Determination of Zalcitabine in Medicaments by Differential Pulse Voltammetry

The zalcitabine (ddC) has been extensively used in the treatment of HIV patients due to its antiretroviral activity. The quality control of this active principle in medications is of outstanding importance to public health. The principal objective of the current study was the development of an alternative analytical methodology for the zalcitabine determination using a voltammetric process. The zalcitabine gives a reduction peak (at ？V versus Ag/AgCl) at the hanging mercury drop electrode (HMDE). The differential pulse voltammetric response is evaluated with respect to the scan rate (20？mV/s), pulse amplitude (50？mV), support electrolyte (Clark-Lubs buffer), pH (2.0), and other variables. The response is linear over the 10.0 to 28.0？mg/L (47 to 133？μM) concentration range, and the detection limit is 2.08？mg/L. The validation of this method was realized using a governmental Brazilian document (Inmetro, 2007) and the results are reported for medication drugs. 1. Introduction The Food and Drug Administration has approved the AIDS drug zalcitabine, commonly known as 2′-3′-dideoxycytidine (ddC). It is the third drug licensed specifically for use in treating the human immunodeficiency virus, the cause of AIDS. Zalcitabine was approved for use in combination with the first approved AIDS drug, zidovudine (or AZT), as a treatment option for adult patients with advanced HIV infection who show signs of clinical or immunological deterioration. Early clinical trial data have shown that increases in CD4 cells (immune cells) were somewhat greater and more sustained in patients treated with the combination of zalcitabine and zidovudine than in those who received zidovudine alone as initial therapy. An increase in CD4 cells is believed to indicate that the body’s disease-fighting capability has been at least transiently enhanced. Zalcitabine is a derivative of the naturally existing deoxycytidine, made by replacing the hydroxyl group in position 3′ with a hydrogen group. It is phosphorylated in T cells and other HIV target cells into its active triphosphate form, ddCTP. This active metabolite works as a substrate for HIV reverse transcriptase, and also by incorporation into the viral DNA, hence terminating the chain elongation due to the missing hydroxyl group. Since zalcitabine is a nucleoside, reverse transcriptase inhibitor (NRTI), it possesses activity only against retroviruses [1, 2]. Zalcitabine has a very high oral absorption rate of over 80%. It is predominantly eliminated by the renal route, with a half-life of 2 hours [3, 4]. Zalcitabine (Figure 1(a)) is an