Evaluation of physical properties and dose equivalency of generic versus branded latanoprost formulations

The purpose of this study was to comparatively evaluate the pharmaceutical characteristics of various marketed generic formulations of prostaglandin analogue latanoprost in the Indian market. Three generics of latanoprost and one branded (Xalatan) formulation (five vials each) were obtained from authorized agents from the respective commercial sourcing having the same batch number. These formulations were coded, and the labels were removed. At a standardized room temperature of 25 °C, the concentration, osmolarity, drop size, pH, and total drops per vial were determined for Xalatan and all the generics of latanoprost. The concentration of various brands varied between 50.49 ± 0.36 and 58.90 ± 0.52 µg/ml as compared to the standard labeled concentration of 50 µg/ml on the latanoprost vials. The concentration of drugs in individual drop varied from 1.30 ± 0.05 to 1.78 ± 0.04 µg/drop. The volume of drug formulation per bottle varied from 2.4 ± 0.12 to 2.6 ± 0.09 ml/bottle. The number of drops per bottle varied from minimum of 88.60 ± 0.10 drops to maximum of 102.0 ± 4.3 drops across all the formulations, while the drop size varied from 25.72 ± 2.70 to 29.97 ± 1.38 µl. The osmolarity of 2/4 drugs was within 300 mOs M (±10 %). The specific gravity varied between 0.98 ± 0.01 and 1.007 ± 0.01, while pH was between 7.05 ± 0.004 and 7.13 ± 0.005. Two of the generic brands were outside the United States pharmacopoeia limits (±10%) for ophthalmic formulation, with concentration exceeding the limits by 3 % (p = 0.151) and 8 % (p = 0.008), respectively. This pilot study highlights that there are significant variations in the drug concentrations and physical properties of generic latanoprost formulations. Although none of the brands had concentrations below the recommended level, two of the brands had concentrations exceeding the limits by 3 and 8 %, respectively.