The Clinical Pharmacology and Therapeutic Evaluation of Non-Steroidal Anti-Inflammatory Drugs in Adult Horses.

This review firstly examines the underlying pathophysiology of pain and inflammation associated with orthopedic disease and endotoxemia. Then, it reviews the clinical pharmacology (pharmacokinetics and pharmacodynamics) of both conventional and non-conventional NSAIDs in the adult horse, and finally provides an overview of different modalities to evaluate the therapeutic efficacy of NSAIDs in research.

Pharmacokinetics and efficacy of orally administered acetaminophen (paracetamol) in adult horses with experimentally induced endotoxemia.

BACKGROUND: Acetaminophen has been evaluated in horses for treatment of musculoskeletal pain but not as an antipyretic. OBJECTIVES: To determine the pharmacokinetics and efficacy of acetaminophen compared to placebo and flunixin meglumine in adult horses with experimentally induced endotoxemia. ANIMALS: Eight university owned research horses with experimentally induced endotoxemia. METHODS: Randomized placebo controlled crossover study. Horses were treated with acetaminophen (30 mg/kg PO; APAP), flunixin meglumine (1.1 mg/kg, PO; FLU), and placebo (PO; PLAC) 2 hours after administration of LPS. Plasma APAP was analyzed via LC-MS/MS. Serial CBC, lactate, serum amyloid A, heart rate and rectal temperature were evaluated. Serum IL-1ß, IL-6, IL-8, IL-10, and TNF-α were evaluated by an equine-specific multiplex assay. RESULTS: Mean maximum plasma APAP concentration was 13.97 ± 2.74 µg/mL within 0.6 ± 0.3 hour after administration. At 4 and 6 hours after treatment, both APAP (P = <.001, P = .03, respectively) and FLU (P = .0045 and P < .001, respectively) had a significantly greater decrease in rectal temperature compared to placebo. FLU caused greater heart rate reduction than APAP at 4 and 6 hours (P = .004 and P = .04), and PLAC at 4 hours (P = .05) after treatment. CONCLUSIONS AND CLINICAL IMPORTANCE: The pharmacokinetics of acetaminophen in endotoxemic horses differ from those reported by previous studies in healthy horses. Acetaminophen is an option for antipyresis in clinical cases, particularly when administration of traditional NSAIDs is contraindicated.

Pharmacokinetics and clinical efficacy of acetaminophen (paracetamol) in adult horses with mechanically induced lameness.

BACKGROUND: Acetaminophen has been used clinically in horses alone or combined with traditional non-steroidal anti-inflammatory drugs for treatment of musculoskeletal pain in horses. OBJECTIVES: To determine the pharmacokinetics and efficacy of acetaminophen at two doses in horses with mechanically induced lameness compared with phenylbutazone or placebo control. STUDY DESIGN: In vivo experiment. METHODS: Nine healthy mares with mechanical lameness induced via a reversible sole pressure horseshoe model were treated with acetaminophen (20 mg/kg PO; A20), acetaminophen (30 mg/kg PO; A30), phenylbutazone (2.2 mg/kg, PO; PB) and oral placebo (C) in a randomised four-way Latin square model. Plasma concentrations for A20 and A30 were analysed via LC-MS/MS and noncompartmental pharmacokinetic analysis. Heart rate and heart rate variability were measured using a portable telemetry. Lameness was scored by three blinded boarded equine surgeons using the AAEP and 10-point scales. RESULTS: Mean maximum plasma concentration (Cmax ) for A20 was 20.01 µg/ml within 0.66 h (Tmax ) after administration; The mean Cmax for A30 was 30.02 µg/ml with a Tmax of 0.43 h. Post-treatment heart rate for A30 was significantly lower than A20 at 1 and 7 h; lower than PB at 2, 3, 4.5 and 7 h; lower than C at 2, 3.5, 4.5, 6, 7 and 8 h. 10-point Lameness scores were significantly improved for A30 than C at 2 and 4 h post-treatment; PB was significantly improved than C at 8 h post treatment. There were no significant differences in lameness between A20, A30 and PB. MAIN LIMITATIONS: Small sample size, lack of objective lameness measurement. CONCLUSIONS: Acetaminophen at 30 mg/kg produced a more rapid improvement in lameness scores and heart rate compared with other treatments in this model. Further evaluation of the pharmacokinetics and safety of repeated oral dosing of acetaminophen at 30 mg/kg is needed to determine clinical utility.

CONTEXTO: Acetaminofeno tem sido usado rotineiramente em cavalos com dor musculoesquelética, tanto como terapia solo quanto em associação com outros anti-inflamatórios não esteroides tradicionais. OBJETIVOS: Determinar a farmacocinética e eficácia de duas doses de acetaminofeno em cavalos com claudicação mecanicamente induzida, e comparar com fenilbutazona e placebo. DELINEAMENTO DO ESTUDO: Estudo randomizado, cego e controlado utilizando quadrado latino. METODOLOGIA: Nove éguas adultas com claudicação induzida mecanicamente pelo método de aplicação de pressão na sola através de ferradura foram tratadas com acetaminofeno (20 mg/kg VO; A20), acetaminofeno (30 mg/kg VO; A30), fenilbutazona (2.2 mg/kg, VO; PB) e placebo oral (C) em um estudo quadrado latino de forma randômica. Concentração plasmática dos grupos A20 e A30 foram analisadas pelo método LC-MS/MS e análise farmacocinética não compartimentar. Frequência cardíaca e variação da frequência cardíaca foram mensuradas usando telemetria portátil. O grau de claudicação foi avaliado usando a escala de 10 pontos da AAEP por três cirurgiões especialistas (board-certified) que estavam cegos ao tratamento. RESULTADOS: A média máxima da concentração plasmática (Cmax ) do grupo A20 foi 20.01 µg/ml dentro de 0.66 h (Tmax ) da administração. A média Cmax do grupo A30 foi 30.02 µg/ml dentro da Tmax de 0.43 h. A frequência cardíaca do grupo A30 foi significativamente mais baixa do que a do grupo A20 nos momentos 1 e 7 h; mais baixa do que o grupo PB nos momentos 2, 3, 4.5 e 7 h; e mais baixa do que as do grupo C nos momentos 2, 3.5, 4.5, 6, 7 e 8 h. O grau de claudicação diminuiu significativamente no grupo A30 quando comparado com o grupo C nos momentos 2 e 4 h pós tratamento, e no grupo PB quando comparado com o grupo C no momento 8 h pós tratamento. Não houve diferença significativa em grau de claudicação quando os grupos A20, A30 e PB foram comparados. PRINCIPAIS LIMITAÇÕES: Número pequeno de animais, ausência de mensuração de claudicação objetiva. CONCLUSÕES: A dose de 30 mg/kg de acetaminofeno proporcionou uma superior melhora na escala de claudicação e frequência cardíaca quando comparada com os outros tratamentos avaliados neste estudo. Mais informações sobre a farmacocinética e efeitos da repetida dosagem de 30 mg/kg de acetaminofeno precisam ser avaliadas para determinar a sua aplicabilidade clínica.