What are the side effects of Stemetil (prochlorperazine) injection?

Side Effects of Stemetil (Prochlorperazine) Injection

Stemetil injection causes significant neurological side effects, particularly extrapyramidal symptoms (EPS) in 4-16% of patients, with elderly patients at substantially higher risk for sedation, falls, cognitive impairment, and anticholinergic toxicity. 1, 2

Common Side Effects

Central Nervous System Effects

• Sedation and drowsiness occur frequently and can impair mental and physical abilities, especially during initial therapy 1, 2
• Cognitive impairment including confusion and slowed comprehension, particularly problematic in elderly patients 1, 2
• Extrapyramidal symptoms (EPS) occur in approximately 4% of patients receiving standard doses, but emergency department studies show rates as high as 16% 1, 2, 3
  • Akathisia (restlessness) is the most common EPS manifestation, occurring in 14-16% of patients 3, 4
  • Dystonia (muscle spasms) occurs in approximately 4% of patients 2, 3
  • Pseudoparkinsonism with tremor and rigidity 1, 2

Anticholinergic Effects

• Dry mouth, constipation, urinary retention, and blurred vision are common anticholinergic side effects 1, 2
• These effects are particularly problematic in elderly patients with pre-existing conditions like benign prostatic hypertrophy or glaucoma 1, 2

Cardiovascular Effects

• Hypotension, tachycardia, and arrhythmias can occur, with orthostatic hypotension being particularly concerning in elderly patients 1, 2
• Alpha-adrenergic blockade may cause postural hypotension and increase fall risk 2

Serious and Life-Threatening Side Effects

Tardive Dyskinesia

• Potentially irreversible movement disorder characterized by involuntary movements of the tongue, face, mouth, or jaw 2
• Risk increases with long-term use and higher cumulative doses 2, 5
• Fine vermicular tongue movements may be an early warning sign requiring immediate discontinuation 2

Neuroleptic Malignant Syndrome (NMS)

• Potentially fatal syndrome presenting with hyperpyrexia, muscle rigidity, altered mental status, and autonomic instability 2
• Requires immediate discontinuation of prochlorperazine and intensive supportive care 2

Blood Disorders

• Drug-induced leukopenia, neutropenia, agranulocytosis, and thrombocytopenic purpura can occur 1, 2
• Elderly patients have higher incidence of agranulocytosis compared to younger individuals 2

Falls and Injuries

• Somnolence, postural hypotension, and motor instability significantly increase fall risk, particularly in elderly patients 2

Special Population Considerations

Elderly Patients (Age ≥65)

• The American Geriatrics Society identifies prochlorperazine as potentially inappropriate due to strong anticholinergic properties and high sedation risk 1, 2
• Elderly patients experience:
  • Higher rates of sedation, confusion, and delirium 1, 2
  • Increased fall risk from orthostatic hypotension 1, 2
  • Greater susceptibility to EPS and tardive dyskinesia 1, 2
  • Higher incidence of agranulocytosis 2
• Dose reduction is mandatory in elderly patients, starting at the low end of the dosing range 2

Pediatric Patients

• Children with acute illnesses (chickenpox, CNS infections, measles, gastroenteritis) or dehydration are much more susceptible to neuromuscular reactions, particularly dystonias 2, 6
• Neurological side effects in children include impaired consciousness, dyskinesia, pyramidal signs, and hypertonus, with dyskinesia being most frequent 6
• Side effects are independent of dosage and resolve spontaneously after discontinuation 6

Patients with Organ Impairment

• Hepatic or renal impairment increases risk of adverse effects due to reduced drug clearance 1, 2

Critical Drug Interactions and Contraindications

• Avoid in patients with glaucoma due to anticholinergic effects causing mydriasis 2
• Lowers seizure threshold; use with extreme caution in patients with epilepsy 2
• Potentiates CNS depressants including alcohol, opiates, barbiturates, and benzodiazepines 2
• Contraindicated with metrizamide myelography; discontinue 48 hours before and do not resume for 24 hours after procedure 2

Clinical Pitfalls to Avoid

• Failing to recognize akathisia early: This distressing symptom occurs within the first week and may be mistaken for anxiety or worsening of underlying condition 3, 4
• Underestimating fall risk in elderly: Combination of sedation, orthostatic hypotension, and motor instability creates substantial injury risk 2
• Missing early signs of tardive dyskinesia: Fine tongue movements require immediate drug discontinuation to prevent irreversibility 2
• Overlooking contact dermatitis risk: Avoid skin contact with injection solution 2

Safer Alternatives

• For nausea/vomiting: Ondansetron or granisetron (serotonin antagonists) do not cause EPS, though they may worsen constipation 7, 5
• For elderly patients: Second-generation antihistamines or alternative antiemetics without anticholinergic burden are preferred 1