by Sina

Created on: January 30, 2009

Zyprexa or olanzapine is an atypical antipsychotic originally approved for use in patients with schizophrenia. Later olanzapine in combination with fluoxetine (formulated as Symbyax) was approved for use in bipolar patients, managing depressive and manic episodes. What follows is the pharmacology, dosing and administration, and side effects. (It should be noted that only olanzapine in its Zyprexa formulation will be dealt with in this article)

Pharmacology

Pharmacology is the study of chemcials and the interaction they have with living organisms. Olanzapine is pharmacologically categorized as a thienobenzodiazepine due to it's chemical structure. Olanzapine is a monoaminergic antagonist with high affinity binding to serotonin (5HT2), dopamine (D2), histamine, and adrenergic alpha one receptors. The drug has moderate affinity binding for serotonin (5HT3) and muscarinic (M1-5) receptors.

The specific mechanism of action for olanzapine in schizophrenia patients isn't known. The high efficacy in treating schizophrenia is thought to be mediated by the drugs high affinity antagonism of serotonin and dopamine type two receptors. The drugs antagonism at the histamine, adrenergic, and muscarinic is thought of as the underlaying cause of some of the side effects of this drug.

Dosing and Administration

Olanzapine is administrated orally in 2.5mg, 5mg, 7.5mg, 10mg, 15mg, and 20mg tablets or sublingual disintegrating wafers. In case of emergencies the drug can be administrated intra muscularly. When the drug is absorbed it often reaches peak concentrations in 6 hours being distributed extensively throughout the body, and being highly metabolized (i.e. broken down or changed by the body).

Side Effects

The most common side effect of olanzapine is weight gain with the vast majority of patients effected by this. Note that this side effect isn't dose dependent, meaning whether the patient is on 5mg or 20mg they will more than likely experience weight gain. This side effect can be managed simply by the patient by observing and being attentive to their diet. Most of the other side effects of olanzapine are experienced in the beginning of therapy with this drug and often become less severe as the appropriate dosing is established.

One of the more severe consequences of using any drug that effects the central nervous system directly is tardive dyskinesia. This condition is characterized by involuntary, repetitive, and purposeless motions. This is one of the side effects that often will stay with the patient even if they have stopped therapy with the drug. Though, olanzapine is a newer drug and more specific in its mode of action it is still a possibility.

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