Oral bioavailability of sulphadiazine and trimethoprim in fed and fasted pigs.
The disposition of sulphadiazine (SDZ) and trimethoprim (TMP) was measured after intravenous and oral administration. Six healthy pigs weighing 17 to 34 kg received 20 mg kg-1 SDZ plus 4 mg kg-1 TMP intravenously, and 40 mg kg-1 SDZ plus 8 mg kg-1 TMP orally in both a fed and a fasted condition in a three-way cross-over design. After intravenous administration SDZ and TMP were present in plasma for 30 and 12 hours, respectively. The volume of distribution was 0.5 litre kg-1 bodyweight for SDZ and 1.8 litre kg-1 bodyweight for TMP. The oral bioavailabilities for SDZ and TMP in the fed pigs were 85 per cent and 92 per cent, and in the fasted pigs 89 per cent and 90 per cent, respectively. Although the presence of food did not affect the almost complete absorption of both drugs, it did prolong the absorption phase. Mean absorption time was nearly twice as long in the fed as in the fasted pig. Based on bioavailability and the resulting plasma concentrations it is concluded that the oral administration of SDZ and TMP was efficient in both the fed and fasted pigs.