ABSTRACT
The effect of three pH values [5.8, 7.4, and 8.0] and human serum on the activity of ampicillin, cefazolin, and cefotaxime alone and in combination with four aminoglycoside antibiotics [streptomycin, tobramycin, gentamicin, and amikacin] against sensitive and resistant strains of Staphylococcus aureus and Pseudomonas aeruginosa was evaluated. The change of pH from 5.8 to 8 noticeably affected the activity of all studied combinations. In general, the five B-lactam aminoglycoside combinations were more active at alkaline pH [pH 8]. However, pH shift towards the acidic side [pH 5.8] decreased their activity and increased their FIC indices. Addition of human serum decreased the in vitro antibacterial activity of B-lactam and aminoglycoside antibiotics, as well as their combinations against the used strains. The degree of influence was related to the ability of each antibiotic to bind with serum albumin. Cefazolin/streptomycin and cefazolin/tobramycin combinations showed the highest degree of protein binding effect
Subject(s)
Lactams/pharmacokinetics , Drug Therapy, Combination/bloodABSTRACT
Effects of inoculum size on the comparative activity of cefotaxime, cefazolin, ampicillin, gentamicin, streptomycin, amikacin and tobramycin against two strains of Pseudomonas aeruginosa and two strains of Staphylococcus aureus were studied by using 104, 106 and 107 cfu/ml. Inoculum size markedly affected the susceptibility of the studied strains to these antibiotics as well as their combinations. An increase in the inoculum size from 104 to 106 cfu/ml had more effects on the MIC than its increase from 106 to 104 cfu/ml. As regards the effect of inoculum size on the activity of the combinations, it was shown that the increase of inoculum size from 104 to 107 cfu/ml decreased the activity of cefazolin/streptomycin, ampicillin/tobramycin and cefazolin/tobramycin combinations, whereas inoculum size change did not exhibit any effect on cefotaxime gentamicin and ampicillin/amikacin