Hydrophobic drug adsorption loss to syringe filters from a perspective of drug delivery.

Filtering with a syringe filter is a common operation in pharmaceutical analysis. Ophthalmic research often has a limited amount of sample and low amount of drug which is vulnerable to filtering membrane adsorption loss but not well recognized in the research community. Current study investigated drug adsorption by 11 types of syringe filters for 4 hydrophobic compounds commonly encountered in transscleral drug delivery. Among the 11 types of syringe filters surveyed, polytetrafluoroethylene - NBA, polytetrafluoroethylene - NLA, and polypropylene filters caused the least adsorptive drug loss for these four drugs studied. The magnitude of drug adsorption was filter- and drug-specific. Polytetrafluoroethylene-NLA caused the least adsorptive loss (1%) for triamcinolone acetonide, polytetrafluoroethylene-NBA caused the least adsorptive loss (5.4%) for diclofenac, and polypropylene caused the least adsorptive loss for cyclosporine A, 16.8% on average. Tacrolimus had the least adsorptive loss to the filters of polytetrafluoroethylene - NLA and polypropylene; however, the percentage of adsorptive loss from filtration was the highest (32% loss in average) among the four drugs surveyed. CONCLUSION: Low drug concentrations as seen in samples from ophthalmic researches are vulnerable to filtration drug loss. Selecting the right filter via validation is critical to avoid underestimating the drug level and distorting the resultant distribution/clearance profile in the ocular pharmacokinetic analysis.