Olanzapine Tmax (Time to Peak Plasma Concentration)
Olanzapine reaches peak plasma concentrations approximately 6 hours after oral administration and 15-45 minutes after intramuscular injection. 1, 2
Oral Administration
Peak plasma concentrations occur at approximately 6 hours following oral dosing, whether using standard tablets or orally disintegrating formulations (ZYPREXA ZYDIS), as both are bioequivalent 1. One study reported a slightly narrower range of 4-6 hours 3.
- Olanzapine is well absorbed with approximately 85% bioavailability 3
- Food does not affect the rate or extent of absorption 1
- First-pass metabolism is extensive, with approximately 40% of the dose metabolized before reaching systemic circulation 1
Intramuscular Administration
Peak plasma concentrations occur within 15-45 minutes after intramuscular injection 1, 2, representing significantly more rapid absorption compared to oral dosing.
- A 5 mg IM dose produces maximum plasma concentrations approximately 5 times higher than the same oral dose 1, 2
- Despite higher peak concentrations, the total area under the curve (AUC) is similar between IM and oral routes 1, 2
- The elimination half-life after IM administration is similar to oral dosing (21-54 hours, mean 30 hours) 1, 2
Clinical Implications
The 6-hour Tmax for oral olanzapine explains why modified-release formulations are not ideal for dose titration, as they produce delayed peak concentrations at 2-6 hours with attenuated peaks 4. The rapid absorption after IM administration makes this route preferable for acute agitation, with therapeutic effects expected within 15-30 minutes of injection 1, 2.