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DESCRIPTION
Minoxidil is a medication used orally for control of hypertension and topically to stimulate hair growth.
FORMS AND USES
- Hypertension. 5 mg orally daily increased to a maximum of 100 mg daily.
- Hair regrowth. 1 ml of 2% solution to dry scalp twice a day.
- Pharmaceutical preparations include minoxidil in 2.5-mg tablets, Loniten in 10-mg tablets, and Rogaine in a 2% solution.
TOXIC DOSE
Experience with overdose is limited. However, the topical solution contains a large amount (2 g/100 ml) of drug, and significant toxicity has been reported.
PATHOPHYSIOLOGY
- Minoxidil is a prodrug that is metabolized by the liver to its active form, causes direct vasodilation, and affects arterioles more than veins.
- Arteriolar vasodilation can result in orthostatic hypotension at therapeutic doses and profound hypotension in overdose.
EPIDEMIOLOGY
- Poisoning is rare.
- Toxic effects are typically mild.
- Death occurs rarely, even in large overdose.
- No reports of death following acute ingestion of minoxidil alone could be found.
CAUSES
- Poisoning occurs usually through accidental ingestion.
- Child neglect should be considered if the patient is less than 1 year of age, suicide attempt if the patient is over 6 years of age.
DRUG AND DISEASE INTERACTIONS
Coingestion of other antihypertensive agents could exacerbate hypotension.
PREGNANCY
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 either animals or women.
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DIFFERENTIAL DIAGNOSIS
- Toxicologic causes of hypotension include beta-receptor or calcium channel blockers, class 1a antidysrythmics, tricyclic antidepressant drugs, monoamine oxidase inhibitors, clonidine, imid-azolines, alpha-methyldopa, nitrates, and alpha-1-receptor blocking agents.
- Nontoxic causes include sepsis, adrenal insufficiency, hypovolemia, and autonomic dysfunction from diabetes or alcohol.
SIGNS AND SYMPTOMS
Vital Signs
Peripheral vasodilatation causes hypotension and reflex tachycardia.
Dermatologic
- Diaphoresis follows acute ingestion.
- Contact dermatitis from minoxidil-containing topical products occurs rarely.
- Hypertrichosis is common during chronic use.
Cardiovascular
- Tachycardia, hypotension, and palpitations may occur.
- Pericardial effusions have been reported with chronic use.
Gastrointestinal
Nausea and vomiting occur with overdose.
Fluids and Electrolytes
Sodium retention has been reported with chronic use.
Neurologic
After a large overdose, lethargy, disorientation, dizziness, slurred speech, and coma may occur.
Reproductive
Breast tenderness and gynecomastia have been reported with chronic use.
PROCEDURES AND LABORATORY TESTS
Essential Tests
No test may be needed for asymptomatic patients.
Recommended Tests
- Serum electrolytes, BUN, creatinine, glucose to evaluate other causes of hypotension
- ECG, serum acetaminophen and aspirin levels in overdose setting to detect occult ingestion
- Adrenocorticotropic hormone stimulation test in patients with suspected adrenal in sufficiency
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- Treatment should focus on hemodynamic monitoring and maintaining blood pressure.
- Dose and time of exposure should be determined for all substances involved.
DIRECTING PATIENT COURSE
The health-care provider should call the poison control center when:
- Hypotension, altered mental status, or other serious effects are present.
- Toxic effects are not consistent with minoxidil poisoning.
- Coingestant, drug interaction, or underlying disease presents an unusual problem.
The patient should be referred to a health-care professional when:
- Attempted suicide or homicide is possible.
- Patient or caregiver seems unreliable.
- Toxic effects develop.
- Coingestant, drug interaction, or underlying disease presents an unusual problem.
Admission Considerations
Inpatient treatment is warranted for patients with hypotension or other clinically significant effects.
DECONTAMINATION
Out of Hospital
Emesis should be induced with ipecac within 1 hour of ingestion for alert pediatric or adult patients if health-care evaluation will be delayed.
In Hospital
- Emesis should be induced with ipecac within 1 hour of ingestion for the patient who is too small to undergo effective gastric lavage.
- Gastric lavage should be performed in pediatric (tube size 24-32 French) or adult (tube size 36-42 French) patients presenting within 1 hour of a large ingestion or if serious effects are present.
- One dose of activated charcoal (1-2 g/kg) is administered if a substantial ingestion has occurred within the previous few hours.
ANTIDOTES
There is no specific antidote for minoxidil poisoning.
ADJUNCTIVE THERAPIES
Hypotension
- Treatment includes infusion and isotonic fluid infusion (10-20 ml/kg) and placement in the Trendelenburg position.
- If needed, a vasopressor is used; dopamine is preferred, and norepinephrine is used for refractory hypotension.
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PATIENT MONITORING
All patients should undergo hemodynamic and cardiac monitoring.
EXPECTED COURSE AND PROGNOSIS
- Hemodynamic effects may last 1 to 2 days following ingestion.
- Possible complications related to prolonged hypotension may occur, although this is rare.
DISCHARGE CRITERIA/INSTRUCTIONS
- From the emergency department. Asymptomatic patients (with orthostatic hypotension) following decontamination, observation for 6 to 10 hours, and, if needed, a psychiatric evaluation.
- From the hospital. The patient may be discharged when: signs of toxicity have resolved, blood pressure has been normal for 12 hours, and the psychiatric evaluation, if needed, is complete.
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TREATMENT
Tachycardia is a compensatory mechanism due to vasodilatation. Therefore, control of heart rate may be detrimental.
FOLLOW-UP
For geriatric patients, lower initial doses and slower increases in daily dose are recommended due to the increased risk of orthostatic hypotension.
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ICD-9-CM 972.6Poisoning by agents primarily affecting the cardiovascular system: other antihypertensive agents.
976.4
See Also: SECTION II, Hypotension chapter.
RECOMMENDED READING
MacMillan AR, Warshawski FG, Steinberg RA. Minoxidil overdose. Chest 1993;103:1290-1291.
McCormick MA, Forman MH, Manoguerra AS. Severe toxicity from ingestion of a topical minoxidil preparation. Am J Emerg Med 1989;7:419-421.
Author: Lada Kokan
Reviewers: Gerald F. O'Malley and Kennon Heard