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Propiomazine (Systemic)

Primary: CN309

Commonly used brand name(s): Largon.

Note: For a listing of dosage forms and brand names by country availability, see Dosage Forms section(s).

Not commercially available in Canada.





Anesthesia, adjunct—Propiomazine is indicated for the relief of restlessness and apprehension, preoperatively or during surgery {01} {03}.

Analgesia adjunct, during labor—Propiomazine is indicated as an adjunct to analgesics for the relief of restlessness and apprehension during labor {01} {03}.


Physicochemical characteristics:
Molecular weight—

Mechanism of action/Effect:

Unknown. Propiomazine is a phenothiazine compound with sedative action.

Other actions/effects:

Propiomazine also has antiemetic and antihistaminic properties.


Unknown, but probably hepatic as with other phenothiazines.

Time to peak serum concentration

1 to 3 hours following intramuscular administration {03}.

Time to peak effect:

Intramuscular—Within 40 to 60 minutes.

Intravenous—Within 15 to 30 minutes.

Duration of action:

About 3 to 6 hours.

    Unknown, but probably renal and biliary as with other phenothiazines.

Precautions to Consider

Cross-sensitivity and/or related problems

Patients sensitive to other phenothiazines may be sensitive to this medication also.


Problems in humans have not been documented.


Problems in humans have not been documented.


Appropriate studies on the relationship of age to the effects of propiomazine have not been performed in the pediatric population. However, no pediatrics-specific problems have been documented to date.


No information is available on the relationship of age to the effects of propiomazine in geriatric patients.

Drug interactions and/or related problems
The following drug interactions and/or related problems have been selected on the basis of their potential clinical significance (possible mechanism in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):

Note: Combinations containing any of the following medications, depending on the amount present, may also interact with this medication.

» Alcohol or
» Central nervous system (CNS) depression–producing medications, other{05}{06} (See Appendix II )    (concurrent use may increase the CNS depressant effects of either these medications or propiomazine; caution is recommended and dosage of one or both agents should be reduced; dosage adjustments of barbiturates to approximately one-half of the usual dose and narcotic analgesics to approximately one-fourth to one-half of the usual dose are recommended {01} {03})

Epinephrine    (concurrent use with propiomazine may block the alpha-adrenergic effects of epinephrine, allowing beta-adrenergic effects to predominate, thus possibly resulting in severe hypotension {01})

Hypotension-producing medications, other (See Appendix II )    (concurrent use may potentiate the hypotensive effect of propiomazine; dosage adjustments may be necessary)

    (concurrent use of mecamylamine or trimethaphan with propiomazine may potentiate the hypotensive response, with increased risk of severe hypotension, shock, and cardiovascular collapse during surgery)

    (caution is advised during titration of calcium channel blocker dosage for those patients taking medication, such as propiomazine, known to promote hypotension, since the combination may result in excessive hypotension)

Ketamine    (concurrent use of ketamine, especially in high doses or when rapidly administered, with propiomazine may increase the risk of hypotension and/or respiratory depression)

Laboratory value alterations
The following have been selected on the basis of their potential clinical significance (possible effect in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):

With diagnostic test results
Phentolamine    (propiomazine may cause false-positive phentolamine test; it is recommended that all medications be withdrawn at least 24 hours, preferably 48 to 72 hours, prior to a phentolamine test)

Medical considerations/Contraindications
The medical considerations/contraindications included have been selected on the basis of their potential clinical significance (reasons given in parentheses where appropriate)— not necessarily inclusive (» = major clinical significance).

Risk-benefit should be considered when the following medical problem exists
Sensitivity to propiomazine or other phenothiazines

Side/Adverse Effects
The following side/adverse effects have been selected on the basis of their potential clinical significance (possible signs and symptoms in parentheses where appropriate)—not necessarily inclusive:

Those indicating need for medical attention
Thrombophlebitis{01} (redness, swelling, or pain at injection site)
Incidence rare
Neuroleptic malignant syndrome (NMS){03} (difficult or unusually fast breathing; fast or irregular heartbeat or pulse; high fever; high or low [irregular] blood pressure; loss of bladder control; mental changes; severe muscle stiffness; seizures; unusual increase in sweating; unusually pale skin; unusual tiredness or weakness)

Note: NMS has been reported in association with antipsychotic medications; occurrence of NMS does not appear to be related to the dose or the duration of therapy; propiomazine should be discontinued immediately because of possible fatal results {02}

Those indicating need for medical attention only if they continue or are bothersome
Incidence more frequent
drowsiness, prolonged
dryness of mouth{03}

Incidence less frequent
fast heartbeat{03}
nausea or vomiting
shortness of breath or troubled breathing
skin rash
stomach pain

Patient Consultation
As an aid to patient consultation, refer to Advice for the Patient, Propiomazine (Systemic).

In providing consultation, consider emphasizing the following selected information (» = major clinical significance):

Before receiving this medication
»   Conditions affecting use, especially:
Sensitivity to propiomazine or other phenothiazines
Other medications, especially alcohol or other CNS depression–producing medications

Proper use of this medication

» Proper dosing

Precautions after receiving this medication
» Possibility of psychomotor impairment following use of propiomazine; using caution in driving or performing other tasks requiring alertness and coordination {03} until the effects of propiomazine have subsided or until the day after receiving propiomazine, whichever is longer

» Avoiding use of alcohol or other CNS depressants within 24 hours after receiving propiomazine except as directed by physician or dentist

Side/adverse effects
Signs of potential side effects, especially thrombophlebitis and neuroleptic malignant syndrome (NMS)

General Dosing Information
Intra-arterial injection is not recommended because of chemical irritation, which may be severe enough to cause arteriospasm, possibly resulting in local impairment of circulation {01} {03}.

Intravenous injections should be made only into undamaged veins since propiomazine may cause irritation, possibly resulting in thrombophlebitis {01} {03}.

Intravenous injections should be administered slowly, as too rapid administration may produce a transient fall in blood pressure.

Care should be used to avoid perivascular extravasation since chemical irritation may be severe {01} {03}.

For treatment of adverse effects

Neuroleptic malignant syndrome (NMS):
Treatment is essentially symptomatic and supportive {03} and may include the following {02}

   • Discontinuing propiomazine immediately {03}.
   • Hyperthermia—Administering antipyretics (aspirin or acetaminophen); using cooling blanket.
   • Dehydration—Restoring fluids and electrolytes.
   • Cardiovascular instability—Monitoring blood pressure and cardiac rhythm closely. Use of sodium nitroprusside may allow vasodilation with subsequent heat loss from the skin in patients with less dominant muscle rigidity.
   • Hypoxia—Administering oxygen; intubation and mechanical ventilation may be necessary.
   • Muscle rigidity—Administering dantrolene sodium (100 to 300 mg per day in divided doses; 1.25 to 1.5 mg per kg of body weight [mg/kg], intravenously); or administering amantadine 100 mg twice daily, or bromocriptine, 5 mg three times a day, to restore central balance of dopamine and acetylcholine at the receptor site.

Parenteral Dosage Forms


Usual adult dose
Intramuscular or intravenous, 20 to 40 mg administered in conjunction with 50 mg of meperidine {01} {03}.

Sedation during surgery with local, nerve block, or spinal anesthesia
Intramuscular or intravenous, 10 to 20 mg {01} {03}.

Analgesia adjunct, during labor
Intramuscular or intravenous, 20 to 40 mg in the early stages of labor, then 20 to 40 mg of propiomazine administered in conjunction with 25 to 75 mg of meperidine when labor is definitely established. Doses may be repeated every three hours, if necessary. {01} {03}

Usual pediatric dose
Sedation prior to surgery; preanesthetic; or postoperative
Children up to 27 kg: Intramuscular or intravenous, 550 mcg (0.55 mg) to 1.1 mg per kg of body weight {01} {03}; or for

Children 2 to 4 years of age: Intramuscular or intravenous, 10 mg {01} {03}.

Children 4 to 6 years of age: Intramuscular or intravenous, 15 mg {01} {03}.

Children 6 to 12 years of age: Intramuscular or intravenous, 25 mg {01} {03}.

Strength(s) usually available

20 mg per mL (Rx) [Largon (sodium acetate) (sodium formaldehyde sulfoxylate not more than 1 mg)]
Not commercially available.

Packaging and storage:
Store between 15 and 30 °C (59 and 86 °F). Protect from light.

Do not use the injection if it is cloudy or contains a precipitate {01} {03}.

Aqueous solutions of propiomazine are incompatible with barbiturate salts and other alkaline substances {04}.

Revised: 07/26/1994

  1. Largon (Wyeth) PI, Rev 12/22/87, Rec 6/7/88.
  1. Phenothiazines (Sys) monograph, USP DI 1988.
  1. Largon (Wyeth) package insert, Rev 1/9/90, Rec 4/6/90.
  1. Trissel LA. Handbook on injectable drugs. 5th ed., 1988: 615-6.
  1. Tatro DS, ed. Drug interaction facts. St Louis: Facts and Comparisons, 1990: 489.
  1. Shinn AF, Shrewsbury RP. EDI, Evaluation of drug interactions. 3rd ed. St Louis: Mosby, 1985: 43.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.