Bisoprolol is an effective treatment of hypertension in once-daily doses of 2.5 to 40 mg, while hydrochlorothiazide is effective in doses of 12.5 to 50 mg. In clinical trials of bisoprolol/hydrochlorothiazide combination therapy using bisoprolol doses of 2.5 to 20 mg and hydrochlorothiazide doses of 6.25 to 25 mg, the antihypertensive effects increased with increasing doses of either component.
The adverse effects (see WARNINGS) of bisoprolol are a mixture of dose-dependent phenomena (primarily bradycardia, diarrhea, asthenia, and fatigue) and dose-independent phenomena (eg, occasional rash); those of hydrochlorothiazide are a mixture of dose-dependent phenomena (primarily hypokalemia) and dose-independent phenomena (eg, possibly pancreatitis); the dose-dependent phenomena for each being much more common than the dose-independent phenomena. The latter consist of those few that are truly idiosyncratic in nature or those that occur with such low frequency that a dose relationship may be difficult to discern. Therapy with a combination of bisoprolol and hydrochlorothiazide will be associated with both sets of dose-independent adverse effects, and to minimize these, it may be appropriate to begin combination therapy only after a patient has failed to achieve the desired effect with monotherapy. On the other hand, regimens that combine low doses of bisoprolol and hydrochlorothiazide should produce minimal dose-dependent adverse effects, eg, bradycardia, diarrhea, asthenia and fatigue, and minimal dose-dependent adverse metabolic effects, ie, decreases in serum potassium (see CLINICAL PHARMACOLOGY).
Therapy Guided by Clinical Effect
A patient whose blood pressure is not adequately controlled with 2.5-20 mg bisoprolol daily may instead be given ZIAC. Patients whose blood pressures are adequately controlled with 50 mg of hydrochlorothiazide daily, but who experience significant potassium loss with this regimen, may achieve similar blood pressure control without electrolyte disturbance if they are switched to ZIAC.
Initial Therapy
Antihypertensive therapy may be initiated with the lowest dose of ZIAC, one 2.5/6.25 mg tablet once daily. Subsequent titration (14-day intervals) may be carried out with ZIAC tablets up to the maximum recommended dose 20/12.5 mg (two 10/6.25 mg tablets) once daily, as appropriate.
Replacement Therapy
The combination may be substituted for the titrated individual components.
Cessation of Therapy
If withdrawal of ZIAC therapy is planned, it should be achieved gradually over a period of about 2 weeks. Patients should be carefully observed.
Patients with Renal or Hepatic Impairment: As noted in the WARNINGS section, caution must be used in dosing/titrating patients with hepatic impairment or renal dysfunction. Since there is no indication that hydrochlorothiazide is dialyzable, and limited data suggest that bisoprolol is not dialyzable, drug replacement is not necessary in patients undergoing dialysis.
Geriatric Patients: Dosage adjustment on the basis of age is not usually necessary, unless there is also significant renal or hepatic dysfunction (see above and WARNINGS section).
Pediatric Patients: There is no pediatric experience with ZIAC.
