Which interactions are known for the combination of venlafaxine (Efexor) and sumatriptan (Imigran)?

Fråga: Which interactions are known for the combination of venlafaxine (Efexor) and sumatriptan (Imigran)? A 49-year-old woman with anxiety and depression is treated with venlafaxin 75 mg daily since 6 months and was previously treated with citalopram 40 mg daily for 6 months. She also suffers from migraine which she has successfully treated with oral sumatriptan 50 mg, on average once a month. The last two migraine attacks persisted despite sumatriptane. The first part of the question is if venlafaxin may counteract the effects of sumatriptane. Secondly there is a concern that the patient may develop side-effects because of the combined treatment. She takes no other drugs and is normotensive.

Sammanfattning: Presently, there are no published data which suggest that sumatriptane is contraindicated in venlafaxine treated patients. Neither are there data showing explicity that the combination is safe. Venlafaxine is not known to counter act the effects of sumatriptane on migraine.

Svar: Previous and recent Drugline documents (1-3) deal with the risk of serotonin syndrome when a "triptane" is combined with an SSRI (selective serotonin reuptake inhibitor) or a monoamine oxidase inhibitor (4) and conclude that at present no clinical data support the hypothesis that sumatriptane treatment increases the risk of serotonin syndrome in SSRI-treated patients. Because sumatriptane is metabolised by monoamine oxidase (4) it is unlikely that there will be an interaction with venlafaxine which is a substrate for cytochrome P450 liver enzymes. As venlafaxine is a non-selective noradrenaline and serotonin reuptake inhibitor (5) there is no known factor increasing the risk of a serotonin syndrome.

As venlafaxine is not known to induce monoamine oxidases, there is no immediately apparent metabolic mechanism providing an explanation for the lack of effect of sumatriptane which the patient has experienced recently.