Bioanalytical UHPLC–MS/MS Method for Quantification of Terbinafine in Ungual Delivery Studies

Terbinafine is considered the first-line treatment for dermatophyte-induced onychomycosis. This study aimed to develop a fast, selective, and sensitive UHPLC-MS/MS method for the quantification of terbinafine in porcine hooves, a cost-effective surrogate for human nails. The objectives were to (i) optimise specific chromatographic and detection settings, (ii) evaluate terbinafine extraction recovery, (iii) validate the method with regard to standardised operating procedure guidelines using terbinafine-d3 as an internal standard and (iv) investigate the method's performance through a preliminary study involving deposition of an in-house high-loading topical formulation into fractional laser-ablated porcine hooves. An extraction with MeOH:H₂O (9:1) achieved ~90% recovery. Extracts were centrifuged, filtered and analysed under gradient conditions, with analyte and internal standard detected by selected reaction monitoring. The validated method demonstrated appropriate sensitivity to quantify concentration ranges between 1 and 200 ng/mL with a 7.2-min runtime and a limit of quantification of 1 ng/mL. Preliminary studies detected terbinafine from the formulation within intact and laser-ablated porcine hooves, corresponding to deposited amounts of 89.04 ± 4.02 and 217.49 ± 8.98 μg/cm², respectively. In conclusion, the sensitivity and specificity of the method make it suitable for use in further investigations into ungual delivery enhancement strategies involving terbinafine formulations.