Purpose: To develop a population model capable of describing the profile of the effect of intravitreal triamcinolone acetonide in the treatment of diabetic diffuse macular edema.
Methods: The results of 51 injections in 37 eyes (33 patients) with diffuse diabetic macular edema were studied, by using population pharmacokinetic-pharmacodynamic modeling, without triamcinolone concentration measurements. This approach was supported by the pharmacokinetic hypothesis that the intravitreal triamcinolone concentration decreases in accordance with an exponential biphasic equation. Central macular thickness (CMT), measured by optical coherence tomography was chosen as the pharmacodynamic parameter.
Results: The pharmacodynamic profile of the effect of triamcinolone on CMT was characterized by a curve in three phases: a fast decrease, a steady state, and a relapse. The confidence interval of most of the estimated parameters of the model was narrow. The mean estimated half-life of triamcinolone +/- SD was 15.4 +/- 1.9 days, and the mean maximum duration of its effect (+/-SD), 140 +/- 17 days.
Conclusions: Pharmacokinetic-pharmacodynamic modeling using CMT constitutes a valid alternative to pharmacokinetic studies. This approach worked excellently in the present study, and the results are consistent with those published for the intraocular pharmacokinetics of triamcinolone acetonide in the human eye. The authors conclude that this type of investigation is of interest, as it avoids intraocular measurements as far as possible.