Counterfeit drugs detection by measurement of tablets and secondary packaging colour.

The growth of pharmaceutical counterfeiting is a major public health problem. This growth is resulting in a proportional increase in the number of samples that medicines control laboratories have to test. Thus the need for simple and affordable preliminary screening methods to be used by inspectors to decide in the field whether to collect a sample for further laboratory analysis or not. This paper intends to evaluate the possibility to employ for preliminary examinations of suspicious samples an optical spectrophotometer (colorimeter) used in the graphic industry, capable of measuring the reflectance visible spectrum of solid materials. The colorimeter was tested on original and counterfeited Viagra, Cialis and Levitra by measuring the colour of tablets' surface and of a specific spot of the packages. Various batches of the original drugs were employed both to investigate precision and robustness of the technique and to build spectral libraries. These libraries were used to compare suspicious samples to the corresponding original by means of a wavelength distance pattern recognition method. The method was eventually tested on suspicious samples sized by police authorities in order to evaluate its effectiveness. The device resulted precise and robust toward ambient conditions changes, although some limits emerged: the libraries of original samples need a frequent update and a lower precision is to be expected for tablets which surface is extremely convex.