SULT 1A3 single-nucleotide polymorphism and the single dose pharmacokinetics of inhaled salbutamol enantiomers: Are some athletes at risk of higher urine levels?

The study was designed to investigate the effect of a common genetic variation of the main salbutamol metabolizing enzyme SULT1A3 (single nucleotide polymorphism 105A > G, rs1975350) on the stereoselective pharmacokinetics of salbutamol. Subjects were administered a 400 µg dose of inhaled salbutamol via a large volume spacer and blood samples were collected over 4 h. Plasma levels of (R)- and (S)-salbutamol were determined by an enantioselective liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. Twenty-five subjects with asthma were recruited and underwent SULT1A3 genotyping, from which four SNP homozygote (GG) subjects and nine wild-type (AA) subjects were selected to participated in the pharmacokinetic investigation. There were no differences in pharmacokinetic parameters (t_1/2, C_max, AUC_0-4h) between SNP and wild-type genotypes for either the R- or S-enantiomer. Observed C_max of R- and S-salbutamol [mean (SD)] was 0.64 (0.30) ng/mL and 1.32 (0.98) ng/mL, respectively. The mean t_1/2 of R- and S-salbutamol was estimated at 2.94 (1.17) h and 7.86 (6.14) h respectively. The AUC_0-4h of R- and S-salbutamol was 14.0 (6.8) and 38.3 (19.5) ng/mL.h respectively. In conclusion, the common SULT1A3 SNP 105A > G is not an important determinant of salbutamol enantiomer pharmacokinetics under normal clinical use and does not place some individuals at greater risk of accumulation in the body.