hydrochlorothiazide.
Nonsteroidal anti-inflammatory drugs — In some patients, the administration of a nonsteroidal anti-inflammatory agent can reduce the diuretic, natriuretic, and antihypertensive effects of loop, potassium sparing, and thiazide diuretics. Therefore, when bisoprolol fumarate and hydrochlorothiazide and nonsteroidal anti-inflammatory agents are used concomitantly, the patient should be observed closely to determine if the desired effect of the diuretic is obtained.
In patients receiving thiazides, sensitivity reactions may occur with or without a history of allergy or bronchial asthma. Photosensitivity reactions and possible exacerbation or activation of systemic lupus erythematosus have been reported in patients receiving thiazides. The antihypertensive effects of thiazides may be enhanced in the post-sympathectomy patient.
Laboratory Test Interactions
Based on reports involving thiazides, bisoprolol fumarate and hydrochlorothiazide may decrease serum levels of protein-bound iodine without signs of thyroid disturbance.
Because it includes a thiazide, bisoprolol fumarate and hydrochlorothiazide should be discontinued before carrying out tests for parathyroid function (see PRECAUTIONS — Parathyroid Disease).
Patients, especially those with coronary artery disease, should be warned against discontinuing use of bisoprolol fumarate and hydrochlorothiazide without a physician’s supervision. Patients should also be advised to consult a physician if any difficulty in breathing occurs, or if they develop other signs or symptoms of congestive heart failure or excessive bradycardia.
Patients subject to spontaneous hypoglycemia or diabetic patients receiving insulin or oral hypoglycemic agents, should be cautioned that beta-blockers may mask some of the manifestations of hypoglycemia, particularly tachycardia, and bisoprolol fumarate should be used with caution.
Patients should know how they react to this medicine before they operate automobiles and machinery or engage in other tasks requiring alertness. Patients should be advised that photosensitivity reactions have been reported with thiazides.
Bisoprolol fumarate and hydrochlorothiazide
Long-term studies have not been conducted with the bisoprolol fumarate/hydrochlorothiazide combination.
Long-term studies were conducted with oral bisoprolol fumarate administered in the feed of mice (20 and 24 months) and rats (26 months). No evidence of carcinogenic potential was seen in mice dosed up to 250 mg/kg/day or rats dosed up to 125 mg/kg/day. On a body weight basis, these doses are 625 and 312 times, respectively, the maximum recommended human dose (MRHD) of 20 mg, or 0.4 mg/kg/day, based on 50 kg individuals; on a body surface area basis, these doses are 59 times (mice) and 64 times (rats) the MRHD.
Two-year feeding studies in mice and rats, conducted under the auspices of the National Toxicology Program (NTP), treated mice and rats with doses of hydrochlorothiazide up to 600 and 100 mg/kg/day, respectively. On a body weight basis, these doses are 2400 times (in mice) and 400 times (in rats) the MRHD of hydrochlorothiazide (12.5 mg/day) in bisoprolol fumarate and hydrochlorothiazide. On a body surface area basis, these doses are 226 times (in mice) and 82 times (in rats) the MRHD. These studies uncovered no evidence of carcinogenic potential of hydrochlorothiazide in rats or female mice, but there was equivocal evidence of hepatocarcinogenicity in male mice.
The mutagenic potential of the bisoprolol fumarate/ hydrochlorothiazide combination was evaluated in the microbial mutagenicity (Ames) test, the point mutation and chromosomal aberration assays in Chinese hamster V79 cells, and the micronucleus test in mice. There was no evidence of mutagenic potential in these in vitro and in vivo assays.
The mutagenic potential of bisoprolol fumarate was evaluated in the microbial mutagenicity (Ames) test, the point mutation and chromosome aberration assays in Chinese hamster V79 cells, the unscheduled DNA synthesis test, the micronucleus test in mice, and the cytogenetics assay in rats. There was no evidence of mutagenic potential in these in vitro and in vivo assays.
Hydrochlorothiazide was not genotoxic in in vitro assays using strains TA 98, TA 100, TA 1535, TA 1537 and TA 1538 of Salmonella typhimurium (the Ames test); in the Chinese Hamster Ovary (CHO) test for chromosomal aberrations; or in in vivo 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 in the in vitro CHO Sister Chromatid Exchange (clastogenicity) test and in the mouse Lymphoma Cell (mutagenicity) assays, using concentrations of hydrochlorothiazide of 43 to1300 µg /mL. Positive test results were also obtained in the Aspergillus nidulans non-disjunction assay, using an unspecified concentration of hydrochlorothiazide.
Reproduction studies in rats did not show any impairment of fertility with the bisoprolol fumarate/hydrochlorothiazide combination doses containing up to 30 mg/kg/day of bisoprolol fumarate in combination with 75 mg/kg/day of hydrochlorothiazide. On a body weight basis, these doses are 75 and 300 times, respectively, the MRHD of bisoprolol fumarate and hydrochlorothiazide. On a body surface area basis, these study doses are 15 and 62 times, respectively, MRHD.
Reproduction studies in rats did not show any impairment of fertility at doses up to 150 mg/kg/day of bisoprolol fumarate, or 375 and 77 times the MRHD on the basis of body weight and body surface area, respectively.
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/day, respectively, prior to mating and throughout gestation. Corresponding multiples of maximum recommended human doses are 400 (mice) and 16 (rats) on the basis of body weight and 38 (mice) and 3.3 (rats) on the basis of body surface area.
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