Tadalafil CYP3A4 inducers

Rifampicin markedly reduced tadalafil levels, and is predicted to interact simiiariy with sildenafii and vardenafii. Other CYP3A4 inducers are iikeiy to have the same effect with these phosphodiesterase type-5 inhibitors. 

Although the manufacturer of vardenafii does not mention CYP3A4 inducers, like tadalafil and sildenafil, vardenafii is principally metabolised by CYP3A4, and its levels are markedly raised by CYP3A4 inhibitors such as ketoconazole , (p. 1270). It is therefore very likely that vardenafii levels will be reduced by rifampicin and similar drugs, and concurrent use should be monitored. 

An open label study in 12 healthy subjects found that while taking tadalafil 10 mg daily for 14 consecutive days, the pharmacokinetics of a single 15-mg oral dose of midazolam were unchanged. Since midazolam is metabolised by the cytochrome P450 isoenzyme CYP3A4, it was concluded that the absence of any interaction shows that tadalafil does not inhibit or induce the activity of this isoenzyme. No special precautions are therefore needed if midazolam is given with tadalafil. 

Rifampicin induces the activity of the cytochrome P450 isoenzyme CYP3A4, the principal enzyme concerned with the metabolism of sildenafil, tadalafil and vardenafii. 

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