Triamterene measurements in the aqueous humor of rabbits

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 oftriamterene 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 kc.ca = 0.28 +/- 0.05 hr(-1), the loss coefficient of triamterene from the anterior chamber ko = 0.43 +/- 0.16 hr(-1) and the amount of triamterene in the cornea at time zero Mo = 483 +/- 125 ng/ml. The mean of ko = 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 T1/2 = 1.84 +/- 0.65 hr (Mean +/- SD).