Side Effects of Phenergan (Promethazine)
Phenergan (promethazine) has numerous significant side effects including drowsiness, sedation, confusion, extrapyramidal symptoms, respiratory depression, hypotension, and potentially fatal neuroleptic malignant syndrome. 1
Common Side Effects
Central Nervous System Effects
- Drowsiness (most prominent CNS effect) 1
- Sedation and somnolence
- Dizziness and confusion
- Blurred vision
- Fatigue and lassitude
- Nervousness and insomnia
Cardiovascular Effects
- Blood pressure changes (increased or decreased) 1
- Tachycardia or bradycardia
- Faintness
- Hypotension (especially with rapid IV administration) 2
Gastrointestinal Effects
- Dry mouth 1
- Nausea and vomiting
- Jaundice
Respiratory Effects
- Respiratory depression (potentially fatal) 1
- Apnea (potentially fatal)
- Nasal stuffiness
- Asthma exacerbation
Serious Adverse Effects
Extrapyramidal Symptoms
- Oculogyric crisis (abnormal eye movements) 1
- Torticollis (neck twisting)
- Tongue protrusion
- Dystonic reactions ranging from restlessness to oculogyric crises 2
Severe Reactions
- Neuroleptic malignant syndrome (potentially fatal) 1, 3
- Seizures 1, 4
- Hallucinations 1
- Paradoxical reactions (hyperexcitability, agitation) 1
- Tissue damage with extravasation or inadvertent intra-arterial injection (FDA black box warning) 3
Hematologic Effects
- Leukopenia 1
- Thrombocytopenia
- Thrombocytopenic purpura
- Agranulocytosis
Special Population Considerations
Pediatric Patients
- Children may experience paradoxical reactions characterized by hyperexcitability and nightmares 1
- Increased risk of adverse effects in children under 2 years of age 4
- Reports of possible association with apparent life-threatening events or sudden infant death syndrome in very young children 4
Elderly Patients
- Increased sensitivity to anticholinergic effects 5
- Higher risk of sedation and confusion
- Altered drug metabolism with prolonged half-life
- Increased risk of extrapyramidal side effects
Drug Interactions
Enhanced sedation when combined with:
- Alcohol 1
- Sedatives/hypnotics (including barbiturates)
- Narcotics and narcotic analgesics
- General anesthetics
- Tricyclic antidepressants
- Tranquilizers
May interfere with diagnostic pregnancy tests (false-negative or false-positive results) 1
May increase blood glucose levels 1
Interaction with MAOIs causing increased extrapyramidal effects 1
Precautions
Use with caution in patients with:
- Narrow-angle glaucoma 1
- Prostatic hypertrophy
- Stenosing peptic ulcer
- Pyloroduodenal obstruction
- Bladder-neck obstruction
- Cardiovascular disease
- Impaired liver function
Avoid epinephrine for treating hypotension associated with promethazine overdose 1
Avoid prolonged sun exposure due to photosensitivity risk 1
Promethazine should be used only when clearly needed and with careful consideration of its significant side effect profile, particularly in vulnerable populations such as young children and the elderly.