Malathion is an organophosphate insecticide used in dermatologic preparations worldwide for the treatment of ectoparasites, including Pediculus humanus capitis (human lice infestations of the hair and scalp). Malathion is noted for its use as an aerial insecticide in heavily populated areas to control pests that are damaging to horticulture and to dilute mosquitoe populations. Malathion is widely used in this manner due to relative safety to human, mammal, and bird populations versus other organophosphates or DDT. In medical use for the treatment of head lice, malathion exerts a rapid pediculocidal and niticidal action. This is in contrast to other pediculocides, like pyrethrum and permethrin, which kill hatched lice, but have limited activity against lice ova (nits). There is no evidence that malathion is clinically more effective than commonly available over-the-counter lice remedies; permethrin is often the preferred pediculocide due to its safety record and a >= 90% cure rate when proper use and nit-removal methods are employed. Malathion may be helpful in lice infestation resistant to permethrin or pyrethrins. Resistance to malathion is rare but has been documented in Tasmania and the United Kingdom. Malathion lotion (Ovide(R)) was originally approved by the FDA for the treatment of Pediculosis capitis in 1989. It was removed from the market (because of problems related to prolonged application time, flammability, and odor) and then re-introduced in 1999. Malathion has been available in other countries for several years under various brand names, including Prioderm(R), Derbac(R), and Suleo-M(R). Prioderm(R) is no longer available in Canada.
General Administration Information
For storage information, see the specific product information within the How Supplied section.
NOTE: Malathion is a POISON if ingested systemically. The Ovide topical lotion also contains 78% isopropyl alcohol. Contact your emergency services and poison control center immediately for instructions on poisoning management in the case of accidental exposure to malathion.
Route-Specific Administration
Topical Administration
-Topical use only. Do not ingest internally. Keep away from mucosal surfaces. Avoid contact with the eyes or the ear canal.
-If applying malathion to another person, wear disposable gloves during application to prevent lice infestation.
-Instruct patient on the proper procedures for nit (lice egg) removal (see Patient Information). For proper treatment of pediculosis, nits (eggs) should be removed with a nit comb. Remind patient of proper procedures for hygiene and laundry to prevent reinfestation.
Cream/Ointment/Lotion Formulations:
-Ovide lotion: Instruct patient on the proper use of this medication (see Patient Information). Apply only to the affected areas (i.e., head hair and scalp). Allow hair to dry naturally; hair should remain uncovered. Do not use any electric heat source such as a blow dryer, curling iron or electric curlers. Do not smoke.
Malathion lotion, when applied topically for the treatment of head lice, rarely causes serious adverse events. The most commonly reported side effects are skin irritation, stinging of the scalp, and mild conjunctivitis. Chemical burns including second-degree burns have been reported. Ovide lotion contains a high percentage of isopropyl alcohol that may contribute to skin irritation. If mild skin irritation occurs, discontinue malathion use until the irritation clears. According to the manufacturer, the product may be reapplied once the mild skin irritation clears; if irritation occurs on rechallenge the prescriber should be contacted. Rarely, the topical application of malathion may be associated with contact dermatitis or rash (unspecified). Inadvertent ocular exposure may result in ocular irritation or discomfort (ocular pain). An ophthalmologist should be consulted if ocular discomfort continues after flushing eyes with cool, clean water. Malathion lotion is not tumorigenic or carcinogenic according to laboratory studies.
Malathion lotion, when applied topically for the treatment of head lice, rarely causes serious adverse events. Inhalation of malathion vapors may rarely worsen bronchospasm or wheezing in asthmatic or other susceptible individuals. Severe reactions might involve dyspnea. Malathion is a weaker cholinesterase inhibitor than other organophosphate pesticides, and therefore is considered safer than other agents when used topically as directed. Malathion lotion is not tumorigenic or carcinogenic according to laboratory studies. However, serious side effects of malathion may occur upon accidental or deliberate oral ingestion, which is rare. Symptoms of organophosphate overdose reflect cholinergic excess in both the peripheral and central nervous systems. Severe respiratory distress, including respiratory arrest, is the major and most serious symptom of organophosphate poisoning. Other indications of systemic overdose may include the following organ system symptoms. Respiratory: rhinorrhea, chest tightness and wheezing, dyspnea or respiratory distress. Skin and mucous membranes: increased lacrimation, salivation, and increased sweating. Gastrointestinal: increased gastrointestinal peristalsis, diarrhea or fecal incontinence, abdominal pain or cramps, Urinary: urinary incontinence. Ocular: miosis, loss of ocular accommodation or blurred vision, ocular pain. Cardiovascular: bradycardia, hypotension. CNS: confusion, drowsiness or lethargy, seizures. Musculoskeletal: weakness, muscle paralysis and respiratory paralysis. Antidotes to organophosphate overdose include both atropine and pralidoxime to reverse anti-AChE toxicities at the various muscarinic, nicotinic, and cholinergic receptors.
Malathion is contraindicated for use in individuals known to be sensitive to malathion or any of the ingredients (e.g., terpineol, dipentene, pine needle oil) in the topical application vehicle. Avoid inhalation or ocular exposure with use. Significant inhalation of malathion may aggravate bronchial asthma. Ocular exposure during application should be treated by immediately flushing with cool, clean water. Contact an ophthalmologist if eye irritation persists.
Malathion is a poison if ingested systemically. Keep out of reach of kids and pets. Labels for products containing malathion must contain a 'CAUTION' warning under EPA regulations; dispense in the original manufacturer supplied container. The degree of organophosphate toxicity exhibited after an accidental exposure will be dependent on the dose, formulation, and route of exposure. The Ovide topical lotion also contains 78% isopropyl alcohol. The product is FLAMMABLE and should not be used near heat or flame of any kind, including hair dryers, electric curlers, and tobacco smoking. Contact your emergency services and poison control center immediately for instructions on poisoning management in the case of accidental internal exposure to malathion or other injury.
Malathion is contraindicated for use in infants and neonates because their scalps are more permeable which may lead to increased absorption of malathion. Malathion should only be used on children under the direct supervision of an adult and under the prescription of a qualified health care professional. The safety and efficacy of malathion for the treatment of lice in children less than 6 years of age have not been established; well-controlled clinical trial data are not available.
Malathion lotion is classified as FDA pregnancy category B. Studies of topical malathion application to laboratory animals have not shown evidence of teratogenic or other adverse effects on the fetus. Studies in humans have not been done. Depending on the application vehicle, some malathion may be systemically absorbed. Because studies of medication effects on animal reproduction are not always indicative of human response, malathion should be used in pregnancy only when clearly necessary. In general, unnecessary exposure to organophosphate or other pesticides should be avoided during pregnancy; if the expectant mother must treat another person in the household with malathion, it may be sensible to use good ventilation and wear gloves during application to reduce exposure. When chemical treatment is necessary in the expectant mother, malathion is generally considered a second line agent, with permethrin products generally considered as one of the first-line options for the treatment of lice and other ectoparasites during pregnancy. Piperonyl butoxide/pyrethrins can also be considered; all the pyrethrum insecticides are FDA pregnancy risk category B drugs.
Because many drugs are excreted in human milk, caution should be exercised when this lotion is administered to (or handled by) a mother who is breast-feeding. Malathion in an acetone vehicle has been reported to be absorbed through human skin to the extent of 8% of the applied dose. However, percutaneous absorption from the malathion lotion, 0.5% formulation has not been studied, and it is not known whether malathion is excreted in human milk. If a nursing mother must apply malathion-based head lice treatment to a child, the use of a well-ventilated space and using gloves for application are sensible techniques to limit maternal exposure; however, significant malathion exposure is not likely during the treatment of any one child's head. Alternative agents often recommended for head lice treatment in the mother who is breast-feeding include pyrethrins/piperonyl butoxide and permethrin , which are both considered probably compatible with breast-feeding (see respective monographs).
Per the manufacturer, this drug has been shown to be active against most strains of the following microorganisms either in vitro and/or in clinical infections: Pediculus capitis
NOTE: The safety and effectiveness in treating clinical infections due to organisms with in vitro data only have not been established in adequate and well-controlled clinical trials.
For the treatment of pediculosis including pediculosis capitis and pediculosis pubis*:
NOTE: For the proper treatment of lice, nits (eggs) should be removed with a nit comb. All personal headgear, scarfs, coats, and bed linens should be disinfected by machine washing in hot water and drying using the hot cycle of a dryer for at least 20 minutes. Personal articles that cannot be washed may be dry-cleaned, sealed in a plastic bag for 4 weeks, or sprayed with a product specifically designed for this purpose. Personal combs and brushes may be disinfected by soaking in hot water (above 130 degrees F) for 5 to 10 minutes.
-for the treatment of pediculosis capitis:
Topical dosage:
Adults: Shut the eyes tightly to avoid ocular exposure. Apply to dry hair and scalp. Apply as a single topical application in a sufficient amount (roughly 30 mL) to saturate hair and scalp. Include behind the ears and on the nape of the neck. Wash hands after application. Let hair dry naturally. Leave on hair for 8 to 12 hours but no longer. Then, rinse thoroughly and shampoo with a non-medicated shampoo. After rinsing, use a nit comb to remove the dead lice and the nits (eggs) from the hair. Retreatment is not frequently required. A second treatment may be given if live lice are seen 7 to 9 days or more after the first application. Malathion also has significant activity against permethrin-resistant Pediculus capitis.
Children and Adolescents 6 to 17 years: Shut the eyes tightly to avoid ocular exposure. Apply to dry hair and scalp. Apply as a single topical application in a sufficient amount (roughly 30 mL) to saturate hair and scalp. Include behind the ears and on the nape of the neck. Wash hands after application. Let hair dry naturally. Leave on hair for 8 to 12 hours but no longer. Then, rinse thoroughly and shampoo with a non-medicated shampoo. After rinsing, use a nit comb to remove the dead lice and the nits (eggs) from the hair. Retreatment is not frequently required. A second treatment may be given if live lice are seen 7 to 9 days or more after the first application. Malathion also has significant activity against permethrin-resistant Pediculus capitis.
-for the treatment of pediculosis pubis*:
Topical dosage:
Adults: Apply 0.5% lotion to affected areas and then washed off after 8 to 12 hours as an alternative. Malathion can be used when treatment failure is believed to have resulted from drug resistance.
Maximum Dosage Limits:
-Adults
1 application (roughly 30 ml) topically as directed.
-Elderly
1 application (roughly 30 ml) topically as directed.
-Adolescents
1 application (roughly 30 ml) topically as directed.
-Children
>=6 years: 1 application (roughly 30 ml) topically as directed.
2-5 years: Safety and efficacy have not been established.
< 2 years: Do not use.
-Infants
Do not use.
Patients with Hepatic Impairment Dosing
Specific guidelines for dosage adjustments in hepatic impairment are not available; it appears that no dosage adjustments are needed.
Patients with Renal Impairment Dosing
Specific guidelines for dosage adjustments in renal impairment are not available; it appears that no dosage adjustments are needed.
*non-FDA-approved indication
There are no drug interactions associated with Malathion products.
Malathion is an organophosphate with a broad spectrum of activity when used extensively as an insecticide. Malathion inhibits the hydrolysis of acetylcholine (ACh) by acetylcholinesterase (AChE) at the sites of cholinergic transmission in insects. ACh thus accumulates at receptor sites, resulting in excessive stimulation of cholinergic receptors in the central and peripheral nervous sytem. This leads to rapid insect death. Malathion is rapidly pediculocidal and niticidal. In vitro, a 0.5% solution of malathion kills lice and most of their eggs within 5 minutes. The vehicle base also contains terpenoids which have pediculicide activity.
With topical application to mammals, malathion is not associated with significant cholinergic activity. However, upon oral or pulmonary ingestion in humans, malathion may cause central and peripheral nervous system toxicity typical of other organophosphates. Due to rapid systemic metabolism and detoxification, malathion is usually not as potent as other anti-AChE agents in mammals and birds (see Pharmacokinetics). Symptoms of organophosphate toxicity that may be present on significant oral ingestion of malathion include increased gastrointestinal peristalsis; miosis; loss of ocular accommodation; ocular pain; rhinorrhea; chest tightness and wheezing; increased lacrimation, salivation and sweating; bradycardia; hypotension; confusion; convulsions; weakness; muscular paralysis; and respiratory paralysis. The concomitant use of both atropine and pralidoxime can reverse anti-AChE toxicities at the various muscarinic, nicotinic, and cholinergic receptors.
Malathion is applied topically to the hair and scalp.
The pharmacokinetics of malathion are dependent on the dose and route of the exposure; in humans malathion is effectively absorbed by practically all routes including the gastrointestinal tract, mucous membranes, and the lungs. Malathion must be converted in vivo to malaoxon to become an active anticholinesterase agent. Once ingested, malathion undergoes metabolism similar to other organophosphates. Because it is metabolized more quickly than other organophosphates, malathion exposure is safer for human, mammal, and bird species. In vivo detoxification via hydrolysis of the carboxyl ester linkage by plasma carboxylesterase is much more rapid in mammals and birds than in insects; this helps to limit malathion toxicity in higher life forms. Acute malathion toxicity usually only occurs significant oral ingestions. The lethal dose of malathion in mammals is approximately 1 g/kg. Animal studies have revealed that malathion is excreted in the feces, urine, and upon expiration of air; the reported elimination half-life has ranged from 8 hours to 48 hours in a variety of mammals.
-Route-Specific Pharmacokinetics
Oral Route
Once ingested, malathion undergoes metabolism similar to other organophosphates. Acute malathion toxicity usually only occurs significant oral ingestions. The lethal dose of malathion in mammals is approximately 1 g/kg.
Topical Route
In comparison to other pediculocides (e.g., DDT, lindane, parathion), malathion exhibits lower percutaneous absorption. Preclinical studies of malathion lotion 0.5% were negative for absorption, distribution, metabolism, and excretion. Malathion in an acetone vehicle has been reported to be absorbed through human skin to the extent of 8% of the applied dose. However, percutaneous absorption from the OVIDE (malathion) Lotion 0.5% formulation has not been studied. When malathion 0.5% (Ovide) was used topically as directed in normal human volunteers, no changes in plasma cholinesterase activity were noted. According to available material safety data sheets (MSDS), less than 10% of a topically applied malathion dose is expected to be systemically absorbed. Systemic absorption may be increased if malathion is applied to damaged skin. Most chronic occupational topical exposures to malathion have revealed a low incidence of toxicity. Topical malathion residues typically disappear within a few days to 2 weeks time.