| A study of the pharmacodynamics and pharmaceutics of the combination of amikacin (AMK) and trimethoprim (TMP) was carried out to study the synergism of trimethoprim to amikacin, base on which, a study of the prescription and the basic technics flow of the compound amikacin injection was also carried out. The accelerated test and long test run were introduced to evaluate the stability of the compound injection.The effects of the combination of amikacin and trimethoprim in vitro against some main veterinary pathogenic bacteria were reported. The strains used in the experiment were isolated clinically from pigs, including 19 strains of Escherichia Coli, 17 strains of Pasteurellosis Bacillus and 19 strains of Salmonella. The sensitivities of amikacin and trimethoprim on 3 species (55 strains) were evaluated by determinating the minimal inhibitory concentration (MIC) with the method of microdilution, and the synergism of the combination on 3 species (55 strains) Pathogenic bacteria was evaluated with checkerboard microdilution method by fractional inhibitory concentration (FIC) index. For the determination of both drugs in the compound injection, spectrophotometry and high performance liquid chromatography (HPLC) method were introduced. Following the determination, a study of the prescription and the technics of the compound injection carried out to evaluate the stability indexes of the compound injection such as properties and the relative content of the drugs. The accelerated test and the long test run were carried out at the purpose of stability evaluation of the compound injection.Results showed that synergic effect expressed by the combination was 72.7%, additive effect 12.7%, indifferent effect 14.6%, and no antagonistic effect expressed. The average FIC indexes of Escherichia Coli, Pasteurellosis Bacillus and Salmonella in the combined chemosensitivity test are 0.75, 0.43, 0.37respectively, all below 1, showing that the synergic effect of amikacin and trimethoprim is preferable. The combination of amikacin and trimethoprim showed different synergism to Escherichia coli, Pasteurellosis Bacillus and Salmonella, with a boost of 2 to 32 times of antibacterial activity. A spectrophotometry method was adopted for the determination of amikacin in the compound injection. The aborsption and the concentration of amikacin showed a good linearity within the concentration range from 24 to 48μg/mL. The regression equation isY=0.0266X-0.329(r=0.9994). A HPLC method was adopted for the determination of trimethoprim in the compound injection. The peak area of trimethoprim and its concentration showed a good linearity with in the concentration range from 18.75 to 56.25μg/mL. The regression equation is Y=20.952X+10.275(r=0.9999). According to the result of MIC of different proportion of amikacin and trimethoprim to standard strains and the solubility and clinical dose of both drugs yield the standard of the compound injection. The relative content of menstruums, pH, content of antioxidant and the temperature of sterilization of the compound injection can altogether affect its stability. The study evaluated the characteristics, the content and the pH of the compound injection. The prescription and the basic technics flow of the compound amikacin injection was carried out. The stability of the compound injection was evaluated by the accelerated test and long test run. The results showed that all the indexes of the compound injection were stable in the environment of 40±2℃, relative humidity 75±5% for a period of six months. Through a six-month long term test evaluation, three batchs of the compound injection showed no remarkable change in terms of properties, content, pH and all the other indexes, which showed that the prearation can be stable in at least six months under room temperature.
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