In seven hypertensives receiving beta-blocker drugs, an additional reduction in standing blood pressure occurred between 60 and 90 minutes after 40 mg phentolamine by mouth.
The occurrence of the postural hypotensive effect was delayed in relation to the reported time of peak plasma concentration of unchanged phentolamine.
Supine blood pressure and heart rate were unaffected. Phentolamine has no clinically useful anti-hypertensive effect in conjunction with beta-blockers in patients with essential hypertension.
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