Onset of Action of Zyprexa (Olanzapine)
Intramuscular (IM) olanzapine has a rapid onset of action, with effects beginning within 15-30 minutes after injection, while oral olanzapine typically shows initial effects within 1-2 hours. 1, 2
Intramuscular (IM) Olanzapine
- IM olanzapine demonstrates a rapid absorption profile with peak plasma concentrations occurring within 15 to 45 minutes after administration 3
- Clinical studies show that IM olanzapine at doses of 5.0,7.5, or 10.0 mg produces significant reduction in agitation compared to placebo as early as 30 minutes after injection 1
- A 5 mg dose of IM olanzapine produces, on average, a maximum plasma concentration approximately 5 times higher than the maximum plasma concentration produced by a 5 mg dose of oral olanzapine, contributing to its faster onset of action 3
- IM olanzapine is at least as effective as IM haloperidol or lorazepam in the treatment of acute agitation, with evidence suggesting a faster onset of action 2
Oral Olanzapine
- Oral olanzapine is well absorbed and reaches peak plasma concentrations in approximately 6 hours following administration 3
- Initial clinical effects can be observed within 1-2 hours, though full therapeutic effect may take longer 4, 5
- In acute psychosis, high-dose oral loading strategies (15-20 mg) have shown effectiveness for rapid tranquilization, with calming effects observed within several hours 6
- The orally disintegrating tablet (ZYPREXA ZYDIS) begins disintegrating in the mouth within seconds, allowing for faster absorption compared to standard tablets, though both formulations are bioequivalent 3
Factors Affecting Onset of Action
- Patient factors such as smoking status, gender, and age may affect olanzapine's pharmacokinetics, potentially influencing onset of action 3
- Food does not affect the rate or extent of olanzapine absorption 3
- Higher doses generally produce more rapid and pronounced effects, as demonstrated in dose-response studies 1
Clinical Implications
- For acute agitation requiring rapid control, IM olanzapine offers faster onset than oral formulations 7
- When using olanzapine for acute agitation, monitoring should continue until the patient is awake and ambulatory due to potential sedative effects 7
- Caution should be exercised when combining olanzapine with benzodiazepines due to risk of oversedation and respiratory depression 7
Common Pitfalls and Caveats
- Avoid combining high-dose olanzapine with benzodiazepines as fatalities have been reported with this combination 7
- Be aware that olanzapine can cause transient reductions in blood pressure and heart rate in some patients 2
- Olanzapine has a half-life ranging from 21 to 54 hours, meaning that steady-state concentrations are not reached until approximately one week of daily dosing 3
- Common side effects include sedation, dizziness, weight gain, and anticholinergic effects, which may be observed shortly after administration 4