Combination Activity of Standard Antituberculosis Drugs and Extracts of Medicinal Plants Commonly Used in Traditional Treatment of Tuberculosis in Uganda

Background Despite the increasing acceptance of medicinal plant use in combination with conventional antituberculosis drugs in treatment of tuberculosis (TB) in Uganda, there is paucity of knowledge on their combination effect. This research aimed to find combination activity of standard antituberculosis drugs with extracts of Zanthoxylum leprieurii and Rubia cordifolia , the two common antituberculosis medicinal plants, against pansensitive (H37Rv) and multi-drug resistant (MDR) Mycobacterium tuberculosis . Methods Two reference MTB strains (H37Rv and MDR strain) were inoculated on Middlebrook 7H11 medium containing a combination of standard anti-TB drugs and methanol extracts of Z. leprieurii and R. cordifolia at varying concentrations. The number of colonies on the plates were observed and counted weekly for up to 8 weeks. In vitro combination activity was determined using proportion method. Mean percentage inhibition was calculated for the reduction of number of colonies on drug-extract combination medium in relation to drug-extract-free control medium. Results Drug-extract combinations showed good combination effect against Mycobacterium tuberculosis strains when compared with individual standard anti-TB drugs. This was more evident with MDR strain. There was however a reduction in percentage inhibition when extracts were combined with ethambutol and streptomycin against H37Rv strain. Conclusions Therefore, use of medicinal plants in combination with conventional antituberculosis drugs in TB treatment should be done with caution especially with susceptible cases.