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Malathion Lotion, USP 0.5%
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 is an organophosphate agent which acts as a pediculicide by inhibiting choli-nesterase activity in vivo. Inadvertent transdermal absorption of malathion has occurred from its agricultural use. In such cases, acute toxicity was manifested by excessive cho-linergic activity, i.e., increased sweating, salivary and gastric secretion, gastrointestinal and uterine motility, and bradycardia (see OVERDOSAGE). Because the potential for transdermal absorption of malathion from Malathion Lotion is not known at this time, strict adherence to the dosing instructions regarding its use in children, method of application, duration of exposure, and frequency of application is required.
INDICATIONS AND USAGE
Malathion Lotion is indicated for patients infected with Pediculus humanus capitis (head lice and their ova) of the scalp hair.
Malathion Lotion is contraindicated for neonates and infants because their scalps are more permeable and may have increased absorption of malathion. Malathion Lotion should also not be used on individuals known to be sensitive to malathion or any of the ingredients in the vehicle.
Information to Patients
Carcinogenesis, Mutagenesis, Impairment of Fertility
Although carcinogenesis, mutagenesis, and impairment of fertility have not been studied with Malathion Lotion, malathion has been shown to be genotoxic in a number of in vitro and in vivo mutation and clastogenicity assays. However, there was no evidence of a carcinogenic effect following long-termoral administration of malathion in F344 rats after 2 years feeding with up to 0.4% (∼ 200 - 400 mg/kg/day) nor was it tumorigenic in Osborne - Mendel rats or B6C3F1 mice after similar feeding for 80 weeks with 0.8% (∼ 400 - 600 mg/kg/day) or 1.6% (∼ 1,000 - 2,000 mg/kg/day), respectively. Based on body surface area, doses tested are approximately 4 to 40 fold greater than those anticipated in humans (assuming 100% bioavailability).
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 Category 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.
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.
The safety and effectiveness of Malathion Lotion in children less than 6 years of age has not been established via well-controlled trials.
Malathion has been shown to be irritating to the skin and scalp. Accidental contact with the eyes can result in mild conjunctivitis. It is not known if Malathion Lotion has the potential to cause contact allergic sensitization.
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.
DOSAGE AND ADMINISTRATION
Further treatment is generally not necessary. Other family members should be evaluated by a physician to determine if infested, and if so, receive treatment.
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.
Malathion Lotion, USP 0.5%, is supplied in bottles of 2 fl. oz. (59 mL) NDC 68882-014-60.
Store at controlled room temperature 20° to 25°C (68° to 77°F) [see USP].
Flammable. Keep away from heat and open flame.
Revised: 03/2009 Synerx Pharma, LLC
Reproduced with permission of U.S. National Library of Medicine
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