Skin rashes occur quite frequently with transdermal clonidine

Transdermal administration of drugs may be useful to reduce the dose frequency and provide more constant blood levels, thereby reducing toxicity. Trials are underway with a clonidine skin patch which delivers 0.1, 0.2 or 0.3mg daily for ~ 7 days. In a double-blind study, blood pressure was controlled in 11/15 mild hypertensives treated with a weekly clonidine patch and in 4/15 placebo­treated patients. Constant plasma levels were maintained.

Transdermal clonidine may be more acceptable than oral clonidine to the patient because of once­weekly compared with 1-3 times daily dosing. Patients are also concerned about unpleasant side effects, especially mild to moderate hypertensives who are likely to be asymptomatic. There have been no studies to compare side effects with oral and transdermal clonidine, but in one study, recipients of transdermal clonidine reported dry mouth more frequently than placebo recipients. However, the incidence of drowsiness and lethargy was similar in both groups. Rebound hypertension after withdrawal of oral clonidine is avoided with the transdermal route, as plasma drug levels fall slowly when the patch is removed. Skin reactions may limit the use of clonidine skin patches; in some studies these have been experienced by up to one-third of patients and have necessitated drug withdrawal in a few. The incidence of skin reactions is significantly higher than that seen with oral therapy.

Further larger clinical trials are needed to determine whether transdermal clonidine is more acceptable than conventional oral therapy. Lancet 1 : 79-80, 1 0 Jan 1987

0156-2703/87/0124-0003/0$01.00/0 ® ADIS Press /NPHARMA" 24 Jan 1987 3