PT  - JOURNAL ARTICLE
AU  - Jette Peters
AU  - Wiebke Block
AU  - Stefan Oswald
AU  - Johanna Freyer
AU  - Markus Grube
AU  - Heyo K. Kroemer
AU  - Marc Lämmer
AU  - Dieter Lütjohann
AU  - Monica Venner
AU  - Werner Siegmund
TI  - Oral Absorption of Clarithromycin Is Nearly Abolished by Chronic Comedication of Rifampicin in Foals
AID  - 10.1124/dmd.111.039206
DP  - 2011 Sep 01
TA  - Drug Metabolism and Disposition
PG  - 1643--1649
VI  - 39
IP  - 9
4099  - http://dmd.aspetjournals.org/content/39/9/1643.short
4100  - http://dmd.aspetjournals.org/content/39/9/1643.full
SO  - Drug Metab Dispos2011 Sep 01; 39
AB  - 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 (r2 = 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.