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Malathion is an organophosphate agent which acts as a pediculicide by inhibiting cholinesterase activity in vivo. Inadvertent transdermal absorption of malathion has occurred from its agricultural use. In such cases, acute toxicity was manifested by excessive cholinergic 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 OVIDE 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.

Clinical Studies

Two controlled clinical trials evaluated the pediculicidal activity of OVIDE 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 OVIDE 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:

Number of Patients Without Live Scalp Lice

Treatment Immediately A fter 24 Hrs. Afte r 7 Days After
OVIDE Lotion 129/129 122/129 114/126
OVIDE Vehicle 105/105 63/105 31/105

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.

Last reviewed on RxList: 12/27/2011
This monograph has been modified to include the generic and brand name in many instances.

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