What is the recommended treatment for pinworm (Enterobius vermicularis) infection in a pregnant woman?

Treatment of Pinworm Infection in Pregnancy

For pregnant women with pinworm infection, pyrantel pamoate is the preferred treatment option, as it is considered safer in pregnancy compared to albendazole and mebendazole, which should be avoided particularly in the first trimester. 1

Diagnostic Approach

• Confirm the diagnosis using the cellophane tape test (also called the "sellotape test"), performed by placing adhesive tape on the perianal skin in the morning before bathing or defecation to collect eggs for microscopic examination 2, 3
• The sensitivity of a single test is approximately 50%, but increases to 90% when performed on three consecutive mornings 1
• Look for the characteristic symptom of nocturnal perianal itching, which is the most common presenting complaint 2, 3
• In pregnant women, be aware that pinworms may colonize the female genital tract, causing vaginal discharge or vulvovaginitis 2, 4

Treatment Recommendations for Pregnancy

First-Line Treatment

• Pyrantel pamoate 11 mg/kg (maximum 1 gram) orally as a single dose, repeated after 2 weeks 5, 1
• Pyrantel is adulticidal (kills adult worms) but not ovicidal, which is why the repeat dose at 2 weeks is essential to kill newly hatched worms 1
• The FDA-approved dosing for pyrantel pamoate is weight-based, ranging from 125 mg (for 25-37 pounds) up to 1000 mg (for ≥188 pounds) 5

Alternative Considerations

• Mebendazole and albendazole should be avoided during pregnancy, especially in the first trimester, despite being highly effective in non-pregnant populations 1
• While some research suggests mebendazole may be safe after the first trimester (with no increased risk of adverse birth outcomes in large trials) 6, 7, the conservative approach favors pyrantel throughout pregnancy 1
• Standard non-pregnant treatment would be albendazole 400 mg or mebendazole 100 mg as single doses, repeated after 2 weeks 2, 3, 8

Critical Management Points

Household Treatment Strategy

• Treat all household members simultaneously, especially when there are children in the home, as pinworms are highly contagious and reinfection rates are extremely high 1, 4
• Having more than 2 children is strongly associated with pinworm exposure (odds ratio 7.1 for pyrvinium and 20.8 for mebendazole) 9

Hygiene Measures to Prevent Reinfection

• Implement strict hand hygiene: wash hands and fingernails with soap frequently, especially after using the toilet and before meals 5, 1
• Change and wash underwear daily; wear tight-fitting underwear both day and night 5
• Wash bed linens and nightclothes after treatment without shaking them (to avoid dispersing eggs into the air) 5
• Keep fingernails short and discourage nail-biting, finger-sucking, and scratching the perianal area 1
• Clean bedroom floors by vacuuming or damp mopping rather than dry sweeping for several days after treatment 5

Common Pitfalls and Caveats

• Recurrence is common even with effective treatment, typically due to reinfection rather than treatment failure, given the short life span of adult pinworms and the 3-week survival of eggs in the environment 1
• Do not examine stool samples for diagnosis, as pinworms and eggs are not usually passed in stool; the perianal tape test is the appropriate diagnostic method 1
• Eggs can survive in the environment for up to 3 weeks and can be transmitted via fomites (contaminated surfaces, bed clothes, toys) or even through airborne transmission 5, 1
• The prepatent period (time from infection to egg production) is 2-6 weeks, which explains why the repeat dose at 2 weeks is necessary to catch newly matured worms 2

Safety Data

• A Danish nationwide cohort study identified 4,715 pregnant women who redeemed prescriptions for pyrvinium or mebendazole during pregnancy, suggesting exposure is common 9
• Large randomized controlled trials of mebendazole in pregnancy (N=1,042) showed no statistically significant difference in adverse birth outcomes (miscarriages, malformations, stillbirths, early neonatal deaths, or premature births) compared to placebo 7
• However, the conservative approach remains to use pyrantel pamoate as first-line in pregnancy given its established safety profile and the availability of safer alternatives 1