Simultaneous determination of pioglitazone and its two active metabolites in human plasma by LC-MS/MS

Montelukast and zafirlukast do not affect the pharmacokinetics of the CYP2C8 substrate pioglitazone

OBJECTIVE

Pioglitazone, a thiazolidinedione antidiabetic drug, is metabolised mainly by the cytochrome P450 (CYP) 2C8 enzyme. The leukotriene receptor antagonists montelukast and zafirlukast have potently inhibited CYP2C8 activity and the metabolism of pioglitazone in vitro. Our objective was to determine whether montelukast and zafirlukast increase the plasma concentrations of pioglitazone in humans.

METHODS

In a randomised, double-blind crossover study with three phases and a washout period of 3 weeks, 12 healthy volunteers took either 10 mg montelukast once daily and placebo once daily, or 20 mg zafirlukast twice daily, or placebo twice daily, for 6 days. On day 3, they received a single oral dose of 15 mg pioglitazone. The plasma concentrations of pioglitazone and its metabolites M-IV, M-III, M-V and M-XI were measured for 96 h.

RESULTS

The total area under the plasma concentration-time curve of pioglitazone during the montelukast and zafirlukast phases was 101% (range 71-143%) and 103% (range 78-146%), respectively, of that during the placebo phase. Also, the peak plasma concentration and elimination half-life of pioglitazone remained unaffected by montelukast and zafirlukast. There were no statistically significant differences in the pharmacokinetics of any of the metabolites of pioglitazone between the phases.

CONCLUSIONS

Montelukast and zafirlukast do not increase the plasma concentrations of pioglitazone, indicating that their inhibitory effect on CYP2C8 is negligible in vivo, despite their strong inhibitory effect on CYP2C8 in vitro. The results highlight the importance of in vivo interaction studies and of the incorporation of relevant pharmacokinetic properties of drugs, including plasma protein binding data, to in vitro-in vivo interaction predictions.

Identification of oral antidiabetics and their metabolites in human urine by liquid chromatography/tandem mass spectrometry--a matter for doping control analysis

Since 1999, insulin belongs to the list of prohibited substances of the International Olympic Committee and the World Anti-Doping Agency. Except for patients suffering from insulin-dependent diabetes mellitus, the administration of insulin is not allowed. Therapeutics developed to treat non-insulin-dependent diabetes mellitus act as releasing factors of endogenously produced insulin or improve its efficiency mediating the glucose uptake into insulin-dependent tissues. Hence, these compounds are also relevant for sports drug testing, and a fast, robust, and sensitive assay was developed to identify 12 oral antidiabetic agents or respective hydroxylated metabolites in human urine. Urine specimens are enzymatically hydrolyzed; target analytes are extracted by liquid-liquid extraction and identified by means of liquid chromatography interfaced to tandem mass spectrometry by electrospray ionization. Detection limits of respective drugs ranged between 10 and 30 ng/mL, metabolites of therapeutics were characterized by diagnostic fragmentation pathways upon collisionally activated dissociation of protonated molecules, and general fragmentation routes were proposed.