Ask About Additional Symptoms. The patient affected with lice may scratch vigorously to remove them. The pharmacist may notice open sores on the head where the fingernails have penetrated the skin. If they become secondarily infected with staph and/or strep, they are said to have undergone "impetiginization." These lesions may be more or less parallel in arrangement, caused by simultaneous penetration from several scratching fingernails, a phenomenon known as "railroad tracking." Occasionally, a patient is so heavily infested with head lice that systemic symptoms occur. They include enlarged posterior cervical lymph nodes, fever, anorexia, enervation, and malaise. These patients should be referred to a physician to evaluate the need for an antibiotic/antibacterial prescription.

PESTICIDE TREATMENT OF HEAD LOUSE INFESTATION
Treatment of head lice has changed radically in the last decade, as we have gradually turned away from the pesticides known as pediculicides. At that time, a trade named lindane product (Kwell) was widely recommended, a prescription product containing malathion (Ovide) was available, and the nonprescription armamentarium which contained only synergized pyrethrins had recently been expanded with the Rx-to-OTC switch of the pesticide known as permethrin (Nix). Things looked rosy for elimination of this ancient human predator. Unfortunately, the bright promise of these treatments soured in the 90s as the topical pesticides began to lose their luster. What is the current status of the pesticides?

Lindane. Lindane is a cyclodiene pesticide which is also the most toxic pediculicide available(6). It kills very slowly; as the lice die they twitch on the scalp, producing an uncomfortable sensation for the patient.

Lindane has several other attributes that argue against its use. It does not kill all ova (its ovicidal activity is only 45-70 percent), allowing viable ova to survive and prolonging the infestation. Its widespread use has allowed resistance to develop(4,7).

Lindane also carries the risk of human toxicity. Its primary deposition occurs in the brain's white matter(8). Severe adverse reactions have been reported, including seizures, which may occur as uncontrolled motor activity lasting for 48 hours or longer(7,8). The risk of this is enhanced when the patient bathes before treatment, has dermatitis, or excessively thin skin. Aplastic anemia and renal disorders also may occur(7).

Kwell was a major trade name for lindane for many years, but it has been discontinued. However, generic lindane products are still available. The pharmacist dispensing the product should wear gloves while pouring it to prevent unintended contact. Patients should be warned not to use more than two ounces of lindane shampoo per application and to wear gloves while using the shampoo. Since oils enhance absorption, the patient must avoid application of any oil to the hair for several days prior to lindane use. The lather must not touch any areas other than the hair. Lindane should only be reapplied if the physician has advised the patient to do so, and it must not touch broken skin.

I was the pharmacist expert at a roundtable on lice treatment in Boston several years ago. One of the attendees was a structural pest eradication specialist. He reacted in astonishment as I described the dangers of using lindane in humans. When his turn came to speak, he stressed that lindane has been prohibited in structural use for many years due to toxicity. This should cause the pharmacist to question further any application to humans.

Although many of the adverse reactions from lindane were a result of misuse, it is prudent to take great care with a product whose misuse can be deadly. In light of the possibility of serious toxicity and the potential for resistant lice, pharmacists should not recommend that physicians prescribe lindane. Unfortunately, the patient may only be able to obtain medication for head lice by relying on a third-party payer such as the state. If reimbursement is limited to prescription items, both patients and physicians turn to lindane, the only prescription lice pesticide. Once again, the pharmacist may choose to intervene, urging the patient to choose a lice treatment based on safety to the patient rather than only on economic criteria.

Malathion. Malathion was once available as the prescription product Ovide, but the odor of the formulation was offensive to patients. For this reason, its sales were inadequate to continue and the product is no longer available. This organophosphate insecticide was a safer prescription alternative to lindane, in that no systemic effects with use were noted(7). The manufacturer once suggested that the product might be relaunched, but this has not yet happened.

Synergized Pyrethrins. Pyrethrins are chemical insecticides produced naturally by the Chrysanthemum plant. However, lice can easily detoxify these chemicals through oxidation unless a synergizing agent is added to enhance their pesticidal activity. Piperonyl butoxide is a petroleum derivative which accomplishes this. This combination was given Category I status (safe and effective) by the FDA for pediculicidal use(9). Shampoos containing synergized pyrethrins are applied to wet the hair, while adding sufficient water to form a lather. The lather is left in place for 10 minutes only. The patient then washes the hair thoroughly with warm water and soap or nonmedicated shampoo. Since the combination is not completely ovicidal, a second treatment in 7-10 days is mandatory to kill any newly hatched lice. While some synergized pyrethrin products claim to be effective in only one dose, there is insufficient data to support this claim, and a second dose is considered by the FDA to be mandatory.

Patients allergic to either Chrysanthemums, ragweed, kerosene or any petroleum derivative must not use synergized pyrethrins. It must not be used near the eyes or allowed to contact mucous membranes. The hands should be washed thoroughly after application.

Several controversies have recently arisen in regard to synergized pyrethrins. One is the increasing resistance. Patients entering pharmacies are claiming that they have followed the directions exactly, and are still infested with head lice. In many cases, a cursory check confirms the presence of live lice. Upon close questioning, it seems that the parent or caregiver has indeed been conscientious in following the labeled directions, leading the pharmacist to suspect resistance. Although it is poorly documented at present, it seems that resistance to pyrethrins is a growing problem.

Another controversy involves several false advertising claims that were made by manufacturers. Among other things, they claimed that synergized pyrethrin products (e.g., Pronto, RID, Clear Lice Killing Shampoo) are effective in one dose, killing 100% of lice and eggs. One may visit the Federal Trade Commission website to view the results of an agreement by their manufacturers to settle charges of misleading consumers with these false claims. The Director of the FTC stressed that false and misleading claims such as these add insult to injury for the patient already affected with head lice(10).

Permethrin. Permethrin (Nix Creme Rinse) is a synthetic pyrethroid pesticide which was an Rx-to-OTC switch in the early 1990s. The patient should shampoo and towel-dry the hair and apply the product, leaving it in place for 10 minutes. The product is then thoroughly rinsed from the hair.

Permethrin is only 70-95 percent ovicidal; the manufacturer claims that less than one perdent of patients will require a second treatment. The manufacturer also alleges that residual effects protect against reinfestation for 14 days. This is the basis for the advertising claim, "Only Nix--Only Once." However, some patients will require a second treatment. Pharmacists recommending this product should caution patients to be continually vigilant after treatment to discover live lice that indicate the need for the second treatment.