While only interactions between these antifungals and P-gp or the OATPs have been described,

the role of other transport proteins in antifungal–drug interactions will likely be realised as our understanding of other transport proteins continues to evolve. Antifungal–drug interactions that interfere with active transport of other medicines are summarised in Table 2. Itraconazole is a substrate and potent inhibitor of P-gp, and produces clinically relevant interactions with digoxin and the vinca alkaloids (vincristine, vinblastine, etc.) via transport protein-mediated processes. Digoxin undergoes no appreciable CYP-mediated metabolism. Instead, the drug is renally eliminated as unchanged drug, predominately Erlotinib research buy through P-gp-mediated this website tubular secretion.138 P-gp inhibition by itraconazole reduces digoxin renal clearance to nearly 20%, which significantly increases digoxin serum concentrations, exposure and the potential for toxicity. A reduction in the digoxin dose of up to 75% is required to manage this interaction.139 In contrast, voriconazole is not a P-gp inhibitor and it does not affect the steady-state pharmacokinetics of digoxin.140 CYP3A4 and P-gp possess overlapping substrate affinities making it difficult to separate their respective contributions in a given interaction. Nonetheless, inhibiting both proteins can produce significant drug interactions,

as exemplified by the interaction between itraconazole and vincristine. Itraconazole reduces CYP3A4 metabolism and P-gp efflux of vincristine. The resulting accumulation of vincristine produces neurological toxicities (seizures, paraesthesia, sensory deficits, muscle weakness, neuropathy), gastrointestinal disturbances (abdominal pain/distention,

constipation, ileus) hyponatraemia and SIADH.141 Itraconazole also interacts to Teicoplanin a similar degree with vinblastine.142 A similar interaction between posaconazole and vincristine has been reported.143,144 Although there are no data from rigorously controlled studies, voriconazole is believed to interact with vincristine by inhibiting its CYP-mediated metabolism rather than its P-gp mediated transport.145 Due to the severity of the interaction between the vinca alkaloids and itraconazole or posaconazole, and the potential interaction between vincristine and voriconazole, the azoles should not be administered to patients receiving or in need of vincristine or vinblastine containing regimens. If the combination is used, the interaction should be managed by discontinuing the azole.141 Caspofungin is not a CYP substrate or inhibitor. Although caspofungin weakly inhibits P-gp and moderately inhibits several transport proteins in vitro, the inhibitory concentrations are well in excess of those achieved clinically.6 Thus, it is unlikely that this compound inhibits the function of most transport proteins in vivo.6 Therefore, caspofungin, like other echinocandins, interacts with few other medicines.