Tropical Journal of Pharmaceutical Research

Original Research Article | OPEN ACCESS

Comparative Evaluation of Three In Vitro Techniques in the Interaction of Ampicillin and Ciprofloxacin against Staphylococcus aureus and Escherichia coli.

C S Nworu¹ , C O Esimone²

¹Department of Pharmacology and Toxicology; ²Division of Pharmaceutical Microbiology, Department of Pharmaceutics, University of Nigeria, Nsukka, 410001, Enugu State.

For correspondence:- C Nworu Email: csnworu@yahoo.com

Published: 12 December 2006

Citation: Nworu CS, Esimone CO. Comparative Evaluation of Three In Vitro Techniques in the Interaction of Ampicillin and Ciprofloxacin against Staphylococcus aureus and Escherichia coli.. Trop J Pharm Res 2006; 5(2):605-611 doi: 10.4314/tjpr.v5i2.5

© 2006 The authors.
This is an Open Access article that uses a funding model which does not charge readers or their institutions for access and distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0) and the Budapest Open Access Initiative (http://www.budapestopenaccessinitiative.org/read), which permit unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited..

Abstract

Purpose: The study was designed to evaluate the consistency of interpretation of results of interaction between ampicillin and ciprofloxacin against S. aureus and E. coli using three in vitro techniques.
Methods: The interaction between ampicillin and ciprofloxacin was studied using three in vitro methodsCheckerboard technique, Overlay Inoculum Susceptibility Disc technique (OLISD) and the Decimal Assay for Additivity technique (DAA).
Results: In the Checkerboard technique, fractional inhibitory concentration (FIC) indices show that the
ampicillin/ciprofloxacin combination is synergistic against the test organisms. In the DAA approach, a target IZD of 15 mm yielded Biological Equivalent Factors (BEF) of 1.35 µg (amp/Staph), 6.74 µg (cipro/Staph), 9.62 µg (ampicillin/E. coli), and 5.45 µg (cipro/E. coli). Statistical analyses show that all decimal combinations of ampicillin and ciprofloxacin were additive (p< 0.05). The overlay inoculum susceptibility disc method shows inhibition zone diameter increments ranging between 36 ± 8.00 % to 69.2 ± 23.08 % for S. aureus and 28.12 ± 3.13 % to 50 ± 12.50 % for E. coli. These increments are consistent with reported criteria for synergism in the OLISD method.
Conclusion: The study suggests a possible clinical use for the combination of ampicillin and ciprofloxacin against infections caused by these organisms. Equally, the apparent disagreement between DAA and the other two methods raises questions as to the consistency of inferences drawn on interaction studies when different techniques are used.

Keywords: Ampicillin, Ciprofloxacin, Interaction, Decimal Assay, Checkerboard, OLISD method.