Role of efflux transporters in the absorption, distribution and elimination in rodents of a novel PDE4 inhibitor, CHF6001.

CHF6001 is a new and potent PDE4 inhibitor for the treatment of human lung diseases, designed for topical administration by inhalation. In preclinical assessment CHF6001 appeared safe and devoid of emetic effect, which is typical side effect of PDE4 inhibitors in humans. CHF6001 absorption, distribution and excretion were evaluated in rats by PO and IV administration of [14C]CHF6001; additionally the role of transporters was investigated by using transfected cells expressing either human transporters or MDR1 and BCRP KO mice. [14C]CHF6001 intravenously administered as bolus distributed in all the tissues (with very low levels in brain and fetus) and it was mainly eliminated in bile. Following oral administration [14C]CHF6001 about half of the dose was absorbed through the gut. In vitro, CHF6001 was a substrate of human membrane transporters MDR1 and BCRP. In wild and BCRP KO mice CHF6001 was not detectable in brain, whereas it was measurable in Mdr1a/b KO mice. Therefore, in animal species Mdr1a/b plays a significant role in CHF6001 disposition, limiting its distribution into brain and contributing to the safety profile observed in preclinical evaluation. This behavior was confirmed by the results of the first human studies, where CHF6001 was safe and with no emetic effect at all the evaluated doses.

Association of cytochrome P450 induction with oxidative stress in vivo as evidenced by 3-hydroxylation of salicylate.

1. Previous studies have shown that formation of 2,3-dihydroxybenzoate (2,3-DHB) from salicylate in vivo is a sensitive and specific marker of *OH radical generation, since 2,3-DHB is formed exclusively by *OH radicals, whereas both *OH radicals and cytochrome P450 (CYP) contribute to the production of 2,5-DHB. In the present study the salicylate-hydroxylation assay was used to examine whether CYP induction by the administration of dexamethasone, phenobarbital or beta-naphthoflavone to the male rat led to oxidative stress in vivo. 2. Dexamethasone was used under conditions that induced an approximately 50-fold induction of CYP P4503A expression in liver microsomal protein. Treatment with dexamethasone caused a 17.2-fold increase in 2,3-DHB plasma concentration compared with control animals. An increase in total hydroxylated salicylate (2,3-DHB plus 2,5-DHB) of 133.5 micromol/l plasma was produced, of which--assuming that the attack by *OH in position 3 or 5 of salicylate occurs at a similar rate--10.9 micromol/l were due to *OH radical attack and 122.6 micromol/l due to metabolism by CYP. 3. Phenobarbital led to a 4.7-fold increase in 2,3-DHB plasma concentration under conditions that induced CYP P4502B and 3A. An increase in total hydroxylated salicylate of 34.3 micromol/l plasma was observed, 2.0 micromol/l due to *OH radical attack and 32.3 micromol/l due to metabolism by cytochrome P450. 4. In contrast to dexamethasone and phenobarbital, beta-naphthoflavone did not cause a significant increase in 2,3-DHB plasma concentrations. 5. SKF 525A, a mixed-function oxidase inhibitor, caused a significant reduction of mean 2,5-DHB plasma concentration by 35% (p < 0.001), whereas 2,3-DHB was not significantly reduced, indicating that in contrast to the situation after induction by dexamethasone or phenobarbital, *OH radical generation by constitutive CYP contributes only to a minor degree to total in vivo *OH radical generation. 6. This study shows for the first time, to the authors' knowledge, that induction of some (but not all) P450s is associated with the production of hydroxyl radicals in vivo.

Preliminary pharmacokinetic study of ibuprofen enantiomers after administration of a new oral formulation (ibuprofen arginine) to healthy male volunteers.

The pharmacokinetics of ibuprofen enantiomers were investigated in a crossover study in which seven healthy male volunteers received single oral doses of 800 mg racemic ibuprofen as a soluble granular formulation (sachet) containing L-arginine (designated trade name: Spedifen), 400 mg (-)R-ibuprofen arginine or 400 mg (+)S-ibuprofen arginine. Plasma levels of both enantiomers were monitored up to 480 minutes after drug intake using an enantioselective analytical method (HPLC with ultraviolet detection) with a quantitation limit of 0.25 mg/l. Substantial inter-subject variability in the evaluated pharmacokinetic parameters was observed in the present study. After (+)S-ibuprofen arginine, the following mean pharmacokinetic parameters +/-SD were calculated for (+)S-ibuprofen: tmax 28.6 +/- 28.4 min; Cmax 36.2 +/- 7.7 mg/l; AUC 86.4 +/- 14.9 mg.h/l; t1/2 105.2 +/- 20.4 min. After (-)R-ibuprofen arginine, the following mean pharmacokinetic parameters were calculated for (+)S-ibuprofen and (-)R-ibuprofen, respectively: tmax 90.0 +/- 17.3 and 50.5 +/- 20.5 min; Cmax 9.7 +/- 3.0 and 35.3 +/- 5.0 mg/l; AUC 47.0 +/- 17.2 and 104.7 +/- 27.7 mg.h/l; t1/2 148.1 +/- 63.6 and 97.7 +/- 23.3 min. After racemic ibuprofen arginine, the following mean pharmacokinetic parameters were calculated for (+)S- and (-)R-ibuprofen, respectively: tmax 30.7 +/- 29.1 and 22.9 +/- 29.8 min; Cmax 29.9 +/- 5.6 and 25.6 +/- 4.4 mg/l; AUC 105.1 +/- 23.0 and 65.3 +/- 15.0 mg.h/l; t1/2 136.6 +/- 20.7 and 128.6 +/- 45.0 min. Tmax values of S(+)- and (-)R-ibuprofen after a single dose of 400 mg of each enantiomer did not differ significantly from the corresponding parameters obtained after a single dose of 800 mg of racemic ibuprofen arginine, indicating that the absorption rate of (-)R- and (+)S-ibuprofen is not different when the two enantiomers are administered alone or as a racemic compound. An average of 49.3 +/- 9.0% of a dose of the (-)R-ibuprofen arginine was bioinverted into its antipode during the study period (480 minutes post-dosing). The percent bioinversion during the first 30 minutes after (-)R-ibuprofen arginine intake averaged 8.1 +/- 3.9%. The mean AUC of (+)S-ibuprofen calculated after 800 mg racemic ibuprofen arginine (105.1 +/- 23.0 mg.h/l) was lower than the mean AUC value obtained by summing the AUCs of (+)S-ibuprofen after administration of 400 mg (+)S-ibuprofen arginine and 400 mg (-)R-ibuprofen arginine (133.4 +/- 26.6 mg.h/l). In conclusion, the administration of Spedifen resulted in very rapid absorption of the (+)S-isomer (eutomer) with tmax values much lower than those observed for this isomer when conventional oral solid formulations such as capsules or tablets of racemic ibuprofen are administered. This characteristic is particularly favourable in those conditions in which a very rapid analgesic effect is required.