In the present study, we examined the oral pharmacokinetics of the acidic drugs,
diclofenac (DF) and sulfamonomethoxine (SMM), which have different physicochemical
properties, in Shiba goats. DF and SMM were intravenously and orally administered to 5
male goats using a crossover design. The Tmax of DF and SMM were reached 1.5
and 5.6 hr after they have been orally administered, respectively, and this was followed
by their slow elimination. The elimination of both drugs was markedly faster after being
intravenously rather than orally administered, which indicated flip-flop phenomena after
the oral administration. The mean absorption times (MATs) of DF and SMM were 6 and 15 hr,
respectively. This slow absorption may have been due to slow gastric emptying in goats.
The large difference observed in MATs between DF and SMM may have been because DF, which
is more lipophilic than SMM, was partly absorbed from the forestomach. Therefore, these
results suggest that the absorption of highly lipophilic drugs from the forestomach may be
markedly high in Shiba goats. In case of drugs whose elimination is quite fast, their
efficacies may appear from the early stage after oral administration even in ruminants,
because elimination rate is the determinant factor of Tmax in flip-flop
phenomena. Such drugs may be used orally even in ruminants.
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