Vilazodone
Vilazodone
Generic Name
Vilazodone
Brand Names
Viibryd™) is a selective serotonin reuptake inhibitor (SSRI) with added partial agonist activity at the serotonin‑1A (5‑HT₁A) receptor, approved for the treatment of major depressive disorder (MDD) in adults.
Mechanism
- Serotonin reuptake inhibition: Blocks the serotonin transporter (SERT), increasing extracellular serotonin.
- 5‑HT₁A partial agonism: Acts as a partial agonist at presynaptic 5‑HT₁A autoreceptors and postsynaptic heteroreceptors, enhancing serotonergic tone and reducing the lag in antidepressant response.
- Result: Rapid onset of action, lower incidence of SSRI‑associated sexual dysfunction, and generally favorable side‑effect profile.
Pharmacokinetics
| Parameter | Detail |
| Absorption | Oral bioavailability ~60 %; peak plasma concentration (T_max) ~6 h after a 50 mg dose. Food increases absorption; best taken with a meal to reduce GI upset. |
| Distribution | Highly protein‑bound (~99 %; mainly albumin). Crosses the blood–brain barrier. |
| Metabolism | Primarily hepatic via CYP3A4, with minor CYP2D6 involvement. Extensive first‑pass metabolism. |
| Elimination | Excreted as metabolites in feces (≈50 %) and urine (≈35 %). Half‑life ~27 h; steady‑state reached in ~5 days. |
| Drug interactions | Strong CYP3A4 inhibitors (ketoconazole, ritonavir) ↑ vilazodone levels; strong inducers (rifampin, carbamazepine) ↓ levels. Caution with other serotonergic agents (MAOIs, triptans) due to serotonin‑syndrome risk. |
Indications
- Major depressive disorder (MDD) in adults.
- Off‑label use: generalized anxiety disorder (GAD), social anxiety disorder, and other mood‑related conditions, though not FDA‑approved for these indications.
Contraindications
- Contraindicated with MAO‑I use; must wait ≥14 days after discontinuation of an MAOI before starting vilazodone.
- Absolute contraindication: Known hypersensitivity to vilazodone or any excipients.
- Warnings:
- Serotonin syndrome (especially when combined with other serotonergic drugs).
‑Bleeding risk—avoid concomitant NSAIDs, aspirin, or anticoagulants without monitoring.
‑QTc prolongation—rare but observed; use cautiously in patients with congenital long‑QT syndrome or receiving other QT‑prolonging agents.
‑Severe hepatic impairment—dose adjustment or avoidance advised.
Dosing
- Initial dose: 10 mg orally once daily in the evening.
- Titration:
- Day 7 – 30 mg once daily (maintained dose).
- If tolerated, subsequent titration to 15 mg once daily after another 5 weeks.
- Maximum dose: 15 mg once daily.
- Adjustments: For mild‑moderate hepatic impairment → 10 mg once daily. Avoid use in severe hepatic disease.
- Administration: Take with food; a glass of water. If nausea occurs, separate dosing from meals slightly.
Monitoring
| Parameter | Frequency | Rationale |
| Symptom severity (HAM-D or PHQ‑9) | Baseline, then weeks 2, 6, 12 | Track therapeutic response. |
| Serotonin‑syndrome signs | At each visit; advise patients to report symptoms | Early detection of serotonin excess. |
| QTc interval | Baseline ECG; repeat if QT‑prolonging agents added | Detect arrhythmic risk. |
| Liver function tests | Baseline; repeat at week 4 if impaired | Ensure adequate metabolism. |
| Weight, blood pressure | Routine outpatient visit | Routine monitoring for SSRI side‑effects. |
Clinical Pearls
- Rapid onset advantage: 5‑HT₁A partial agonist activity leads to noticeable improvement in anxiety‑related symptoms within the first 2 weeks—helpful in patients with significant anxiety comorbidity.
- Low sexual dysfunction risk: Unlike other SSRIs, vilazodone’s partial agonism reduces SSRI‑induced sexual side‑effects, improving adherence.
- Food interaction: A single high‑fat meal can increase bioavailability by ~30 %; advise patients to take medication consistently relative to meals for stable serum levels.
- Steady‑state window: Because serum concentration peaks at ~6 h post‑dose, taking vilazodone in the evening may minimize insomnia while still providing optimal overnight exposure.
- Drug‑interaction caution: When prescribing with a CYP3A4 inhibitor, check for plasma concentration rises; consider starting at 10 mg and monitor for elevated side‑effects.
- Pregnancy category: C – limited data; weigh risks vs benefits; monitor fetal development if prescribed.
- Switching from other SSRIs: Initiate vilazodone after a washout period of ~7 days to avoid serotonin‑syndrome.
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• *Data derived from FDA label, peer‑reviewed literature, and pharmacology resources (e.g., Harrison’s Principles of Internal Medicine, Goodman & Gilman's. Use this card as a quick reference; confirm patient-specific factors and institutional protocols before initiating therapy.*