Half-Life of Baclofen
Baclofen has a half-life of approximately 3.5 to 5 hours in patients with normal renal function, though this can be significantly prolonged in overdose situations or renal impairment. 1
Pharmacokinetic Properties
Standard Half-Life Parameters:
- The FDA-approved drug label indicates baclofen is rapidly absorbed and eliminated primarily by the kidney in unchanged form 1
- Clinical studies in healthy volunteers demonstrate a half-life of 5.24 hours after oral administration and 5.79 hours after intravenous administration 2
- A large pharmacokinetic study in alcohol use disorder patients found a half-life of 4.4 hours with racemic baclofen 3
- After oral administration in pediatric studies, the half-life ranged from 2.3 to 3.4 hours 4
Clinical Context and Variations
Intrathecal Administration:
- When administered intrathecally for spasticity, baclofen clearance from cerebrospinal fluid occurs with a half-life of 5 hours 5
Overdose Situations:
- In baclofen overdose, the half-life can be dramatically prolonged up to 34 hours, necessitating extended monitoring and potentially requiring hemodialysis or continuous venovenous hemofiltration 6
- During hemofiltration treatment for overdose, the elimination half-life was reduced to 4.8 hours 6
Renal Function Impact
Critical Consideration:
- Baclofen is excreted primarily unchanged by the kidneys, with relatively large intersubject variation in elimination 1
- Patients with renal impairment will have significantly prolonged half-lives, though specific values are not well-established in the literature
- The FDA label notes there is "relatively large intersubject variation in absorption and/or elimination" 1
Practical Implications
Dosing Frequency:
- The short half-life of 3.5-5 hours necessitates three-times-daily dosing for most clinical applications 7
- This contrasts with longer-acting muscle relaxants or GABA agonists that may allow once or twice-daily dosing
Withdrawal Risk:
- The relatively short half-life means abrupt discontinuation can rapidly lead to withdrawal syndrome, as therapeutic levels decline within 15-25 hours (3-5 half-lives) 2