Proposal of a Safe and Effective Study Design for CYP3A-Mediated Drug-Drug Interactions

Numerous drug-drug interaction (DDI) trials have to be conducted in healthy volunteers based on current regulatory guidelines. Because the worst-case scenario of strong cytochrome P450 (CYP) inhibitors has to be tested, the results and their validity have to be balanced with the risk to volunteer safety. The use of ketoconazole in clinical DDI studies has been discouraged by regulatory agencies due to an alleged risk of liver injury. In order to reduce the risk to healthy volunteers, we carried out a study with single-day exposure to each of 6 perpetrator azole fungistatic drugs. They were evaluated regarding their CYP3A inhibition using microdosed midazolam and a limited sampling strategy. Ratios of areas under the concentration-time curves ranged from 1.93 with isavuconazole to 8.42 with ketoconazole. The highest number of adverse events occurred with voriconazole, followed by ketoconazole; 2 dropouts occurred due to adverse events following itraconazole administration. Literature data on adverse events of azole fungistatic drugs in DDI trials are rare and inconclusive. Only in recent years with the newer drugs are they more precise and reliable. It can be concluded that the duration of preexposure of perpetrator drugs can be reduced to 1 hour before administration of the victim drug. This still can be sufficient to achieve the scientific objectives of the trial with the lowest possible risk.