The main metabolic pathway of domperidone is through CYP3A4. In vitro and human data suggest that the concomitant use of drugs that significantly inhibit this enzyme may result in increased plasma levels of domperidone.
Increased risk of occurrence of QT-interval prolongation, due to pharmacodynamic and/or pharmacokinetic interactions.
Concomitant use of the following substances is contraindicated
QTc prolonging medicinal products
• anti-arrhythmics class IA (e.g., disopyramide, hydroquinidine, quinidine)
• anti-arrhythmics class III (e.g., amiodarone, dofetilide, dronedarone, ibutilide, sotalol)
• certain anti-psychotics (e.g., haloperidol, pimozide, sertindole)
• certain anti-depressants (e.g., citalopram, escitalopram)
• certain antibiotics (e.g., erythromycin, levofloxacin, moxifloxacin, spiramycin)
• certain antifungal agents (e.g., pentamidine)
• certain antimalarial agents (in particular halofantrine, lumefantrine)
• certain gastro-intestinal medicines (e.g., cisapride, dolasetron, prucalopride)
• certain antihistaminics (e.g., mequitazine, mizolastine)
• certain medicines used in cancer (e.g., toremifene, vandetanib, vincamine)
• certain other medicines (e.g., bepridil, diphemanil, methadone) (see section 4.3).
• apomorphine, unless the benefit of co-administration outweighs the risks, and only if the recommended precautions for co-administration are strictly fulfilled. Please refer to the apomorphine SmPC.
Potent CYP3A4 inhibitors (regardless of their QT prolonging effects), i.e:
• protease inhibitors
• systemic azole antifungals
• some macrolides (erythromycin, clarithromycin telithromycin) (see section 4.3).
Concomitant use of the following substances is not recommended
Moderate CYP3A4 inhibitors i.e. diltiazem, verapamil and some macrolides. (see section 4.3)
Concomitant use of the following substances requires caution in use
Caution with bradycardia and hypokalaemia-inducing drugs, as well as with the following macrolides involved in QT-interval prolongation: azithromycin and roxithromycin (clarithromycin is contra-indicated as it is a potent CYP3A4 inhibitor).
The above list of substances is representative and not exhaustive.
Separate in vivo pharmacokinetic/pharmacodynamic interaction studies with oral ketoconazole or oral erythromycin in healthy subjects confirmed a marked inhibition of domperidone's CYP3A4 mediated first pass metabolism by these drugs.
With the combination of oral domperidone 10mg four times daily and ketoconazole 200mg twice daily, a mean QTc prolongation of 9.8 msec was seen over the observation period, with changes at individual time points ranging from 1.2 to 17.5 msec. With the combination of domperidone 10mg four times daily and oral erythromycin 500mg three times daily, mean QTc over the observation period was prolonged by 9.9 msec, with changes at individual time points ranging from 1.6 to 14.3 msec. Both the Cmax and AUC of domperidone at steady state were increased approximately three-fold in each of these interaction studies. In these studies domperidone monotherapy at 10mg given orally four times daily resulted in increases in mean QTc of 1.6 msec (ketoconazole study) and 2.5 msec (erythromycin study), while ketoconazole monotherapy (200mg twice daily) led to increases in QTc of 3.8 and 4.9 msec, respectively, over the observation period.
Levodopa: Increase of plasma levels of levodopa (max 30-40%). See section 4.4.