Plasma clonidine concentration and pharmacologic effect.

Analysis of sequential plasma samples in 14 hypertensive subjects receiving their usual oral dose of clonidine (0.1 to 0.6 mg twice daily) indicated that clonidine plasma concentration increased for the first 2 hr and then decreased and stabilized over the next 12 hr. Percent fall in diastolic blood pressure, but not side effects, correlated well with plasma concentration. Our study indicates a potential role for plasma clonidine determination in the treatment of patients with hypertension. It also demonstrates that clonidine can probably be given at 12-hr intervals and be effective.