Development of analytical methods for counterfeit drugs investigation

During this PhD work new analytical methods for the analysis of counterfeit drugs were developed. The Colorimeter is a simple instrument for preliminary and fast screening of suspicious counterfeit drug. It employs an “Eye one” spectrophotometer, that acquires the reflectance spectrum of solid surfaces in the visible; it is portable and very cheap. Since the color both of tablets and of peculiar regions of the packaging are specific to a drug, it is very unlikely that a counterfeit product can imitate them in an accurate way. Thus the reflectance spectrum of a suspicious drug can be compared to that of the original one, obtained through a statistical analysis of a representative amount of original samples. By this comparison it is evaluated if the analyzed drug is probably a counterfeit, hence it needs more in depth analyses, or if it is original. A solid state approach was developed by combining FT-IR, DSC, TGA. This approach is rapid as sample treatments are not necessary. By this approach it is possible to identify the ingredients of an unknown drug, in particular both active substances and excipients can be detected. First a data bank was built analyzing all the possible components of a suspicious drug: active substances, pharmaceutical excipients, low cost widespread materials (from food and construction industry) were analyzed and for each technique the peculiar signals of every ingredient were detected. Then suspicious samples were analyzed: matching the signals with the data bank it was possible to identify which ingredients were present. By this approach it was possible to detect the presence of inappropriate and dangerous ingredients like chalk. A discriminating dissolution method for the analysis of sildenafil citrate tablets was developed and validated (sildenafil citrate is the active substance of Viagra®). By this dissolution method it was possible to highlight differences in the active substance release rate between originals and counterfeit drugs. The dissolution medium was a phosphate buffer of pH 4,5; in this condition sildenafil citrate is weakly soluble, hence the dissolution is slow and informative. The Basket system (Apparatus I Ph.Eur.) was employed since the Paddle system caused a coning effect. Counterfeit and suspicious samples were analyzed and compared to the originals. By this method it was possible to acquire valuable information about formulation and technology of production of these unknown drugs. An NMR method for quantitative determination was validated according to the ICH guideline “Note For Guidance On Validation Of Analytical Procedures: Text And Methodology”. Since a quantitative NMR method doesn’t require a reference standard of the investigated substance but only a generic internal standard, it can have important applications in the counterfeit drugs investigation. In particular it allows to quantitate substances whose reference standard is not available, like the omologues; these are new, not authorized, active substance with a structure that is similar to that of an authorized one; their presence in fake herbal product and food dietary supplements has recently been reported in literature. Three different internal standards were tested during the validation: aciclovir, maleic acid, dinitrobenzoic acid. Deuterated DMSO was employed as solvent since most of the active substances are soluble in it. This method resulted very accurate, precise, with an excellent linearity in the concentration range of interest.