There is an increase in renal blood flow following administration of captopril and glomerular filtration rate is usually unchanged. Reductions of blood pressure are usually maximal 60 to 90 minutes after oral administration of an individual dose of captopril. The duration of effect is dose related and is extended in the presence of a thiazide-type diuretic. The blood pressure lowering effects of captopril and thiazide-type diuretics are additive. In contrast, captopril and beta-blockers have a less than additive effect.
Blood pressure is lowered to about the same extent in both standing and supine positions.
Orthostatic effects and tachycardia are infrequent but may occur in volume-depleted patients. Abrupt withdrawal of captopril has not been associated with a rapid increase in blood pressure. Studies in rats and cats indicate that captopril does not cross the blood-brain barrier to any significant extent. Hydrochlorothiazide Thiazides affect the renal tubular mechanism of electrolyte reabsorption. At maximal therapeutic dosage all thiazides are approximately equal in their diuretic potency.