DRUG FORMULATIONS AND CLINICAL METHODS Automated Chemiluminometric Screening of Counterfeit Drugs of the Antituberculosis Agent Pyrazinamide JOÃO A.V. PRIOR,JOÃO L.M. SANTOS, and JOSÉ L.F.C. LIMA REQUIMTE, Serviço de Química-Física, Faculdade de Farmácia, Universidade do Porto, Rua Aníbal Cunha, 164, 4050-047 Porto, Portugal Finding counterfeit drugs presents a growing challenge in preventing these products from entering health systems and causing serious consequences for consumers, drug manufacturers, and governments. In this investigation a simple, low-cost, and expeditious chemiluminometric approach, relying on a fully automated multipumping flow system for screening pharmaceutical preparations of the antituberculosis drug pyrazinamide, was implemented. The developed chemiluminescent method was based on the scavenging effect of pyrazinamide on the oxidation of luminol by hydrogen peroxide in alkaline medium. For analytical signal monitoring, a homemade chemiluminescence detector relying on a photomultiplier module was developed. Linear calibration plots for pyrazinamide concentrations between 10 and 70 mg/L were obtained (R = 0.9931) with good precision (RSD < 0.99%; n = 21). The limit of detection was 5.79 mg/L, and the sampling rate was about 150 determinations per hour. A t this time, the quality of drugs and therefore their effectiveness and safety are less and less certain, especially for the poorest populations, who are attracted by low-priced drugs sold through venues other than pharmacies. Recent years have seen an increase in the prevalence of counterfeit and substandard drugs on the market. The World Health Organization (WHO) has defined counterfeit drugs as those with the correct active ingredients but fake packaging, with insufficient or no active ingredients, or with incorrect ingredients. WHO defines substandard drugs as those produced with little or no attention to good manufacturing practices. Illegal drug rings seem inclined to manufacture either copies with the appearance of known trademarked drugs or substandard or inadequate pharmaceuticals, including generic drugs. Poor quality may be accidental, with no intention to deceive, but oversights in manufacturing or neglected controls—particularly in terms of dosage—can have tragic consequences. This is particularly true in dealing with such a pathogenic and fast-spreading disease as tuberculosis, a major public health problem in developing countries that WHO declared a world emergency in 1993. Pyrazinamide (PZA) is one of the frontline drugs for treating tuberculosis. The ineffectiveness of monotherapy programs and the outbreak of multidrug-resistant tuberculosis have prompted WHO to recommend 6- or 7-month short-course treatment regimens comprising rifampicin, isoniazid, PZA, and ethambutol. In this context, PZA is an important antituberculosis drug because it helps to shorten the duration of the chemotherapy regimens (1). The therapeutic importance of PZA, along with the hazardous side effects associated with its use—mainly in terms of liver toxicity—and the unpredictable drug half-life that might be prolonged in patients with impaired renal or hepatic function, have prompted the development of distinct analytical methodologies for monitoring this antituberculosis drug. Among these methodologies, the most used are GC (2–4), LC (5–15), potentiometry (16, 17), and UV spectrophotometry, usually associated with chemometric methods (18–21). An imperative issue demanding simple, low-cost, accurate, and easily automated procedures for PZA determination requires the assessment of pharmaceuticals quality in terms of good manufacturing practices and the search for counterfeit drugs. In effect, many developing countries do not have the technical, financial, or human resources required to apply such standards, leaving them, therefore, more vulnerable to fraud. Meanwhile, some developed countries may be less strict when the product being manufactured is destined for exportation versus domestic use. As a consequence, poor-quality PZA pharmaceuticals, mainly faulty in terms of inadequate dosage, can significantly reduce the effect of the therapeutic regimens, providing no benefit to the patients or even worsening their medical conditions, and thus making it even more difficult to control the spread of the disease. In the last decades, flow analysis has demonstrated itself to be a continuously evolving field and a valuable tool for implementing expeditious analytical methodologies that provide analytical chemists with alternatives that most of the time are less expensive, simpler, faster, safer, and more easily operated than the conventional procedures because of the higher automation level attained. The automation of analytical 830 PRIOR ET AL.: JOURNAL OF AOAC INTERNATIONAL VOL. 92, NO. 3, 2009 Received January 15, 2008. Accepted by SW June 1, 2008. Corresponding author’s e-mail: joaoavp@ff.up.pt Downloaded from https://academic.oup.com/jaoac/article/92/3/830/5656019 by guest on 26 November 2022