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Drug treatment has no effect on threadworm eggs. Therefore, treatment success relies upon ensuring strict hygiene to stop the transfer of eggs from the perianal area to the mouth, thus preventing re-infection (see table 1). The worms will die naturally after about six weeks if this cycle is broken.
It is important to treat all family members, whether symptomatic or not. Ideally treatment should commence on the same day for all. For both agents, a second course may be given after an appropriate time interval to reduce the risk of re-infection (refer to NPF).
Mebendazole acts by inhibiting the uptake of glucose by the worms, thus affecting their energy metabolism and killing them within a few days. As it acts mainly in the gut with very little intestinal absorption, most of the drug is excreted in faeces.
In three published randomised controlled trials, a single 100mg dose of mebendazole was found to cure over 90% of patients with threadworm infection.5,6,7 In one of these studies this compared to a cure rate of about 12% with placebo.6 In all of these studies the adhesive tape test was used to measure the response both pre- and post-treatment.
As mebendazole remains largely unabsorbed, systemic side effects are minimal. Transient abdominal pain and diarrhoea may occur if infection involves a large number of threadworms.
Piperazine acts by blocking the neurotransmitter acetylcholine in the worm, leading to paralysis. The worm is then excreted in the faeces. The powder formulation of piperazine with senna (Pripsen) may assist the removal of the paralysed worm due to the laxative effect of the senna. This, however, may not remove eggs that are waiting to hatch.
There appears to be little published evidence assessing the effectiveness of piperazine, either as a single agent or in combination with senna. One study published in 1953 compared piperazine with placebo and other threadworm treatments that are not now available in the UK.8 Dosage of piperazine was adjusted according to the age of the patient. Assessment across the dosage range found cure rates of between 54-83% with piperazine, compared with about 19% in the placebo group.
Like mebendazole, side effects of piperazine occur mainly in the gastrointestinal tract. However, systemic side effects may be more common with piperazine including, rarely, muscular inco-ordination (`worm wobble').
Although both piperazine and mebendazole appear to be effective at killing threadworms, re-infection of patients is relatively common. This is usually because hygiene measures were not adhered to, or that a family member or close contact was not treated. It is also important to check that a second course of drug treatment has been given. Persistently recurrent cases should be referred to the GP, either for further investigation and treatment, orfor referral on to a parasitologist.
Mebendazole is not licensed to be used in children under the age of two. Piperazine (as a single agent) is only licensed for use in children under two years of age on the advice of a doctor. However, nurses and health visitors can prescribe Pripsen powder (piperazine and senna) in infants aged over three months (see NPF for details).
Generally, pregnant women with threadworms should be referred for medical advice. Drug treatment should be avoided in pregnancy, as strict hygiene measures alone will ensure the worms die naturally after about six weeks (see table 1).9 Pregnant women should be reassured that the worms will not pass to the foetus, and that infection of the infant at delivery is also highly unlikely.10
Although neither agent is proven to be safe in pregnancy, piperazine has been used for many years without any evidence that it is harmful to the foetus.9 It may be used in those women who are anxious to eradicate the worms as soon as possible, but should be avoided in the first trimester of pregnancy.
Clinical trial evidence around the treatment of threadworm is limited. Most data are from relatively old, small trials comparing mebendazole with either placebo or drugs not currently available in the UK. It would appear that mebendazole and piperazine produce comparable cure rates of around 90%.
Mebendazole is drug of choice in patients over two years of age as it only needs to be given as two single doses and is cheaper than piperazine. Piperazine should be reserved for those in whom mebendazole is contra-indicated or cannot be tolerated.
References
1) Nathan A. Anthelmintics. Pharm J 1997; 258: 770 _ 771
2) Cook GC. Leading article - Tropical infection of the gastrointestinal tract and liver series. Enterobius vermicularis infection. Gut 1994; 35: 1159-1162
3) Tanowitz HB, Weiss LM, Wittner M. Diagnosis and treatment of common intestinal helminths. II: common intestinal nematodes. The Gastroenterologist 1994; 2: 39-49
4) Ibarra J. The ubiquitous threadworm, Enterobi vermicularis. Parasitology. Nurs Stand 1989; 3: 34-35
5) Miller MJ, Krupp IM et al. Mebendazole. An Effective Anthelmintic for Trichuriasis and Enterobiasis. JAMA 1974; 230:1412-1414
6) Brugmans JP, Thienpont DC et al. Mebendazole in enterobiasis. Radiochemical and pilot clinical study in 1,278 subjects. JAMA 1971; 217: 313-316
7) Fierlafun E, Vanparus OF. Mebendazole in enterobiasis - aplacebo-controlled trial in a paediatric community. Trop Geogr Med 1973; 25: 242-244
8) White RHR, Standen OD. Piperazine in the treatment of threadworms in children. BMJ 1953: 755-757
9) Lee A, Schofield S. Common medical problems in pregnancy. Pharm J 1994; 253: 57-60
10) Pietroni M, Davidson R. Treatments for worm infections seen in the UK. Prescriber 1996; 7: 33-44
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