title: Oral absorption of clarithromycin is nearly abolished by chronic comedication of rifampicin in foals.
abstract: The delivery of clarithromycin (CRL) to its site of action in bronchial/alveolar epithelial cells (EC), bronchial epithelial lining fluid (ELF), and bronchoalveolar lavage cells (BALC) may be influenced by CYP3A4 and the drug transporters, ATP-binding cassette (ABC) B1 and ABCC2 and organic anion-transporting polypeptides (OATPs), which can be modulated and/or up-regulated via the nuclear pregnane X receptor (PXR) by rifampicin (RIF). Therefore, we evaluated the disposition and pulmonary distribution of CLR (7.5 mg/kg b.i.d., 21 days) and expression of ABCB1, ABCC2, OATP1A2, and OATP2B1 in EC and BALC before and after comedication of RIF (10 mg/kg b.i.d., 11 days) in nine healthy foals (41-61 days, 115-159 kg) in which the genetic homology of drug transporters is close to that of their human analogs. After RIF comedication, relative bioavailability of CLR decreased by more than 90%. Concentrations in plasma (29.8 ± 26.3 versus 462 ± 368 ng/ml), ELF (0.69 ± 0.66 versus 9.49 ± 6.12 μg/ml), and BALC (10.2 ± 10.2 μg/ml 264 ± 375 μg/ml; all P < 0.05) were lowered drastically, whereas levels of the metabolite 14-hydroxyclarithromycin were not elevated despite higher 4β-hydroxycholesterol/cholesterol plasma concentration ratio, a surrogate for CYP3A4 induction. In the presence of CLR, ABCC2 and PXR mRNA contents were significantly and coordinately (r(2) = 0.664, P < 0.001) reduced in BALC after RIF. In EC, mRNA expression of OATP1A2 increased but that of OATP2B1 decreased (both P < 0.05). RIF interrupts oral absorption and decreases CRL plasma levels below the minimal inhibitory concentration for eradication of Rhodococcus equi. Evidence that RIF influences the cellular uptake of CLR in bronchial cells and the PXR expression in BALC in the presence of high CLR concentrations exists.
authors.affiliation: Department of Clinical Pharmacology, Ernst Moritz Arndt University, Friedrich-Loeffler-Str. 23d, D-17487 Greifswald, Germany.
authors.forename: Jette
authors.initials: J
authors.lastname: Peters
authors.forename: Wiebke
authors.initials: W
authors.lastname: Block
authors.forename: Stefan
authors.initials: S
authors.lastname: Oswald
authors.forename: Johanna
authors.initials: J
authors.lastname: Freyer
authors.forename: Markus
authors.initials: M
authors.lastname: Grube
authors.forename: Heyo K
authors.initials: HK
authors.lastname: Kroemer
authors.forename: Marc
authors.initials: M
authors.lastname: Lämmer
authors.forename: Dieter
authors.initials: D
authors.lastname: Lütjohann
authors.forename: Monica
authors.initials: M
authors.lastname: Venner
authors.forename: Werner
authors.initials: W
authors.lastname: Siegmund
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000042:Absorption / Q000187:drug effects; D000818:Animals; D001980:Bronchi / Q000378:metabolism; D002784:Cholesterol / Q000097:blood; D017291:Clarithromycin / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics*; D004347:Drug Interactions; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006736:Horses / Q000378:metabolism*; D006888:Hydroxycholesterols / Q000097:blood; D008168:Lung / Q000378:metabolism; D009061:Mouth Mucosa / Q000187:drug effects* / Q000378:metabolism*; D000089762:Multidrug Resistance-Associated Protein 2; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000235:genetics; D011987:Receptors, Steroid / Q000378:metabolism; D012293:Rifampin / Q000494:pharmacology*
chemical_list: C000715087:ABCC2 protein, human; D018528:ATP-Binding Cassette Transporters; D006888:Hydroxycholesterols; D000089762:Multidrug Resistance-Associated Protein 2; D027361:Organic Anion Transporters; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D011987:Receptors, Steroid; C056228:14-hydroxyclarithromycin; C099828:cholest-5-ene-3,4-diol; D002784:Cholesterol; D017291:Clarithromycin; D012293:Rifampin