Triamterene Measurements in the Aqueous Humor of Rabbits

ABSTRACT

The kinetics of topical triamterene penetration were estimated from the time-course measurements of triamterene (in Dyazide®) concentrations in the anterior chamber of six rabbits (n=12, left and right eyes). The two-compartment model of Jones and Maurice (1) was fitted to the measurements. We found the apparent elimination rate constant of triamterene A = 0.33 ± 0.12 hr⁻¹, the apparent absorption rate constant of triamterene B = 2.68 ± 0.55 hr⁻¹, the cornea-aqueous transfer coefficient in reference to the corneal volume of triamterene k_c.ca = 0.28 ± 0.05 hr⁻¹, the loss coefficient of triamterene from the anterior chamber k₀ = 0.43 ± 0.16 hr⁻¹ and the amount of triamterene in the comea at time zero M₀ = 483 ± 125 ng/ml. The mean of k₀ = 0.43 hr⁻¹ is significantly lower (p = 0.04% using ZTEST) than the lower limit of aqueous loss coefficient = 0.58 hr⁻¹ usually found in rabbits (2). We conclude that Dyazide® lowers the aqueous flow rate in the positive direction, considering glaucoma treatment. Peak triamterene concentration in the anterior chamber was P = 120 ± 32 ng/ml. Half-life for elimination from the aqueous humor was T_1/2 = 1.84 ± 0.65 hr (Mean ± SD).