The effect of inflammation on the disposition of phenylbutazone in thoroughbred horses

Types of acute phase reactants and their importance in vaccination

Vaccines are considered to be one of the most cost-effective life-saving interventions in human history. The body's inflammatory response to vaccines has both desired effects (immune response), undesired effects [(acute phase reactions (APRs)] and trade-offs. Trade-offs are more potent immune responses which may be potentially difficult to separate from potent acute phase reactions. Thus, studying acute phase proteins (APPs) during vaccination may aid our understanding of APRs and homeostatic changes which can result from inflammatory responses. Depending on the severity of the response in humans, these reactions can be classified as major, moderate or minor. In this review, types of APPs and their importance in vaccination will be discussed.

Efeito da associação de furosemida e fenilbutazona sobre variáveis hidroeletrolíticas de cavalos antes e após a corrida

Verificaram-se os efeitos da associação de furosemida e fenilbutazona sobre variáveis hidroeletrolíticas de cavalos antes e após a corrida. Dezenove equinos foram distribuídos em três grupos, de acordo com os protocolos de tratamento. O primeiro grupo, de cinco animais, não recebeu medicação (grupo-controle); o segundo grupo, de sete animais, foi tratado com furosemida, na dose de 1mg/kg, por via intramuscular, até quatro horas antes do páreo; o terceiro, de sete animais, recebeu furosemida, por via intramuscular, e fenilbutazona, por via intravenosa, nas doses de 1,0 e 4,4mg/kg, respectivamente, até quatro horas antes da corrida. Amostras de sangue foram colhidas antes, imediatamente após e duas horas após o páreo, para avaliação da osmolalidade plasmática e das concentrações plasmáticas de sódio, potássio e cloreto. A utilização de furosemida e da associação furosemida e fenilbutazona até 4h antes dos páreos nas dosagens descritas alterou (P<0,05) a osmolalidade plasmática dos equinos, mas não alterou (P>0,05) as concentrações de sódio, potássio e cloreto. Os páreos alteraram de forma fisiológica a osmolalidade plasmática e a concentração sanguínea de K+ devido ao exercício de alta intensidade.

Pharmacokinetic/pharmacodynamic approach to assess irrelevant plasma or urine drug concentrations in postcompetition samples for drug control in the horse

The current performance of analytical techniques used for drug control in horses lead the Regulatory Authorities to decide whether trace levels of drugs legitimately used for therapeutic medication should or should not be reported. Here, we propose a well-ordered and nonexperimental pharmacokinetic/pharmacodynamic approach for the determination of irrelevant drug plasma (IPC) and urine concentrations (IUC). The published plasma clearance is used to transform an effective (marketed) dose into an effective concentration (EPC). EPC is transformed into an IPC by applying a safety factor (SF). This method is based on several assumptions (eg, drug effects reversibly driven by plasma concentration, linearity of drug disposition). The suitability of the computed IPC and IUC can be checked by calculating the residual amount of drug at IPC and computing a minimal drug withdrawal time. It is concluded that controlling the drug effect (using drug or any analyte concentration as a marker) rather than the drug exposure will be more demanding and also makes urine a less than ideal matrix.

Adverse drug reactions and interactions in the horse

Drugs undergo extensive evaluation before they are marketed. The occurrence of adverse reactions, however, may be so rare that thousands of patients must receive the drug before reliable data are available. It is necessary that veterinarians be informed about the drugs they use, be able to recognize drug-associated complications, know how to evaluate the patient for evidence of drug-associated toxicity, report adverse effects of drugs to the respective manufacturers, and be prepared to provide medical support and antidotal treatment (if it exists) for a patient if toxicosis occurs.

The effect of the acute-phase response on in vitro drug metabolism and plasma protein binding in the horse

The effect of the acute-phase response (APR) on the activity of the hepatic drug-metabolizing system (DMS) and on the binding of phenylbutazone to plasma proteins was investigated in the horse. An APR was induced by intramuscular injections of Freund's complete adjuvant in five horses and, five days later, these horses together with five clinically normal horses were shot and the right ventral lobe of each liver removed. The hepatic microsomal fractions from the liver samples were isolated and significantly lower (p < 0.01) concentrations of cytochromes P450 and b5 and activities of aniline-p-hydroxylase and aminopyrine N-demethylase (43%, 55%, 45% and 30%, respectively) were measured in the livers from the adjuvant-inflamed horses, compared to the controls. Phenylbutazone (PBZ) was administered intravenously (4.4 mg/kg) to a further four horses and plasma protein binding was measured by ultracentrifugation. Five weeks later, these horses were injected with Freund's complete adjuvant and the intravenous administration of PBZ (4.4 mg/kg) was repeated. Inflammation induced a significant increase (p < 0.01) in the unbound fraction of PBZ (5.2 +/- 0.5 as against 1.4 +/- 0.6%). These results suggest that the APR depresses the hepatic DMS and reduces the binding of PBZ to plasma proteins.