Malathion

If someone swallows malathion lotion, call your local Poison Control Center or seek emergency medical attention right away.

Contraindications

History of hypersensitivity to malathion or any ingredient in the formulation.1

Infants and neonates.1 (See Pediatric Use under Cautions.)

Warnings/Precautions

Warnings

Commercially available 0.5% lotion is flammable.1

Do not expose malathion 0.5% lotion or hair wet with the lotion to an open flame, lighted cigarette, or electric heat source (e.g., hair dryers, electric curlers).1 After application, leave the hair uncovered and allow to dry naturally.1

Individuals applying the lotion and those with hair wet with the lotion should refrain from smoking.1

Sensitivity Reactions

Potential for malathion 0.5% lotion to cause contact allergic sensitization unknown.1 Dermatitis of the scalp has been reported with topical malathion 5% lotion (10 times the usually recommended dosage).16 Contact dermatitis has been reported in individuals exposed to agricultural formulations of malathion.1 73

May be irritating to the skin and scalp;1 slight stinging sensation may occur after application of malathion 0.5% lotion.1 If skin irritation occurs, immediately remove the lotion by washing scalp and hair.1

After irritation clears, lotion may be reapplied.1 If irritation recurs, consult a clinician.1

General Precautions

Avoid contact with the eyes;1 mild conjunctivitis may occur.1 Do not use for treatment of pediculosis of the eyelashes.69

Eyes should be closed tightly and covered with a soft towel or washcloth while the lotion is applied to or washed off of scalp hair.1

If accidental contact with the eyes occurs, the affected eye(s) should be flushed thoroughly with water.1

Specific Populations

Category B.1

Not known whether malathion is distributed into human milk.1 Malathion was not detected in milk samples (minimum limits of detection <5 mcg/L) from nursing women who resided in geographic areas that received extensive aerial spraying with an agricultural formulation of malathion for insect control.48

Use caution when malathion 0.5% lotion is administered to or handled by a nursing woman.1

Safety and efficacy not established in children <6 years of age.1 Contraindicated in infants and neonates because their scalps are more permeable and increased absorption of malathion may occur.1

Keep out of reach of children; use on children only under the direct supervision of an adult.1

Children should be warned to stay away from lighted cigarettes, open flames, and electric heat sources while their hair is wet with the lotion.1 (See Flammability under Cautions.)

Some clinicians recommend that the malathion preparation commercially available in the US not be used on small children or in children with asthma35 51 to prevent exposure to fumes from the isopropyl alcohol vehicle.35 51

Common Adverse Effects

Irritation of skin and scalp,1 stinging or burning.1 14 62 63 88

• Importance of using only as directed.1

• Advise patients of personal protective measures to avoid reinfestation or transmission of lice.69 66 79 81

• Advise patients that malathion 0.5% lotion is flammable.1 Importance of staying away from open flames, lighted cigarettes, and electric heat sources (e.g., hair dryers, electric curlers) while the hair is wet with the lotion.1 Importance of not smoking while applying the lotion or while hair is wet with the lotion.1

• Importance of thoroughly washing hands after applying malathion 0.5% lotion.1

• Advise patients to avoid contact of malathion 0.5% lotion with the eyes.1 If accidental contact with the eyes occurs, immediately flush the affected eye(s) with water.1 If eye irritation persists or if visual changes occur, consult a clinician.1

• Importance of immediately consulting clinician and/or poison control center if malathion 0.5% lotion is accidentally ingested.1

• Advise patients that a slight stinging sensation may occur when malathion 0.5% lotion is applied.1 If skin irritation occurs, immediately wash lotion from scalp and hair.1 After irritation clears, the lotion can be reapplied.1 If irritation reoccurs, consult a clinician.1

• Importance of informing clinician of existing or contemplated concomitant therapy, including prescription and OTC drugs.1

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.1

• Importance of informing patients of other important precautionary information.1 (See Cautions.)

• Tell all of your health care providers that you take malathion. This includes your doctors, nurses, pharmacists, and dentists.
• This medicine may catch on fire. Do not use near an open flame, while smoking, or near electric heat sources (blow dryer, curling iron). Avoid these heat sources when hair is wet from this medicine.
• Do not give malathion to an infant.
• This medicine may cause harm if swallowed. If this medicine is swallowed, call a doctor or poison control center right away.
• Tell your doctor if you are pregnant or plan on getting pregnant. You will need to talk about the benefits and risks of using malathion while you are pregnant.
• Tell your doctor if you are breast-feeding. You will need to talk about any risks to your baby.

Malathion lotion contains 0.005 g of Malathion per mL in a vehicle of isopropyl alcohol (78%), terpineol, dipentene, and pine needle oil. 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:

Malathion lotion is indicated for patients infected with Pediculus humanus capitis (head lice and their ova) of the scalp hair.

1. Malathion lotion is flammable. The lotion and wet hair should not be exposed to open flames or electric heat sources, including hair dryers and electric curlers. Do not smoke while applying lotion or while hair is wet.
   Allow hair to dry naturally and to remain uncovered after application of Malathion lotion.
2. Malathion lotion should only be used on children under the direct supervision of an adult.
3. If Malathion lotion comes into contact with the eyes, flush immediately with water. Consult a physician if eye irritation persists.
4. If skin irritation occurs, discontinue use of product until irritation clears. Reapply the Malathion lotion, and if irritation reoccurs, consult a physician.
5. Chemical burns including second-degree burns and stinging sensations may occur with the use of Malathion lotion.

General

Keep out of reach of children. Close eyes tightly during product application. If accidentally placed in the eye, flush immediately with water. Use only on scalp hair.

Information to Patients

1. Malathion lotion is flammable. The lotion and hair wet with lotion should not be exposed to open flames or electric heat sources, including hair dryers and electric curlers. Do not smoke while applying lotion or while hair is wet.
   The person applying Malathion lotion should wash hands after application. Allow hair to dry naturally and to remain uncovered after application of Malathion lotion.
2. Malathion lotion should only be used on children under the direct supervision of an adult. Children should be warned to stay away from lighted cigarettes, open flames, and electric heat sources while the hair is wet.
3. In case of accidental ingestion of Malathion lotion by mouth, seek medical attention immediately.
4. If you are pregnant or nursing, you should contact your physician before using Malathion lotion.
5. If Malathion lotion comes into contact with the eyes, flush immediately with water. Consult a physician if eye irritation persists or if visual changes occur.
6. If skin irritation occurs, wash scalp and hair immediately. If the irritation clears, Malathion lotion may be reapplied. If irritation reoccurs, consult a physician.
7. Burns and stinging sensations may occur when using Malathion lotion.
8. Apply Malathion lotion on the scalp hair in an amount just sufficient to thoroughly wet hair and scalp. Pay particular attention to the back of the head and neck when applying Malathion lotion. Anyone applying Malathion lotion should wash hands immediately after the application process is complete.
9. Allow hair to dry naturally and to remain uncovered. Shampoo hair after 8 to 12 hours, again paying attention to the back of the head and neck while shampooing.
10. Rinse hair and use a fine - toothed (nit) comb to remove dead lice and eggs.
11. If lice are still present after 7 - 9 days, repeat with a second application of Malathion lotion.
12. Further treatment is generally not necessary. Other family members should be evaluated by a physician to determine if infested, and if so, receive treatment.

Laboratory Tests

There are no special laboratory tests needed in order to use this medication.

Carcinogenesis, Mutagenesis, and Impairment of Fertility

Carcinogenesis, mutagenesis and impairment of fertility have not been studied with Malathion lotion (0.5% pharmaceutical grade Malathion). However, following long-term oral administration of technical grade Malathion to rodents via dietary supplementation, increased incidences of hepatocellular neoplastic lesions were observed in B6C3F1 mice dosed for 18 months at Malathion doses greater than 1500 mg/kg/day, and in female F344 rats dosed for 2 years at Malathion doses greater than 400 mg/kg/day. These tumors occurred only in association with severe hepatic toxicity and chronic suppression of acetylcholinesterase activity, or at doses causing excessive mortality. Based on body surface area, doses at which carcinogenic effects were observed in rodents following life-time exposures to Malathion were approximately 14- to 26-fold greater than the maximum dose anticipated in a 10 kg child following a single use of Malathion lotion, assuming 100% bioavailability. Actual systemic exposures are expected to be less than 10% of the administered dose.

The Malathion of greater than pharmaceutical-grade purity used in Malathion lotion has not been tested for genotoxicity. The technicalgrade Malathion (95% pure) was found to be negative in Salmonella typhimurium, equivocally positive in the mouse lymphoma cell assay, and positive in in vitro chromosomal aberration and sister chromatid exchange assays. Fifteen separate in vitro gene mutation studies with Malathion of unknown purity have reported negative results, while three studies reported Malathion to be mutagenic in bacterial cells. Both technical grade (94–96.5%) and purified (98-99%) Malathion have been reported to cause chromosomal aberrations and sister chromatid exchanges in vitro in human and hamster cell lines. In vivo chromosomal aberration and micronucleus studies of technical-grade Malathion are reported to be positive, whereas an in vivo chromosomal aberration study of >99% pure Malathion was reported to be negative.

Furthermore, mice exposed to Malathion in their drinking water for 7 weeks demonstrated no evidence of chromosome damage in bone marrow cells, spermatogonia, or primary spermatocytes. Lack of details makes independent evaluation of the results of these assays impossible. Ashby and Purchase have suggested that impurities may be responsible for some of the observed genetic activity of Malathion.

Reproduction studies performed with Malathion in rats at doses over 180 fold greater than those anticipated in a 60 kg adult (based on body surface area and assuming 100% bioavailability) revealed no evidence of impaired fertility.

Pregnancy

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.

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.

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.

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Concerns related to adverse effects:

• Dermatologic effects: Discontinue use temporarily if skin irritation occurs. Chemical burns, including second-degree burns, and stinging sensations may occur with use.

Other warnings/precautions:

• Appropriate use: For topical use on scalp hair only; leave hair uncovered after application (allow hair to dry naturally). Avoid contact with eyes; flush immediately with water if eye contact occurs. Wash hands immediately after application.

• Flammable: Lotion is flammable; do not expose lotion or hair wetted with malathion to open flames or electric heat sources (eg, hair dryer, curling iron, flat iron). Do not smoke while applying lotion or while hair is wet.

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience burning or stinging. Have patient report immediately to prescriber severe scalp irritation or severe skin irritation (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for healthcare professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience and judgment in diagnosing, treating and advising patients.