The maximal effect of antihypertensive therapy could be estimated between one and two weeks after starting treatment, a UK study has concluded.

The authors of a systematic review, published in Heart, modelled blood pressure (BP) response from trial data. They looked at the BP response after initiating antihypertensive medication as monotherapy in hypertensive patients who were either drug naive or had a placebo washout from previous drugs. Data were sourced from electronic databases such as Medline, Embase and the Cochrane Register. The trials had to include office BP measurements at a minimum of two weekly intervals for at least four weeks.

The data were used to derive parameters for a model of the effect of time on BP response with separate derivations for systolic and diastolic BP responses after starting antihypertensive therapy.

Eighteen trials were identified with 4,168 patients who met the inclusion criteria. The authors found that the time to reach 50% of the maximum estimated BP lowering effect was around one week: systolic BP 0.91 weeks (95% CI: 0.74-1.10); diastolic 0.95 weeks (95% CI: 0.75-1.15).

Models incorporating drug class as a source of variability did not improve the fit of the data. The use of a titration schedule, however, did improve the model fit for both systolic and diastolic pressure. Titration increased both the predicted maximum effect and the time taken to reach 50% of the maximum (systolic 1.2 vs 0.7 weeks; diastolic 1.4 vs 0.7 weeks).

Antihypertensive drugs are titrated according to BP response and tolerability. If drugs are up-titrated too quickly the full response per dose may be missed and if titrated too slowly the patient is left at risk of cardiovascular events for longer than necessary.

To judge titration requires knowledge of the size and rate of BP reduction of different doses of different drugs.

The authors conclude that estimation of the maximal effect of antihypertensive therapy could be made between one and two weeks after initiation. They postulate that this knowledge can guide physicians in deciding when a newly started drug is ineffective and could facilitate the rapid establishment of effective drug regimens which could be particularly important in the early recovery phase from an acute vascular event.

Dr Peter Savill