Setting: The prevalence of substandard anti-tuberculosis drugs is unknown. To maximize the effectiveness of tuberculosis (TB) control efforts, simple, inexpensive drug quality screening methods are needed.
Design: Isoniazid (INH) and rifampin (RMP) single- and fixed-dose combination (FDC) formulations were collected from selected TB programs and pharmacies in Colombia, Estonia, India, Latvia, Russia and Vietnam. Samples were screened using a recently developed thin-layer chromatography (TLC) kit. All abnormal samples and a 40% random sample of normal formulations were further analyzed using confirmatory techniques. Samples outside of 85% to 115% of stated content, and/or containing compounds other than the stated drug, were defined as being substandard.
Results: Overall, 10% (4/40) of all samples, including 13% (4/30) RMP samples, contained <85% of stated content. More FDCs (5/24, 21%) than single-drug samples (2/16, 13%) were substandard. A comparison of TLC with the confirmatory analysis for RMP analysis showed a sensitivity of 100% (4/4), a specificity of 92% (24/26), a positive predictive value (PPV) of 67% (4/6), and a negative predictive value (NPV) of 100% (24/24). An analysis of INH showed a specificity of 90% (9/10). However, sensitivity, PPV, and NVP could not be determined.
Conclusion: A substantial number of anti-tuberculosis drugs from several countries, in particular FDCs, were found to be substandard. Such drugs may contribute to the creation of drug-resistant TB. TLC is an effective, convenient, and inexpensive method for the detection of substandard drugs.