Toxic Effects of Antiworm or Antihelminthic Drugs

There are a variety of antiworm/antihelminthic drugs used to treat worm infestations/infections. Though the effects and side effects of antiworm/ antihelminthic drugs are well evaluated before the clinical trials but the real time toxic effects with respect to age, sex and associated medication of patients should always be kept in mind. For your benefit, toxic effects of some commonly used antiworm/antihelminthic drugs are summarized below.

1. Piperazine:  Piperazine is considered safe and cheap and widely used in large scale treatment programs for roundworm infestations/infections. It acts by producing a neuromuscular block in Ascaris (roundworm) through anticholinergic action at myoneural junction and decrease the succinic acid production by worm. Piperazine is easily absorbed from the gastrointestinal tract. Around 20% of it is metabolized and rest is excreted in the urine. Its mild side effects are: Intestinal discomfort, dizziness, nausea and vomiting may occur occasionally. Over dose can cause urticaria or allergic respiratory reaction. Severe toxic effects could be referable to the 'central nervous system' (CNS) leading to confusional states, inordination, dropping of objects, vertigo, muscular weakness and myoclonic contractions. Severe epileptic seizures have also been reported. Piperazine should not be prescribed to patients with history of epilepsy, renal or liver disease and neurological disease. Use of piperazine should be avoided during the first trimester of pregnancy.
2. Pyrantel pamoate:  Pyrantel pamoate is highly effective broad spectrum antihelminthic. Pyrantel pamoate induces paralysis of roundworms. It is very effective as single dose therapy with moderate side effects. Adverse reactions such as abdominal disturbance, headache and dizziness occur occasionally.
3. Tetramisole:  Tetramisole is very effective against nematodes especially Ascaris lumbricoides or roundworms. It acts by inhibiting the action of enzyme succinate dehydrogenate in the muscles of Ascaris lumbricoides or roundworms, inhibiting the conversion of fumerate to succinate, resulting in paralysis of muscles of worms. Nausea, vomiting, abdominal disturbance, headache and dizziness are minor side effects of tetramisole.
4. Mebendazole:  Mebendazole is extremely effective and well tolerated broad spectrum antihelminthic like pyrantel pamoate. Cure rates of 100% have been documented in the treatment of roundworm infections. Mebendazole inhibit the glucose intake by worms and thus kill them. Mebendazole also kills the ova of nematodes. Only 5-10% drug is absorbed from intestine and excreted in urine as metabolite. Around 90% of drug is utilized to kill the worms in the intestine. Mebendazole is embryotoxic and teratogenic. Its use should be avoided in children below 2 years of age and during pregnancy.