Antiamoebic drugs

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ANTI-AMOEBIC DRUGS Dr.S.P.Dhanya Assistant Professor Department of Pharmacology Govt TDMC Alappuzha

Therapeutic Classification:

Therapeutic Classification Tissue Amoebicides For both intestinal and extraintestinal amoebiasis Nitroimidazole : METRONIDAZOLE TINIDAZOLE SECNIDAZOLE ORNIDAZOLE SATARNIDAZOLE Alkaloids : EMETINE DEHYDROEMETINE For extraintestinal amoebiasis CHLOROQUINE

Luminal amoebicides:

Luminal amoebicides Diloxanide furoate , Nitazoxanide Quiniodoclor , Diiodohydroxyquin Paramomycin,Tetracycline


Metronidazole Nitroimidazole Spectrum G. lamblia T.vaginalis H.pylori B.fragilis , Fusobacterium Cl.perfringens,Cl.difficle Peptcocci,Spirochetes,anaerobic streptococci

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Infected cell Reduced to highly reactive nitro radicals Ferredoxin MOA

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Competes with biological electron acceptor Acts as electron sink –electrons by PFOR p/w Energy metabolism disrupted Reduced to highly reactive nitro radicals

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Deficiency in mechanism generating nitro radicals Not a therapeutic problem. Some strains of T. vaginalis,H.pylori Resistance

Pharmacokinetics :

Pharmacokinetics Oral, I/V infusion, topical gel, cream. Absorption ----- well & almost complete from GIT, some unabsorbed drug reaches colon . Distribution------- Rapid & wide. Distributed to all tissues & high concentrations in body fluids– CSF, Vaginal secretions ,saliva, semen Metabolism --------- liver t ½ -------- 8 hrs Excretion : urine.

Adverse Effects :

Adverse Effects GIT: Dry mouth, metallic taste --- most common. Nausea, anorexia, abdominal cramps , Diarrhea. Neurotoxicity: Headache, Insomnia, numbness or paraesthesias , dizziness Disulfiram like action with alcohol. Rarely glossitis , dryness of mouth, neutropenia,rash , seizures.

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Contraindications Neurological diseases ,Blood dyscrasias, First trimester pregnancy, alcoholics Drug interactions Potentiate Anticoagulant effect of Warfarin. Metabolism of Metronidazole induced by Phenytoin & Phenobarbitone & Cimetidine may inhibit it. - Metronidazole increases Lithium toxicity-decrease renal elimination

Therapeutic Uses:

Therapeutic Uses Amoebiasis : DOC in all tissue infections Acute intestinal Amoebiasis / Amoebic colitis with dysentery- - 800 mg TDS-10 d course with a luminal amoebicide Mild intestinal amoebiasis - 400mg TDS for 5-7 days Hepatic Amoebiasis :1g iv followed by 0.5g every 8-12 hr till oral therapy-------------10 d course cures 95 % cases For cases in which initial therapy fails – Aspiration of abscess & addition of Chloroquine

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Giardiasis Treatment of choice--- 400mg TDS 7days or 2g/d for 3 days Trichomoniasis : DOC , 400mg TDS 7days Vaginal & urethral Trichomoniasis ----- topically. Bacterial vaginosis : Can be used topically as a gel.

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Anaerobic bacterial infection -after pelvic surgery, appendicectomy Eradication of H. Pylori in Peptic ulcer- -a component of 14 days triple therapy regimen . Metronidazole 500mg BD along with a proton pump inhibitor BD, Clarithromycin 500mg BD Pseudomembranous enterocolitis by Clostridium difficile . DOC . ( Vancomycin is the drug of second choice)

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Ulcerative Gingivitis, Trench mouth Facilitates extraction of adult guinea worm in Dranculosis Acne rosacae .

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second generation congener longer acting –once daily dose. Short course – 2g daily, single dose- - for 3 days. similar to Metronidazole Better tolerated Effective against cysts of E.histolytica . Amoebiasis,Trichomoniasis,Giardiasis,H pylori Tinidazole


Secnidazole,Ornidazole Longer acting ------t1/2=17-29h Single 2gm dose is given Amoebiasis,Trichomoniasis,Giardiasis,Non specific vaginosis

Satarnidazole :

Satarnidazole Longer acting----t1/2=14h Better tolerability No nausea,vomiting,metallic taste No neurological effects or disulfiram like reaction Doesnot produce acetamide metabolite which is a weak carcinogen


Emetines Source: Emetine --- Alkaloid— Cephaelis iIpecacuanha Effective against the trophozoites of EntAmoeba histolytica . MOA - inhibits protein synthesis……arrest intraribosomal translocation of t RNA-AA complex Symptomatic relief in 1-3 days but used only in acute conditions where other drugs are not tolerated- ---- used S/C or I/M injection in a supervised setting

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Adverse Effects Highly toxic- hypotension,tachycardia,ECG changes,myocarditis,Cardiac arrhythmias, Cardiac failure Diarrhea , nausea & vomiting Pain & tenderness at site of injection/ sterile abscess. Muscle weakness & discomfort. Dehydroemetine ---Synthetic analog-less toxic Contraindications: Cardiac /renal disease Young children , pregnancy.


Chloroquine Antimalarial drug Tissue Amoebicide specially against Amoebic Hepatitis & Liver Abscess. Concentrated in liver; kills trophozoites of E. histolytica Not effective for amoebic colitis or luminal amoebae because absorbed in upper intestine. Long duration, frequent relapse but safe-----complete eradication USE: Hepatic amoebiasis / abscess; not responding to Metronidazole

Diloxanide Furoate (Luminal amoebicide):

Diloxanide Furoate (Luminal amoebicide ) Highly effective against cysts Pharmacokinetics: Given orally, in gut splits into Diloxanide & furoic acid. 90% Diloxanide is absorbed & conjugated to form glucuronide -- excreted in urine MOA: Directly kill trophozoite responsible for production of cyst Single course-high cure rate in mild intestinal amoebiasis and asymptomatic cyst passers Given after tissue amoebicide to eradicate cysts Adverse effects-Flatulence, nausea, itching, urticaria


Nitazoxanide Prodrug Following oral administration, rapidly hydrolyzed to i active metabolite, tizoxanide Mechanism-interference with PFOR enzyme dependent electron transfer reaction. Uses- Giardiasis,Cryptosporidiasis,Amoebic dysentery Adverse effects-abdominal pain, nausea, vomiting, diarrhea, headache


IODOQUINOL Luminal amobecide used with metronidazole to treat Amoebic infections. Only effective against trophozoites in lumen. 90% unabsorbed → amoebicide . 1 0% absorbed →Metabolized to Glucronides ,excreted in urine. Half life 11-14 hrs. Adverse effects Iodism : Dermatitis, urticaria , pruritis ,fever. Diarrhoea , anorexia, nausea, vomiting, abdominal pain. Headache, severe neurotoxicity,SMON

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Aminoglycoside antibiotic. Not significantly absorbed Less toxic Superior to Diloxanide furoate in clearing asyptomatic infections. No effect on extra-intestinal amoebic infections. Also used in visceral leishmaniasis parenterally . A/E: Abdominal Distress & diarrhea . Paromomycin sulphate

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Tetracycline Luminal amoebicide Disturbs the symbiosis between normal intestinal flora & E . histolytica -----------amoebae grow at expense of normal intestinal flora . Tetracyclines are broad spectrum antibiotics & kill these flora leading to death of E . histolytica also. Used in resistant and chronic cases.

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Treatment of specific forms of Amoebiasis : Asymptomatic intestinal infection. Generally not treated in endemic area. In non-endemic area treated with luminal Amoebicide . Diloxanide furoate alternating with metronidazole / tinidazole Iodoquinol Paromomycin . May be combined with tetracyclines .

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Amoebic Colitis with dysentery: Mild to moderate intestinal infection: DOC ---- Metronidazole & Luminal agent. Alternative ---- Diloxanide furoate , Iodoquinol , Paromomycin + Tetracycline Severe intestinal infection DOC ---- Metronidazole & Luminal agent Alternative ---- dehydroemetine or emetine ,Diloxanide furoate , Iodoquinol , Paromomycin + Tetracycline

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Hepatic abscess, Amoeboma & other Extra intestinal Infections DOC ---- Metronidazole & luminal agent. For unusual cases--- not responding to Metronidazole Chloroquine + Luminal agent. Dehydroemetine or emetine.

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