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Promethazine and Phenylephrine (Promethazine Hydrochloride / Phenylephrine Hydrochloride) - Drug Interactions, Contraindications, Overdosage, etc

 
 



DRUG INTERACTIONS

Promethazine

CNS Depressants Promethazine may increase, prolong, or intensify the sedative action of other central-nervous-system depressants, such as alcohol, sedatives/hypnotics (including barbiturates), narcotics, narcotic analgesics, general anesthetics, tricyclic antidepressants, and tranquilizers; therefore, such agents should be avoided or administered in reduced dosage to patients receiving promethazine HCl. When given concomitantly with promethazine, the dose of barbiturates should be reduced by at least one-half, and the dose of narcotics should be reduced by one-quarter to one-half. Dosage must be individualized. Excessive amounts of promethazine HCl relative to a narcotic may lead to restlessness and motor hyperactivity in the patient with pain; these symptoms usually disappear with adequate control of the pain.

Epinephrine Because of the potential for promethazine to reverse epinephrine’s vasopressor effect, epinephrine should NOT be used to treat hypotension associated with promethazine overdose.

Anticholinergics Concomitant use of other agents with anticholinergic properties should be undertaken with caution.

Monoamine oxidase inhibitors (MAOI) Drug interactions, including an increased incidence of extrapyramidal effects, have been reported when some MAOI and phenothiazines are used concomitantly.

Phenylephrine
Drug
Phenylephrine with prior administration of monoamine oxidase inhibitors (MAOI).
Effect
Cardiac pressor response potentiated.

May cause acute hypertensive crisis.

Drug

Phenylephrine with tricyclic antidepressants.

Effect

Pressor response increased.

Drug
Phenylephrine with ergot alkaloids.

Effect
Excessive rise in blood pressure.

Drug
Phenylephrine with bronchodilator sympathomimetic agents and with epinephrine or other sympathomimetics.
Effect
Tachycardia or other arrhythmias may occur.

Drug

Phenylephrine with atropine sulfate.

Effect
Reflex bradycardia blocked; pressor response enhanced.

Drug

Phenylephrine with prior administration of propranolol or other ß-adrenergic blockers.

Effect
Cardiostimulating effects blocked.

Drug

Phenylephrine with prior administration of phentolamine or other α-adrenergic blockers.

Effect

Pressor response decreased.

Drug

Phenylephrine with diet preparations, such as amphetamines or phenylpropanolamine.

Effect

Synergistic adrenergic response.

OVERDOSAGE

Promethazine:

Signs and symptoms of overdosage with promethazine HCl range from mild depression of the central nervous system and cardiovascular system to profound hypotension,

respiratory depression, unconsciousness, and sudden death. Other reported reactions include hyperreflexia, hypertonia, ataxia, athetosis, and extensor-plantar reflexes (Babinski reflex).

Stimulation may be evident, especially in children and geriatric patients. Convulsions may rarely occur. A paradoxical reaction has been reported in children receiving single doses of 75 mg to 125 mg orally, characterized by hyperexcitability and nightmares.

Atropine-like signs and symptoms - dry mouth, fixed dilated pupils, flushing, as well as gastrointestinal symptoms, may occur.

Phenylephrine:

Signs and symptoms of overdosage with phenylephrine include hypertension, headache, convulsions, cerebral hemorrhage, and vomiting. Ventricular premature beats and short paroxysms of ventricular tachycardia may also occur. Headache may be a symptom of hypertension. Bradycardia may also be seen early in phenylephrine overdosage through stimulation of baroreceptors.

Treatment:

The treatment of overdosage with promethazine and phenylephrine is essentially symptomatic and supportive. Only in cases of extreme overdosage or individual sensitivity do vital signs including respiration, pulse, blood pressure, temperature, and EKG need to be monitored. Activated charcoal orally or by lavage may be given, or sodium or magnesium sulfate orally as a cathartic. Attention should be given to the reestablishment of adequate respiratory exchange through provision of a patent airway and institution of assisted or controlled ventilation. Diazepam may be used to control convulsions. Acidosis and electrolyte losses should be corrected. Note that any depressant effects of promethazine are not reversed by naloxone. Avoid analeptics which may cause convulsions.

Severe hypotension usually responds to the administration of norepinephrine or phenylephrine. EPINEPHRINE SHOULD NOT BE USED, since its use in a patient with partial adrenergic blockade may further lower the blood pressure.

Limited experience with dialysis indicates that it is not helpful.

CONTRAINDICATIONS

Promethazine is contraindicated in comatose states, and in individuals known to be hypersensitive or to have had an idiosyncratic reaction to promethazine or to other phenothiazines.

Antihistamines are contraindicated for use in the treatment of lower respiratory tract symptoms, including asthma.

Phenylephrine is contraindicated in patients with hypertension or with peripheral vascular insufficiency (ischemia may result with risk of gangrene or thrombosis of compromised vascular beds). Phenylephrine should not be used in patients known to be hypersensitive to the drug or in those receiving a monoamine oxidase inhibitor (MAOI).

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