Initial blood pressure as a predictor of the response to antihypertensive therapy.

1. The relationship between fall in systolic blood pressure and initial systolic blood pressure has been investigated in 255 mixed normotensive and hypertensive subjects given placebo or one of five types of antihypertensive drug (ACE inhibitors, calcium antagonists, direct vasodilators, alpha-adrenoceptor blocker, beta-adrenoceptor blocker). 2. In all cases there was a significant correlation between the change in blood pressure and initial blood pressure. When Oldham's transformation was used (replacing the initial blood pressure by the mean of the initial and minimum pressures) the correlation coefficients were all reduced, although five out of six were still statistically significant. 3. In a subset of 43 hypertensive subjects given four antihypertensive agents, concentration-effect analysis was carried out. For three of the agents a linear model was used to relate effect to concentration; for the remaining agent a Langmuir type model was used. 4. For all four sets of data for which concentration-effect analysis was carried out, there was a significant correlation between the sensitivity of response and the initial blood pressure. 5. The observed relationships between initial blood pressure, change in blood pressure and sensitivity of response can be qualitatively explained by postulating a general form of dose-response relationship for all antihypertensive agents.