Malathion

Malathion
Adult Indications & Dosage
Pediatric Indications & Dosage
Contraindications
Warnings & Precautions
Adverse Reactions
Drug Interactions
Use in Specific Populations
Administration & Monitoring
Overdosage
Pharmacology
Clinical Studies
How Supplied
Images
Patient Counseling Information
Precautions with Alcohol
Brand Names
Look-Alike Names

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alberto Plate [2]

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Overview

Malathion is an organophosphate that is FDA approved for the treatment of pediculus humanus capitis (Pediculus humanus capitis). Common adverse reactions include application site irritation, skin irritation.

Adult Indications and Dosage

FDA-Labeled Indications and Dosage (Adult)

• (1)Apply Malathion Lotion on dry hair in amount just sufficient to thoroughly wet the hair and scalp. Pay particular attention to the back of the head and neck while applying Malathion lotion. Wash hands after applying to scalp.
• (2)Allow hair to dry naturally - use no electric heat source, and allow hair to remain uncovered.
• (3)After 8 to 12 hours, the hair should be shampooed.
• (4)Rinse and use a fine - toothed (nit) comb to remove dead lice and eggs.
• (5)If lice are still present after 7 - 9 days, repeat with a second application of Malathion Lotion.
• (6)Further treatment is generally not necessary. Other family members should be evaluated by a physician to determine if infested, and if so, receive treatment.

Off-Label Use and Dosage (Adult)

Guideline-Supported Use

Infestation by Phthirus pubis

• Dosage: Malathion 0.5% lotion applied for 8 to 12 hours and washed off

Non–Guideline-Supported Use

Infestation by Phthirus pubis

Pediatric Indications and Dosage

FDA-Labeled Indications and Dosage (Pediatric)

There is limited information regarding Malathion FDA-Labeled Indications and Dosage (Pediatric) in the drug label.

Off-Label Use and Dosage (Pediatric)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Malathion in pediatric patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Malathion in pediatric patients.

Contraindications

There is limited information regarding Malathion Contraindications in the drug label.

Warnings

There is limited information regarding Malathion Warnings' in the drug label.

Adverse Reactions

Clinical Trials Experience

Dermatologic Effects

• Irritation of Skin and Scalp

Ophthalmologic Effects

• Conjuntivitis

Postmarketing Experience

There is limited information regarding Malathion Postmarketing Experience in the drug label.

Drug Interactions

There is limited information regarding Malathion Drug Interactions in the drug label.

Use in Specific Populations

Pregnancy

Pregnancy Category (FDA): B There was no evidence of teratogenicity in studies in rats and rabbits at doses up to 900 mg/kg/day and 100 mg/kg/day malathion, respectively. A study in rats failed to show any gross fetal abnormalities attributable to feeding malathion up to 2,500 ppm (∼ 200 mg/kg/day) in the diet during a three-generation evaluation period.

These doses were approximately 40 to 180 times higher than the dose anticipated in a 60 kg adult (based on body surface area and assuming 100% bioavailability). Because animal reproduction studies are not always predictive of human responses, this drug should be used (or handled) during pregnancy only if clearly needed.
Pregnancy Category (AUS): There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Malathion in women who are pregnant.

Labor and Delivery

There is no FDA guidance on use of Malathion during labor and delivery.

Nursing Mothers

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. Because many drugs are excreted in human milk, caution should be exercised when Malathion Lotion is administered to (or handled by) a nursing mother.

Pediatric Use

The safety and effectiveness of Malathion Lotion in children less than 6 years of age has not been established via well-controlled trials.

Geriatic Use

There is no FDA guidance on the use of Malathion in geriatric settings.

Gender

There is no FDA guidance on the use of Malathion with respect to specific gender populations.

Race

There is no FDA guidance on the use of Malathion with respect to specific racial populations.

Renal Impairment

There is no FDA guidance on the use of Malathion in patients with renal impairment.

Hepatic Impairment

There is no FDA guidance on the use of Malathion in patients with hepatic impairment.

Females of Reproductive Potential and Males

There is no FDA guidance on the use of Malathion in women of reproductive potentials and males.

Immunocompromised Patients

There is no FDA guidance one the use of Malathion in patients who are immunocompromised.

Administration and Monitoring

Administration

There is limited information regarding Malathion Administration in the drug label.

Monitoring

There is limited information regarding Malathion Monitoring in the drug label.

IV Compatibility

There is limited information regarding the compatibility of Malathion and IV administrations.

Overdosage

Consideration should be given, as part of the treatment program, to the high concentration of isopropyl alcohol in the vehicle. Malathion, although a weaker cholinesterase inhibitor than some other organophosphates, may be expected to exhibit the same symptoms of cholinesterase depletion after accidental ingestion orally. If accidentally swallowed, vomiting should be induced promptly or the stomach lavaged with 5% sodium bicarbonate solution. Severe respiratory distress is the major and most serious symptom of organophosphate poisoning requiring artificial respiration, and atropine may be needed to counteract the symptoms of cholinesterase depletion.

Repeat analyses of serum and RBC cholinesterase may assist in establishing the diagnosis and formulating a long-range prognosis.

Pharmacology

Mechanism of Action

Malathion is an organophosphate agent which acts as a pediculicide by inhibiting cholinesterase activity in vivo.

Structure

The chemical name of malathion is (±) - [(dimethoxyphosphinothioyl) - thio] butanedioic acid diethyl ester. Malathion has a molecular weight of 330.36, represented by C10H19O6PS2, and has the following chemical structure:

Pharmacodynamics

There is limited information regarding Malathion Pharmacodynamics in the drug label.

Pharmacokinetics

There is limited information regarding Malathion Pharmacokinetics in the drug label.

Nonclinical Toxicology

There is limited information regarding Malathion Nonclinical Toxicology in the drug label.

Clinical Studies

Two controlled clinical trials evaluated the pediculicidal activity of Malathion Lotion. Patients applied the lotion to the hair and scalp in quantities, up to a maximum of 2 fl. oz., sufficient to thoroughly wet the hair and scalp. The lotion was allowed to air dry and was shampooed with Prell shampoo 8 to 12 hours after application. Patients in both the Malathion Lotion group and in the vehicle group were examined immediately after shampooing, 24 hours after, and 7 days after for the presence of live lice. Results are shown in the following table:

The presence or absence of ova at day 7 was not evaluated in these studies. The presence or absence of live lice or ova at 14 days following treatment was not evaluated in these studies. The residual amount of malathion on hair and scalp is unknown.

How Supplied

Malathion Lotion, USP 0.5%, is supplied in bottles of 2 fl. oz. (59 mL)

Storage

Store at controlled room temperature 20° to 25°C (68° to 77°F)

Images

Drug Images

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Package and Label Display Panel

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Patient Counseling Information

There is limited information regarding Malathion Patient Counseling Information in the drug label.

Precautions with Alcohol

Alcohol-Malathion interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.

Brand Names

• Ovide

Look-Alike Drug Names

There is limited information regarding Malathion Look-Alike Drug Names in the drug label.

Drug Shortage Status

Price

References

The contents of this FDA label are provided by the National Library of Medicine.

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File:Malathion-3D-sticks.png

3D representation of malathion

File:Malathion-3D-vdW.png

Space-filling model of malathion, showing van der Waals radii for each atom

Malathion is an organophosphate parasympathomimetic which binds irreversibly to cholinesterase. Malathion is an insecticide of relatively low human toxicity.

In the former USSR it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion.

Risks

Malathion breaks down into malaoxon, which is 60 times more toxic than malathion. For this reason, if malathion is used in or somehow enters an indoor environment, as it breaks down into malaoxon, it can seriously and chronically poison the occupants living or working in this environment. Malathion present in untreated water is converted to malaoxon during the chlorination phase of water treatment, so malathion should not be used in waters that may be used as a source for drinking water, or any upstream waters.

In 1976, numerous malaria workers in Pakistan were poisoned by isomalathion, a common impurity in malathion, which is capable of inhibiting carboxyesterase enzymes in those exposed to it; the original toxicity evaluation for malathion had not anticipated isomalathion coexposure.

Clinical uses

Malathion is used as a treatment for head lice, body lice and scabies. It effectively kills both the eggs and the adult lice.

Instances of use

In the US, it is the most commonly used organophosphate insecticide.

Malathion was used in the 1980s in California to combat the Mediterranean Fruit Fly. This was accomplished on a wide scale by the near weekly aerial spraying of suburban communities for a period of several months. Formations of three or four agricultural helicopters would overfly suburban portions of San Bernardino county releasing a mixture of malathion and corn syrup, the corn syrup being a bait for the fruit flies. Malathion has also been used to combat the Mediterranean Fruit Fly in Australia.

Malathion was sprayed in many cities to combat West Nile virus. In the Fall of 1999 and the Spring of 2000, Long Island and the five boroughs of New York City were sprayed with malathion. Use of the insecticide has been blamed for large lobster die-off in Long Island Sound.

Manitoba, Province of Canada, ordered the city of Winnipeg, Manitoba to be sprayed in July 2005 as part of the West Nile virus campaign. Prior to this, Malathion was used over the last couple of decades on regular basis during summer months to kill nuisance mosquitos, but homeowners were allowed to exempt their properties if they chose. Today, Winnipeg is the only major city in Canada with an ongoing Malathion nuisance adult mosquito control program.

Malathion is also used in conjunction with diesel to fog an area where there are plenty of mosquitoes. By diluting the mixture, it becomes much weaker. It is possible to dilute the mixture to the point where mosquitoes are not killed, but become more resistant to the mixture, making it less effective in subsequent foggings.

See also

• Pesticide toxicity to bees

External Links

• Malathion Technical Fact Sheet - National Pesticide Information Center
• Malathion General Fact Sheet - National Pesticide Information Center
• Malathion Pesticide Information Profile - Extension Toxicology Network