Anti-Protozoals and Anti-Helminthics Flashcards
List the protozoal infections of the GI tract
Small intestine:
- giardia lambila
- cryptospordium parvum
Large intestine:
- entamoeba histolytica
Describe the life cycle of G. lamblia and how it causes disease
2 stages of life cycle:
Trophozoite:
- flagellated and binucleated
- lives in upper part of small intestines
- adheres to brush border of epithelial cells (how it causes disease)
Cyst:
- formed when it forms resistant wall
- passes out in stools
- can survive for several weeks outside of host
How would you treat G.lamblia?
intestinal trophozoite is treated with metronidazole or tinidazole in a single dose
Describe the life cycle of C. parvum
- asexual and sexual development within host
- host ingests resistant oocysts
- release of infective sporozoites in small intestine
- invasion of intestinal epithelium
- divides to form merozoites that re-infect cells
- after sexual phase, oocytes are released
What is the treatment for C. parvum?
proposed:
- paromomycin
- nitazoxanide
- spiramycin
Describe the life cycle of E. histolytica
- cysts pass through stomach and excyst in small intestine to give rise to progeny
- these adhere to epithelial cells and cause damage through cytolysis
- after mucosal invasion cysts invasde RBCs to give rise to amoebic colitis
- trophozoite stages live in large intestines and pass out resistant infective cysts
How do you treat amoebiasis?
- intestinal infection: metronidazole
- if chronic infection, cysts will survive and cause relapse that is resistant to metronidazole
- so treated with diloxanide furoate
- if abscess then treat with metronidazole at higher and longer doses
How does metronidazole work?
- under aerobic conditions can generate toxic radicals that damage bacterial and protozoal DNA
- penetrates well in tissue
- used for E. histolytica and G. lambila
What are the side effects of metronidazole?
- metallic taste
- acute nauseous reaction to alcohol
What does diloxanide furoate do?
its an aminoglycoside that kills cystic amoebas but does not eradicate them from the gut
What are the side effects of diloxanide furoate?
- flatulence
- itchiness
- hives
What does paromomycin do?
its an aminoglycoside that kills cystic amoebas. Not absorbed by GI tract
What are the side effects of paromomycin?
- abdo cramps
- diarrhoea
- heartburn
- nausea
- vomiting
How can you prevent protozoal infections of GIT?
- improve hygiene and water supplies
- eat only freshly prepared food served hot
- avoid salads and fruit that cannot be peeled
- avoid tap water and ice cubes
What are the different classes of helminths?
- nematodes (round worms)
- crestodes (flat worms)
- trematodes (flukes - leaf shaped)
What are the pathological mechanisms of helminthic infections and its treatment?
- inflammation: anti-inflammatory drugs
- competition for nutrients: reduce worm burden and support nutrition
- space occupying lesions: helminth eradication and treatment of secondary effects
- stimulation of fibrosis: helminth eradication and treatment of secondary effects
What are the intestinal helminths (of nematode class) and their pathological mechanism?
- ascaris (competition for nutrients, space occupying lesions)
- hookworm (competition for nutrients)
- enterobius (inflammation)
- trichiuris (competition for nutrients)
What are the clinical features of trichiuris?
- whipworm that causes vague abdo symptoms
- trichiuris dysentery syndrome
- growth retardation
- intellectual compromise (due to micronutrient deficiency and mucosal integrity)
What is the clinical manifestation of E. vermicularis?
- threadworm that causes intense itching
- secondary bacterial infection
- mild catarrhal inflammation
- diarrhoea
- slight eosinophilia
What are the drugs used to treat intestinal helminths?
- praziquantel
- albendazole
- piperazine
- pyrantel
- levamisole
- ivermectin
- niclosamide
How does praziquantel work?
- increases calcium permeability of membranes depolarising them (may interfere with purine synthesis)
- cestodes
What are the side effects of praziquantel?
- dizziness
- headache
- drowsiness
- abdo cramps and nausea
- rash
- interacts with rifampicin, carbamazine, phenytoin
How does albendazole work?
- for nematodes, some protozoa and some cestode
- binds to colchicine sensitive receptor or tubulin to prevent polymerisation into tubules
- impaires glucose uptake and depletes glycogen stores
What are the side effects of albendazole?
- may be teratogenic
- persistent sore throat
- headaches
- dizziness
- acute liver failure
- aplastic anaemia and marrow suppression
