| Sulfamonomethoxine (SMM) is a kind of sulfonamides with the highest anti-bacterial effect in vitro and in vivo. It also has obviously therapeutic effect on Coccidiosis , Toxoplasmosis, Leucocytozoonosis and Eprythrozoonosis. In this study an Injectable Solution of SMM was successfully developed. Stability and Pharmacokinetics of this formulation was also studied.Temperature accelerated test (6m) under 40℃ and light accelerated test (10d) had undergone. Assy of SMM in sample was determined with HPLC method. The linearity of the standard curves for SMM were perfect in the range of 30~150μg.ml-1, r=0.9996(n=5). The result of accelerated test showed that the Injectable Solution of SMM were stable either to heat or to light.Swines were given intravenously(i.v.) and intramuscularly(i.m.) with dose of 50mg.kg-1 and 100mg.kg-1 SMM respectively. Blood samples were collected at time of 0,0.08, 0.25, 0.5,1, 2, 3, 4, 6, 8, 10, 12, 24h (i.v.) and 0, 0.25, 0.5, 1, 2, 4, 6,8, 12, 24, 48, 72, 96, 120h (i.m.), respectively. And seperated blood plasma then. Plasma protein was precipitated with acetonitrile directly and then centrifuged at 15000 r.min-1 for 10 minutes. The supernatant was filtered and then injected into reverse phase HPLC system with 20μl. The linearity of the standard curves for SMM in blood plasma were perfect in the range of 0.1~100ug.ml-1, r=0.9996(n=5). Recoveries of three spiked sample concentration(0.25, 2, 18μg.ml-1) were 110.4±3.6%, 102.9±3.8% and 101.3±2.4%. Pharmacokinetic analysis of plasma drug concentration-time data for SMM was carried out with a computer program (3P97, China Pharmacology Association). Plasma drug concentration-time data after i.v. and i.m.administration all were best described by a one-compartment open model. After 100 and 50mg.kg-1 i.v. .administration, AUC were 1032 ± 86. 4μg.h ml-1 and 537. 7±37. 6μg.h.ml-1, V(c) 为 0. 41±0. 02 and 0.38 ± 0. 02L.kg-1, t1/2 ke were 2. 94±0. 13h and 2. 84±0. 08h, CL (s) were 0. 1±0. 005L .kg-1 .h-1 and 0. 09 ± 0. 005L .kg-1 .h-1 After 100 and 50mg.kg-1 i.m. .administration, t1/2ka were 0. 78±0. 38 h and 0. 87 ± 0. 14h, t1/2ke were 17. 42 ± 1. 1h and 16. 3 ± 1. 9h, C(max) were 29.04±1.37μg.ml-1 and 15. 4±0. 6μg.ml-1, AUC were 842.4±49.3μg.h.ml-1 and 427 ± 43μg.h. ml-1, F were 81. 6±4. 8% and 79. 5 ± 8. 0%; Average absolute bioavailability of intramuscular administration was about 80.6%, SMM was absorbed completely. Elimination half life of intramuscular administration was more than 16 hours.Regarding 0.5μg.ml-1 as SMM minimum effective blood concentration(Streptococcus pyogenes), sustaining time of effective blood concentration of 100 and 50mg.kg-1 i.m. .administration were 120 and 72 hours, suggested that the formulation was long acting.Moreover, pH of the formulation was modest, tissue tolerance was good.Above all, administration and dosage of recommendation for the formulation : Intramuscular, 50 mg per kg body weight for treatment of S.pyogenes infection, once every three day.
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