ANTIPARASITICS Flashcards
AMEBIASIS
•Amebiasis (amebic dysentery) is an intestinal tract
infection caused by Entamoeba histolytica
- GI disease can be acute or chronic
- Infection can be symptomatic or latent
- Symptoms can range from mild diarrhea to fulminating dysentery
- E.Histolytica exists in two forms
(1) cysts (can survive outside body)
(2) trophozoites (do not survive outside body)
- Trophozoites are liberated from ingested cysts within the intestinal lumen
- Liberated trophozoites migrate to the large intestine where they multiply and invade the intestinal mucosa.
- Trophozoites can enter bloodstream to result in a systemic invasion
- Life cycle completes by trophozoites returning to the cyst
form in the rectum and being expelled in the feces
ANTIAMEBICS: GAOLS OF THERAPY
1) Eliminate invading trophozoites
&
2) Eradicate intestinal carriage of the organism
ANTIAMEBICS:
• Luminal
Act on parasite in bowel lumen
• Systemic
Active both in intestinal wall and liver
• Mixed
Active against both luminal & systemic disease
MIXED ANTIAMEBICS
METRONIDAZOLE
TINIDAZOLE
METRONIDAZOLE
MOA:
• Once absorbed, metronidazole is non-enzymatically
reduced by reacting with reduced FERREDOXIN
- This reduction causes the production of cytotoxic compounds
- The cytotoxic compounds bind to proteins & DNA, resulting in unstable molecules and cell death
METRONIDAZOLE
PK
AE
MIXED LUMINAL + SYSTEMIC AGENT
PK:
- Oral
- Well distributed (inc. vaginal & seminal fluids, saliva, breast milk & CSF)
- Undergoes hepatic oxidation & glucuronidation (CYP P450’s)
AE:
- GI distress
- ***_Disulfiram-like reaction***_ (avoid alcohol intake)
- Unpleasant metallic taste
- Oral moniliasis
- Dark coloration of urine
- Leukopenia, dizziness, ataxia.
- _Safety in pregnancy NOT established*****_
TINIDAZOLE
MIXED LUMINAL + SYSTEMIC AGENT
- 2nd generation nitroimidazole
- Similar to metronidazole but better tolerated and has shorter treatment course
Clinical Applications
_• Amebiasis
• Amebic liver abscess_
_• Giardiasis
• Trichomoniasis_
AE:
• Same as metronidazole but reports indicate shorter duration of effects with tinidazole
LUMINAL ANTIAMEBICS
- 1) Diloxanide furoate
- 2) Iodoquinol
- 3) Paromomycin
DILOXANIDE FUROATE
- Used as sole agent for treatment of ASYMPTOMATIC AMEBIASIS
- Converted in gut to active form
Adverse Effects
• Mild (GI distress)
Not currently available in US – however remains
luminal amebicide of choice
IODOQUINOL
LUMINAL AGENT (ANTIAMEBIC)
- Orally active against luminal trophozoite and cyst forms of E.histolytica
- Used as an alternative to diloxanide furoate for mild- severe infections
Adverse Effects
- Rash, diarrhea, dose-related ***_peripheral neuropathy**** (exam Q)_
- Long term use should be avoided (due to risk of optic neuritis)***
PAROMOMYCIN
LUMINAL ANTIAMEBIC
- Aminoglycoside antibiotic
- Effective only against luminal forms of E.histolytica and tapeworm
- Sometimes used with tetracyclines for mild intestinal
disease
• Alternative agent for cryptosporidiosis in AIDS patient
MOE/AE:
- AmebiCIDAL (causes cell membranes to leak)
- Interferes with bacterial protein synthesis (binds to 30S ribosomal subunits)
- Reduces intestinal flora population
Adverse Effects
- GI distress & diarrhea
- Systemic absorption may lead to headaches, dizziness, rashes and arthralgia
SYSTEMIC ANTIAMEBICS
1) CHLOROQUINE
2) EMETINE
3) DEHYDROEMETINE
- useful for treating liver abscesses or intestinal wall infections
CHLOROQUINE
SYSTEMIC ANTIAMEBIC
• Used in combination with
- metronidazole & (“mixed” luminal and systemic agent)
- diloxanide furoate (luminal agent)
MOA
• Eliminates trophozoites in liver abscesses
EMETINE +
DIHDROEMETINE
SYSTEMIC ANTIAMEBIC
- BACKUP DRUGS for treatment of SEVERE intestinal or hepatic amebiasis
- Used in combination with a luminal agent
MOA
• Inhibit protein synthesis by blocking ribosomal movement along messenger RNA
PK:
- IM or SC
- Concentrate in liver (persists for 1 month)
• Slowly metabolized & eliminated
EMETINE +
DIHDYROEMETINE
AE:
_• Pain at site of injection****** on exam!!!_
• Transient nausea
• Cardiotoxicity
• Neuromuscular weakness
- Dizziness
- Rash
TREATMENT OF AMEBIASIS
ASYMPTOMATIC, INTESTINAL INFECTION
DOC:
1) DILOXANIDE FUROATE
ALTERNATIVE DRUG(S):
1) IODOQUINOL
2) PAROMOMYCIN
TREATMENT OF AMEBIASIS
MILD-MODERATE INTESTINAL INFECTION
DOC:
1) METRONIDAZOLE AND
2) DILOXANIDE FUROATE
ALTERNATIVE DRUGS:
1) Tinidazole OR
2) Tetracycline OR
3) Erythromycin + diloxanide furoate
TREATMENT OF AMEBIASIS
SEVERE INTESTINAL INFECTION
DOC:
1) METRONIDAZOLE OR TINIDAZOLE
AND
2) DILOXANIDE FUROATE
ALTERNATIVE DRUGS:
1) Tetracycline OR Emetine OR Dihydroemetine
AND
2) DILOXANIDE FUROATE
TREATMENT OF AMEBIASIS
HEPATIC ABSCESS + OTHER EXTRAINTESTINAL DISEASE
DOC:
1) METRONIDAZOLE OR TINIDAZOLE
AND
2) DILOXANIDE FUROATE
Alterative drugs:
1) Emetine OR Dihydroemetine
AND
2) Chloroquine
AND
3) Diloxanide Furoate
HELMINTHS
Nematodes
- Elongated roundworms that possess a complete digestive system.
- Cause infections of intestine as well as blood & tissue.
Trematodes
• Leaf-shaped flatworms generally characterized by tissues they infect: liver, intestinal, blood flukes
Cestodes
- Flat, segmented body which attach to host’s intestine
- Lack mouth & digestive system throughout life cycle
ANTIHELMINTHIC DRUGS
• In most cases broad spectrum agents cure or control most human worm infections
• Some systemic infections only respond partially to
antihelminthic drugs (cysticercosis, echinococcosis,
filariasis, trichinosis)
Antihelminthic drugs can act either:
- locally (to expel worms from GI tract) or,
- systemically (to eradicate adult helminths or developmental forms)
BENZIMIDAZOLES
ANTIHELMINTHICS
1) ALBENDAZOLE
2) MEBENDAZOLE
3) THIABENDAZOLE
NOTE: ALL are CATEGORY C and CONTRINDICATED IN PREGNANCY!!!!
ALBENDAZOLE
BENZIMIDAZOLE - an ANTIHELMINTHIC DRUG
• Used in the treatment of CESTODE infestations, such as
- cysticercosis (Taenia solium larvae) and
- hydatid disease (Echinococcus granulosis)
MOA
- Inhibits microtubule synthesis & glucose uptake
- ATP production is decreased resulting in worm immobilization and death
PK:
- Oral (erratically absorbed, enhanced by high-fat meal)
- Extensive first-pass metabolism, including rapid sulfoxidation to active metabolite
ALBENDAZOLE
AE
- Short course therapy (1-3 days) = mild & transient (headache, nausea)
- ****HYDATID treatment (3 months) = risk of hepatotoxicity, agranulocytosis or pancytopenia**************
- Treatment is _associated with inflammatory responses to dying parasites in CNS*******_ (headache, vomiting, hyperthermia, convulsions, mental changes)
- Contraindicated in pregnancy & children < 2y (FDA Category C)
MEBENDAZOLE
DOC FOR?
BENZIMIDAZOLE - ANTIHELMINTHIC DRUG
Drug of choice in the treatment of infections by:
- 1) Whipworm (Trichuris trichiura) (in tunnel) pig with spirals on his suit
- 2) Pin worm (Enterobius vermicularis) (in tunnel, “vermin lady” who’s first character introduced, going into the hole)
- 3) Hookworms (Necator americanus & Ancylostoma duodenale) (in tunnel, is american dude swinging)
- 4) Roundworm (Ascariasis lumbricoides) (in tunnel, huge lumbering tree man in back)
MEBENDAZOLE
BENZIMIDAZOLE (Antihelminthic drug)
• Inhibits formation of helminth microtubules
- Irreversibly blocks glucose uptake
- Affected parasites are expelled with feces
Pharmacokinetics
- Oral (chewable) – nearly insoluble in aqueous solution, take with high-fat meal
- Undergoes first-pass metabolism to inactive compounds