Medicinal products with pH-dependent absorption pharmacokinetics
Because of profound and long-lasting inhibition of gastric acid secretion, pantoprazole may reduce the absorption of medicinal products for which an acidic gastric pH value is an important factor for oral bioavailability (e.g. some azole antifungals as ketoconazole, itraconazole, posaconazole and other medicines, e.g. erlotinib).
HIV protease inhibitors
The simultaneous use of pantoprazole with HIV protease inhibitors (such as atanazavir), the absorption of which is dependent on an acidic gastric pH value, is not recommended due to the significantly reduced bioavailability (see section 4.4). If the combination of HIV protease inhibitors with a proton pump inhibitor cannot be avoided, close clinical monitoring (e.g. viral load) is recommended. Pantoprazole dose of 20 mg per day should not be exceeded. Adjustment of the dose of HIV protease inhibitors may be necessary.
Coumarin anticoagulants (phenprocoumon or warfarin)
Co-administration of pantoprazole with warfarin or phenprocoumon did not affect the pharmacokinetics of warfarin, phenprocoumon or International Normalised Ratio (INR). However, there have been isolated reports of increased INR and prothrombin time in patients receiving PPIs and warfarin or phenprocoumon concomitantly. Increases in INR and prothrombin time may lead to abnormal bleeding, and even death. Patients treated with pantoprazole and warfarin or phenprocoumon may need to be monitored for increase in INR and prothrombin time.
Methotrexate
Concomitant use of high-dose methotrexate (e.g. 300 mg) and proton-pump inhibitors has been reported to increase methotrexate levels in some patients. Therefore, temporary discontinuation of pantoprazole may be considered when high doses of methotrexate are used, such as for the treatment of cancer and psoriasis.
Other interactions studies
Pantoprazole is extensively metabolised in the liver via the cytochrome P450 enzyme system. The main metabolic pathway is demethylation by CYP2C19, other metabolic pathways include oxidation by CYP3A4.
Interaction studies with medicinal products also metabolized with these pathways, like carbamazepine, diazepam, glibenclamide, nifedipine, and an oral contraceptive containing levonorgestrel and ethinyl oestradiol, did not reveal clinically significant interactions.
An interaction of pantoprazole with other medicinal products or compounds that are metabolised via the same enzyme system cannot be ruled out.
Results from a range of interaction studies demonstrate that pantoprazole does not affect the metabolism of active substances metabolised by CYP1A2 (such as caffeine, theophylline), CYP2C9 (such as piroxicam, diclofenac, naproxen), CYP2D6 (such as metoprolol), CYP2E1 (such as ethanol), or does not interfere with p-glycoprotein related absorption of digoxin.
There were no interactions with concomitantly administered antacids.
In interaction studies, no clinically relevant interactions were found when pantoprazole was administered concomitantly with the corresponding antibiotics (clarithromycin, metronidazole, amoxicillin).
Medicinal products that inhibit or induce CYP2C19
Inhibitors of CYP2C19 such as fluvoxamine can increase the systemic exposure of pantoprazole. A dose reduction may be considered for patients treated long-term with high doses of pantoprazole, or those with hepatic impairment.
Enzyme inducers affecting CYP2C19 and CYP3A4 such as rifampicin and St John´s wort (Hypericum perforatum) may reduce the plasma concentrations of PPIs that are metabolised through these enzyme systems.