Half-Life of Quetiapine (Seroquel)
The elimination half-life of quetiapine is approximately 6 hours at therapeutic doses in adults 1.
Key Pharmacokinetic Details
Standard Therapeutic Dosing
- Mean terminal half-life: ~6 hours within the proposed clinical dose range 1
- Steady-state concentrations are achieved within 2 days of dosing 1
- Peak plasma concentrations occur at 1.5 hours after oral administration 1
Active Metabolite (Norquetiapine)
The active metabolite N-desalkyl quetiapine (norquetiapine) has a significantly longer half-life of approximately 12-18 hours 2. This metabolite contributes to quetiapine's overall clinical effects, particularly at serotonin 5HT2A receptors where it has greater activity than the parent drug 1.
Important Clinical Variations
Overdose Situations
The half-life is substantially prolonged in overdose, ranging from 16.5 to 22 hours 3, 4. This occurs because:
- Higher concentrations reveal a biexponential elimination pattern with a much longer terminal phase 4
- The 6-hour half-life reported in standard literature reflects only the distribution phase, not true elimination 4
Special Populations
Elderly patients (≥65 years):
- Half-life extends to 11-13 hours 5
- Oral clearance reduced by 40% compared to younger patients 1
- Dose adjustment necessary 1
Pediatric patients (10-17 years):
- Similar half-life to adults for the parent compound
- However, when adjusted for weight, children have 41% lower AUC, suggesting faster relative clearance 1
Renal impairment:
- Severe renal insufficiency (CrCl 10-30 mL/min): 25% lower oral clearance 1
- Dose adjustment recommended
Hepatic impairment:
- Clearance reduced; dose adjustment necessary 1
Clinical Implications
The relatively short 6-hour half-life at therapeutic doses means:
- Twice-daily dosing is often needed for immediate-release formulations to maintain stable plasma levels
- Extended-release formulations (Seroquel XR) were developed to enable once-daily dosing 2
- Drug accumulation is predictable and reaches steady state quickly (within 48 hours) 1
Critical caveat: The published 6-hour half-life may underestimate the true duration of clinical effects, particularly in overdose situations where the terminal elimination phase becomes clinically relevant 4. Physicians should be aware that detectable serum concentrations and clinical effects may persist much longer than the standard half-life would suggest, especially at higher doses.