An S-warfarin and AZD1981 interaction: in vitro and clinical pilot data suggest the N-deacetylated amino acid metabolite as the primary perpetrator.

AIM: AZD1981 is an orally bioavailable chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTh2) receptor antagonist progressed to phase II trials for the treatment of allergic asthma. Previously performed in vitro human hepatocyte incubations identified N-deacetylated AZD1981 as a primary metabolite. We report on metabolite exposure from a clinical excretion balance, on in vitro studies performed to determine the likelihood of a metabolite-dependent drug-drug interaction (DDI) and on a clinical warfarin DDI study. The aim was to demonstrate that N-deacetylated AZD1981 is responsible for the observed interaction. METHODS: The excretion and biotransformation of [14 C]-AZD1981 were studied in healthy male volunteers, and subsequently in vitro cytochrome P450 (CYP) inhibition and hepatocyte uptake investigations were carried out with metabolites and the parent drug. A clinical DDI study using coadministered twice-daily 100 mg and 400 mg AZD1981 with 25 mg warfarin was performed. RESULTS: The excretion balance study showed N-deacetylated AZD1981 to be the most abundant metabolite present in plasma. In vitro data revealed the metabolite to be a weak CYP2C9 time-dependent inhibitor, subject to more active hepatic uptake than the parent molecule. Clinically, the S-warfarin area under the plasma concentration-time curve increased, on average, 1.4-fold [95% confidence interval (CI) 1.22, 1.50] and 2.4-fold (95% CI 2.11, 2.64) after 100 mg (n = 13) and 400 mg (n = 11) AZD1981 administration, respectively. In vitro CYP inhibition and hepatocyte uptake data were used to explain the interaction. CONCLUSIONS: N-deacetylated AZD1981 can be added to the small list of drug metabolites reported as sole contributors to clinical drug-drug interactions, with weak time-dependent inhibition exacerbated by efficient hepatic uptake being the cause.

Effects of Fostamatinib on the Pharmacokinetics of the CYP2C8 Substrate Pioglitazone: Results From In Vitro and Phase 1 Clinical Studies.

Fostamatinib is a prodrug that undergoes gastrointestinal tract dephosphorylation to form the active metabolite, R406. Here we report its cytochrome P450-inducing potential. In vitro, R406 3 and 10 µM induced CYP2C8 to levels representing 53% and 75%, respectively, of the level achieved by the positive control, rifampicin. Induction of other enzymes was minor. The effect of fostamatinib (100 mg twice daily) on the pharmacokinetics of a single oral 30-mg dose of the CYP2C8 substrate pioglitazone and its metabolite, hydroxy pioglitazone, was then investigated (open-label, nonrandomized, 2-period phase I study [n = 15]). Coadministration of fostamatinib and pioglitazone (vs pioglitazone alone) was associated with lower mean maximum plasma concentration values for pioglitazone (geometric least-squares mean ratio, 82.8; 90% confidence interval, 64.2-106.8) and hydroxy pioglitazone (90.9; 78.6-105.1), an increase in pioglitazone AUC (117.8; 108.4-128.0), a decrease in hydroxy pioglitazone AUC(0-t) (89.7; 78.9-101.9), and an increase in pioglitazone geometric mean t1/2λz (9.4-12.8 hours). No tolerability concerns were identified upon coadministration. These data suggest that although clinical significance has not been formally evaluated, fostamatinib is unlikely to have a clinically significant effect on the pharmacokinetics of pioglitazone (which may be extrapolated to other CYP2C8 substrates). However, vigilance is advised should these agents be prescribed together.

Effects of CYP3A4 Inhibitors Ketoconazole and Verapamil and the CYP3A4 Inducer Rifampicin on the Pharmacokinetic Parameters of Fostamatinib: Results from In Vitro and Phase I Clinical Studies.

BACKGROUND: Fostamatinib (R788) is a spleen tyrosine kinase (SYK) inhibitor. The active metabolite of fostamatinib, R406, is primarily metabolized by CYP3A4. OBJECTIVES: The aim of this study was to characterize hepatic microsomal metabolism of R406 and confirm the role of CYP3A4 in R406 metabolism, determining whether co-administration of CYP3A4 inhibitors (ketoconazole, verapamil) or inducers (rifampicin) affects R406 pharmacokinetics. METHODS: R406 stability was determined using human hepatic microsomes. The CYP450 isoforms responsible for R406 metabolism in humans were identified using expressed CYP450 isoforms and specific chemical inhibitors. The ketoconazole interaction study (double-blind, randomized, placebo-controlled, two-period crossover) involved fostamatinib administration (single 80-mg dose), alone and with ketoconazole (200 mg twice daily). The verapamil and rifampicin interaction studies (open-label, two-period, fixed-sequence) involved fostamatinib administration (single 150-mg dose), alone and with immediate-release verapamil (80 mg three times daily) or rifampicin (600 mg once daily). Standard pharmacokinetic parameters were calculated in all studies. RESULTS/DISCUSSION: Hepatic microsomes showed time-dependent loss of R406 and formation of para-O-demethylated R406. Microsomal metabolism of R406 was markedly inhibited by CYP3A4 inhibitors and, in the expressed CYP450 studies, the rate of R406 disappearance was greatest with CYP3A4. In the clinical studies, co-administration of ketoconazole caused a 2-fold (CI 1.77-2.30) increase in R406 exposure. Verapamil increased R406 exposure (39% increase, CI 8-80), whereas rifampicin co-administration decreased exposure by 75% (CI 68-81). Fostamatinib was well tolerated. CONCLUSION: The oxidative metabolism of R406 is predominantly catalyzed by CYP3A4. In clinical studies, exposure to R406 is affected by concomitant administration of CYP3A4 inducers/inhibitors. These findings should be taken into account when considering co-prescription of fostamatinib with such agents.

Effects of Fostamatinib on the Pharmacokinetics of Digoxin (a P-Glycoprotein Substrate): Results From in Vitro and Phase I Clinical Studies.

PURPOSE: Fostamatinib, a spleen tyrosine kinase inhibitor and prodrug of the active metabolite R406, is being developed as an anti-inflammatory drug for several indications for which polypharmacy is likely. Digoxin, indicated for congestive cardiac failure, may be used for certain supraventricular dysrhythmias. The studies reported herein examined whether fostamatinib and R406 are inhibitors of P-glycoprotein (P-gp) in vitro and evaluated the effect of fostamatinib on the pharmacokinetic parameters of digoxin to understand drug-drug interaction (DDI) potential in the clinic. METHODS: Inhibition of P-gp-mediated digoxin transport by fostamatinib and R406 was determined across Caco-2 cell monolayers. Apparent permeability of digoxin was determined and used to calculate efflux ratios and percentage inhibition. Half maximal inhibitory concentrations (IC50) and theoretical gastrointestinal concentration [I2] (dose in moles per 250 mL) were calculated to gauge clinical DDI potential. In a subsequent Phase I study, the plasma concentration-time profiles and resulting pharmacokinetic parameters were examined across 2 treatment periods: (1) oral digoxin loading dose of 0.25 mg BID on day 1 and 0.25 mg once daily on days 2 to 8, and (2) oral digoxin 0.25 mg once daily and oral fostamatinib 100 mg BID on days 9 to 15. FINDINGS: Fostamatinib (but not R406) was determined to be a P-gp inhibitor in vitro (IC50 = 3.2 µM). On the basis of a theoretical gastrointestinal concentration (I2)/IC50 ratio of 216 ([I2] = 691 µM), predictions indicated the potential for absorption-based DDI in vivo through inhibition of intestinal P-gp. In the clinical study, when digoxin was co-administered with fostamatinib, digoxin levels were higher before dosing and throughout the dosing interval, and an increase in exposure to digoxin was observed. Co-administration led to a 1.70-fold increase in digoxin maximum plasma concentration at steady state (Cmax,ss) versus digoxin administration alone (2.18 vs 1.32 ng/mL). Median digoxin time of Cmax was earlier when digoxin was co-administered with fostamatinib (1.00 vs 1.48 hours). The digoxin AUC during the dosing interval at steady state was increased 1.37-fold with co-administration. No severe or serious adverse events or deaths were reported. IMPLICATIONS: Fostamatinib was confirmed to be a P-gp inhibitor in vitro and in vivo, and a DDI with digoxin was apparent. Co-administration of digoxin and fostamatinib was generally well tolerated. However, continued review of digoxin response and dose is advisable should these agents be prescribed concomitantly. ClinicalTrials.gov identifier: NCT01355354.