Haemostasis
Vitamin E may have antagonist activity with respect to vitamin K. K, and so may increase the tendancy to bleeding.
High doses of vitamin E may increase the risk of bleeding in patients taking concomitant:
• anticoagulants (e.g., warfarin or phenprocoumon)
• inhibitors of platelet aggregation (e.g., acetylsalicylic acid, clopidogrel, ticlopidine, dipyridamole, eptifibatide, tirofiban and abciximab) or
• thrombolytics (e.g. recombinant tissue plasminogen activator).
Vitamin E should not be administered concomitantly with Ibrutinib as it may enhance the antiplatelet effect of Ibrutinib.
Tipranavir, used in the treatment of HIV-1 infection, is associated with an increased risk of bleeding and fatal and non-fatal intracranial haemorrhages and these risks may be increased with high dose vitamin E.
Vitamin E may increase the risk of thrombosis in patients taking oestrogens.
Sequestrants
Sequestrants bind to vitamin E and reduce absorption. Any of these agents should be administered more than two hours before or after vitamin E.Colestyramine and colestipol reduce gastrointestinal absorption of vitamin E.
Orlistat may impair absorption of fat-soluble vitamins, including vitamin E.
Concomitant use of iron-containing medicines reduces activity of vitamin E, therefore a few hours interval should be maintained between taking both medications.
Metabolic Interactions
High-dose vitamin E, either alone or in combination with other antioxidants, may alter the pharmacokinetics of ciclosporin and decrease its serum concentration.
Anticonvulsants (e.g., phenobarbital, phenytoin and carbamazepine), as inducers of P450 enzymes, may lower plasma vitamin E levels.
Vitamin E increases the absorption, utilisation and storage of vitamin A.
Vitamin E may be present in significant quantities as an excipient, for example Selumetinib contains D-alpha-tocopheryl and should not be taken with vitamin E (Selumetinib 10 mg capsule contains 32 mg vitamin E; 25 mg capsule contains 36 mg vitamin E).
Vitamin E has been shown to induce the expression of the cytochrome P450 enzyme CYP3A4. This enzyme is responsible for the reduced physiological effects of vitamin K and for the reduction in ciclosporin levels.