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
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
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
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