Detection of substandard fixed-dose combination tuberculosis drugs using thin-layer chromatography

A convenience sample of 13 fixed-dose combination (FDC) tuberculosis (TB) drugs from 'The Fixed Dose Combination Project' was analysed in laboratories at the University of Botswana and the US Food and Drug Administration (FDA).

To determine actual versus stated content of drugs in these FDCs.

Chemical analysis was performed using thin-layer chromatography (TLC) as a screening method, and ultraviolet (UV) spectrophotometry or liquid chromatography (LC) as confirmation. FDCs with content outside of 85-115% of stated concentration were defined as substandard.

All 13 FDCs contained the stated drugs. However, four (31%) were substandard, including two (15%) with low rifampicin content, one (8%) with excessive rifampicin, and one (8%) with excessive pyrazinamide. Both FDCs with low rifampicin contained four drugs and failed TLC screening. The FDC with excessive rifampicin was not detected by TLC screening. Using UV as the gold standard, the sensitivity of TLC for low rifampicin was 2/2 (100%), and the specificity was 9/10 (90%).

This study found that 31% of the FDCs in 'The Fixed Dose Combination Project' had substandard content, irrespective of bioavailability. Low rifampicin content, which can be reliably detected by TLC screening, was identified in both four-drug FDC products and is particularly worrisome. TB drugs should be screened for quality using TLC to optimise treatment outcomes and to prevent increases in acquired drug resistance.