Longitudinal evaluation of fentanyl concentrations in equine plasma and synovial fluid following application of transdermal fentanyl patches over one carpal joint

Abstract

ObjectiveTo determine if transdermally delivered fentanyl can achieve greater concentrations of fentanyl in synovial fluid when applied over a synovial structure.Study designRandomized, experimental study.AnimalsSix healthy adult horses.MethodsEach horse had two 100 μg/h fentanyl matrix patches applied on the dorsal aspect of one, randomly assigned, carpometacarpal joint (CMCJ) for 48 h. Whole blood and bilateral synovial samples from the intercarpal joint were obtained at 0, 2, 6, 12, 24, 36 and 48 h. Fentanyl concentrations were measured with liquid chromatography–mass spectrometry.ResultsAll subjects achieved detectable concentrations of fentanyl in both plasma and synovial fluid. Time to peak synovial and plasma concentration was 12 h. At 6 h, the synovial concentration in the untreated carpus (0.104 ng/mL ± 0.106) was lower than plasma fentanyl concentrations 0.31 ± 0.27 (p = .036). At 12 h, both treated (0.55 ng/mL ± 0.3) and untreated (0.53 ng/mL ± 0.28) synovial fluid fentanyl concentrations were lower than plasma (0.87 ng/mL ± 0.48) concentrations (p < .001 and p = .001, respectively). Synovial concentrations of fentanyl did not differ between treated and untreated joints (p > 0.608 for all time points).ConclusionApplication of fentanyl matrix patches directly over the CMCJ did not result in increased fentanyl concentrations in the synovial fluid of the treated intercarpal joint in normal horses.Clinical significanceThere is likely no analgesic advantage to placing fentanyl patches directly over the affected joint, as it did not result in increased synovial concentrations at the tested site.

Plasma concentrations of buprenorphine administered via matrix-type transdermal patches applied at three different anatomical locations in healthy adult horses

“…For the present study, the aim was to determine buprenorphine plasma concentrations in healthy horses from transdermal patches applied at three different locations i.e., the ventral aspect of the tail base, the metacarpal region, and the gaskin area. Skin preparation and the process of patch application were followed as per the standard published in other equine studies to maintain uniformity in the technique ( 26 , 27 , 33 – 36 ). The plasma buprenorphine concentrations were consistently >0.1 ng ml −1 as quickly as 2 h and lasted up to 32 h for the Tail TDP group.…”