Monograph: |
Malathion
Indications: Lice, head
DESCRIPTION:
Malathion lotion is a liquid for topical application to the hair and scalp as a lousicide and ovicide. Each mL contains 0.005 mg of malathion in a vehicle of isopropyl alcohol (78%), terpineol, dipentene and pine needle oil.
Malathion insecticide, has a molecular weight of 330.36 represented by C10H19O6PS2.
CLINICAL PHARMACOLOGY:
Malathion is lousicidal and ovicidal in vitro .
Louse eggs succumb to 3 seconds of exposure to 0.062% malathion in acetone and lice to about 0.003% respectively. Resistance to malathion could not be induced.
Human safety studies included a 21-day cumulative irritancy and others undertaken to determine the potential for contact sensitization, phototoxicity, and photo-contact sensitization.
Application of malathion lotion showed no evidence of sensitization and a very low level of irritation.
INDICATIONS AND USAGE:
Malathion lotion is indicated for the treatment of head lice and their ova.
CONTRAINDICATIONS:
Malathion lotion should not be used by individuals with known sensitivity to malathion lotion or to any of its components.
WARNINGS:
This product is flammable and open flames or hair dryers should be avoided to allow the hair to dry naturally and uncovered.
PRECAUTIONS:
If accidentally placed in the eye, flush immediately with water.
Carcinogenesis, Mutagenesis, and Impairment of Fertility: Malathion is neither carcinogenic in male or female F344 rats after 2 years feeding with up to 4000 ppm (0.4%) nor is it tumorigenic in Osborn-Mendel rats or B6C3F1 mice after a similar feeding for 80 weeks with 8,000 ppm (0.8%) and 16,000 ppm (1.6%) respectively. Tests for mutagenicity have not been conducted.
Pregnancy Category B: There was no evidence of teratogenicity in studies utilizing single ip.
injections of malathion at 600 and 900 mg/kg in pregnant rats or oral dosing with up to 300 mg/kg on days 6 through 15 of gestation. A reproduction study in rats failed to show any gross fetal abnormalities attributable to feeding malathion up to 2,500 ppm in the diet during a three-generation evaluation period. These studies employed at least 50-70 times the adult human topical dose.
Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Nursing Mothers: Malathion in an acetone vehicle has been reported to be absorbed through human skin only to the extent of 8% of the applied dose. However, percutaneous absorption from the malathion lotion formulation has not been studied and it is not known whether malathion is excreted in human milk. Caution should be exercised when malathion lotion is administered to the nursing mother.
ADVERSE REACTIONS:
Irritation of the scalp has been reported.
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 and therefore safer than other organophosphates, may be expected to exhibit the same symptoms of cholinesterase depletion after accidental ingestion orally. 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 large doses of im or iv atropine. The usual starting dose of atropine is 1-4 mg with supplementation hourly as needed to counteract the symptoms of cholinesterase depletion. Repeat analyses of serum and RBC cholinesterase assist in establishing the diagnosis and formulating a long-range prognosis.
DOSAGE AND ADMINISTRATION:
1. Sprinkle malathion lotion on DRY hair and rub gently until the scalp is thoroughly moistened. Pay special attention to the back of the head and neck.
2. Allow to dry naturally--use no heat and leave uncovered.
3. After 8-12 hours, the hair should be washed with a non-medicated shampoo.
4. Rinse and use a fine-toothed comb to remove dead lice and eggs.
5. If required, repeat with second application of malathion lotion in 7 to 9 days.
Further treatment is generally not necessary.
Other family members should be evaluated to determine if infested and if so, receive treatment.
|