Short report: Ramipril and hydrochlorothiazide combination therapy in hypertension: a clinical trial of factorial design

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ObjectiveTo identify appropriate dosages of ramipril and hydrochlorothiazide (HCT) when given in combination once a day for the treatment of essential hypertension.DesignA 2- or 4-week placebo run-in followed by 6-week, double-blind, parallel-group phase: 4 x 3 factorial (2.5, 5 and 10 mg ramipril; 12.5 and 25 mg HCT; all six combinations; placebo).SettingOffice practice (21 centres).Patients and participantsPatients with mild-to-moderate essential hypertension (World Health Organization stage I—II; supine diastolic blood pressure 100—115 mmHg in last 2 weeks of run-in): 581 enrolled, 534 randomly assigned to double-blind therapy and 517 completed.Main outcome measuresReduction in supine and standing blood pressure.ResultsIn pairwise comparisons, the combinations of 5 mg ramipril with 12.5 and 25 mg HCT and 10 mg ramipril with 12.5 mg HCT consistently produced significantly greater blood pressure reductions than their respective components. Response surface analyses were performed, and a stairstep model was constructed to characterize the shape of the dose-response surface. The combinations involving 5 and 10 mg ramipril with 12.5 and 25 mg HCT were again more effective than their components. Withdrawals and adverse effects were minimal for all treatments. A large drop in serum potassium was observed on 25 mg HCT, but not on combination therapy. Addition of ramipril appeared to reduce the hyperuricaemic effect of HCT.ConclusionsSeveral dosage combinations of ramipril plus HCT produced significantly greater blood pressure reductions than the monotherapies at the same dosages. Overall, the combination of 5 mg ramipril and 25 mg HCT gave the best mean reduction. Combination therapy with ramipril plus HCT was safe and effective for patients with mild-to-moderate essential hypertension.

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