Molecule

Drug Groups

approved; investigational

Description

A wide spectrum aliphatic organophosphate insecticide widely used for both domestic and commercial agricultural purposes. [PubChem]

Indication

For patients infected with Pediculus humanus capitis (head lice and their ova) of the scalp hair.

Pharmacology

Malathion is an organophosphate insecticide commonly used to control mosquitos and other flying insects. Pharmaceutically, malathion is used to eliminate head lice. The principal toxicological effect of malathion is cholinesterase inhibition, due primarily to malaoxon and to phosphorus thionate impurities.

Toxicity

Malathion is slightly toxic via the oral route, with reported oral LD₅₀ values of 1000 mg/kg to greater than 10,000 mg/kg in the rat. It is also slightly toxic via the dermal route, with reported dermal LD₅₀ values of greater than 4000 mg/kg in rats. Moderate poisoning can result in chest tightness, difficulty breathing, bradycardia, tachycardia, tremor/ataxia, blurred vision, and confusion. Severe, life-threatening signs include coma, seizures, respiratory arrest, and paralysis. Malathion may also be irritating to the skin and eyes.

Affected Organisms

Biotransformation

The major metabolites of malathion are the diacid and monoacid metabolites, namely, malathion dicarboxylic acid (DCA) and malathion monocarboxylic acid (MCA). Malaoxon, the active cholinesterase-inhibiting metabolite of malathion, is a minor metabolite. Both malathion and malaoxon are detoxified by carboxyesterases leading to polar, water-soluble compounds that are excreted.

Absorption

Malathion in an acetone vehicle has been reported to be absorbed through normal human skin only to the extent of 8% of the applied dose. Absorption may be increased when malathion is applied to damaged skin. Malathion is rapidly and effectively absorbed by practically all routes including the gastrointestinal tract, skin, mucous membranes, and lungs. However, it is readily excreted in the urine, and does not accumulate in organs or tissues.

Half Life

8-24 hours

References

External Links