The study was undertaken in male patients aged 61-73 years with essential hypertension. 2. The patients had previously had their blood pressure controlled with the drug studied. 3. A randomized crossover study compared the effect of different drug doses on peak (3 h) and trough (24 h) blood pressure compared to placebo. 4. All drug doses used lowered blood pressure at peak response and the responses with different doses of angiotensin converting enzyme inhibitors were similar. The peak response to felodipine had some dose dependency. 5. Trough blood pressure was not different from placebo with enalapril, 5 and 10 mg, perindopril, 2 mg, felodipine, 2.5 mg but was different with enalapril, 20 and 40 mg, perindopril, 4 and 8 mg and felodipine, 5 and 10 mg. 6. Trough peak ratio was dose dependent, with the greatest dependency seen with enalapril which has the shortest half-life. 7. When low doses of enalapril (5 or 10 mg), perindopril (2 mg) or felodipine ER (2.5 mg) are used it is important to check blood pressure prior to the next dose to ensure that control is achieved and maintained.
