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malathion (ma-la-thye-on)



Therapeutic: pediculocides

Pharmacologic: acetylcholinesterase inhibitor


Treatment of head lice and their eggs (Pediculus humanus capitus).


Acts as a cholinesterase inhibitor, causing death of lice and their eggs. Therapeutic Effects: Eradication of head lice and their eggs.

Adverse Reactions/Side Effects

EENT: ocular irritation (with accidental eye exposure). Derm: scalp irritation.


Examination and Evaluation

  • Monitor the scalp for local irritation or inflammation. Report severe or prolonged scalp reactions to the physician.


  • Avoid touching the affected area. Use care to wash hands thoroughly, change pillowcases, and disinfect equipment (whirlpools, electrotherapeutic devices, treatment tables, and so forth) to help prevent the spread of head lice.

Patient/Client-Related Instruction

  • Check that the patient and family or caregivers understand topical application procedures and adhere to the recommended dosing schedule.

  • Caution patient and family/caregivers about avoiding accidental contact with the eyes. If this occurs, eyes should be flushed thoroughly with water. Health care professional should be contacted if eye irritation persists.

  • Instruct patient about proper hygiene; e.g., do not share combs or hair brushes, thoroughly wash hats or clothing that may be infested, and so forth.


Absorption: Minimal absorption (<10%) with topical application.

Distribution: Binds to hair shaft, which may protect against reinfestation.

Metabolism and Excretion: Metabolized to malaoxon and excreted.

Half-life: 8 hr.

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TIME/ACTION PROFILE (pediculicidal effect)

Topical 6 hr 12 hr persists after application*

*Due to binding to hair shaft.


Contraindicated in: Hypersensitivity; Known alcohol intolerance.

Use Cautiously in: Pregnancy (use only if needed); lactation (use cautiously, safety not established); children <2 yr (safety not established).


Drug-Drug: These interactions would only occur if large amounts of malathion were absorbed. Additive toxicity may occur with carbamate or organophosphate-type insecticides/pesticides. May cause additive respiratory depression with parenteral aminoglycosides. ↑ risk of systemic toxicity with ester-type local anesthetics, antimyasthenics, or cholinesterase inhibitors (including ophthalmics). May alter the response to edrophonium in patients with myasthenic weakness.


Topical (Adults and Children ≥2 yr): Apply lotion to dry hair and rub until scalp is moistened; follow 8–12 hr later with nonmedicated shampoo; additional application may be required after 7–9 days.


Lotion: 0.5% in 59-mL bottles (contains 78% isopropyl alcohol, terpineol, dipentene, ...

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