Medicines Q&As
Q&A 202.2
How should threadworms be treated during pregnancy?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
Before using this Q&A, read the disclaimer at www.ukmi.nhs.uk/activities/medicinesQAs/default.asp
Date prepared: 11th May 2011
Background
Infestation with threadworms (also known as pinworms or Enterobius vermicularis) occurs as a result
of ingestion of the eggs, which then hatch in the intestine. Eggs are laid by the female worm in the
perianal area, usually at night (1,2). This can cause intense itching with subsequent transfer by hand
to the mouth, which continues the cycle. The lifespan of an adult threadworm, which is a parasite, is
approximately six weeks (1).
Due to the high risk of transmission and reinfestation, all members of the household should be treated
with an anthelmintic and follow hygiene measures at the same time (1). This recommendation often
causes concern to a pregnant woman, particularly if she is not infected herself (2).
General information about prescribing in pregnancy can be found here. If you are not familiar with this
information, you are advised to review it before reading further.
Answer
Hygiene measures
Threadworm infestation can be eradicated with meticulous attention to hygiene (2,3) and this is
considered to be first line management for pregnant women (2,3,4).
Strict hygiene measures should be adopted for at least six weeks to break the cycle of re-infection (1).
These include washing hands and scrubbing nails after visiting the toilet and before each meal,
bathing or showering every morning to remove any eggs laid at night, and changing bed linen
frequently (1,3).
However, whilst threadworms are harmless and the condition is not life-threatening (5) drug treatment
may be considered, provided the woman is not in the first trimester of pregnancy (4).
Mebendazole
For the control of threadworms a single 100mg dose of mebendazole should be administered but a
second 100mg dose is recommended after two weeks, if re-infection is suspected (6). There are
limited published data on the use of mebendazole during pregnancy; such use is contra-indicated by
the manufacturer (6). However, it is poorly absorbed from the gastrointestinal tract in humans (7)
suggesting that limited amounts enter the maternal circulation.
There are individual unpublished case reports of both poor outcomes and healthy births following
exposure to mebendazole (7), but formal studies with multiple exposures are described below.
In a US surveillance study, 64 infants were exposed to mebendazole during the first trimester. Four
(6.3%) major birth defects were seen (three expected), including one limb reduction defect (none
expected) (8).
In a retrospective case-control study in Sri Lanka, 5275 pregnant women received mebendazole (93%
took 100mg twice daily for 3 days – a dose higher than the UK dose for threadworm). 2.5% of the 407
women taking mebendazole in the first trimester experienced major congenital defects compared to
1.5% of the control group, but this was not statistically significant (odds ratio 1.66 [95% CI 0.81-3.56],
p=0.23). The overall data suggest that mebendazole therapy is not associated with a statistically
significant increase in the risk of major congenital defects at any stage of pregnancy. However, the
authors note that an increase in relative risk (RR) of up to two-fold cannot be ruled out (9).
From the NHS Evidence website www.evidence.nhs.uk
1
Medicines Q&As
A prospective study followed 192 women exposed to mebendazole during pregnancy, mostly during
the first trimester (71.5%). All were exposed to between one and three doses of mebendazole 100mg.
The rate of major anomalies following exposure to mebendazole compared with the control group was
5/150 (3.3%) versus 3/175 (1.7%). This difference was not statistically significant (p=0.478; RR 1.94
[95% CI 0.47-8.00]), although these wide confidence intervals should be noted. The number of
ectopic pregnancies, miscarriages, or stillbirths did not differ significantly (5).
The authors of one retrospective case-control study, concluded that mebendazole did not present an
increased teratogenic or fetotoxic risk during pregnancy. However there were a limited number of
cases and controls exposed to mebendazole in this study (14 in each group) (10).
In a more recent randomised, double-blind, placebo-controlled study (n=1042), mebendazole was
given as a 500mg single dose to 522 women in their second trimester for hookworm (22 treated
patients were lost to follow-up). Both groups also received iron supplements. There was no
statistically significant difference in adverse birth outcomes (5.6% vs 6.25%) or malformations (1.4%
vs 1.61%) compared with placebo (11).
If hygiene measures are ineffective in controlling threadworm infestation then mebendazole is
considered appropriate for use. Treatment should be delayed until after the first trimester of
pregnancy if possible. The available data do not suggest that mebendazole causes a significantly
increased risk of malformations, although this cannot be excluded. The United Kingdom Teratology
Information Service (UKTIS) advises that inadvertent exposure to mebendazole at any stage of
pregnancy is not an indication for termination or any specific fetal monitoring (7).
Piperazine
Pripsen sachets contain piperazine phosphate 4g plus standardised senna 15.3mg. The adult dose
for eradication of threadworms is one sachet as a single dose, repeated after 14 days (12). There are
no published studies on the effects of piperazine/senna during pregnancy (13) but piperazine is
systemically absorbed to a greater extent than mebendazole (14). Sennosides are poorly absorbed
orally and there is no evidence that their therapeutic use is associated with fetal harm (13).
The manufacturer of Pripsen states that “isolated instances of foetal malformation have been reported
but no causal relationship to piperazine has ever been established. Use in the first trimester of
pregnancy is therefore not advised. Unless symptoms warrant immediate treatment, the
administration of Pripsen should be postponed until after parturition” (15).
There has been a report of one baby with bilateral hare lip, cleft palate and anophthalmia who was
exposed to Pripsen at 12 and 14 weeks gestation, and another report of an infant with an abnormality
of the right foot whose mother took Pripsen at 6 and 8 weeks of pregnancy (3). There are published
data on three babies who were normal at birth following first trimester exposure to piperazine and one
case report of a normal birth following second trimester piperazine exposure. One case report of a
child born with limb deformities is described in a secondary source but further details of piperazine
exposure are not available (13).
The UKTIS conclude that data on the use of piperazine in pregnancy is limited but does not suggest
that there is an increased risk of malformations or other adverse pregnancy outcome. Piperazine, with
or without sennosides, may be used in pregnancy if clinically indicated. Exposure to piperazine at any
stage of pregnancy would not usually be regarded as medical grounds for termination of pregnancy or
any additional fetal monitoring (13).
From the NHS Evidence website www.evidence.nhs.uk
2
Medicines Q&As
Summary

The first line management for pregnant women with threadworms is strict hygiene measures
(2,3,4).
 There is little published information available on the use of mebendazole in pregnancy. If
hygiene measures are ineffective in controlling threadworm infestation then mebendazole is
considered appropriate for use (7). However, it should not be used during the first trimester of
pregnancy for the management of threadworms (4). Mebendazole is contra-indicated by the
manufacturer throughout pregnancy (6).
 There is also little published information available on the use of piperazine in pregnancy.
Piperazine is not advised in the first trimester (4,15) and the manufacturer advises delaying
treatment until after delivery if possible (15).
 If drug treatment is considered necessary, the available data do not suggest that either
piperazine-with-senna or mebendazole increase the risk of malformations (2).
 Pregnant women exposed inadvertently to piperazine or mebendazole should be reassured
that the risks of fetal toxicity are likely to be no greater than those for the general population
(2).
Limitations
 Limited published data are available on the safety of mebendazole or piperazine in
pregnancy.
 Unpublished data has not been included.
 This Medicines Q&A has addressed the management of threadworms during pregnancy. The
use of mebendazole or piperazine for the management of other conditions during pregnancy,
where the risk:benefit ratio may differ, is beyond the scope of this Q&A.
References
1. National Prescribing Centre. Management of threadworms in primary care. MeReC Bulletin
March 2008; 18(4): 11-13. Accessed via
http://www.npc.nhs.uk/merec/therap/infest/resources/merec_bulletin_vol18_no4_threadworm.
pdf on 19th May 2011.
2. The United Kingdom Teratology Information Service. Use of anthelmintics in pregnancy.
Updated June 2009. Accessed via http://www.toxbase.org/ on 19th May 2011.
3. Leach FN. Management of threadworm infestation during pregnancy. Arch Dis Child
1990;65:399-400.
4. Clinical Knowledge Summaries. Threadworm in pregnancy/breastfeeding (last revised June
2007). Clinical Knowledge Summaries Service. Accessed via
http://www.cks.nhs.uk/threadworm/management/detailed_answers/threadworm_in_pregnancy
_breastfeeding on 23rd May 2011.
5. Diav-Citrin O, Shechtman S, Arnon J et al. Pregnancy outcome after gestational exposure to
mebendazole: a prospective controlled cohort study. Am J Obstet Gynecol 2003;188:282-5.
6. Summary of Product Characteristics. Vermox 100mg tablets (mebendazole). Janssen-Cilag
Ltd. Accessed via http://emc.medicines.org.uk/medicine/943/SPC/Vermox Tablets/ on 19th
May 2011. [SPC last updated on the eMC 30th March 2011].
7. The United Kingdom Teratology Information Service. Use of mebendazole in pregnancy.
Updated June 2009. Accessed via http://www.toxbase.org/ on 19th May 2011.
8. Mebendazole monograph. Briggs GG, Freeman RK, Yaffe SJ. Drugs in Pregnancy and
Lactation: A Reference Guide to Fetal and Neonatal Risk. 9th edition. Philadelphia: Lippincott
Williams and Wilkins; 2011 p880-881.
9. De Silva NR, Sirisena JLGJ, Gunasekera DPS et al. Effect of mebendazole therapy during
pregnancy on birth outcome. Lancet 1999;353:1145-1149.
10. Ács N, Bánhidy F, Puhó E et al. Population-based case-control study of mebendazole in
pregnant women for birth outcomes. Congenital Anomalies 2005;45:85-88.
11. Gyorkos TW, Larocque R, Casapia M et al. Lack of risk of adverse birth outcomes after
deworming in pregnant women. Pediatr Infect Dis J 2006;25:791-794.
From the NHS Evidence website www.evidence.nhs.uk
3
Medicines Q&As
12. Joint Formulary Committee. British National Formulary. No 61 ed. London: British Medical
Association and Royal Pharmaceutical Society; March 2011. Accessed via www.bnf.org.uk on
19th May 2011.
13. The United Kingdom Teratology Information Service. Use of piperazine in pregnancy. March
2011. Accessed via http://www.toxbase.org/ on 19th May 2011.
14. Rubin P, Ramsay M editors. Prescribing in Pregnancy. 4th edition. London: Blackwell
Publishing. BMJ Books; 2008. p31.
15. Summary of Product Characteristics. Pripsen Piperazine Phosphate Powder. Thornton and
Ross Ltd. [Date of revision of the text 4th May 2004].
Quality Assurance
Prepared by
Kate Pickett, Medicines Q&A Pharmacist, Wessex Drug and Medicines Information Centre,
Southampton University Hospitals NHS Trust.
Date Prepared
11th May 2011
Checked by
Sue Gough (based on the Q&A checked by Sandra Hicks), Critical Evaluation Pharmacist, Wessex
Drug and Medicines Information Centre, Southampton University Hospitals NHS Trust.
Date of check
23rd June 2011
Search strategy
 Medline via NLH Search 2.0:
exp ENTEROBIUS/ AND exp PREGNANCY/ AND exp PIPERAZINES/
exp PREGNANCY/ AND exp PIPERAZINES/ AND pinworm.af
exp PREGNANCY/ AND exp PIPERAZINES/ AND threadworm.af
exp PREGNANCY/ AND piperazine.af (Limits:LG=EN)
exp PREGNANCY COMPLICATIONS/ AND piperazine.af (Limits:LG=EN)
exp PREGNANCY/ AND pinworm.af AND piperazine.af
exp PREGNANCY/ AND exp MEBENDAZOLE/ (Limits: LG=EN)
exp PREGNANCY/ AND exp MEBENDAZOLE/ AND exp ENTEROBIUS/ (Limits:LG=EN)
exp PREGNANCY COMPLICATIONS/ AND exp MEBENDAZOLE/ AND exp ENTEROBIUS/
(Limits:LG=EN)
exp PREGNANCY/ AND pinworm.af AND exp MEBENDAZOLE/
exp PREGNANCY/ AND exp MEBENDAZOLE/ AND threadworm.af
 Embase via NLH Search 2.0:
exp PREGNANCY/ AND exp PIPERAZINE/
exp PREGNANCY/ AND pinworm.af AND exp PIPERAZINE/
exp PREGNANCY/ AND threadworm.af AND exp PIPERAZINE/
exp ENTEROBIUS VERMICULARIS/ AND exp PREGNANCY/ AND exp MEBENDAZOLE/
(Limits:LG=EN)
exp PREGNANCY/ AND exp MEBENDAZOLE/ AND pinworm.af (Limits:LG=EN)
exp PREGNANCY/ AND exp MEBENDAZOLE/ AND threadworm.af







Micromedex - Drugdex
Motherisk
Electronic medicines compendium
National electronic Library for Medicine (NeLM) “threadworm”
Toxbase
National Prescribing Centre (NPC)
Personal communication with Janssen-Cilag Ltd via email on 25th May 2011
From the NHS Evidence website www.evidence.nhs.uk
4
Medicines Q&As


Personal communication with Thornton and Ross Medical Information via telephone 19th May
2011
In-house textbooks
From the NHS Evidence website www.evidence.nhs.uk
5