parasitic%20infections
PARASITIC INFECTIONS
Gastrointestinal parasitic infection symptoms include abdominal pain, diarrhea, dysentery, flatulence, malabsorption and symptoms of biliary obstruction.
It can be caused by protozoan parasites and helminths.
Host susceptibility factors in gastrointestinal parasitic infections are nutritional status, intercurrent disease, pregnancy, immunosuppressive drugs and presence of a malignancy.
Knowledge of the geographic distribution of parasites is helpful in the diagnosis of patients.

Pharmacotherapy

 Recommended Therapy For Protozoan Parasites
Pathogen Drug 
Preferred Agents Alternative Agents 
Cryptosporidium sp (Cryptosporidiosis) Nitazoxanide or
Paromomycin + Azithromycin
 -

Entamoeba histolytica (Amoebiasis)

  • Asymptomatic cyst passer
Iodoquinol or Paromomycin Diloxanide furoate or Etofamide

E histolytica (Amoebiasis)

  • Mild-moderate intestinal disease
Metronidazole or Tinidazole Ornidazole or Secnidazole

E histolytica (Amoebiasis)

  • Severe intestinal disease or liver abscess
Metronidazole or Tinidazole Chloroquine or Secnidazole
Giardia lamblia (Giardiasis) In most immunocompetent patients, giardiasis is self-limiting & does not require treatment. In nonendemic areas, asymptomatic carriers of giardiasis are treated
Metronidazole Albendazole, Furazolidone, Nitazoxanide, Ornidazole, Paromomycin, Quinacrine, Secnidazole or Tinidazole

 Recommended Therapy For Helminths
Pathogen Drug 
Preferred Agents Alternative Agents 
Cestodes (Tapeworms)
Taenia saginata, Taenia solium, Diphyllobothrium caninum, Diphyllobothrium latum Praziquantel Niclosamide
Nematodes (Roundworms)
Ascaris lumbricoides (Ascariasis) Albendazole, Ivermectin, Mebendazole or Nitazoxanide Levamisole, Piperazine or Pyrantel pamoate
Ancylostoma duodenale, Necator americanus (Ancylostomiasis) (Hookworms) Albendazole, Mebendazole or Pyrantel pamoate Levamisole
Capillaria philippinensis (Capillariasis) Mebendazole Albendazole
Enterobius vermicularis (Pinworm or Threadworm) Albendazole, Mebendazole or Pyrantel pamoate Piperazine
Strongyloides stercoralis (Strongyloidiasis) Albendazole, Ivermectin, Mebendazole or Thiabendazole  -
Trichuris trichiura (Whipworm) Mebendazole Albendazole, Ivermectin or Nitazoxanide
Trematodes (Flukes)
Clonorchis sinensis (Oriental liver fluke) Albendazole orPraziquantel  -
Fasciola hepatica (Fascioliasis) Bithionol or Triclabendazole Nitazoxanide
Fasciolopsis buski, Heterophyes heterophyes Metagonimus yokogawai (Intestinal flukes) Praziquantel  -
Opisthorchis viverrini (Southeast Asian liver fluke) Albendazole or Praziquantel  -
Paragonimus westermani (Lung flukes) Praziquantel Bithionol
Schistosoma haematobium Praziquantel Metrifonate
Schistosoma japonicum Praziquantel  -
Schistosoma mansoni Praziquantel Oxamniquine

Drugs for Treatment of Amoebiasis

Luminal Amoebicides

  • Eg Diloxanide furoate, Iodoquinol, Paromomycin
  • These agents are effective in treating organisms in the bowel lumen
    • May be used in patients w/ asymptomatic E histolytica infection
  • Recommended for asymptomatic cyst passers
    • To avoid the risk of developing invasive disease
    • To prevent secondary spread
  • When asymptomatic cyst carriage persists after treatment for amoebic dysentery or liver abscess, further treatment w/ a luminal amoebicide is mandatory, otherwise relapse is frequent
  • Paromomycin
    • Acts directly on amoeba w/ antibacterial activity against normal & pathogenic organisms in GI tract; binds to 30s ribosomal subunits interfering w/ bacterial protein synthesis
    • Temporarily eliminates diarrhea in human immunodeficiency virus (HIV) patients who have cryptosporidiosis
    • May also be used in treatment of cryptosporidiosis & giardiasis

Tissue Amoebicides

  • Eg Chloroquine & Nitroimidazole derivatives (Metronidazole, Nimorazole, Ornidazole, Secnidazole & Tinidazole)
  • These agents are effective in treating invasive amoebiasis but are less effective in treating organisms in the bowel lumen
  • Chloroquine binds & inhibits DNA & RNA polymerase; it also raises parasite’s internal pH, restricting its growth
  • Nitroimidazole derivatives cause damage to parasite DNA helical structure resulting in strand breakage & impaired template function

Other Antiprotozoan Drugs

  • Eg Furazolidone, Nitazoxanide, Quinacrine

Furazolidone

  • Used for the treatment of giardiasis
  • Furazolidone is as effective as Metronidazole in the treatment of giardiasis
  • Action: Causes damage to intracellular components

Nitazoxanide

  • Action: Inhibits growth of sporozoites & oocysts of Cryptosporidium sp & trophozoites of G lamblia

Quinacrine (Mepacrine)

  • Action: Suggested action is binding to parasite DNA thereby inhibiting RNA transcription & protein translation

Anthelminthic Drugs

Albendazole

  • Has an exceptionally broad spectrum of antiparasitic activity
  • Widely used for intestinal nematode infections
  • Decreases ATP production in worms

Bithionol

  • Preferred agent for F hepatica
  • Release of worm antigens may cause reactions eg urticaria, photosensitivity reactions & GI symptoms

Ivermectin

  • As effective as Thiabendazole against S stercoralis but has fewer untoward effects
  • Action: Causes hyperpolarization of muscle & nerve cells of parasite leading to paralysis

Levamisole

  • Action: Causes muscle paralysis in susceptible worms

Mebendazole

  • Widely used for treatment of intestinal nematodes
  • Poorly absorbed from the GI tract resulting in a low frequency of side effects
  • Action: Blocks glucose & nutrient uptake irreversibly in susceptible worms

Metrifonate

  • Alternative to Praziquantel in the treatment of S haematobium infection
  • Action: Inhibits acetylcholinesterase

Niclosamide

  • Action: Causes necrosis of head & segments of tapeworms

Oxamniquine

  • Used only for S mansoni infection
  • Action: Causes blood fluke to transfer from mesenteric veins to the liver where the males are retained; females return to mesentery but cannot release eggs anymore

Piperazine

  • Action: Blocks acetylcholine effects at neuromuscular junction causing muscle paralysis

Praziquantel

  • Highly effective against all Schistosoma sp that infect humans, adult & larval form of cestodes
    • Drug of choice for liver flukes
  • Action: Increases cell permeability in helminths w/ loss of intracellular calcium & paralysis of musculature
  • Drug resistance is a possibility, especially in countries practicing mass chemotherapy as a control measure

Pyrantel pamoate

  • Used for the treatment of intestinal nematodes (roundworm, hookworm & pinworm)
  • Action: Blocks acetylcholine effects at neuromuscular junction causing muscle paralysis

Thiabendazole

  • Active against many intestinal adult nematodes & larval forms in tissues
  • High frequency of untoward effects & the availability of alternative agents have limited its usefulness

Non-Pharmacological Therapy

Adequate Hydration & Nutrition

  • Patients w/ parasitic infections frequently suffer from malabsorption, vomiting & diarrhea, resulting in malnutrition
  • Ensure that patient’s nutritional & hydration status are maintained at acceptable levels

Replacement of Fluid & Electrolyte Losses

  • Vomiting & diarrhea result in fluid & electrolyte losses, mainly Na & K

Blood Transfusion & Treatment w/ FeSO4

  • These measures may be necessary in hookworm infections which may cause severe anemia
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