Can dextromethorphan/quinidine (Austedo XR) be safely co‑prescribed with venlafaxine?

Can Austedo XR and Venlafaxine Be Safely Co-Prescribed?

Yes, Austedo XR (deutetrabenazine) and venlafaxine can be co-prescribed together, but this combination requires careful monitoring for serotonin syndrome and awareness of potential drug interactions, particularly if the patient is a CYP2D6 poor metabolizer or is taking other CYP2D6 inhibitors.

Key Safety Considerations

Serotonin Syndrome Risk

The primary concern with combining Austedo XR and venlafaxine is the risk of serotonin syndrome. The 2019 American Geriatrics Society Beers Criteria specifically notes that dextromethorphan/quinidine (the active components in Austedo XR) should be "used with caution" due to limited efficacy data and potential for drug-drug interactions 1.

Multiple guidelines emphasize that combining serotonergic medications requires vigilance. Serotonin syndrome symptoms include 2:

• Mental status changes (confusion, agitation, anxiety)
• Neuromuscular hyperactivity (tremors, clonus, hyperreflexia, muscle rigidity)
• Autonomic hyperactivity (hypertension, tachycardia, diaphoresis, shivering)
• Advanced symptoms: fever, seizures, arrhythmias, unconsciousness

Clinical Action: Start with low doses, increase slowly, and monitor closely especially in the first 24-48 hours after any dosage changes 2.

CYP2D6 Interaction

Venlafaxine has minimal effect on the CYP450 system compared to other antidepressants 2. Research demonstrates that venlafaxine causes only a 2.1-fold increase in dextromethorphan metabolism ratios at steady state, compared to a 17.1-fold increase with fluoxetine 3. This makes venlafaxine a relatively safer choice among antidepressants when combined with Austedo XR.

However, the FDA label for Austedo XR states that strong CYP2D6 inhibitors increase exposure to deutetrabenazine's active metabolites by approximately 3-fold 4. While venlafaxine is not a strong CYP2D6 inhibitor, if the patient is:

• A CYP2D6 poor metabolizer
• Taking other CYP2D6 inhibitors concurrently
• Taking multiple serotonergic medications

Then additional caution is warranted.

Practical Prescribing Algorithm

Before Initiating Combination:

1. Screen for contraindications:

   • Current MAOI use (contraindicated) 4
   • Concurrent tetrabenazine or valbenazine use (contraindicated) 4
   • History of serotonin syndrome

2. Assess medication list for:

   • Other serotonergic agents (SSRIs, TCAs, tramadol, other opioids, stimulants, dextromethorphan-containing products) 2
   • Strong CYP2D6 inhibitors (paroxetine, fluoxetine, quinidine, bupropion) 4

3. Consider genetic testing for CYP2D6 status if:

   • Patient has treatment-resistant symptoms
   • History of unusual medication responses
   • Taking multiple concurrent medications 5

During Treatment:

1. Start low, go slow: Begin venlafaxine at 37.5 mg once or twice daily, increasing by 75 mg each week as tolerated 6

2. Monitor closely for 24-48 hours after each dose increase for serotonin syndrome symptoms 2

3. Regular monitoring should include 2:

   • Blood pressure and pulse (venlafaxine can cause hypertension)
   • Mental status changes
   • Neuromuscular symptoms
   • Sedation/somnolence (additive with Austedo XR) 4

4. Maximum Austedo XR dose: If adding a strong CYP2D6 inhibitor later, do not exceed 36 mg/day of Austedo XR 4

Common Pitfalls to Avoid

• Don't overlook over-the-counter medications: Many cold/cough preparations contain dextromethorphan, which would create dangerous serotonergic excess 2
• Don't abruptly discontinue venlafaxine: It requires slow tapering due to discontinuation syndrome 6, 2
• Don't ignore alcohol use: Both medications can cause sedation; alcohol has additive effects 4
• Don't forget cardiac monitoring: Venlafaxine can cause blood pressure increases and has been associated with cardiac conduction abnormalities in some patients 6

Special Populations

In older adults, use extra caution as the combination increases fall risk through sedation and potential orthostatic effects 1. The Beers Criteria specifically highlight concerns about dextromethorphan/quinidine in this population 1.

For patients with cardiac disease, venlafaxine should be prescribed cautiously due to potential blood pressure increases and rare cardiac conduction abnormalities 6.