malathion

Malathion is a synthetic phosphorous compound (organophosphate) approved for topical use to kill head lice and also used off-label for pubic lice infestation that is resistant to other treatments.

Malathion solution is applied to the scalp and washed off after several hours. Malathion is an insecticide that has been used to kill insects on farm crops, garden plants, and outdoor spaces, and to kill fleas on pets. Malathion kills all live lice and some of the eggs.

Malathion is a neurotoxin that exerts its action on the nervous system of the head lice by inhibiting cholinesterase, an enzyme that breaks up acetylcholine. Acetylcholine is a chemical (neurotransmitter) that nerve cells (neurons) release to enable muscle contraction, and the breaking up of acetylcholine is an essentially natural process to allow the neuron to return to its normal resting state. Inhibition of cholinesterase results in the accumulation of acetylcholine, which leads to muscle spasms and death of the lice.

Malathion should be used as a part of a whole lice removal program of the patient’s household, including evaluation of all family members for head lice infestation, and treatment, if necessary. All the clothing, hats, bedding, towels, hair care, and other articles used by the patient should be disinfected by washing in hot soapy water.

• Do not use malathion in patients with hypersensitivity to any of its components.
• Do not use malathion on newborns or infants younger than 2 years old. Use on immature baby skin can result in higher systemic absorption and toxicity.
• Safety and efficacy of use in children younger than 6 years of age is not established. Malathion should only be used in children under the direct supervision of an adult.
• There have been reports of chemical burns with the use of malathion, including second-degree burns. Use with caution.
• Keep eyes closed while applying malathion to prevent contact with eyes. In case of accidental contact, flush your eyes with plenty of water. Consult a physician if eye irritation persists or if visual changes occur.
• Wash off the scalp and hair immediately if malathion causes skin irritation. Malathion may be reapplied if irritation clears, but if it reoccurs, wash off and consult a physician if irritation persists.

Common side effects of malathion include:

• Skin and scalp irritation
• Stinging of skin
• Chemical burns, including second-degree burns
• Contact allergic sensitization
• Inflammation of the outer eye membrane (conjunctivitis), in case of accidental contact with the eyes

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

• Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
• Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
• Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
• Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

Topical Lotion

• 0.5%

Adult and Pediatric:

Head Lice (Pediculus humanus capitis):

Children below 6 years

• Safety and efficacy not established

Adults and Children above 6 years

• Apply to dry hair, leave in 8-12 hours
• Allow hair to dry naturally and leave head uncovered
• Shampoo hair and use a fine-toothed comb to remove dead lice and eggs
• May repeat if lice are present after 7-9 days

Adult:

Pubic lice (Pediculosis pubis) Off-label:

• Following treatment failure of pediculicides
• Apply to the affected area
• Wash off after 8 to12 hours

Overdose

• Excessive topical application of malathion may result in overdose from systemic absorption and can cause cholinergic effects including increased sweating, salivary and gastric secretion, gastrointestinal and uterine motility, and slow heart rate (bradycardia). Overdose may be treated with symptomatic and supportive care.
• Overdose from oral ingestion can cause severe respiratory distress requiring artificial respiration. Oral overdose is treated with induced vomiting, gastric lavage with sodium bicarbonate solution, respiratory support, and administration of atropine, if required, to counteract cholinesterase depletion.

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

• Malathion has no known severe, serious, moderate, or mild interactions with other drugs.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider about all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or healthcare provider if you have any questions about the medication.

• Animal reproductive studies do not show evidence of fetal harm with topical use of malathion during pregnancy. Malathion may be used for the treatment of head lice by pregnant women only if clearly needed. Off-label use for pubic lice should be avoided during pregnancy.
• It is not known if topical application of malathion results in sufficient systemic absorption to be excreted in breastmilk. Nursing mothers should use or handle malathion with caution because many drugs are excreted in breastmilk.

• Use malathion exactly as directed. Use only enough to wet hair and scalp thoroughly.
• Malathion is inflammable:
  • Do not smoke, and keep away from flames and electric heat sources while applying malathion or while the hair is wet with the lotion.
  • Do not use an electric hair dryer, keep hair uncovered and allow it to dry naturally.
• Wash hands thoroughly immediately after malathion application.
• Store malathion safely out of reach of children.
• In case of accidental ingestion, seek immediate medical help or contact Poison Control.