From the FDA Drug Label
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. The maximum recommended dose of hydrochlorothiazide for treating edema and hypertension is 50 mg per day 1.
From the Research
The maximum recommended dose of hydrochlorothiazide (HCTZ) for treating edema is 100 mg daily, while for hypertension the maximum dose is 50 mg daily. For edema, treatment typically starts at 25-100 mg daily, which can be given as a single dose or divided into two doses. For hypertension, the initial dose is usually 12.5-25 mg daily, with gradual increases as needed, as seen in a study where low dose hydrochlorothiazide (12.5 to 25 mg daily) was used as monotherapy in black patients with mild to moderate hypertension 2. HCTZ works by increasing sodium and water excretion in the kidneys, reducing fluid volume in the body, which helps decrease edema and lower blood pressure. Side effects increase at higher doses, including electrolyte imbalances (particularly potassium depletion), elevated blood glucose, and increased uric acid levels, as noted in a study where a significant decrease in serum uric acid and a rise in serum potassium occurred when the dose of hydrochlorothiazide was reduced from 50 to 25 mg/d 3. Patients taking the maximum dose should have regular monitoring of electrolytes, kidney function, and blood glucose. Elderly patients and those with kidney impairment may require lower doses, as they may be more susceptible to the side effects of HCTZ, such as noncardiogenic pulmonary edema, which has been reported in rare cases 4. HCTZ should be taken in the morning to prevent nighttime urination disrupting sleep. It's also important to consider the comparative antihypertensive effects of hydrochlorothiazide and chlorthalidone, as chlorthalidone has been shown to be more effective in lowering systolic blood pressures than hydrochlorothiazide at lower doses 5. However, the choice of diuretic and dosage should be individualized based on the patient's specific needs and medical history. In general, the goal is to use the lowest effective dose to minimize side effects while achieving adequate blood pressure control, as seen in a study where the effects of reduction in dose and discontinuation of hydrochlorothiazide were evaluated in patients with controlled essential hypertension 3. Additionally, a study found that low dose hydrochlorothiazide (12.5 to 25 mg daily) as monotherapy in black patients with mild to moderate hypertension had only a moderate effect on blood pressure control and 24-h blood pressure load, while the higher 25 mg dose was associated with significant decrease in serum potassium level 2. Another study compared the effects of 25 mg vs 50 mg of hydrochlorothiazide in elderly patients with isolated systolic hypertension, and found that the reductions in blood pressure and proportion of patients in whom blood pressure was controlled were similar in the lower- and higher-dose groups, but serum potassium level was reduced more in the higher-dosage group 6. Overall, the maximum recommended dose of HCTZ should be used judiciously and with careful monitoring to minimize the risk of side effects and maximize the benefits of treatment.