In recent years, the development of easy-to-use devices to continuously monitor blood pressure over 24 hours demonstrated that not only do blood pressure (BP) levels in normotensive and hypertensive patients clearly depend on time of day, but also that drugs can affect the blood pressure rhythm depending on the circadian time of drug intake. In healthy subjects, BP is higher during daytime, followed by a nightly drop of about 10%, named “dippers”. In different forms of hypertension the BP fall at night can be more pronounced (super-dippers), absent (non-dippers), or even increased (risers). These pathological BP patterns are of diagnostic value, differentiating subtypes of hypertension as well as having an impact on cardiovascular risk factors. The European Society of Hypertension  has established the procedure of ambulatory BP measurement (ABPM) as well as the day- and nighttime BP range for identifying hypertension. Thus, monitoring the 24hr BP profile is now regarded as the state of the art in diagnosing and treating hypertensive patients.
We now have the great advantage that several groups of antihypertensive drugs are available, which have different mechanisms and sites of action . It is well documented that these drugs differentially affect the 24-hr-BP profile when taken during the day or night. This knowledge is sufficient to restore a normal BP pattern in nearly all hypertensive patients when applied on an individual basis / ABPM-profile. In fact, it should be emphasized that the individual ABPM pattern and the prescribed drug should be matched to each other according to these mechanisms. This contrasts with the recent proposal by a Spanish group that all antihypertensive drugs should be taken only in the evening to reduce cardiovascular risk , a study has been criticized by various experts [4,5,6] and cannot be regarded as a guideline for the optimum timing of hypertension treatment. The main points of criticism were that the baseline BP values were in the normotensive range — non-hypertensive patients were treated — and both treated and untreated patients were included in the same group, making a general recommendation of evening antihypertensive drug intake incorrect.
Björn Lemmer MD, PhD, Professor emeritus, is a leading chronopharmacologist who pioneered studies of circadian rhythms in blood pressure and hypertension medication.