Blood Pressure Monitoring for Assessing the Duration of Action of Antihypertensive Treatment

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Abstract
The duration of antihypertensive action of the alpha‐adrenergic blocking agent, prazosin, was studied in 12 hypertensive patients in whom twice‐daily doses of this agent were found to be effective and well tolerated during a preliminary titration period. The patients then entered a cross‐over phase of study. On a randomized basis, they were given prazosin either twice daily for eight weeks followed by an eight‐week period in which they received the same total dose once daily (each morning), or they were given the treatment for a once‐daily period followed by a twice‐daily period. Using the conventional sphygmomanometer, there were no significant differences in blood pressures for the patients as a whole between the measurements during once‐daily dosage (measured approximately 24 hours after the last administration of drug) and those during twice‐ daily dosage (measured approximately 12 hours after the last administration); but for both methods of administration, blood pressures were signrficantly lower than pre‐treatment values. Automated whole‐day ambulatory blood pressure monitoring showed a tendency for blood pressures to be lower with once‐daily than with twice‐daily treatment during the first 12 hours after the morning doses were given, but there was a reversal of this pattern during the early morning hours preceding the next dose. However, for at least half of the patients these differences were only minimal. Thus, prazosin may be effective in some patients as once‐daily treatment, especially after several weeks of therapy. Moreover, automated whole‐day blood pressure monitoring appears to be a valuable technique for guiding dosage requirements for patients on an individual basis.