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Pharmacological particulars
Pharmacotherapeutic group: Antibacterials for systemic use, Sulfonamides and Trimethoprim.
ATCvet code: QJ01EW10
Pharmacodynamic properties
Both active substances produce a sequential double blockade of bacterial synthesis of folic acid. This results in a synergistic and bactericidal action inhibiting sequential steps in the synthesis of purines, which are required for DNA synthesis. The combination has a broad action against many Gram-positive and Gram-negative bacteria such as staphylococci, streptococci and E.coli.
MIC-breakpoints mg/l for susceptible organisms (EUCAST v. 3.1, February 2013):
S (susceptible)
R (resistance)
Streptococcus spp.
Staphylococcus spp.
(E. coli)
(breakpoints are expressed as the trimethoprim concentration, when used in cominbation with sulfamethoxazole)
Pharmacokinetic properties
After a single oral administration of 5 mg trimethoprim and 25 mg sulfadiazine per kg body weight to horses, the following parameters (mean ± sd) were observed:
Cmax (μg/ml)
Tmax (hour)
T1/2 el (hour)
2.35 ± 0.59
0.91 ± 0.32
2.74 ± 0.91
14.79 ± 3.47
1.90 ± 0.76
7.4 ± 1.8
Food intake appeared to affect the pharmacokinetic profile as both trimethoprim and sulfadiazine have been absorbed more rapidly in fasted horses.
Excretion of both actives is chiefly by the kidneys, by both glomerular filtration, and tubular secretion.
Urine concentrations of both trimethoprim and sulfadiazine are several fold higher than blood
concentrations. Neither trimethoprim nor sulfadiazine interferes with the excretion pattern of the other.