In vitro studies on drug--antibiotic interactions I: analgesics, antipyretics, antimalarials, and tranquilizers

The antimicrobial effects of some analgesics, antipyretics, antimalarials, and tranquilizers were determined. The phenothiazines were the most active group. The effect of the chosen drugs when combined with a selected number of antibiotics was studied on Staphylococcus aureus and Escherichia coli to determine the type of interaction. Most analgesics, antipyretics, and antimalarials showed either no effect or a synergistic action. However, some exhibited antagonistic effects. All tested tranquilizers were synergistic. Preliminary studies, using electronic absorption spectrometry, indicated that the antagonistic action may be attributed to a physical interaction.