Plasma hydroxyurea determined by gas chromatography–mass spectrometry

Hydroxyurea treatment is efficiently used to ameliorate the clinical course of patients affected with sickle cell disease. To understand the patient's wide variation in the clinical response to that drug and monitor its plasma levels, a new method was developed and validated. Fifty μL plasmatic samples containing hydroxyurea are added with internal standard, deproteinized, evaporated to dryness, silanized, and analyzed by gas chromatography–mass spectrometry, which operates in the selected ion mode after electron impact fragmentation. Linearity was found to extend to at least 100 mg/L. Over a 1–25 mg/L concentration range, coefficients of variation for intra-day and inter-day precision are 5.3% and 7.7%, respectively. Plasma blank-samples reveal endogenous hydroxyurea at a level ≤0.2 mg/L. The performances of the method, which is fast and simple, encounter the analytical goals needed for evaluation of hydroxyurea treatment and for pharmacokinetic studies.