Oral reserpine administration in horses results in low plasma concentrations that alter platelet biology
[um_loggedin show_lock=yes]Authors: Jessica M. Gilbertie (1,2), Jennifer L. Davis (3), Gigi S. Davidson (4), Amanda M. McDonald (4), Jenna M. Schirmer (1), Lauren V. Schnabel (1,2)
Affiliations: (1) Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University
(2) Comparative Medicine Institute, North Carolina State University
(3) Department of Biomedical Sciences & Pathobiology, Virginia-Maryland College of Veterinary Medicine, Blacksburg, VA 24061
(4) Clinical Pharmacy Services, College of Veterinary Medicine, North Carolina State University. Raleigh, NC 27607
Introduction: Reserpine is a popular drug in the equine industry for long-term tranquilization of horses undergoing forced rest due to injury. Our group has observed the production of hypercoagulable biologic products, and in particular IRAPII (Arthrex Vet Systems, Naples FL USA), from horses being administered oral reserpine at the clinical dose of 2.5mg once daily. No studies have documented the pharmacokinetics of orally administered reserpine, nor the effects of reserpine on platelet biology in horses.
Hypothesis/Objectives: The objectives of this study were to evaluate the pharmacokinetics of oral administration of reserpine in horses and to then evaluate the effects of physiologic concentrations of reserpine on equine platelet functionality in vitro. Our hypothesis was that physiologic doses of reserpine would result in increased platelet aggregation and adhesion.
Materials and Methods: The pharmacokinetics of oral reserpine (single clinically-used dose of 2.5 mg/horse) were determined in six healthy nonfasted adult horses. Plasma samples were collected and concentrations of reserpine determined by UPLC-MS/MS. Using this data, the in vitro effects of reserpine on platelets were examined. Aggregation, adhesion, and releasate assays for serotonin and thromboxane B2 were performed on platelets treated with varying concentrations of reserpine (0.01-10ng/mL), aspirin (negative control) and saline (untreated control).
Results: Oral reserpine administration demonstrated low plasma concentrations with a Cmax of 0.2±0.06ng/mL and a prolonged half-life of 23.6±6.24hr. Simulations over a dose range of 2-8μg/kg predicted Cmax at steady state between 0.06-0.9ng/mL. Platelets treated with reserpine in vitro at physiologic (<1ng/mL) concentrations displayed significantly increased aggregation and adhesion (both to collagen and IRAPII beads) compared to untreated or aspirin-treated platelets as well as higher concentrations of reserpine. These functional changes correlated with signifcantly lower concentrations of serotonin and significantly higher concentrations of thromboxane B2 in the platelet suspension supernatant. Conclusions: Oral reserpine demonstrates low plasma concentrations and a prolonged half-life in adult horses. At these concentrations, reserpine causes significant changes in platelet function, most likely due to serotonin release and re-uptake which in turn primes platelets for activation and the release of thromboxane B2. These findings suggest that clinicians should likely harvest blood for generation of biologics, and especially those with beads which can act as a substrate for platelet adhesion, prior to the onset of oral reserpine administration.
Acknowledgements, Funding, and Conflicts of Interest: This work was supported by the Fund for Orthopedic Research in honor of Gus and Equine athletes (F.O.R.G.E; LVS). The authors would like to thank Mrs. Julie Long for her technical assistance and the NCSU Laboratory Animal Resources staff for their help with animal care and handling. The authors also would like to thank Arthex Vet Systems for their generous donation of the Arthrex IRAPII System kits used in this study. The authors declare no conflicts of interest.[/um_loggedin]