Purpose: To investigate the effect of excipients on latanoprost penetration into the aqueous humor with clinically available 6 products with different solutions mainly in the types and concentrations of preservatives.
Methods: In 363 patients with cataracts, we instilled 1 latanoprost drop in 1 eye before surgery. The drop was randomly selected by brand name product (A) and 5 generic products (B-F) composed with different excipients. B contains similar excipients to A. C and D contain lower concentrations of benzalkonium chloride than A. E includes sodium benzoate, and F contains no preservatives. At 0.5-1, 3, and 6 h after instillation, samples of aqueous humor were collected to determine the latanoprost free acid by mass spectrometry. The time course of intraocular concentration and the areas under the aqueous humor latanoprost free acid concentration-time curves (AUCs) were calculated.
Results: At 0.5-1 h, the aqueous humor concentration of latanoprost free acid was 8.5 ± 1.0 ng/mL for C, which was significantly higher (P < 0.01) than that of A (3.4 ± 0.5 ng/mL). At 3 and 6 h, however, no significant difference was noted in the concentrations of latanoprost free acid between the brand name and generic products. For each of the generic products, the peak free acid concentration was above the known threshold concentration for biological activity. At 6 h postdose, however, the levels of latanoprost free acid were below the threshold for Products C, E, and F. Comparisons of AUC0-6h and AUC0-24h values showed that these parameters were the greatest with A, and E was significantly inferior to A (P < 0.05).
Conclusions: Currently available latanoprost solutions with different preservatives showed sufficient intraocular concentration to activate the FP receptor, but different pharmacokinetic profiles of absorption or elimination.
Keywords: drug delivery; latanoprost; pharmacokinetics; preservative.