In many countries, the quality of industrially manufactured pharmaceutical products is assured primarily through appropriate licensing and inspection systems and by the application of good manufacturing practice (GMP) by manufacturers. Until recently, analytical controls in the drug distribution system were regarded merely as supplemental. Quality surveillance following licensing/authorization was considered as a means of detecting: (1) any unintentional errors in the manufacture of drugs by legitimate producers; and/or (2) any degradation which might occur in the course of normal distribution. Since such events were considered to occur infrequently, heavy sampling was seldom recommended (25).
Today, owing to the widespread danger of trade in counterfeit drugs, quality control in the distribution system has acquired new dimensions. When unlicensed/unauthorized products are suspected of being in circulation and adherence to GMP cannot be assumed, a greater number of samples have to be tested in order to maintain an appropriate assurance of drug quality. At the same time, however, pharmacopoeial analyses have become more expensive. The use of simple tests should facilitate a balance between the need to increase the frequency and extent of testing on the one hand, and the need to contain costs on the other. Such first-line simple tests or screening methods would not replace pharmacopoeial, compendial or legally accepted test methods but would identify those products requiring further investigation. No regulatory action could be initiated on the basis of their results, and all samples considered to be potentially counterfeit or substandard would need to be referred for testing according to the pharmacopoeial, compendial or legally accepted reference method(s) to validate the findings of the initial screenings (7,8).
The principal requirement for a suitable screening procedure is the identification of the active drug substance. Depending on the capabilities and resources available, this can be achieved through test-tube colour reactions, melting-point determination or thin-layer chromatography (TLC). However, such tests provide only an estimation of the amount of drug substance; any other ingredients, which may be harmful, would not necessarily be detected and quantified. Practical considerations suggest that screening procedures should be performed according to a consistent method, and should have sufficient sensitivity and specificity to permit accurate testing of a large number of products.
Test methods for the detection of counterfeit products will be effective only within the framework of a national DRA with overall responsibility for control of importation and manufacturing procedures for drugs, and the inspection of drug distribution channels.