What is the recommended treatment regimen for Enterobius vermicularis (pinworm) infection, including drug choice, dosing, repeat dosing, and special considerations for pregnancy and children under 2 years?

Treatment for Pinworms (Enterobius vermicularis)

Albendazole 400 mg as a single oral dose, repeated exactly 2 weeks later, is the recommended first-line treatment for pinworm infection in adults and children over 24 months of age. 1

First-Line Treatment Regimen

Standard dosing for all patients ≥24 months:

• Albendazole 400 mg orally as a single dose, with a mandatory repeat dose at exactly 2 weeks 1, 2, 3
• The two-dose schedule is essential because eggs present at the time of the first dose hatch into new adult worms within 2–4 weeks, and the second dose eliminates these newly emerged worms 1
• Both doses should be taken with food, preferably a fatty meal, to maximize absorption 1

Alternative first-line agents with equal efficacy:

• Mebendazole 100 mg as a single oral dose, repeated in 2 weeks 2, 4, 5
• Pyrantel pamoate 11 mg/kg (maximum 1 gram) as a single dose, repeated in 2 weeks 3, 6, 5

Special Populations

Children 12–24 Months

• Albendazole 400 mg or mebendazole 100 mg may be used, but expert consultation is required before treatment in this age group 1, 3
• The same two-dose schedule (initial dose plus repeat at 2 weeks) applies 3

Children Under 12 Months

• Pyrantel pamoate should not be used in children under 25 pounds or under 2 years unless directed by a physician 6
• Expert consultation is mandatory for treatment decisions in infants 3

Pregnancy

• Pyrantel pamoate is the preferred agent during pregnancy over albendazole and mebendazole 5
• Albendazole should only be used when therapeutic benefit clearly outweighs potential fetal risk 1

Household and Contact Management

All household members should be treated simultaneously, even if asymptomatic:

• Reinfection is extremely common due to environmental contamination and the ease of egg transmission 5, 7
• Treatment of sexual partners is also recommended to prevent reinfection 7
• Approximately 30–40% of infected individuals are asymptomatic but can still transmit infection 2, 5

Environmental Decontamination (Critical for Success)

On each treatment day (day 1 and day 14):

• Thoroughly vacuum bedroom floors and furniture to remove pinworm eggs from surfaces 1
• Clean bathroom fixtures, especially toilet seats and door handles, to eliminate environmental reservoirs 1
• These measures are essential to prevent reinfection from viable eggs in the environment 1

Monitoring and Follow-Up

For standard two-dose therapy (<14 days total):

• No routine laboratory monitoring is necessary 1
• Patients should return if symptoms persist 3 weeks after completing treatment 4, 5

For recurrent or refractory cases requiring prolonged therapy:

• Complete blood counts should be monitored at the start of each 28-day cycle and every 2 weeks, as leukopenia occurs in up to 10% of patients on prolonged albendazole 1
• Liver enzymes should be checked at the beginning of each cycle and at least every 2 weeks, as elevated transaminases occur in up to 16% of patients 1

Management of Treatment Failure or Recurrence

If symptoms persist after standard two-dose therapy:

• Persistent symptoms usually indicate reinfection rather than medication resistance, which is rare 2, 5
• Reassess household treatment compliance and environmental hygiene measures 5, 7

For recurrent vaginal pinworm infection in girls:

• Standard two-dose therapy may be insufficient, as the vagina can serve as a reservoir for E. vermicularis 8, 9
• Consider extended treatment: albendazole 400 mg given at 2-week intervals for three total doses (weeks 0,2, and 4) 8
• Alternatively, mebendazole 100 mg daily for 3 days, repeated at 3-week intervals over 3 months, has been successful 9

For truly refractory cases:

• A "pulse scheme" with prolonged treatment for up to 16 weeks may be necessary 7
• Specialist consultation is recommended for cases failing standard therapy 7

Preventive Hygiene Measures (Essential Counseling Points)

Personal hygiene interventions to prevent reinfection:

• Frequent handwashing, especially after bowel movements and before meals 5, 7
• Keep fingernails short and clean 5
• Avoid finger-sucking, nail-biting, and scratching the perianal area 5, 7
• Bathe in the morning to remove eggs deposited overnight 5
• Change and wash underwear, pajamas, and bed linens frequently in hot water 5

Clinical Presentation (For Diagnosis)

Most common symptom:

• Nocturnal perianal itching (pruritus ani) is the hallmark symptom 1, 2, 3, 5

Other manifestations:

• Weight loss, irritability, diarrhea, and abdominal pain 1, 2, 3
• Vulvovaginitis in females due to worm migration into the genital tract 1, 3, 9
• 30–40% of infected patients are completely asymptomatic 2, 5

Diagnostic Confirmation

The perianal adhesive tape (cellophane tape) test is the preferred diagnostic method:

• Apply clear adhesive tape to the perianal region first thing in the morning before bathing or bowel movement 2, 3
• A single test has approximately 50% sensitivity, but three tests performed on consecutive mornings increase sensitivity to approximately 90% 5
• Stool examination is not recommended because pinworms and eggs are rarely passed in stool 2, 5

Common Pitfalls to Avoid

• Failing to treat all household members simultaneously is the most common cause of treatment failure and reinfection 5, 7
• Omitting the second dose at 2 weeks allows newly hatched worms to mature and perpetuate infection 1
• Neglecting environmental decontamination on treatment days leaves viable eggs that cause reinfection 1
• Not taking albendazole with food significantly reduces absorption and treatment efficacy 1
• Assuming treatment failure when symptoms recur without first ruling out reinfection from untreated contacts or environmental sources 2, 5