Pharmacokinetics of topical clonidine

The ocular penetration and systemic bioavailability following topical instillation between 0.125% and 0.06% clonidine were studied in rabbit eyes. The clonidine was bound to Tc 99m and assayed with a sensitivity of 0.006 mg/100 ul. In aqueous peak levels of clonidine were measured one hour after instillation, being 0.064 ug/100 ul with 0.125% clonidine and 0.061 ug/100ul with 0.06% clonidine. In the blood half an hour after administration 0.009 ug/100 ul of clonidine was present using 0.125% clonidine and 0.008 ug/100ul with 0.06% clonidine. Both concentrations of clonidine achieve similar aqueous and serum levels, suggesting an almost equal effect on intraocular pressure, with a small and transient effect on blood pressure.