Measurement of brimonidine concentrations in human plasma by a highly sensitive gas chromatography/mass spectrometric assay

• Published in: Journal of pharmaceutical and biomedical analysis 1995-07, Vol.13 (8), p.995-1002
• Main Authors: Acheampong, Andrew, Tang-Liu, Diane D.-S.
• Format: Article
• Language: English
• Subjects: Adrenergic alpha-Agonists - blood; Adrenergic alpha-Agonists - pharmacokinetics; Adult; Assay; Biological and medical sciences; Brimonidine; Brimonidine Tartrate; Calibration; Chemical ionization; Chromatography, High Pressure Liquid; Eye; Gas Chromatography-Mass Spectrometry; Humans; Male; Medical sciences; Pharmacology. Drug treatments; Picogram; Plasma concentrations; Quality Control; Quinoxalines - blood; Quinoxalines - pharmacokinetics
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/0731-7085(95)01526-Q

Brimonidine is an α 2-adrenergic agonist that is efficacious in lowering intraocular pressure in humans. A highly sensitive and selective gas chromatography/mass spectrometry (GC/MS) assay is described for quantitation of brimonidine in human plasma following ocular installation. Brimonidine in 1 ml of plasma was extracted together with tetradeuterated brimonidine (internal standard) and clonidine (carrier) by solvent extraction. After solvent evaporation, 3,5-bis(trifluoromethyl)benzoyl derivatives were formed and injected onto a GC/MS appartus under negative chemical ionization conditions. The ions monitored for derivatized brimonidine and tetradeuterated brimonidine were m/ z 691 [M - HBr] and m/ z 694 [M - DBr], respectively. Calibration curves were linear from 2 to 1000 pg ml −1 ( r 2 = 0.981-0.996). The method was specific for brimonidine relative to endogenous compounds in plasma. The inter-day relative standard deviation for analysis of quality controls was 12% or less, and the inter-day assay accuracy ranged from 97 to 104% of nominals. The GC/MS assay showed adequate sensitivity for analysis of human samples from volunteers ocularly dosed with 0.5% brimonidine tartrate solution. Overall, the GC/MS assay showed excellent precision and accuracy, and a minimum quantifiable concentration of 2 pg ml −1.