Pharmacokinetics of Oral Co-Trimazine and the Penetration of Its Components Sulfadiazine and Trimethoprim into Peripheral Human Lymph

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Abstract
Five healthy informed male volunteers received oral doses of 820 mg sulfadiazine (SDZ) plus 180 mg trimethoprim (TMP) (co-trimazine) every 24 h. Concentrations in serum, peripheral lymph from the leg and urine were determined after the first dose, and on the 4th day to reflect approximate steady-state conditions. TMP was assayed microbiologically and unchanged SDZ by high-pressure liquid chromatography. There was a rise in concentrations from the first dose to the 4th day. The rise for SDZ was a by a factor of 1.6 in both serum and lymph; the rise of TMP was also 1.6 in serum, but 1.5 in lymph. The peak concentrations at steady state were 27.7 mg/l (SD) .+-. 4.3 SDZ, and 1.6 .+-. 0.68 mg/l TMP. The serum values at that time were 31.7 .+-. 5.8 mg/l SDZ and 2.3 .+-. 0.51 mg/l TMP. The simultaneous concentrations of both SDZ and TMP were always somewhat lower in lymph than in serum, also at the end of the observation periods, i.e., 12 h after the first dose and 72 h after the final one. But the serum concentrations of both SDZ and TMP were only slightly higher than in lymph. After the final dose, the ratio between the 12-hour areas under the concentration curves of lymph and serum was 0.68 .+-. 0.12 for SDZ and 0.59 .+-. 0.14 for TMP. The values after the first dose were similar, 0.63 .+-. 0.17 and 0.57 .+-. 0.05, respectively. The elimination half-life in serum during steady state was 16.5 h for SDZ, 8.6 h for acetylated SDZ and 9.4 h for TMP. In lymph the corresponding values were 19.2, 19.2 and 8.9 h.