Vilazodone Therapeutic Range
There is no established therapeutic plasma concentration range for vilazodone. Unlike tricyclic antidepressants and some other older antidepressants, vilazodone does not have a defined therapeutic window based on plasma drug monitoring studies.
Key Pharmacokinetic Parameters
The FDA label provides specific steady-state pharmacokinetic values for vilazodone at the standard 40 mg daily dose 1:
- Mean Cmax: 156 ng/mL
- Mean AUC (0-24 hours): 1645 ng·h/mL
- Terminal half-life: approximately 25 hours
- Time to peak (Tmax): 4-5 hours
These values represent expected plasma concentrations at therapeutic doses rather than a therapeutic range for monitoring purposes.
Clinical Implications
Therapeutic drug monitoring (TDM) is not recommended for vilazodone. The AGNP-TDM expert consensus guidelines from 2005 do not include vilazodone (which was approved in 2011), but they classify newer antidepressants like SSRIs and SNRIs as having no clearly established plasma concentration-clinical effectiveness relationship 2. Vilazodone falls into this same category.
Why TDM Is Not Used for Vilazodone:
- No established concentration-response relationship: Clinical trials have not demonstrated a clear correlation between plasma vilazodone levels and therapeutic efficacy 3, 4
- Dose-based efficacy: The drug's effectiveness is established at fixed doses (40 mg daily) rather than plasma concentrations 1
- Extensive hepatic metabolism: With only 1% urinary excretion and 2% fecal excretion as unchanged drug, plasma levels are highly variable and don't reliably predict clinical response 1
Important Dosing Considerations:
Food requirement is critical: Vilazodone must be taken with food, as fasting can decrease AUC and Cmax by approximately 50% and 60%, respectively 1. Administration without food results in inadequate drug concentrations that may reduce effectiveness.
No dose adjustment needed for organ impairment: Pharmacokinetic studies demonstrate that mild to severe renal impairment 5 and mild to severe hepatic impairment 6 do not significantly affect vilazodone clearance or exposure, so dose adjustments are not required.
When Plasma Levels Might Be Considered
While routine TDM is not recommended, knowledge of expected plasma concentrations at therapeutic doses may be useful in specific clinical situations 2:
- Suspected non-compliance
- Lack of response despite adequate dosing
- Suspected drug interactions (particularly with CYP3A4 inhibitors or inducers)
- Unusual adverse effects
In these scenarios, the expected steady-state values (Cmax ~156 ng/mL) can serve as a reference point, though clinical decision-making should remain primarily dose-based rather than concentration-based.