Alice E. Loper

Initial Evaluation of Transdermal Timolol: Serum Concentrations and β-Blockade

The serum concentrations and β-blockade after dermal application of timolol ointment were evaluated in six healthy men (21–31 years old; 74–82 kg). Two patches (25 cm2) containing placebo and either 30 (n = 2) or 60 mg (n = 4) timolol base were randomly applied to the chest for 30 h. Serial serum concentrations of timolol were measured by a radioligand receptor assay. Bicycle ergometry, at a predetermined workload, was performed before and at 3, 8, 24, and 48 h after patch application; mean ± SD heart rates (beats/min) at these times were 167 ± 2. 158 ± 7, 125 ± 7, 120 ± 5, and 150 ± 5 (last 3 values: p < 0.05 from pretreatment), and β-blockade was evident in all subjects. Measurable serum concentrations in the therapeutic range were achieved in all subjects. The change in exercise-induced heart rate (y) was closely related to log timolol serum concentration (x) (y = −36 × −5.3: r = −0.92: p < 0.001). Based on the amount of timolol in the residual ointment. 50–60% of the original timolol dosage was delivered from the patch. Skin irritation under the patch compared with placebo was minimal. Further studies are warranted to assess the potential clinical utility of transdermal timolol.