Malathion

Malathion (roughly "bad sulphur") is a non-systemic insecticide and acaricide known for 6 decades and chemically belongs to the dithiophosphoric acid triesters. It is present as a clear, colourless to slightly yellowish liquid. Malathion is difficult to mix with water and solidifies at about 3°C. The molecular formula of malathion is: C10H19O6PS2.

Malathion is insecticidal through its metabolite malaoxone. It irreversibly binds to acetylcholinesterase, which is thereby inactivated, so that acetylcholine accumulates in the nervous system of the parasites and thus has a neurotoxic effect.

Malathion in pediculosis: Fertilized nits are not killed directly. However, non-hatched larvae are damaged in such a way that they can no longer hatch. In addition, malathion apparently has a residual effect (remains on the hair for several days) and is therefore able to kill lice that get on the head as a result of renewed infestation, or due to inadequate treatment or hatching. In various smaller studies, eradication rates of 97-98% were achieved in pediculosis capitis (Idriss S et al. 2009). Resistances are described. In a large Danish study, resistance rates of 50-100% for head lice have been reported in various populations (Kristensen M et al. 2006). The ovicidal effect of malathion is classified as insufficient.

Malathion in scabies: Malathion has been described in smaller studies as successful in scabies (Thianprasit M et al.1984; Hanna NF et al.1987). However, the studies on the indication scabies do not sufficiently meet the current scientific requirements.

Massage 5 cm of shampoo (short hair, double the amount for longer hair) into damp scalp hair, let it work for 4 to 5 minutes, rinse with lukewarm water, repeat the application immediately in the same way; the procedure should be repeated after 7 days.

Malathion has only a low warm-blooded toxicity. Resorbed malathion is rapidly broken down by humans and other mammals. The organophosphate is highly toxic to fish and other aquatic organisms. The LD 50 of the rat orally is 1200 mg / kg KG, the MAK value is 15 mg / m3 air and the ADI value is 0,02 mg / kg KG / d.

Malathion has an unpleasant inherent odor. Contact allergic reactions are known but rare. In the technical information of a 1% malathion shampoo (Prioderm ®) offered in Switzerland, skin and eye irritation as well as hair loss are mentioned in rare cases.

With the preparation Infectopedicul Malathion®, a generic drug containing malathion for the treatment of head lice and crabs in adults and children aged 2 months and over has been available on prescription since 2012 (1% shampoo).

1. Cabello G et al(2003) Organophosphorous pesticides in breast cancer progression. J Submicrosc Cytol Pathol 35:1-9.
2. Goldust M et al (2014) Comparing the efficacy of oral ivermectin vs. malathion 0.5% lotion for the treatment of scabies. Skinmed 12:284-287.
3. Hanna NF et al (1987) Sarcoptes scabiei infestation treated with malathion liquid. Br J Vener Dis 54:354.
4. Idriss S et al (2009) Malathion for head lice and scabies: treatment and safety considerations. J Drugs Dermatol 8:715-720.
5. Kristensen M et al (2006) Survey of permethrin and malathion resistance in human head lice populations from Denmark. J Med Entomol 43:533-538.
6. Mundipharma (Switzerland): Information on Prioderm. Status Apr et al. 2010
7. Thianprasit M et al (1984) Prioderm lotion in the treatment of scabies. Southeast Asian J Trop Med Public Health 15:119-121.