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Appl Environ Microbiol. 1971 September; 22(3): 329-333
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

In Vitro Chemotherapeutic Combinations Against Isoniazid-Resistant Mycobacterium tuberculosis and Mycobacterium fortuitum

Section of Infectious and Immunologic Diseases, Department of Internal Medicine, School of Medicine, University of California, Davis, California 95616
Channing Laboratory, Boston City Hospital and Mattapan Hospital, Boston, Massachusetts 02118
Harvard Medical Unit, Boston City Hospital and Mattapan Hospital, Boston, Massachusetts 02118

ABSTRACT

It is an acceptable medical practice to use second-line antimycobacterial drugs in combination with isoniazid in treatment of isoniazid-resistant tuberculosis. Recent investigations have demonstrated the importance of determining chemotherapeutic interaction in instances of multiple antibiotic use. We studied the inhibitory effect of combinations of isoniazid with ethambutol, rifampin, ethionamide, cycloserine, viomycin, and kanamycin against three isoniazid-resistant strains of Mycobacterium tuberculosis and three strains of M. fortuitum. The isobologram technique with drug concentrations of 0.4 to 100 µg/ml was used. With the exception of single instances in which kanamycin plus isoniazid (M. tuberculosis strain 9999) and ethionamide plus isoniazid (M. fortuitum strain 2080) seemed to have a synergistic effect, neither synergy nor antagonism was noted for any of the combinations. These studies show that the combined use of isoniazid and a second line antimycobacterial agent results in vitro in indifferent inhibitory activity.

¹ Present address: Section of Infectious and Immunologic Diseases, Department of Internal Medicine, School of Medicine, University of California, Davis, Calif. 95616.