CYP3A4 and chronic obstructive pulmonary disease: With the slight decrease of high blood levels, other drug–drug interactions may be of concern: cytochrome P450 3A4 (CYP3A4) inhibitors (e.g., protease inhibitors leading to additional blood level increase although the impact seems limited in pharmacokinetic models) [86], serotonergic drugs (serotonin syndrome), QT-prolonging drugs, including alcohol, cocaine and amphetamine (cardiac arrhythmia), and other opioids.