Effects of Concentration and Temperature on the Stability of Nevirapine in Whole Blood and Serum

Abstract

In sub-Saharan Africa, India, Southeast Asia, and other resource-poor regions of the world, the antiretroviral nonnucleoside reverse transcriptase inhibitor nevirapine (NVP) is widely prescribed for HIV treatment and prevention because of its relative safety, long half-life, and low cost. Furthermore, pregnant women are often prescribed NVP therapy to decrease the rate of mother-tochild HIV transmission or as part of a combination therapeutic regimen in more developed countries. As one example, measuring NVP concentrations in pregnant women and their infants, in particular, has increased as clinics in developing countries attempt to better assess NVP "coverage" (e.g., universal treatment regardless of HIV status vs targeted treatment) (1 ). Because most developing countries currently do not have state-of-theart sample collection, processing, and/or storage capabilities, more data are needed on how various procedures in these countries may affect NVP stability.In clinical chemistry, drug stability during sample processing and storage is an important consideration for the interpretation of drug concentrations. If drugs do not remain stable in a given matrix under the conditions used for storage and/or processing, inaccurate drug concentrations will be obtained. Blood samples taken in resourcepoor regions are often sent to laboratories in the developed world for drug measurements. However, these samples may not be processed and handled in the same manner as they would be in the US. In resource-poor regions, blood is often collected in red-top (no additive) tubes to separate serum from cells. Samples may not be placed on ice immediately but instead left on the laboratory bench for a period of up to 24 h before packaging and shipping for antiretroviral analysis. Furthermore, because of clinical settings in tropical climates, samples may be exposed to high temperatures for an undisclosed amount of time. Currently, NVP stability data under these conditions are not available. The objective of the present study was to assess the short-term stability of NVP in human whole blood and serum as a function of storage time, concentration, and temperature.Four drug-free samples of EDTA-whole blood, heparinwhole blood, and anticoagulant-free serum (25 mL) were obtained, with each sample coming from a different patient. NVP was then added to all three sample types at low (250 g/L) and high (2500 g/L) concentrations. The NVP-enriched samples were subsequently divided and transferred to three environments: the laboratory bench at room temperature (20 -25°C), the refrigerator (4°C), and an incubator (37°C) for a 24-h period. At each time point, (0, 1, 2, 4, 8, or 24 h), 1 mL of NVP-enriched blood product (EDTA and heparin) was removed from the samples stored at each temperature and centrifuged (15 000g for 5 min) to separate the plasma. Three 100-L aliquots of the separated plasma from whole blood or anticoagulant-free serum were taken, and 50-L of internal standard was added to each aliquot. Internal standards were 20 mg/L and 2 mg/...

Effect of temperature on storage of ethionamide during susceptibility testing

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