What are the adverse effects associated with injectable antipsychotic medications (both typical and atypical)?

Side Effects of Injectable Antipsychotic Medications

Injectable antipsychotics carry significant risks including extrapyramidal symptoms, metabolic disturbances (particularly weight gain), cardiac effects (QT prolongation), and rare but life-threatening complications like neuroleptic malignant syndrome and agranulocytosis. 1

Neurological Side Effects

Extrapyramidal Symptoms (EPS)

• Acute dystonia presents as involuntary motor tics or spasms involving the face, extraocular muscles (oculogyric crisis), neck, back, and limb muscles, typically occurring after the first few doses or dosage increases 1
• Laryngeal dystonia is a rare but potentially life-threatening adverse event presenting as choking sensation, difficulty breathing, or stridor 1
• Akathisia manifests as subjective restlessness, generally occurring within the first few days of treatment 1
• Drug-induced Parkinsonism requires consideration for early diagnosis, as rapid withdrawal may improve the possibility of complete recovery 1
• Tardive dyskinesia occurs in 5% of young patients per year, characterized by rapid involuntary facial movements (blinking, grimacing, chewing, tongue movements) and extremity or truncal movements 1
• Tardive dystonia presents as slow movements along the long axis of the body culminating in spasms, often quite disabling and associated with tardive dyskinesia 1

Important distinction: Atypical antipsychotics have lower risk for EPS than traditional neuroleptics, though risperidone appears most likely among atypicals to produce extrapyramidal side effects 1

Neuroleptic Malignant Syndrome (NMS)

• Life-threatening tetrad: mental status changes, fever, hypertonicity/rigidity, and autonomic dysfunction 1
• Incidence ranges from 0.02% to 3%, with mortality decreased from 76% in the 1960s to <10-15% currently 1
• Can theoretically occur with any antipsychotic agent, including atypicals 1

Seizures

• Antipsychotic medications lower seizure threshold in a dose-dependent manner 1
• Generally rare (<1%) at therapeutic doses, except clozapine which has 5% incidence at high dosages 1
• Risk increases with rapid dosage escalation 1

Cognitive Effects

• Traditional neuroleptics may cause sedation, cognitive blunting, apathy, and memory deficits, especially low-potency agents with greater anticholinergic activity 1
• Atypical antipsychotics show consistent benefits in fine motor function, memory, and executive function compared to traditional neuroleptics 1

Metabolic Side Effects

Weight Gain

• The most common significant problem associated with atypical antipsychotic use 1
• Weight gain may be extreme 1
• Generally higher with olanzapine pamoate versus risperidone long-acting injectable 2

Hyperglycemia

• Metabolic adverse effects including hyperglycemia are documented concerns 1

Cardiac Side Effects

QT Prolongation

• Almost all antipsychotics cause some degree of QT prolongation due to quinidine-like effect 1
• Thioridazine and droperidol carry FDA black box warnings for potential association with prolonged QT interval, torsades de pointes, and sudden death 1
• Mean QT prolongation varies by agent: thioridazine (25-30 ms), ziprasidone (5-22 ms), haloperidol (7 ms), risperidone (0-5 ms), aripiprazole (0 ms) 1
• Youth may be more susceptible to cardiac effects of medications 1

Orthostatic Hypotension

• Can be a significant problem, particularly with certain agents 1

Other Cardiac Effects

• Tachycardia documented with clozapine 1

Hematological Side Effects

Agranulocytosis

• Clozapine: occurs in approximately 1% of patients, potentially fatal but usually reversible if drug stopped immediately 1
• Can occur with any antipsychotic agent, though primarily associated with clozapine 1
• Clozapine requires extensive monitoring: weekly blood cell counts during first 6 months, then every 2 weeks thereafter, including 4 weeks after discontinuation 1

Leukocytopenia

• Case reports in teenagers receiving risperidone 1
• Precipitous drops in absolute neutrophil count and platelets reported with quetiapine 1

Hepatic Side Effects

• Atypical agents may produce elevations in hepatic transaminase levels 1
• Elevations often transient and generally resolve with cessation 1
• Case reports of liver enzyme abnormalities and fatty infiltrates associated with obesity in adolescent males during risperidone therapy 1
• Prudent to check baseline liver functions prior to initiating treatment with periodic monitoring during ongoing therapy 1
• Cholestatic jaundice documented with phenothiazines 1

Injection Site Reactions

• Rare problems with injection site reactions for long-acting injectable formulations 2
• Patients exposed to injectable treatments generally prefer to continue injections 2

Post-Injection Delirium Sedation Syndrome

• Infrequent but serious complication occurring after 1% of olanzapine pamoate injections 2

Other Side Effects

Common Effects

• Sedation 1
• Activation 1
• Dizziness 1
• Hypersalivation (particularly clozapine) 1
• Fever (particularly clozapine) 1

Endocrine Effects

• Sexual dysfunction 1
• Hyperprolactinemia 1

Ocular Effects

• Quetiapine associated with cataracts in dog studies (not reported in humans) 1
• FDA recommends baseline and 6-month follow-up eye examinations when prescribing quetiapine 1
• Lenticular stippling with thioridazine 1

Other Specific Effects

• Photosensitivity with phenothiazines 1
• Somnolence, anxiety, agitation, oral hypoesthesia, headache, nausea, vomiting, insomnia, tremor with various atypical antipsychotics 1

Critical Monitoring Considerations

Common pitfall: Discontinuation rates due to adverse effects are uncommon with long-acting injectable formulations, suggesting good tolerability when properly monitored 2. However, the serious nature of potential complications (NMS, agranulocytosis, cardiac events) requires vigilant surveillance even when overall rates are low.