Effect of pH and human serum on the in-vitro activity of B-lactam and aminoglycoside combinations

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

Effect of magnesium and calcium supplementation on the in-vitro activity of some -lactam-aminoglycoside combinations agents staphylococcus aureus

The effect of physiological levels of Mg +2 and Ca +2 on the in vitro activity of cephradine [Cep], cefoperazone [Cef] and cefotaxime [Ctx] alone and in combination with three aminoglycoside antibiotics [gentamicin [Gm], tobramycin [Tm], and netilmicin [Nt]] was evaluated against ten strains of Staphylococcus aureus. Adding Mg +2 or Ca +2 to commercial media deficient to these cations increased the MICs and MBCs of the three cephalosporins 2 to 4-fold, while aminoglycoside antibiotics revealed 4 to 8-fold increase in their MICs and MBCs. The combined antibacterial activity of the studied cephalosporin/aminoglycoside combinations decreased by the addition of Mg +2 or Ca +2

Post antibiotic effect of gentamicin in combination with cephradine, cefotaxime on pseudomonas aeruginosa

The post-antibiotic effect [PAE] of gentamicin [Gm] alone and in combination with cephradine [Cef] or cefotaxime [Ctx] was studied for five isolates of Pseudomonas aeruginosa. Cultures of Pseudomonas aeruginosa isolates were incubated with cephradine or cefotaxime [4 MIC] for one hour. Two different concentrations of gentamicin [0.5 and 1.0 MIC] were then added. Incubation of the combinations continued for one more hour. The antibiotics were eliminated by dilution. The post-antibiotic effects produced by the drugs in combination were longer than the sum of the individual effects of the drugs when they were used alone. A synergic post-antibiotic effect was also found when Pseudomonas aeruginosa strain No. 1 simultaneously exposed to gentamicin combination with cephradine or cefotaxime for 2 hours

Antibacterial activity of cefoperazone alone and in combination with aminoglycoside antibiotics

The in-vitro antibacterial activities of cefoperazone [Cef], amikacin [Am], tobramycin [Nn] and gentamicin [Gm] as well as the combinations of cefoperazone with the three aminoglycoside antibiotics were tested againts five strains of each of Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus using the checkerboard agar dilution method. All antimicrobial combinations demonstrated some synergy and no antagonism was observed. A synergistic effect was observed with the combinations of cefoperazone plus amikacin, cefoperazone plus tobramycin and cefoperazone plus gentamicin against four of five and three of five of the tested clinical isolates of Pseudomonas aeruginosa and Escherichia coli respectively. Staphylococcus aureus clinical isolates exhibit an additive or indifferent effect towards all tested combinations. No antagonistic activities were found with any of the strains using such combinations

Interaction of rifampicin with piroxicam and prednisolone

The effect of rifampicin on the anti-inflammatory activities of both piroxicam and prednisolone was studied using two models of inflammation. Carrageenin-induced rat hind paw edema model revealed that intraperitoneal administration of rifampicin [50 mg/kg] in combination with piroxicam [5 mg/kg] significantly diminished the anti-inflammatory effect of the tater. The anti-inflammatory activity of prednisolone [10 mg/kg] in this model was only slightly implantation. Sponge implantation-induced granuloma model showed that the intraperitoneal administration of rifampicin [50 mg/kg] in combination with piroxicam [5 mg/kg] or prednisolone [10 mg/kg] once daily for 8 days resulted in a significant reduction in the anti- inflammatory activities of both piroxicam and prednisolone. The effect of piroxicam and prednisolone on the bactericidal activity of rifampicin was also evaluated both in broth and in rat serum after i.p. injection. In vitro broth studies of the bactericidal activity of rifampicin [5 mug/ml] or prednisolone [3 mug/ml] against Staphylococcus aureus did not show any significant difference between the killing rats of these regimens. Studies on rat sera showed that the bactericidal activity of sera of rats injected with rifampicin [50 mg/kg i.p.] alone against Staphylococcus aureus was significantly higher than those sera of rats received rifampicin in combination with prednisolone [10 mg/kg]. The anti-staphylococcal activity of rifampicin in rat serum was not significantly affected by concomitant administration of piroxicam [5 mg/kg i.p.]