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Assay for HIV protease inhibitors in patient blood developed to improve patient care

Protease inhibitors (PIs) are a class of drugs often used in combination with other drugs to make up what is known as highly active antiretroviral therapy (HAART). Monitoring blood concentration of PIs, which can indicate both therapeutic and toxic levels of the drugs as well as patient noncompliance with the medication, may improve the care of both HIV-infected adults and children, but pediatric data are limited. A study was undertaken in 1998 by researchers at Ohio State University and the Columbus, OH, Children's Hospital in an attempt to develop an assay suitable for use with pediatric samples. The study was supported in part by the Agency for Healthcare Research and Quality (HS10397) through the agency's Centers for Education and Research in Therapeutics (CERTs) program.

Researchers used a high-performance liquid chromatographic (HPLC) assay to quantify blood concentrations of several PIs (indinavir, ritonavir, saquinavir, and nelfinavir) in 0.2 mL of plasma in 10 adults and 15 children with HIV disease. Nondetectable (ND) concentrations (below 25-50 ng/mL) were found in 33 percent of adult samples and 24 percent of pediatric samples. Four patients prescribed from 13.7 to 28 mg/kg/day of ritonavir had concentrations ranging from ND to 11.4 µg/mL, levels quite different from what would be expected given the doses they were prescribed.

Using HPLC drug monitoring, the clinicians were able to identify and correct important clinical problems, including drug-drug interactions, drug administration problems, and confirmed noncompliance. They conclude that routine PI monitoring and interpretation could improve the care of adult and pediatric HIV patients, especially those patients who do not respond as expected to treatment, develop viral resistance or toxicity, or have questionable compliance.

More details are in "Clinical use of a simultaneous HPLC assay for indinavir, saquinavir, ritonavir, and nelfinavir in children and adults," by Philip D. Walson, M.D., Shareen Cox, Ilya Utkin, and others, in the December 2003 Therapeutic Drug Monitoring 25, pp. 650-656.

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