Mirtazapine interaction with other drugs

V. Drug or laboratory interactions. There is some evidence that milk thistle may inhibit CYP2C9 and CYP3A4 enzyme activity, which might theoretically increase plasma levels of dmgs metabolized by these enzymes, including amitriptyline, diazepam, clozapine, warfarin, mirtazapine, ketoconazole, and others. Drug interactions with milk thistle extract have not been reported in humans. 

Also note that the development of the serotonin syndrome has been attributed to the sequential use of an SSRI (fluoxetine, paroxetine, or sertraline) and venlafaxine. It has also occurred with concurrent use of venlafaxine and mirtazapine or trazodone. The manufacturers of venlafaxine caution its use with other drugs that affect serotonergic transmission, such as the SSRIs because of the potential risks of the serotonin syndrome. For more about the serotonin syndrome see Additive or synergistic interactions , (p.9). 

The manufacturers advise that if carbamazepine or other drugs that induce drug metabolism (such as phenytoin) are given with mirtazapine, the mirtazapine dose may have to be inereased. Further, if treatment with an inducer is stopped, the mirtazapine dosage may have to be reduced. - Although not specifically named, phenobarbital and primidone can also induce CYP3A4, and they therefore may interact similarly. Note that. 

Mirtazapine has been shown to reduce anxiety symptoms and sleep disturbances associated with depression, as early as 1 week after the start of treatment. Other advantages are minimal sexual dysfunction, minimal nausea, and once-daily dosing. In addition, mirtazapine is unlikely to be associated with cytochrome P450-mediated drug interactions. The disadvantages of mirtazapine are weight gain and prominent early sedation. 

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