Apparent resistance to hypotensive effect of clonidine.
Clonidine failed to reduce the blood pressures of two patients with essential hypertension. On was given 5-4 mg/day and the other 6 mg/day, and their respective peak plasma clonidine concentrations were 26-2 ng/ml and 14-4 ng/ml. Several months after the end of clonidine treatment a single oral dose of 0-3 mg of clonidine produced maximum falls in blood pressure of 30/22 mm Hg and 88/41 mm Hg with peak plasma clonidine concentrations of 1-4 ng/ml and 0-9 ng/ml. Resistance to the hypotensive effect of high doses of clonidine may be due to stimulation of peripheral alpha-adrenoceptors causing vasoconstriction, which maintains a raised blood pressure.
D000328:Adult; D001794:Blood Pressure / Q000187:drug effects*; D003000:Clonidine / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D004351:Drug Resistance; D005260:Female; D006801:Humans; D006973:Hypertension / Q000188:drug therapy; D008297:Male; D008875:Middle Aged; D013997:Time Factors
D003000:Clonidine