Transdermal clonidine application: long-term results in essential hypertension.

Skin patches of a clonidine transdermal therapeutic system (clonidine-TTS) with a constant release rate of either 0.1 or 0.2 mg clonidine/24 h continuously over 7 days were used in 32 essential hypertensives. These self-adhesive drug delivery systems (3.5 cm2), which were affixed to the upper outer arm, were changed by the patients at weekly intervals. During a mean observation period of 7 months (range 1-19 months) transdermal clonidine reduced the blood pressure from 162 +/- 15/107 +/- 5 mmHg to normal values (diastolic less than or equal to 95 mmHg) in 63% of our patients. However, chronic use of clonidine-TTS was accompanied by a high frequency of contact dermatitis (type IV allergy) in nearly half of our patients (n = 15, 47%). In 11 of these 15 patients transdermal clonidine administration had to be stopped because of intolerable local skin reactions (pruritus, erythema, vesiculation, and/or infiltration). Subsequent patch testing with all components of clonidine-TTS was performed in eight cases. Whereas in seven cases an allergic contact dermatitis to clonidine was found, only one patient showed an allergy to another component of clonidine-TTS (polyisobutylene). We conclude that this strikingly high incidence of local allergic skin reactions limits the use of clonidine-TTS in essential hypertension.