Cyclosporin oral bioavailability

A., Comparison of methods to calculate cyclosporine A bioavailability from consecutive oral and intravenous doses,/. Pharmacokinet. Biopharm. 

Ketoconazole (a potent inhibitor of CYP3A4) has been shown to increase the oral bioavailability of cyclosporin from 22 to 56% [50]. This consisted of a 1.8-fold decrease in systemic clearance combined with a 4.9-fold decrease in oral clearance. The authors estimated that hepatic extraction was decreased only 1.15-fold, whereas the oral bioavailability increased 2.6-fold and the observation was attributed to decreased intestinal metabolism. Erythromycin was also shown to increase the oral bioavailability of cyclosporin A 1.7-fold, while pre-treatment with rifampin (an inducer of CYP3A4) decreased oral bioavailability of cyclosporin from 27% to 10% due to a 4.2-fold increase in oral clearance but only a 1.2-fold increase in systemic clearance. Floren et al. [51] have also shown that ketoconazole can double the oral bioavailability of tacrolimus in man by inhibiting gut wall CYP3A4. 

Lown KS, Mayo RR, Leichtman AB, et al. Role of intestinal P-glycoprotein (mdrl) in interpatient variation in the oral bioavailability of cyclosporine. Clin Pharmacol Ther 1997 62 248-260. 

Other mechanisms of interaction have also been reported, such as altered activity of other enzymes within the CYP450 family (14—17). Moreover, GFJ may also inhibit the intestinal P-glycoprotein (P-gp)-mediated efflux transport of drugs such as cyclosporine to increase its oral bioavailability (18-21). GFJ and other fruit juices have recently been shown to be potent in vitro inhibitors of a number of organic anion-transporting polypeptides (OATPs) (22,23). 

Gonz ez, R.C.B. et al. (2002) Improved oral bioavailability of cyclosporin Ain male wistar rats comparison of a Solutol HS 15 containing self-dispersing formulation and a microsuspeihstoA. Pharm., 245 143-151. 

These two prehepatic systems have been shown to contribute to the limited oral bioavailability of many lipophilic drugs including cyclosporine [8], terfenadine [9], saquinavir [10], midazolam [11], tacrolimus [12], atorvastatin [13], and others. 

Paclitaxel is an antitumor drug, with a low oral bioavailability (6%) [96] due to poor water solubility, hydrophobicity (log P = 4), and its high affinity to P-gp and CYP3A4. A novel SMEDDS of paclitaxel increased the bioavailability by up to 1.5-fold in comparison to the commercial micellar solution taxol. Concomitant intake of cyclosporine A, a known P-gp inhibitor, further increased paclitaxel bioavailability (1.8-fold in comparison to taxol) [97]. 

The transport-enhancing effect of Zot was shown to be reversible and nontoxic (Fasano et al. 1991 Cox et al. 2002). More recently a smaller fragment of Zot in the size of 12 kDa referred to as /1G was identified (Di Pierro et al. 2001). AG displayed significant potential as permeation enhancer. In vitro studies showed that it is capable of significantly increasing the apparent permeability coefficients for a wide variety of drugs across Caco-2 monolayer (Salama et al. 2003, 2004). In the presence of peptidase inhibitors AG improved the bioavailability of mannitol, inulin and PEG 4000 after intraduodenal administration to rats (Salama et al. 2003, 2004). In another in vivo study the oral bioavailability of cyclosporin A was increased up to 50-fold due to the co-administration of AG when metabolic protection was provided (Salama et al. 2005). Results of this study are illustrated in Fig. 5.2. 

Some studies reported that polyoxyethylene (POE) stearates (under the brand name Myrj) and alkyl-polyethyleneoxide (PEO) surfactants (under the brand name Brij) can inhibit efflux pumps. The oral bioavailability of the P-gp substrate cyclosporine A administered in a solid dispersion of polyoxyethylene 40 stearate (Myrj 52) was in the same range as the oral bioavailability of the commercial product Sandimmune Neoral (Liu et al. 2006). In a study by Lo, it has been shown that apical to basolateral epirubicin transport across Caco-2 cells was enhanced in the presence of polyoxyethylene 40 stearate and the basolateral to apical transport was decreased. These results indicate that polyoxyethylene stearates effect efflux pumps (Lo 2003). Similar results were gained when using polyoxyethylene laurylether (Brij 30). In another study, tablets based on polyoxyethylene 40 stearate containing the P-gp substrate rhodamine 123 increased the oral bioavailability in rats by about 2.4-fold (Foger et al. 2006a). 

Sitaxsentan is a potent and selective agent which inhibits ET-1 binding to ETA receptors (IC50 = 1.4 nM), while being essentially inactive at ETB receptors (IC50 = 9.8 pM).23 In the clinic, it was found to have excellent oral bioavailability (70-100%) and a terminal elimination half-life of 10 h, and is administered as a once daily 100 mg dose. It is highly protein bound in plasma (> 99%) and extensively metabolized in the liver to inactive metabolites, predominantly by CYPs 2C9 and 3A4. Excretion is 50 60% renal, with the balance in the feces.25 Sitaxsentan inhibits CYP 2C9, and was observed to increase exposure to warfarin by over twofold. The use of cyclosporine A is also contraindicated, but no interactions were observed with sildenafil.15 Sitaxsentan was well tolerated in trials, with only minor side effects reported. Reversible liver enzyme abnormalities were also observed, but less frequently than with bosentan.15 25... 

Fig. 4 This cartoon depicts the various processes leading to an oral bioavailability of 27%, following an oral dose of the Sandimmune formulation of cyclosporine. The values at the bottom of the figure indicate the average fraction of the dose lost in each of the processes i.e., 14% of the dose is either unabsorbed, counter transported (effluxed) by P-gp, or degraded in the gut lumen, 51% of the drug is metabolized in the enterocytes of the gut wall, and only 8% is lost due to hepatic first-pass metabolism.

R.P. Scherersol system Liquid formulations for softgels, which incorporates the drug in a microemulsion preconcentrate or microemulsion form. Oral delivery of proteins and peptides enhanced oral bioavailability with reduced inter- and intraindividual variability in pharmacokinetics of certain drugs. Sandimmune Neoral (cyclosporine). 

---