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Causes
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Circumstances for referral
When correct application of two complete cycles of different insecticides or other treatments has failed to eradicate infection, carbaryl preparations, which are prescription-only medicines (POMs), can be prescribed as fallback treatment.
Treatment
Preparations of three insecticidal compounds are available without prescription to treat head lice infestation.
A non-insecticidal treatment containing dimeticone is also available.
Wet combing is a mechanical method of removing head lice without the use of chemicals.
A head lice repellent, containing piperonal, is also available.
Insecticides
The insecticides (pediculicides) available without prescription for the treatment of head lice are:
malathion permethrin phenothrin.
Malathion
Malathion is an organophosphorus compound.
It is a potent cholinesterase inhibitor that prevents the breakdown of acetylcholine and interferes with neuromuscular transmission in the head louse, paralysing it and preventing it from feeding. It is oil-soluble and absorbed by a process of passive diffusion through the lipid coat of both insect and egg; achieving a lethal dose depends on the concentration of the product and the length of contact.
Malathion is poorly absorbed through human skin, and is much more efficiently detoxified by human metabolic processes than by those of insects.
It is therefore safe for occasional or intermittent use at low concentrations as a pediculicide.
There are no contraindications to the use of malathion apart from known sensitivity.
Permethrin and phenothrin
Permethrin and phenothrin are synthetic pyrethroids with low mammalian toxicity.
They are rapidly absorbed across the insect cuticle and exert their action on the sodium channels of louse nerve axons, causing initial excitement and then paralysis.
Dimeticone
Dimeticone lotion has no conventional insecticide activity. It contains 4% long- chain linear silicone (dimeticone) in a volatile silicone base (cyclomethicone).
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It appears to act against head lice by coating the insects and thus disrupting their ability to breathe and to absorb and excrete water.
Wet combing (‘bug busting’)
Wet combing is an alternative method for tackling the problem of head lice and resistance without the use of insecticides.
The technique involves combing the hair while it is damp, with a fine-tooth comb for about 30 minutes after shampooing and using conditioner. If evidence of lice is found, the process should be repeated twice weekly for 2 weeks to remove lice emerging from eggs before they can spread and reproduce.
Piperonal
Piperonal has no insecticidal activity, but acts as a head lice repellent. Its mechanism of action is unknown, but it is thought to provoke a negative response from the lice antennae receptors, causing them to avoid movement into treated areas.
The main use is to prevent inadvertent reinfestation after treatment with insecticides, before all cases have been traced and the lice eradicated. It is not intended to be used as a routine prophylactic.
Formulations and methods of use
Head lice preparations are available as aqueous and alcoholic lotion, creme rinse and mousse and shampoo formulations.
Malathion is available as aqueous and alcoholic lotions and a shampoo.
Phenothrin is available as an alcoholic lotion, aqueous liquid and a mousse.
Permethrin is available as a creme rinse.
Dimeticone is available as an aqueous lotion.
Use of aqueous liquid preparations
The solution is gently rubbed into the scalp, extending to the neck area and behind the ears, until all the hair and scalp is thoroughly moistened.
The hair should be allowed to dry naturally, and the lotion left on for 12 hours, usually overnight. The hair is then shampooed in the normal way.
While the hair is still wet after shampooing, it should be combed with a fine- tooth comb to remove dead and dying lice from the scalp and empty egg cases attached to the hair shafts.
A second application after 7 days is recommended to kill any lice emerging from eggs that may have survived the initial treatment.
The process is the same for phenothrin mousse, except that it is left on for only half-an-hour after drying before being shampooed off.
Use of alcoholic lotions
Alcoholic lotions are applied in the same way as aqueous lotions. It is important that no heat is applied to dry the hair because the vehicle is flammable. The room should be well ventilated with no naked flames.
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Alcoholic lotions should not be used by asthmatics and young children as the alcohol may precipitate bronchospasm. Neither should they be used by patients with eczema as alcohol may cause inflammation and stinging.
Use of shampoo
Malathion shampoo is much less effective than lotions and not recommended.
It is more concentrated, but:
– it is diluted between 15 and 30 times with water when applied – it has a much shorter time in contact with the hair and scalp – the insecticide may be inactivated by hot water.
To use shampoo, the hair should be thoroughly wetted and sufficient shampoo applied to work up a rich lather and cover the entire scalp and neck area. The shampoo is left on for at least 5 minutes, rinsed off and the process repeated.
The hair is then wet-combed.
The procedure must be carried out three times at 3-day intervals.
Additional advice
When head lice have been found, everyone who has been in close contact with the person in the previous weeks should be examined for lice by wet combing, and treated if necessary.
Only those in whom current infection has been identifi ed should be treated.
Head lice preparations have no lasting prophylactic effect and their unnecessary use encourages resistance to the insecticides.
Ensure that manufacturers’ directions for use of preparations are followed closely. Incorrect use is often the cause of treatment failure.
The mosaic model of treatment should be used to limit the development of resistance: as patients come forward for treatment they are each given a different pediculicide in rotation.
Children with head lice do not need to stay away from school.
Self-assessment
A woman asks your medicines counter assistant for malathion shampoo for head lice. Your standard operating procedure for sales of P medicines instructs staff to refer to the pharmacist all requests for this product, which your assistant does. When you ask the woman why she wants it, she says that she has received a letter from her 6-year-old daughter’s school that some children there have been found to have head lice. She is pretty sure that her daughter does not have them but wants to use the shampoo on all the family to make sure that they do not get them. How do you respond to her request?
Case study
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Multiple choice questions
1. (Closed-book, simple completion)
Which one of the following, used for treatment of head lice infestation, is a POM?
a. carbaryl lotion b. dimeticone lotion c. malathion lotion d. permethrin lotion e. phenothrin creme rinse 2–5.(Open-book, classifi cation)
Questions 2–5 concern the following products licensed for the treatment of head lice:
a. Carylderm liquid b. Hedrin lotion
c. Prioderm cream shampoo d. Quellada M cream shampoo e. Suleo-M lotion
Which of the above:
2. is not prescribable under the NHS?
3. is prescribable under the NHS but is not recommended for prescribing?
4. is a POM?
5. could also be used for the treatment of crab lice infestation?
Head lice
There are no trick questions or traps in the registration examination, but you will need to use problem-solving skills to answer some questions.
Tips
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