Head Lice Infestation: Single Drug Versus Combination Therapy WithOne Percent Permethrin and Trimethoprim/Sulfamethoxazole

Ronaldo B. Hipolito, MD*; Florinda G. Mallorca, MD‡; Zoraya O. Zuniga-Macaraig, MD‡;Patricia C. Apolinario, MD§; and Jan Wheeler-Sherman, PhDi

ABSTRACT. Background. Head lice infestation (HLI)is a vexing problem for pediatricians and families be-cause lice are becoming resistant to approved antipedicu-losis agents.

Objective. This study compared the efficacy of 3 dif-ferent treatments for HLI and determined whether com-bination therapy reduced treatment failures.

Design and Setting. A randomized, clinical trial per-formed in 3 private practices.

Participants. The population was children ranging inage from 2 to 13 years.

Methods. HLI was diagnosed by direct inspection ofthe hair and scalp. Children were assigned to 1 of 3groups: 1) 1% permethrin creme rinse (1% PER; n 5 39);2) oral administration of trimethoprim/sulfamethoxazole(TMP/SMX; n 5 36); and 3) a combination of 1% PER andTMP/SMX (n 5 40). Follow-up visits were done 2 and 4weeks later, and parents or caregivers of those who didnot return were interviewed by telephone. If HLI waspresent at the 2-week follow-up, the child was retreatedper their protocol. We defined successful treatment as theabsence of adult lice and nymphal stage or eggs (nits).The presence of nits alone was not considered a treat-ment failure.

Results. At the 2-week follow-up visit, successfultreatment for groups 1, 2, and 3 was 79.5%, 83%, and 95%,respectively. At the 4-week follow-up, successful treat-ment was 72%, 78%, and 92.5% for groups 1, 2, and 3,respectively. The absolute risk reduction for recurrencecomparing group 1 versus group 2 was 6%, group 2versus group 3 was 14%, and group 1 versus group 3 was20%. No major adverse complications were seen in anytreatment group.

Conclusion. Our findings indicate that a combinationof 1% PER and TMP/SMX is an effective alternativetherapy for HLI. We recommend that the dual therapywith 1% PER and oral TMP/SMX be used and reserved incases of multiple treatment failures or suspected cases oflice-related resistance to therapy. Pediatrics 2001;107(3).URL: http://www.pediatrics.org/cgi/content/full/107/3/e30;lice, Pediculus humanus var capitis, trimethoprim/sulfame-thoxazole, resistance, permethrin.

ABBREVIATIONS. HLI, head lice infestation; PPB, pyrethrinswith piperonyl butoxide; 1% PER, 1% permethrin creme rinse;TMP/SMX, trimethoprim/sulfamethoxazole.

Head lice infestation (HLI) caused by Pediculushumanus var capitis is a worldwide publichealth concern that affects mostly school-

aged children.1 In the United States, ;6 to 12 millionpersons are infested with head lice,2 with an esti-mated $100 million being spent annually on treat-ment.3 HLI does not produce an illness, but it isphysically unpleasant and bears a significant nega-tive social stigma.4

Historically, permethrin creme rinse has been thedrug of choice in treating pediculosis5,6 because of itslong-lasting residual effect, which may be useful inkilling nymphs.7 However, resistance to permethrinas well as other antipediculosis agents, includingpyrethrins with piperonyl butoxide (PPB) and lin-dane, has recently been reported.6–10 Pediatriciansand other pediatric health care workers are nowfaced with finding new strategies to combat drugresistance associated with HLI. In other countries,clinicians have found rotational therapy with differ-ent agents a useful approach.1 The rotation of thera-peutic agents may slow the emergence of resistance,1although this has yet to be proven.

Other methods to treat HLI include applying aheavy layer of petroleum jelly, olive oil, or mayon-naise to the scalp and covering the scalp overnightwith a shower cap. This method reportedly kills licethrough asphyxiation, immobilization, and/or an in-ability to feed.1,4,6 Head shaving is also used to treatHLI.11 This treatment is effective for male childrenbut is not socially acceptable for the female popula-tion in which the majority of HLI occurs. Of partic-ular concern is that parents and caretakers may useunsafe and dangerous methods, such as kerosene,alcohol, insecticides, and other toxic chemicals totreat HLI.4,11,12

Three agents are currently approved by the USFood and Drug Administration for the treatment ofHLI: lindane (Kwell, Jersey City, NJ), PPB (RID,Pronto, A-200, and others), and 1% permethrin cremerinse (1% PER; Nix, Research Triangle Park, NC).4,6

Because treatment resistance has become a primaryconcern for clinicians, they are beginning to use ex-perimental treatments, such as trimethoprim/sulfa-methoxazole (TMP/SMX), 5% permethrin (5% PER;Elimite, Irvine, CA), malathion, ivermectin, and car-

From the *Department of Pediatrics, University of California, Davis, Cali-fornia; ‡Yosemite Medical Group, Tracy and Manteca, California; §Depart-ment of Pediatrics, San Joaquin General Hospital, Stockton, California; andthe iDepartment of Nursing, University of California, San Francisco, Cali-fornia.Received for publication Jun 12, 2000; accepted Sep 26, 2000.Reprint requests to (R.B.H.) University of California, Davis, School of Med-icine, Department of Pediatrics, Section of Neonatology, TB 193, Davis, CA95616. E-mail: rbhipo@aol.comPEDIATRICS (ISSN 0031 4005). Copyright © 2001 by the American Acad-emy of Pediatrics.

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baryl to control HLI.4,13–15 Of these agents, TMP/SMX is a more commonly used medication in thepediatric population. Parents are more familiar withTMP/SMX compared with 5% PER, malathion, iver-mectin, or carbaryl.

Although TMP/SMX is unpopular in treating HLIbecause of its potential side effects, it is an emergingpractice among clinicians to treat HLI with a combi-nation of 1% PER and oral TMP/SMX. To the best ofour knowledge, no one has reported the therapeuticefficacy of combining the 2 medications in the treat-ment of HLI, especially when patients have experi-enced recent treatment failures or when lice-relatedresistance is suspected. The purpose of this studywas to compare the efficacy of using single therapy(1% PER or oral TMP/SMX alone) versus combina-tion therapy with 1% PER and oral TMP/SMX intreating P humanis var capitis infestation. This ap-proach might represent a better and safer alternativefor treating HLI when treatment failure has occurredor lice-related resistance is suspected.

METHODS

Population, Enrollment, and AssignmentThe study was conducted between July 1996 and December

1999 in San Joaquin County, California. The study sites were 3private pediatric and family practices. The sample population wascomprised of children ranging from 2 to 13 years old who werediagnosed with HLI in the physicians’ offices. The diagnosis ofHLI was confirmed by clinical inspection of scalp and hair for thepresence of adult lice, nymphal stage, or eggs (nits). Inclusioncriteria for the study included a positive diagnosis of HLI byvisual inspection and informed consent from the parents or care-givers that they understood the study design and were willing toparticipate. Exclusion criteria for the study included a hypersen-sitivity to TMP/SMX, a hypersensitivity to 1% PER, and/or ahistory of parental noncompliance or neglect.

Demographic data including age, race, sex, and childcare at-tendance were obtained for all participants. A history of previousHLI was obtained from medical records and parental anecdotes.

All children who met the inclusive criteria and whose caregiv-ers gave informed consent were enrolled in the study. Childrenwere randomly assigned to 1 of 3 groups. Participants assigned togroup 1 received 1% PER for 10 minutes over hair and scalp (permanufacturer’s instruction), with a repeat application after 1 weekif necessary. Participants assigned to group 2 were prescribed oralTMP/SMX suspension 10 mg/kg/day based on TMP in 2 divideddoses for 10 days. Participants assigned to group 3 were treatedwith a combination of 1% PER and TMP/SMX as described forgroups 1 and 2.

During the visual inspection of lice, parents were educated onhow to recognize different stages of lice (adult lice, nymphal stage,or eggs/nits). Photographs of different stages of lice were alsoshown. Parents of all participants were given information onrecognition of HLI and methods to prevent reinfestation (cleaningof the home, bedding, and personal hygiene items; treatment ofother family members; and other precautions to prevent reinfes-tation).

Drug Administration and Compliance

Group 1Participants were given 1% PER as described by manufacturer’s

insert package. In brief, the parents were instructed to wash theirchild’s hair with regular shampoo and then rinse clean, shake thebottle of 1% PER, and apply the creme rinse to the scalp and hairfor 10 minutes. Thereafter, the hair was rinsed with water and wastowel dried. Nits were removed using the comb provided with the1% PER. Parents or caretakers were asked to comb participant’shair as many strokes as they can after using the medication. Theprocedure was repeated after 1 week if HLI was still evident.

Group 2Participants were given oral TMP/SMX (suspension or tablet)

at a dosage of 10 mg/kg/day based on TMP for 10 days in 2divided doses. Children who were able to swallow tablets wereprescribed 1 tablet twice daily or 1 double strength tablet twicedaily for 10 days depending on their weight. Parents or caretakerswere instructed to use a regular shampoo. Nits were removedusing a lice meister, and if not available, we recommended usinga very fine teethed comb. Parents or caretakers were asked tocomb the participant’s hair as many strokes as they could duringthe course of the treatment.

Group 3Participants were prescribed both 1% PER and TMP/SMX as

same protocol outlined above. Nits were removed using a combprovided by 1% PER. Parents or caretakers were asked to combthe participant’s hair as many strokes as they could during thecourse of the treatment.

Compliance in taking TMP/SMX was determined using 1 of 2methods. The child’s parents recorded the administration of eachdose in a small diary that was supplied at study entry and/or theamount of dispensed medication (liquid volume or tablets) thatremained was evaluated at the follow-up visit.

Follow-Up Observations and Subsequent TreatmentChildren were reexamined at 2 and 4 weeks after treatment for

HLI. A pediatrician or family practice physician performed exam-inations of scalp and hair. We defined treatment failures as thepresence of adult lice, and nymphal stage, or eggs (nits) and notjust the presence of nits alone. On follow-up visits, we used amagnifying glass to identify a true viable egg with an empty eggcasing to confirm HLI. If the child at 2 weeks still had HLI, theparticipants were retreated. The protocol for retreatment was asfollows: group 1: reapplication of 1% PER; group 2: another courseof oral TMP/SMX suspension; and group 3: another course of 1%PER and oral TMP/SMX suspension. The participants were thenevaluated 4 weeks after the initial diagnosis. If the participants didnot return for their follow-up visit, telephone interviews with theparents or caregivers were used for deciding outcome.

A retrospective review of charts on all the participants who hadtheir follow-up by telephone interviews in both first and secondfollow-up was performed at least 6 months after the enrollment.The review involved recording any repeat office visit(s) attribut-able to HLI.

StatisticsThe sample size was estimated based on the recommendations

of Cohen.16 Using an a of 0.05, a power of 0.80, and an effect sizeof 0.50, a minimum of 39 participants were necessary for eachgroup.

Statistical analysis of results was performed using the Fisher’sexact test and Student’s t test as was appropriate.16,17 Absoluterisk reduction was calculated to compare the efficacy of treatmentbetween groups.

RESULTS

Population CharacteristicsOver a 3-year period from July 1996 to December

1999, 115 children were entered into the study. Therewere a total of 125 participants recruited with HLI,but 10 participants were excluded. Seven partici-pants with HLI were not entered into the studybecause of previous hypersensitivity to TMP/SMX(n 5 2), hypersensitivity to 1% PER (n 5 2), and aparental history of noncompliance/neglect (n 5 3).Three participants were removed from the studybecause of rash caused by TMP/SMX. The attritionrate was 2%.

Demographic characteristics of the participants areshown in Table 1. Analysis of the demographic dataamong the 3 treatment groups revealed no differ-ences. In all groups, ;53% of the children were be-

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tween the ages of 6 and 10 years. The predominantgender was female (female 70% and male 30%). Thepredominant ethnicity was Hispanic (48.7%).

Treatment GroupsAt 2 weeks after therapy began, HLI was still

present in 16 participants (Fig 1). The success rate oftreatment for groups 1, 2, and 3 was 79.5%, 83%, and95%, respectively. After 4 weeks of therapy, failureswere present in 22 participants (Fig 1). The successrate for treatment at the 4-week follow-up for groups1, 2, and 3 was 72%, 78%, and 92.5%, respectively.

Table 2 shows the calculation of the absolute riskreduction comparing the efficacy of treatment amonggroups. Treatment with 1% PER and TMP/SMX wasmore likely to prevent recurrence of HLI.

Follow-Up Observations and Subsequent TreatmentTable 3 shows the numbers of office visits versus

telephone interviews that were required at the firstand second follow-up visits. All treatment failures ingroups 1, 2, and 3 showed up for their follow-upoffice visits.

Group 1At first follow-up, 8 participants were retreated

with 1% PER. At the second follow-up, there were 11treatment failures. Of 8 treatment failures in the firstfollow-up, 4 participants needed another course oftreatment, while 4 participants were free of lice bothadult and nymphal stage or eggs (nits). Seven par-

Fig 1. Relationship between the number of enrolled patients andthe number of treatment failures at the first (2-week) and second(4-week) follow-up appointments. Group 1 5 1% PER; group 2 5oral administration of TMP/SMX (10 mg/kg/day divided intotwice-daily dosing); and group 3 5 combined 1% PER and TMP/SMX.

TABLE 1. Demographic Characteristics of the Study Population With Head Lice Infestation

Treatment Groups

Group 11% PER(n 5 39)

Group 2TMP/SMX

(n 5 36)

Group 31% PER 1TMP/SMX

(n 5 40)

Total(n 5 115)

n (%) n (%) n (%) n (%)

Age (y)2–5 10 (26) 9 (25) 10 (25) 29 (25)6–10 20 (51) 21 (58) 22 (55) 63 (55)11–13 9 (23) 6 (17) 8 (20) 23 (20)

RaceWhite 10 (26) 10 (28) 9 (22.5) 29 (25)Black 5 (13) 4 (11) 5 (12.5) 14 (12)Hispanic 15 (38) 20 (55.5) 21 (52.5) 56 (49)Asian 9 (23) 2 (5.5) 5 (12.5) 16 (14)

SexMale 13 (33) 11 (31) 10 (25) 34 (30)Female 26 (67) 25 (69) 30 (75) 81 (70)

Previous history of HLI 13 (33) 12 (33) 15 (37.5) 40 (35)Day care attendees

Yes 15 (38.5) 12 (33) 14 (35) 41 (36)No 24 (61.5) 24 (67) 26 (65) 74 (64)

TABLE 2. ARR* Shows the Efficacy of Treatment Among theGroups

Groups ARR (%) P Value*

Group 1 vs 2 6 .74Group 2 vs 3 14 .14Group 1 vs 3 20 .03†

ARR indicates absolute risk reduction.* Fisher’s exact test 5 P value.† Statistically significant.

TABLE 3. Numbers of Enrolled Participants Who Kept Ap-pointed Follow-Up Visits at Two or Four Weeks After TreatmentBegan or Required Telephone Follow-Up Interviews to DetermineOutcome

First Follow-Up Second Follow-Up

OfficeVisits

TelephoneInterviews

OfficeVisits

TelephoneInterviews

Group 1(n 5 39)

23 (58%) 16 (42%) 21 (54%) 18 (46%)

Group 2(n 5 36)

25 (69%) 11 (31%) 18 (50%) 18 (50%)

Group 3(n 5 40)

16 (40%) 24 (60%) 20 (50%) 20 (50%)

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ticipants on second follow-up were new treatmentfailures and needed to be retreated again.

Group 2At the first follow-up, 6 participants were retreated

with TMP/SMX. At the second follow-up, there were8 treatment failures. Of 6 participants retreated in thefirst follow-up, 3 participants needed another courseof treatment, while 3 participants were free of liceboth adult and nymphal stage or eggs (nits). Fiveparticipants on second follow-up were treatmentfailures and needed to be retreated again. Group 2had a better posttreatment follow-up than group 1(Table 3), and we attributed this to the fact that group2 protocol is new to the parents or caretakers.

Group 3At the first follow-up, 2 participants were retreated

with 1% PER and TMP/SMX. At the second follow-up, all of the participants retreated at first follow-upwere free of lice both adult and nymphal stage oreggs (nits), while 3 participants were new treatmentfailures and needed to be retreated again. Group 3had more telephone interviews that were used forfollow-up (Table 3), and we attributed this to the factthat combination therapy had a greater success ratefor treatment.

A retrospective review of charts on all the partic-ipants who underwent telephone interviews for de-ciding outcomes in group 1, 2, and 3 during first andsecond follow-up revealed that there were no officevisits attributable to HLI in a span of at least .6months. This signifies that HLI was treated ade-quately.

Adverse ReactionsOf 115 participants, 8 had minor adverse reactions

to the treatment. Three participants had mild scalpirritation after a 10-minute application of 1% PER.Five participants had nausea, vomiting, and/or mi-nor rash from oral TMP/SMX. One quarter of par-ticipants (n 5 9) in group 2 developed intense pru-ritus after 3 to 4 days of treatment, but the treatmentwas continued because the pruritus disappearedwithin 1 to 3 hours. Two participants in group 2 and1 participant in group 3 were removed from thestudy because of an allergic-appearing rash causedby TMP/SMX. Participants who developed nauseaand vomiting (n 5 3) on TMP/SMX were not ex-cluded from the study because the symptoms weretransient. Participants who developed mild scalp ir-ritation related to 1% PER were also not excludedfrom the study. No major side effects of TMP/SMX—such as Stevens-Johnson syndrome; erythemamultiforme; and clinical signs and symptoms of meg-aloblastic anemia, hemolytic anemia, neutropenia,and renal impairment—were observed.

DISCUSSIONTreatment of P humanis var capitis infestation has

been a long-term problem for clinicians and parents.1The management is complicated by increasing resis-tance to the presently approved antipediculosisagents.6–10 Drug resistance has also increased the

risk of infestation among family members. HLI in-flicts a negative social stigma on the children andtheir parents or caretakers. Because of parental andcaretaker’s frustration with resistant head lice, dan-gerous methods of treating HLI (use of kerosene,insecticides, gasoline, and head shaving) may beused. In this trial, combination therapy had less re-currences of HLI compared with treatment with ei-ther 1% PER or TMP/SMX alone. This study sug-gests an alternative therapy in the management ofHLI where treatment failure or suspected lice-relatedresistance exists.

The mechanism by which permethrin and TMP/SMX kills lice differs from each other. Permethrin isa synthetic compound derived from pyrethrin andacts on the nerve cell membranes of the parasitescausing disruption of the sodium channel, delayednerve repolarization, and paralysis of exoskeletalmuscles. This inhibits respiration and the lice suffo-cate.18 By comparison, TMP/SMX applies the prin-ciple of a symbiotic relationship. According toBurns,19 TMP/SMX kills lice by inhibiting their in-testinal flora. When lice suck the blood of treatedpatients, they ingest TMP/SMX. The TMP/SMX killsthe bacterial flora in the gut that synthesize B vita-mins. Lice lose their ability to obtain B vitamins anddie as a result.19 Other antibiotics can also be used inthe treatment of HLI, but they are still under inves-tigation by other researchers.20 So far, TMP/SMX isthe only antibacterial agent being used as an exper-imental therapy for HLI.

Historically, TMP/SMX was accidentally discov-ered by Shashindran and colleagues21 as a therapyfor lice in 1978. These physicians were giving TMP/SMX to a 12-year-old girl with a bacterial upperrespiratory infection and HLI, and they noted a con-current improvement in her HLI. In their study, theyused 2 courses of TMP/SMX spaced 10 days apart (1tablet twice daily for 3 days), and they found thatthis approach eradicated the infestation without re-quiring any external antipediculosis therapy. Morsyand colleagues20 also studied the efficacy of TMP/SMX in treating HLI. In their study, the lice demon-strated decreased movement and death by the fourthto seventh day of oral TMP/SMX. The complicationsseen in that study included severe pruritis, skin rash,nausea, and vomiting. For unknown reasons, pa-tients in our study that combined 1% PER and TMP/SMX therapy did not experience severe pruritus, al-though intense pruritis was seen in some childrentreated with TMP/SMX alone.

We propose that using both 1% PER and oralTMP/SMX can provide a synergistic effect. Per-methrin can kill lice immediately during the appli-cation and it may still have a residual effect onemerging nymphs. Paradoxically, the waning resid-ual levels of permethrin may promote the emergenceof resistant lice.1,7 If there is a development of resis-tance in some lice to permethrin, the ingestion of theTMP/SMX may lead to their ultimate eradication.Moreover, after a full course of TMP/SMX, we spec-ulate that blood levels of the medication may stillafford protection to newly emerging lice that ingestblood from the human scalp.

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Aside from using TMP/SMX, primary healthworkers can choose other experimental drugs in themanagement of resistant head lice. These include 5%permethrin cream, carbaryl, malathion, and ivermec-tin.4,13–15 Five percent permethrin cream still wasassociated with reinfestation and required retreat-ment.4 Malathion was reported recently by Dawes10

to have double resistance to lice. Carbaryl is carcino-genic, whereas ivermectin is neurotoxic.1 Hence us-ing these alternative drugs in treating HLI would beless appealing to pediatric health professionals and isnot commonly used in the United States.

Although TMP/SMX has serious side effects suchas Stevens-Johnson syndrome, neutropenia, hemoly-sis, and even renal impairment,23 these are rare com-plications and were not seen in our trial. Comparedwith the above-mentioned medications, parents areoften more familiar with TMP/SMX.

Dual therapy with 1% PER and TMP/SMX mayreduce parental frustration with the recurrence ofHLI. Although dual therapy with 1% PER and TMP/SMX is a more expensive therapy compared with asingle drug regimen, the parents seemed more satis-fied with its effectiveness in this trial. Cost savingsmay be realized by fewer clinic visits and less needfor retreatments. We speculate that dual therapywith 1% PER and TMP/SMX may lower the emo-tional and economic costs of HLI in infants and chil-dren, but larger clinical trials with more outcomevariables will be required to draw that conclusion.

CONCLUSIONOur findings suggest that using both 1% PER and

oral TMP/SMX is a more effective therapy in themanagement of HLI. We recommend that dual ther-apy with 1% PER and TMP/SMX be used by pedi-atric health care professionals in cases of treatmentfailures or suspected cases of lice-related resistanceto therapy. The dual therapy should be reserved onlyin cases of multiple treatment failures or suspectedcases of lice-related resistance to therapy and not afirst line of therapy. We also recommend that haircare and HLI education and awareness should be apart of anticipatory guidance during well-child vis-its, especially in school-aged female children.

ACKNOWLEDGMENTSWe thank Steve Bennett and Drs Jay Milstein and Michael

Sherman, Department of Pediatrics, University of California,

Davis; Dr Ernesto Hipolito, Daly City, California; and my wife,Anna Corina Hipolito, for their helpful suggestions regarding thepreparation of this manuscript.

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DOI: 10.1542/peds.107.3.e30 2001;107;e30Pediatrics

Apolinario and Jan Wheeler-ShermanRonaldo B. Hipolito, Florinda G. Mallorca, Zoraya O. Zuniga-Macaraig, Patricia C.

Percent Permethrin and Trimethoprim/SulfamethoxazoleHead Lice Infestation: Single Drug Versus Combination Therapy With One

  

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Apolinario and Jan Wheeler-ShermanRonaldo B. Hipolito, Florinda G. Mallorca, Zoraya O. Zuniga-Macaraig, Patricia C.

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