Trying to Keep Ahead of Lice: A Therapeutic Challenge

C. E. Malcolm, MD, CCFP; J. N. Bergman MD, FRCPC


Skin Therapy Letter. 2006;11(10):1-6. 

In This Article

Treatment Failures

While treatment failures may be due to drug resistance, it is important to recognize many treatment failures are a result of reinfestation from an untreated classmate, inadequate quantity of pediculicide applied, or improper duration of product application.4 A recent paper suggested that a second treatment of the prescribed standard pediculicides (except permethrin) should be administered ideally 10 days after the start of treatment to kill all active stages of the louse.[9] However, in practice many physicians retreat in 7 days instead of 10. Resistance should be suspected after the second treatment if live lice are still present 2-3 days after a product has been used correctly and no other cause for failure can be identified.1 If lice are present after 2 correctly applied treatments, resistance is certain.[1] Resistant infestations should be treated with an agent from a different class of pediculicides or with newer nonpediculicide agents.

Since permethrin resistance may be a relative phenomenon, some clinicians will use higher concentrations and longer durations of contact in an attempt to overcome this resistance. Whether increasing the permethrin concentration from 1% to 5% and leaving it on overnight affects the cure rate is unclear. Certainly this pattern of treatment may cause a higher rate of skin irritation, but longer contact with the same products is already used with other ectoparasites, such as scabies.

'No nit´ policies exclude children from school unnecessarily and are not recommended.[4] The presence of nits alone should not be the basis for exclusion of children from school. The child should be allowed to return to school or child care facilities after proper treatment.[5]


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as: