Olanzapine is thought to modify the actions of several chemicals in the brain. Onlanzapine is chemically related to another atypical antipsychotic agent, clozapine, but differs both chemically and pharmacologically from the earlier phenothiazine antipsychotics.
Olanzapine is available as 2.5-mg, 5-mg, 7.5-mg, 10-mg, 15-mg, and 20-mg tablets that can be swallowed (Zyprexa) and 5-mg, 10-mg, 15-mg, and 20-mg tablets that disintegrate when placed under the tongue (Zyprexa Zydis). Olanzapine is broken down by the liver.
The dosage of olanzapine varies depending upon the reason for its use. When used to treat schizophrenia, 5–10 mg is the typical starting dosage. If dosage adjustments are needed, increases are made in 5-mg increments once a week. When treating schizophrenia, a total daily dosage of 10–15 mg is usually effective. When olanzapine is used to treat acute manic episodes, initial doses of olanzapine are often 10–15 mg; 20 mg per day may be needed for maximum effect. The safety of doses greater than 20 mg per day has not been determined.
Olanzapine is eliminated from the body more quickly in young people than in older (over age 60) individuals, in men than in women, and in smokers faster than in non-smokers. Dosage adjustments may be needed based upon individual patient characteristics.
Caution should be used in patients with heart disease because the drug may cause blood pressure to fall too low resulting in dizziness, rapid heartbeats, or fainting. Olanzapine should be used carefully in people with known seizure disorders since olanzapine may alter properties of the brain making seizures occur more easily. People with liver disease should have their liver function monitored regularly while taking olanzapine. Women who are pregnant or breast-feeding should not take olanzapine. People with phenylketonuria, a disorder in which the body is unable to metabolize a protein called phenylalanine, should avoid olanzapine disintegrating tablets, because this form of the drug contains phenylalanine.
Side effects that occur in more than 5% of patients taking olanzapine include involuntary movements, weakness, dizziness, extreme drowsiness, nonviolent objectionable behavior, constipation, weight gain, dry mouth, low blood pressure, stomach upset, increased appetite, cold-such as symptoms, or fever.
Other side effects that are possible include rash, body aches and pains, elevated liver enzymes, vision abnormalities, chest pain, or rapid heartbeats.
Olanzapine has the potential to produce a serious side effect called tardive dyskinesia. This syndrome consists of involuntary, uncoordinated movements that may appear late in therapy and not disappear even after the drug is stopped. Tardive dyskinesia involves involuntary movements of the tongue, jaw, mouth or face or other groups of skeletal muscles. The incidence of tardive dyskinesia increases with increasing age and with increasing dosage of olanzapine. Women are at greater risk than men for developing tardive dyskinesia. There is no known effective treatment for tardive dyskinesia, although gradual (but rarely complete) improvement may occur over a long period.
An occasionally reported side effect of olanzapine is neuroleptic malignant syndrome. This is a complicated and potentially fatal condition characterized by muscle rigidity, high fever, alterations in mental status, and cardiac symptoms such as irregular pulse or blood pressure, sweating, tachycardia (fast heartbeat), and arrhythmias (irregular heartbeat).
Any drug that causes drowsiness may lead to decreased mental alertness and impaired motor skills when taken with olanzapine. Some examples include alcohol, antidepressants such as imipramine (Tofranil) or paroxetine (Paxil), antipsychotics such as thioridazine (Mellaril), and some antihistamines. Because olanzapine may lower blood pressure, it may reduce blood pressure to dangerously low levels if taken with drugs that are used to treat high blood pressure. Carbamazepine (Tegretol), a drug commonly used to treat seizures, may decrease the effectiveness of olanzapine.
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Kelly Karpa, RPh, Ph.D.