Does super C or Hepar interact with quetiapine?/nA 48-year-old woman with bipolar disorder is treat

Fråga: Does super C or Hepar interact with quetiapine?

A 48-year-old woman with bipolar disorder is treated with quetiapine 400 mg/d. The woman has had extrapyramidal symptoms after treatment initiation and it has been difficult to find an optimal dose. The intention is to give her a maintenance dose of 200 mg/d. The patient uses the two supplements superC and Hepar.

Sammanfattning: Theoretically the grape fruit oil in super C may increase the concentration of quetiapine. Withdrawal of super C is recommended.

Svar: Super C is a food supplement containing vitamin C in a dose of 650 mg vitamin C/tablet and the daily recommended intake is 1-2 tablets. Super C also contains calcium, zinc, manganese, potassium, citrus bioflavonoids, rutin and essential oils from orange (Citrus sinensis), tangerine (Citrus nobilis), grapefruit (Citrus paradisi), lemon (Citrus limon), lemongrass (Cymbopogon flexuosus) (1).

Hepar is a natural remedy containing extract from Milk thistle (Silybum marianum). The main active substance in Hepar is silymarin (2). Milk thistle extract is use in many countries as a liver enhancer and is given to patient with liver diseases. The efficacy of Milk thistle in liver disease is not clearly proven (3).

Quetiapine is an antipsycothic drug that is mainly metabolised by CYP3A4 although CYP2D6 is also partly involved (4).

In Stockley´s drug interactions there are no interaction with vitamin C that has caused an increase of the concentration of any other drug. There are occasional case reports where the concentration of the coadministered drug has decreased (5). Calcium, zinc, manganese and potassium are not suspected to interact with quetiapine and no such reports have been found. No interactions with rutin have been found. Grapefruit is a known inhibitor of CYP3A4 (5), and if the concentration of grapefruit is high enough in Super C, an increase in the concentration of quetiapine may be observed. Some other citruses may also inhibit CYP3A4 although none of the other citruses in this preparation have been proven to inhibit CYP3A4. Tangerine appears to not been studied in this regard. No interactions with lemongrass have been found.

Several studies have investigated the effect of Milk thistle extract on the metabolism of other drugs. Milk thistle appears not to inhibit CYP2D6 and is not an inducer or an inhibitor of CYP3A4 (5).

Generally, studies of herb-drug interactions are lacking, and the absence of data does not mean that there is a lack of interactions. Concomitant use of herbal remedies and prescription drugs should always be avoided, especially when patients are treated with drugs with a narrow therapeutic interval. One other problem with herbal preparations is that they do not always contain the same amount of a certain substance which means that the interaction potential may vary between batches of the same brand.

In the present case we recommend that super C is withdrawn. If the patient still has extrapyramidal symptoms after withdrawal measuring of the quetiapine concentration is recommended. One option to rule out if there really is an interaction between super C and quetiapine is to measure the drug concentration before and three days after super C withdrawal. Super C(TM): Simply the best vitamin C supplement anywhere. http://www.therapeutic-grade.com/products/supplements/superC.html (cited 2008-10-08) Hepar 140 180 st. http://www.med24.se/kosttilskott/ortextrakt/tabletter/hepar-140-180-st/product_info.php/ (cited 2008-10-08) Drugline no 23023 (year 2006) DeVane CL, Nemeroff CB. Clinical pharmacokinetics of quetiapine: an atypical antipsychotic. Clin Pharmacokinet 2001;40(7):509-522