Loxapine

Indications

• Oral loxapine is FDA-approved for the treatment of schizophrenia in adults, given in divided doses after gradual titration.
• Inhaled loxapine is FDA-approved for acute agitation associated with schizophrenia or bipolar I disorder in adults, limited to one dose per day.
• The inhaled product is dispensed only through a restricted REMS program at healthcare facilities equipped for advanced airway management.
• Off-label oral use for acute agitation and for augmentation in partially responsive psychosis when a different receptor profile is wanted.
• Off-label low-dose use has been described for anxiety and for migraine, but evidence is thin and the boxed warning still applies.
• Not indicated for dementia-related psychosis, and inhaled loxapine is contraindicated in any patient with active airway disease.

Mechanism of action

• Blocks dopamine D2 receptors with mid-range potency, providing antipsychotic efficacy at total daily doses of roughly 60 to 100 milligrams.
• Substantial 5-HT2A antagonism gives a serotonin-to-dopamine ratio resembling second-generation agents, which may soften extrapyramidal effects at low doses.
• The metabolite 7-hydroxyloxapine is a potent D2 blocker, while 8-hydroxyloxapine contributes little, shaping the overall clinical response.
• Loxapine is structurally related to amoxapine, and small amounts of that antidepressant metabolite give weak norepinephrine reuptake inhibition.
• Moderate histamine H1, muscarinic, and alpha-1 blockade account for sedation, dry mouth, and orthostatic hypotension during titration.

Pharmacokinetics

• Oral absorption is rapid but bioavailability is limited by first-pass metabolism, with peak plasma concentrations reached in 1 to 2 hours.
• Inhaled loxapine reaches peak plasma levels in about 2 minutes, which explains the calming effect within 10 minutes of a single dose.
• The plasma half-life is roughly 6 to 8 hours for the parent drug, with hydroxylated metabolites persisting substantially longer.
• Metabolism proceeds through CYP1A2, CYP2D6, and CYP3A4 plus glucuronidation, so smoking and 2D6 inhibitors both shift exposure meaningfully.
• Elimination is mainly biliary and renal as conjugated metabolites, with negligible unchanged loxapine recovered in the urine.

Dosing

• Start oral loxapine at 10 mg twice daily; severe presentations may begin at 50 mg/day in divided doses under close observation.
• Titrate over 7 to 10 days to a usual maintenance range of 60-100 mg/day divided two to four times daily; the labeled maximum is 250 mg/day.
• Inhaled loxapine is a single 10 mg oral inhalation, not to be repeated within 24 hours, with the patient observed for bronchospasm.
• Before each inhaled dose, screen for asthma, COPD, or other lung disease, and examine the chest for wheezing; those conditions are contraindications.
• No formal renal or hepatic dose adjustment exists, but lower doses and slower titration are prudent when clearance is likely reduced.
• Taper oral therapy over weeks; abrupt discontinuation risks cholinergic rebound, insomnia, nausea, and withdrawal dyskinesias.

Adverse effects

• Sedation is the most common effect of both formulations, and dizziness with orthostatic hypotension is frequent during oral titration.
• Extrapyramidal symptoms including akathisia and parkinsonism occur in a dose-dependent fashion, generally less than with haloperidol.
• Bronchospasm is the defining risk of the inhaled product and can progress to respiratory distress or arrest in patients with airway disease.
• Dysgeusia and throat irritation affect a substantial minority after inhalation, and are usually transient and self-limited.
• Tardive dyskinesia, neuroleptic malignant syndrome, and hyperprolactinemia occur as class effects with sustained oral treatment.
• Loxapine lowers seizure threshold appreciably, so use caution in patients with epilepsy, withdrawal states, or head injury.

Monitoring

• Before any inhaled dose, take a respiratory history and auscultate the chest; monitor for wheeze and dyspnea every 15 minutes for at least 1 hour.
• Keep a short-acting bronchodilator and advanced airway equipment immediately available wherever inhaled loxapine is administered.
• Perform baseline and semiannual AIMS testing plus an extrapyramidal exam at each visit for patients on continuing oral therapy.
• Check orthostatic blood pressure during oral titration, and obtain an ECG when cardiac disease or other QT-prolonging agents are present.
• Weight, fasting glucose, and lipids at baseline and annually, with CBC and liver enzymes if symptoms suggest dyscrasia or hepatic injury.

Interactions

• CYP1A2 inducers such as tobacco smoke and CYP3A4 inducers such as carbamazepine reduce loxapine exposure and may cause symptom breakthrough.
• CYP2D6 and CYP1A2 inhibitors including fluvoxamine, paroxetine, and ciprofloxacin raise levels and increase sedation and movement effects.
• Additive CNS and respiratory depression with opioids, benzodiazepines, and alcohol, which is especially hazardous with the inhaled route.
• Additive anticholinergic and hypotensive effects with antihistamines, tricyclics, and antihypertensives; combined QT drugs merit ECG review.
• Inhaled loxapine is contraindicated in asthma, COPD, other bronchospastic lung disease, and in patients with acute wheezing on examination.

Special populations

• Pregnancy data are limited; third-trimester exposure carries the class risk of neonatal extrapyramidal symptoms and withdrawal.
• Loxapine and its metabolites appear in breast milk, so nursing infants should be observed for sedation and feeding difficulty.
• Safety and efficacy in patients under 18 have not been established for either the oral or the inhaled formulation.
• Older adults are more sensitive to sedation and hypotension, and the boxed dementia mortality warning limits use in that group.
• No formal renal or hepatic dosing guidance exists; start low and titrate slowly when either organ system is compromised.

Clinical pearls

• Inhaled loxapine calms agitation in about 10 minutes but needs a REMS site and an hour of watching.
• Its 5-HT2A blockade makes low-dose loxapine behave more like an atypical than a classic typical agent.
• Ask about asthma and listen to the lungs before every single inhaled dose, not just the first.