What is the recommended treatment and dosage for Ascaris lumbricoides infection in a woman in her first trimester of pregnancy?

Treatment of Ascaris in First Trimester of Pregnancy

Pregnant women with ascariasis in the first trimester should be treated with pyrantel pamoate, as albendazole and mebendazole carry teratogenic risks during early pregnancy and should be avoided until after the first trimester. 1, 2

Recommended Treatment Regimen

First-line therapy:

• Pyrantel pamoate is the drug of choice for pregnant women with ascariasis 1, 2
• This recommendation applies specifically to first trimester exposure when organogenesis occurs and teratogenic risk is highest 3

Drugs to Avoid in First Trimester

Albendazole:

• Contraindicated in first trimester due to demonstrated teratogenicity in animal studies, causing embryotoxicity and skeletal malformations in rats (at 0.10-0.32 times human dose) and rabbits (at 0.60 times human dose) 3
• FDA labeling explicitly warns of potential fetal harm when administered during pregnancy 3
• Pregnancy testing is recommended before initiating albendazole, and effective contraception should be used during treatment and for 3 days after the final dose 3

Mebendazole:

• Should be avoided during first trimester despite limited human data showing adverse outcomes 4
• While a large randomized controlled trial (N=1042) in Peru found no significant difference in adverse birth outcomes (miscarriages, malformations, stillbirths) when mebendazole was given after the first trimester, this study specifically administered treatment after the first trimester 4
• Standard dosing for ascariasis is 100 mg twice daily for 3 consecutive days 5

Treatment After First Trimester

If treatment must be delayed:

• After the first trimester, both albendazole and mebendazole become acceptable options with demonstrated safety profiles 4, 6
• Mebendazole 500 mg single dose plus iron supplements showed no increased risk of adverse birth outcomes in a large trial conducted in the second and third trimesters 4

Clinical Context and Rationale

Why treatment is important even in asymptomatic patients:

• All patients with confirmed A. lumbricoides infection warrant anthelminthic treatment, even if asymptomatic, to prevent complications from worm migration 1, 2
• Complications in pregnancy include biliary ascariasis, intestinal obstruction, and nutritional deficiencies that can affect both mother and fetus 7, 1

Special considerations in pregnancy:

• Pregnant women in endemic areas are particularly prone to developing biliary ascariasis, which poses significant management challenges 7
• The majority of biliary ascariasis cases in pregnancy (66.6%) occur in the third trimester, but prevention through early treatment is preferable 7

Monitoring and Follow-up

• No special procedures such as fasting or purging are required with anthelminthic treatment 5
• If the patient is not cured three weeks after treatment, a second course should be considered 5
• Average cure rates with appropriate anthelminthic treatment exceed 95%, though reinfection is common in endemic areas 1

Prevention in Endemic Areas

• Routine deworming of women in child-bearing years is recommended in endemic areas to prevent ascariasis during pregnancy 7
• This preventive approach is preferable to treating established infection during the vulnerable first trimester 7