Parasiticidal Preparations

Although all parasiticidal preparations have proven to be effective, there is evidence of the development of resistance to some insecticidal preparations, especially in the treatment of head lice. In order to slow this process, treatment failure should be followed by treatment with a different class of insecticide.
All the topical preparations are available over-the-counter.

• Aqueous preparations are preferable to alcoholic preparations for scabies as they are less irritant to excoriated skin and the genitalia.
• For head lice treatment, a 12-hour or overnight treatment with an insecticidal lotion or liquid is recommended, except for permethrin rinse and phenothrin foam application which require a shorter contact time.
• Aqueous head louse preparations are preferred in small children, asthmatic patients and in cases of severe eczema.

Malathion¹

• The risk of systemic effects is considered to be very low but applications of lotion repeated at intervals of less than 1 week or application for more than 3 consecutive weeks should be avoided, especially as the likelihood of eradication of lice is not increased.¹
• Malathion is indicated for scabies, head lice and crab lice. it is ineffective against eggs and so must be reapplied after seven days.
• For scabies, application should be applied to the body and to the scalp, neck, face, and ears.
• Cautions: contact with eyes, broken or secondarily infected skin must be avoided. Do not use lotion more than once a week for 3 consecutive weeks. Alcoholic lotions are not recommended for head lice in severe eczema, asthma or in small children, or for scabies or crab lice.
• Side-effects: skin irritation

Synthetic pyrethroids

• Permethrin:
  • Used to treat both crab lice and scabies, and is effective against both adult lice and eggs Permethrin is active against head lice² but because of the formulation of current products, permethrin creme rinse is classed as less suitable for treating head lice.³
  • Cautions: contact with eyes, broken or secondarily infected skin must be avoided.
  • Side-effects: pruritus, erythema, and stinging.
  • Application should be to the body and also to the scalp, neck, face, and ears.
• Phenothrin:
  • Recommended for head lice and crab lice.
  • Cautions: contact with eyes, broken or secondarily infected skin must be avoided. Should not be used more than once a week for 3 weeks at a time.
  • Side-effects: skin irritation.

Benzyl benzoate (Ascabiol®)

• Classed as less suitable for treating scabies and much less often used than in the past because of skin irritation.
• Application. There are two methods of applying:
  • After a hot bath and drying, apply to body except head and face; second application made within five days of first application.
  • Apply to whole body, except head and face, on three occasions at 12-hourly intervals; hot bath 12 hours after last application.
• Indications: scabies; apply over the whole body; repeat without bathing on the following day and wash off 24 hours later; a third application may be required in some cases.
• Cautions: not recommended in children. Contact with eyes and mucous membranes, and on broken or secondarily infected skin should be avoided. Breast-feeding should be stopped until the benzyl benzoate has been washed off.
• Side-effects: skin irritation and burning sensation, especially on genitalia.

Dimeticone

• Acts as a physical inhibitor by smothering the louse, preventing its ability to excrete surplus water.
• Is effective in treatment of head lice.

Petroleum jelly

• Very effective for treating lice in areas such as the eyelashes.
• Its mechanism is thought to be occlusive and acts by drowning the parasites.

Head combing⁴

• Involves combing of wet hair with a fine-toothed comb every three to four days for two weeks to remove all lice as they hatch.
• In one study comparing wet combing with malathion, the cure rate for bug busting was only 38 per cent as compared to 78 per cent for the drug treatment.
• Head combing should be used in addition to a topical pediculocide, especially when resistance has developed to all the topical agents.

Alternative treatments⁴

• Several alternative treatments such as tea tree oil and aromatherapy oils have been used to treat head lice.
• However there are no formal controlled clinical trials showing their efficacy, potential side-effects or toxicity.

Ivermectin

• This is the only systemic agent of proven efficacy against scabies mites, but is only available from the manufacturer on a named-patient basis.
• A single oral dose has been used, in combination with topical drugs, for the treatment of hyperkeratotic (crusted or 'Norwegian') scabies that does not respond to topical treatment alone.
• It is an effective treatment for scabies in otherwise healthy patients and in many patients with HIV infection.
• Should not be used in pregnancy, breast-feeding mothers or in children under five years or 15kg.⁴