Side effects and interactions of promethazine with other substances
Promethazine is a phenothiazine derivative. Promethazine competitively blocks histamine H1-receptors, has anti-allergic, anti-exudative, local anesthetic, anti-inflammatory, adrenolytic, central and peripheral cholinolytic effects. Promethazine reduces swelling of mucous membranes, capillary permeability, itching. Anticholinergic effect causes drying effect on mucous membranes of oral and nasal cavities. It depresses central nervous system, lowers body temperature, has anxiolytic, sedative, hypnotic, antipsychotic effect.
Side effects of promethazine
Nervous system and sensory organs: Dizziness, sedation, drowsiness, agitation, restlessness, nightmares, disorientation, fatigue, lethargy, movement coordination disorders, headache, increased nighttime apnea, confusion, increased seizure activity, seizures, tinnitus, nervousness, euphoria, insomnia, catatonic status, oculogyric crisis, hysteria, psychomotor agitation, extrapyramidal disorders, tinnitus or ringing in the ears, nystagmus, accommodation and visual disturbances, visual acuity disorders.
Cardiovascular system and blood: hypertension, orthostatic hypotension, bradycardia, tachycardia, palpitation, syncope, arrhythmias, thrombocytopenia, leukopenia, agranulocytosis, aplastic anemia, thrombocytopenic purpura.
Digestive system: dryness and anesthesia in the mouth, nausea, cholestasis, vomiting, constipation, diarrhea, jaundice.
Respiratory system: dryness in the pharynx, nose, irregular breathing.
Genitourinary system: painful or difficult urination, urinary retention.
Allergic reactions: dermatitis, urticaria, asthma, bronchospasm, exanthema, angioedema, anaphylactic reactions.
Other: photosensitization, increased sweating, pain and infiltrates (when parenteral administration).
Interaction of promethazine with other substances
Prometazine attenuates the effect of m-cholinomimetics, amphetamine derivatives, anticholines, guanethidine, ephedrine, dopamine, levodopa.
Promethazine enhances the effects of sleeping pills, analgesics, neuroleptics, tranquilizers, anesthetics, m-cholinoblockers, local anesthetics, hypotensive drugs (correction of doses is necessary).
Beta-adrenoblockers mutually increase the plasma concentration of promethazine (irreversible retinopathy, arrhythmias, severe hypotension, tardive dyskinesia are possible).
Barbiturates accelerate excretion and reduce promethazine activity.
Promethazine increases serum prolactin content and attenuates the effect of bromocriptine.
Anticholinergic drugs and tricyclic antidepressants increase m-cholin-blocking activity of promethazine, clopheline, ethyl alcohol, antiepileptic drugs increase central nervous system suppression by promethazine.
Quinidine increases the likelihood of cardiodepressive effects of promethazine.
Monoamine oxidase inhibitors (contraindicated simultaneous use) and phenothiazine derivatives increase the risk of extrapyramidal disorders and hypotension.