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DESCRIPTION
Trimethobenzamide (Tigan) is an antiemetic medication.
FORMS AND USES
The usual dosage is 250 mg orally three times a day or 200 mg intramuscularly or by rectum every 6 to 8 hours.
TOXIC DOSE
Toxic dose is poorly characterized; very large doses would have to be ingested to induce toxicity.
PATHOPHYSIOLOGY
- Trimethobenzamide is a nonphenothiazine antiemetic that directly depresses the chemoreceptor trigger zone.
- Toxic effects arise primarily from anticholinergic action; however, in some cases, alpha-receptor blockade is apparent (e.g., miosis).
EPIDEMIOLOGY
Poisoning is uncommon and toxic effects are typically mild.
CAUSES
- Poisoning is usually suicidal.
- Child abuse or neglect should be considered in patients less than 1 year of age; suicide attempt in patients over 6 years of age.
PREGNANCY AND LACTATION
US FDA Pregnancy Category C. The drug exerts animal teratogenic or embryocidal effects, but there are no controlled studies in women, or no studies are available in animals or women.
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DIFFERENTIAL DIAGNOSIS
Toxic causes of anticholinergic effects include atropine, scopolamine, or antihistamines.
SIGNS AND SYMPTOMS
Acute overdose primarily produces anticholinergic symptoms.
Vital Signs
Tachycardia, hyperthermia, and either hypertension or hypotension can occur.
HEENT
- Dry mouth and dysphagia have been reported.
- Mydriasis is most common, but miosis also may occur.
Cardiovascular
- Hypotension can occur due to vasodilation.
- Quinidine-like effects may result in myocardial depression and ventricular dysrhythmia in massive overdose.
Pulmonary
Respiratory depression can occur due to muscle weakness.
Gastrointestinal
Vomiting can occur with overdose.
Hepatic
Hepatitis has been reported.
Musculoskeletal
- Dystonic reactions may occur.
- In large overdoses muscle paralysis may occur.
Neurologic
- Somnolence progressing to coma occurs with overdose.
- Tremors, hallucinations, and seizures also have been reported.
PROCEDURES AND LABORATORY TESTS
Essential Tests
No tests may be needed in asymptomatic patients.
Recommended Tests
- Serum electrolytes, BUN, creatinine, glucose, and other studies may be needed to evaluate other causes of altered mental status.
- Pulse oximetry or arterial blood gases are performed to evaluate oxygenation in symptomatic patients.
- ECG is used to evaluate for widened QRS complex interval.
- Serum acetaminophen and aspirin levels are obtained in an overdose setting to detect occult ingestion.
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- Supportive care is the mainstay of therapy.
- Dose and time of exposure should be determined for all substances involved.
DIRECTING PATIENT COURSE
The health-care professional should call the poison control center when:
- Severe or persistent effects develop.
- Coingestant, drug interaction, or underlying disease presents an unusual problem.
The patient should be referred to a health-care facility when:
- Suicide or homicide attempt is possible.
- Toxic effects develop.
- Coingestant, drug interaction, or underlying disease presents an unusual problem.
Admission Considerations
Extended observation or hospital admission is rarely needed, but would be appropriate for CNS depression or cardiovascular effects.
DECONTAMINATION
Out of Hospital
Induction of emesis is not recommended.
In Hospital
- Gastric lavage should be performed in pediatric (tube size 24-32 French) or adult (tube size 36-42 French) patients presenting within 1hour of a large ingestion or if serious effects are present.
- One dose of activated charcoal (1-2 g/kg) should be administered without a cathartic if a substantial ingestion has occurred within the previous few hours.
ANTIDOTES
There is no specific antidote available for trimethobenzamide poisoning.
ADJUNCTIVE TREATMENT
Seizures
- Patent airway must be maintained.
- A benzodiazepine should be administered for initial control.
- If seizures persist or recur, another anticonvulsant such as phenobarbital can be added.
Dystonic Reactions
- These should be treated with diphenhydramine 25 to 50 mg intravenously, intramuscularly, or orally, every 6 hours.
- Patients should have oral treatment continued for 3 to 5 days to prevent recurrence.
Hypotension
- Atropine can be used to correct hypotension related to bradycardia.
- Patient should receive 10 to 20 ml/kg 0.9% saline intravenously and be placed in the Trendelenburg position.
- Further fluid therapy should be guided by central pressure monitoring to avoid volume overload.
- Vasopressor may be added if needed.
- Dopamine. 2 to 5 µg/kg/min should be infused intravenously and titrated upward to effect.
- Rates above 20 µg/kg/min is unlikely to offer additional benefit.
- If pressure is unresponsive, norepinephrine (0.1-0.2 µg/kg/min) may be added and titrated upward to effect.
- High infusion rates may cause tissue ischemia.
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PATIENT MONITORING
Patients with symptoms should be placed on a cardiac monitor, given oxygen, and have intravenous access established.
EXPECTED COURSE AND PROGNOSIS
Anticholinergic effects peak within hours, but may require 24 hours or more for resolution.
DISCHARGE CRITERIA/INSTRUCTIONS
- From emergency department. Asymptomatic patients with normal vital signs can be discharged after decontamination, 4 to 6 hours of observation, and psychiatric evaluation, if needed.
- From hospital. Patients may be discharged when capable of caring for themselves and following psychiatric evaluation, if needed.
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TREATMENTFailure to treat dystonic reactions for 3 to 5 days may allow recurrence.
ICD-9-CM 973Poisoning by agents primarily affecting the gastrointestinal system.
See Also: SECTION II, Hypotension and Seizures chapters.
RECOMMENDED READING
POISINDEX editorial staff. Trimethobenzamide. In: Rumack BH, Sayre NK, Gelman CR, eds. POISINDEX system. Englewood, CO: Micromedex, Inc. (edition expires May 31, 1998).
Author: Kennon Heard
Reviewer: Richard C. Dart