Estudo da variação da concentração sérica de fenobarbital em cães cronicamente medicados

Com a finalidade de avaliar a variacao na concentracao serica do fenobarbital durante um intervalo de 12 horas da sua administracao, as concentracoes sericas foram mensuradas a cada duas horas em 30 caes cronicamente medicados, durante no minimo um mes. A determinacao dos valores sericos de fenobarbital, por meio de Imunofluorescencia polarizada. Os valores de meia-vida obtidos variaram de 13-131 horas, sendo que a maioria dos caes atingiram o estado de equilibrio dinâmico por volta de 15 dias, e todos apos quatro semanas, recomendando-se assim monitoracao apos quatro semanas do inicio da terapia ou apos cada ajuste de dose. Houve diferenca significante entre as medias das amostras coletadas duas e quatro horas (pico) com as das amostras coletadas imediatamente antes e oito, 10 e 12 horas apos sua administracao. Assim, para a monitoracao, pode-se realizar a coleta sanguinea, imediatamente antes da administracao do fenobarbital, ou em qualquer horario, entre oito a 12 horas apos sua administracao e nos casos suspeitos de intoxicacao uma segunda amostra pode ser coletada dentro de duas a quatro horas apos a sua administracao.(AU) In order to evaluate daily changes of concentration of phenobarbital during the interval of 12 hours of its administration, serum phenobarbital concentration were measured each two hours in 30 dogs submitted to the referred drug therapy for at least one month. All serum phenobarbital drug concentration were determined by use of a fluorecence polarization immunoassay. The values of half-lives obtained varied from 13 to 131 hours, most dogs reached steaty state serum concentrations by 15 days, and all dogs after four weeks. Therefore, clinicians should monitor serum phenobarbital concentrations four weeks after initiating treatment or after a change in dosage. There was significant difference among the averages of the samples two and four hours (peak) with the ones samples colected immediately before, and eight, 10 and 12 hours after its administration. In order to monitore serum phenobarbital concentrarions, its is suggest that blood collection is measured just before the dose or at any time between eight and 12 hours after its administration. If a concern arises regarding toxicity, a second sample should be colleted between two and four hours after phenobarbital administration.(AU)