Olanzapine

BRAND NAMES

• Zyprexa – the original and most widely recognized brand, available in oral tablets and injectable forms. 

• Zyprexa Zydis – orally disintegrating tablet formulation for easier administration.

MECHANISM OF ACTION

Olanzapine is a second-generation (atypical) antipsychotic that works by modulating multiple neurotransmitter systems in the brain. It primarily antagonizes dopamine D2 receptors, reducing positive symptoms of schizophrenia such as hallucinations and delusions, while blocking serotonin 5-HT2A receptors helps improve negative symptoms and cognitive deficits.

PHARMACOKINETICS:

Absorption: 

Olanzapine toxicity is uncommon at therapeutic doses but can occur with overdose or rapid dose escalation. Acute toxicity primarily affects the central nervous system and cardiovascular system, leading to sedation, agitation, coma, tachycardia, or hypotension. Severe overdose may also cause respiratory depression, extrapyramidal symptoms, or anticholinergic effects such as urinary retention and dry mouth. Management of olanzapine toxicity is largely supportive, focusing on airway protection, cardiovascular monitoring, and symptomatic treatment, as there is no specific antidote.

Distribution

After absorption, olanzapine is widely distributed throughout the body, with a volume of distribution of approximately 10–20 L/kg, reflecting extensive tissue uptake. It is highly protein-bound (approximately 93%), mainly to albumin, which influences its free, active concentration in plasma. Olanzapine readily crosses the blood-brain barrier, allowing it to act on central nervous system receptors, and is also distributed to other tissues, including the liver and kidneys.

Metabolism

Olanzapine is extensively metabolized in the liver, primarily by cytochrome P450 enzymes, including CYP1A2 and to a lesser extent CYP2D6. The drug undergoes oxidation and direct glucuronidation to form pharmacologically inactive metabolites. Factors such as smoking, age, and co-administration of enzyme inducers or inhibitors can alter the metabolism of olanzapine, particularly through CYP1A2, potentially affecting plasma concentrations and therapeutic response. The extensive hepatic metabolism is a key factor in olanzapine’s long half-life and sustained antipsychotic effects.

Elimination:

Olanzapine and its inactive metabolites are primarily excreted via the urine (about 57%) and feces (about 30%). Only a small fraction of unchanged drug (<1%) is eliminated in the urine. The elimination half-life ranges from 21 to 54 hours, depending on patient factors such as age, smoking status, and hepatic function. This relatively long half-life supports once-daily dosing and contributes to steady plasma levels with repeated administration.

PHARMACODYNAMICS

Olanzapine is a second-generation (atypical) antipsychotic that produces its therapeutic effects by modulating multiple neurotransmitter systems in the brain. Its primary action is dopamine D2 receptor antagonism, which reduces positive symptoms of schizophrenia such as hallucinations and delusions. At the same time, serotonin 5-HT2A receptor antagonism helps improve negative symptoms and cognitive deficits while reducing the risk of extrapyramidal side effects compared with first-generation antipsychotics. 

ADMINISTRATION

Olanzapine is administered orally or via intramuscular injection, depending on the formulation and clinical need. Oral tablets and orally disintegrating tablets are taken once daily, with or without food, at the same time each day to maintain consistent plasma levels. The long-acting intramuscular injection (Relprevv) is used for maintenance therapy in patients with schizophrenia and is administered every 2–4 weeks by a healthcare professional.

DOSAGE AND STRENGTH

Olanzapine is available in oral tablets (2.5–20 mg), orally disintegrating tablets (5–20 mg), and long-acting intramuscular injections (210–405 mg per vial). For adults with schizophrenia, the typical oral dose is 10–20 mg once daily, with 10 mg often used as the starting dose. In bipolar disorder, oral doses of 10–20 mg once daily are used for acute mania, with lower doses for maintenance. The long-acting intramuscular formulation is administered every 2–4 weeks at 210–405 mg, depending on prior oral dosing and clinical response.

DRUG INTERACTIONS

Olanzapine’s effects can be influenced by drugs that affect its metabolism or central nervous system activity. Medications that induce CYP1A2, such as carbamazepine, rifampin, or cigarette smoke, can increase olanzapine clearance and reduce its therapeutic effect, while CYP1A2 inhibitors like fluvoxamine or ciprofloxacin can raise plasma levels and increase the risk of sedation, weight gain, and other adverse effects.

FOOD INTERACTIONS
Olanzapine canbe taken with or without food, as meals do not significantly affect its overall absorption or bioavailability. However, a high-fat meal may slightly delay the time to reach peak plasma concentration, although the total amount absorbed remains unchanged. Clinically, this means olanzapine’s efficacy is notsubstantiallyalteredby food, and patients can take it at a consistent time daily with their usual meals.

CONTRAINDICATIONS

Olanzapine is contraindicated in patients with a known hypersensitivity to olanzapine or any of its formulation components, including mannitol or other excipients. It should also be avoided in individuals with severe central nervous system depression, coma, or acute alcohol intoxication.

SIDE EFFECTS

• Sedation and drowsiness 

• Weight gain and increased appetite 

• Orthostatic hypotension. 

TOXICITY

Olanzapine toxicity is uncommon at therapeutic doses but can occur with overdose or rapid dose escalation. Acute toxicity primarily affects the central nervous system and cardiovascular system, leading to sedation, agitation, coma, tachycardia, or hypotension. Severe overdose may also cause respiratory depression, extrapyramidal symptoms, or anticholinergic effects such as urinary retention and dry mouth. Management of olanzapine toxicity is largely supportive, focusing on airway protection, cardiovascular monitoring, and symptomatic treatment, as there is no specific antidote.