Anthelmintic Drugs

Anthelmintic Drugs

• Target metabolic processes present in parasites but not in the host
• Goal: eliminate organisms from the host and control the spread of infections

Drugs for the Treatment of Nematodes

• Nematodes: elongated roundworms with a complete digestive system, cause infections in the intestines, blood, and tissues
• Mebendazole:
  • Synthetic benzimidazole compound
  • First-line treatment for whipworms, pinworms, hookworms, and roundworms
  • Acts by binding to parasite β-tubulin, inhibiting microtubule polymerization, and expelling affected parasites in feces
  • Adverse effects: abdominal pain, diarrhea, rare but serious effects like convulsions in infants and increased risk of Stevens–Johnson syndrome or toxic epidermal necrolysis when combined with metronidazole
  • Contraindicated in pregnancy
• Diethylcarbamazine:
  • Preferred treatment for filariasis caused by Wuchereria bancrofti, Brugia malayi, or Brugia timori
  • Effectively kills microfilariae and targets adult worms
  • Administered orally with meals, rapidly absorbed, and primarily excreted through urine
  • Adverse effects: fever, nausea, vomiting, arthralgia, and headache
• Pyrantel Pamoate:
  • Effective treatment for pinworm and hookworm infections, particularly in the intestines
  • Functions as a depolarizing neuromuscular blocking agent, causing acetylcholine release and cholinesterase inhibition, resulting in worm paralysis and expulsion
  • Poorly absorbed after oral administration, acts locally
  • Adverse effects: generally mild, include nausea, vomiting, and diarrhea
• Ivermectin:
  • Drug of choice for cutaneous larva migrans, strongyloidiasis, and onchocerciasis (river blindness)
  • Effective in treating scabies and head lice through a topical formulation
  • Targets glutamate-gated chloride channel receptors, enhances chloride influx, leading to hyperpolarization, paralysis, and death of the worm
  • Administered orally, does not easily cross the blood–brain barrier
  • Contraindicated in pregnancy due to potential risks
  • May induce a Mazzotti reaction in onchocerciasis, with symptoms alleviated by antihistamines or steroids
• Moxidectin:
  • Alternative to ivermectin for treating onchocerciasis, sharing a similar mechanism of action without affecting adult worms

Drugs for the Treatment of Trematodes

• Trematodes: flatworms with a leaf-shaped structure, identified based on the tissues they infect, such as the liver, lung, intestine, or blood
• Praziquantel:
  • Preferred treatment for various parasitic infections, including schistosomiasis, most trematode infections (excluding fascioliasis), and certain cestode infections like taeniasis
  • Mechanism involves inducing contracture and paralysis in parasites by enhancing cell membrane permeability to calcium
  • Rapidly absorbed orally, should be taken with food
  • Metabolized extensively, inactive byproducts are primarily excreted through urine
  • Common side effects: dizziness, malaise, headache, and gastrointestinal disturbances
  • Phenytoin is contraindicated
  • Should not be used to treat ocular cysticercosis due to the risk of irreversible damage to the eye
• Triclabendazole:
  • Benzimidazole derivative used to treat fascioliasis caused by liver flukes (Fasciola hepatica and Fasciola gigantica)
  • Inhibits tubulin function, protein synthesis, and enzyme synthesis
  • Common side effects: abdominal pain, hyperhidrosis, and nausea
  • Use in pregnancy should be approached with caution due to limited available data

Drugs for the Treatment of Cestodes

• Cestodes: flat, segmented body that attaches to the host's intestine, lack a mouth and digestive tract throughout their life cycle
• Niclosamide:
  • No longer available in the United States, serves as an alternative to praziquantel for treating taeniasis, diphyllobothriasis, and other cestode infections
  • Mechanism involves inhibiting mitochondrial phosphorylation of adenosine diphosphate in the parasite, causing lethality for the cestode's scolex and segments, but not for the ova
  • To enhance efficacy, a laxative is administered before oral intake to purge the bowel of dead segments and improve ova liberation
  • Recommended to avoid alcohol within 1 day of niclosamide use