Distribution kinetics of trimethoprim (TMP) was investigated with five made rabbits at a dose of 15.3 mg/kg body weight. After intravenous administration of TMP, it took only about 18 min to reach the steady-state distribution based on the blood data. The apparent distribution volume in the central compartement (Vc) was 0.496 +- 0.073 1/kg (mean +- SEM), at steady-state (Vss) was 0.944 +- 0.147 1/kg, in terms of area (Varea) was 1.18 +- 0.14 1/kg and by extrapolation (Vextrap) was 1.30 +- 0.15 1/kg. The rate at which Vc approaches Vss was estimated to be 1.61 t 0.24 1/kg/h; whereas the second distribution stage (Vss to Varea) was slow and was 0.58 +- 0.18 1/kg/h. Wilcoxon signedrank test revealed that erroneous large Vc, tss and tarea values as well as slow dV/dt values were resulted (P < 0.05) when the parameters were estimated with the plasma data. The results indicate the distribution of TMP in blood cells may affect the in vivo disposition of TMP. Jhe rapid rate of equilibration may explain the unusual excellent tissue permeability of TMP observed in the clinical investigations. 本報告是以5隻雄性家兔為實驗動物探討Trimethoprim ( TMP )在動物體內之分佈動力學特性。根據靜脈注射後所獲得之全血濃度變化可推定TMP在中心室之分佈容積(Vc )為0.496土0.073 l/kg(mean士SEM)，在穩定狀態(Vss )為0.944士0.147 1/ kg而Varea為1.18士0.14 1/ kg,Vextrap為1.30士0.15 1/ kg。由Vc至Vss之分佈速率為1.61士0.24 1 / kg/ h, tss為0.307士0.034 h ;而由Vss至Varea之分佈速率為0.58 +- 0.18 1/ kg/ h, tarea為0.62士0.13 h。統計分析顯示，若使用血漿濃度之變化推定之Vc ，tss及tarea皆會錯誤地變大，同時分佈速率也會錯誤地變慢。藥物對組織之作用是決定於藥物在體內平衡分佈速率之快慢，tss不但反映藥物對組織分佈的親和力同時也表現其分佈能力。TMP有極優異之組織分佈性，能在通常藥物雖於分佈之腦脊髓液、攝護腺及骨等組織中有效的分佈，這種特異性可由其分佈動力學特性加以說明。
