Anti-Parasitic Medications

how to approach treatment for parasites

1. group the organism based on whether its a helminth or a protozoa

2a. if its a protozoa, start with metronidazole for broad-spec and then get more specific

2b. if its a helminth, start with albendazole or mebendazole + praziquantel then get more specific

MOA of bendazoles (albendazole, mebendazole, thiabendazole)

bind to tubulin dimer to prevent polymerization and inhibit nematodal systems and microtubule assembly, leads to impaired glucose uptake and energy store depletion

AE's of albendazole

epigastric distress, liver dysfunction (C/I with cirrhosis)

AE's of mebendazole

N/V/D, hypersensitivity rxns, caution with cirrhosis, C/I in pregnancy

AE's of thiabendazole

chelating agent (more toxic than other bendazoles or ivermectin), GI and neuropsych symptoms, C/I in pregnancy, hepatic, and renal disease

MOA of pyrantel pamoate

neuromuscular blocking agent, induces activation of nicotinic ACh receptor (causes spastic paralysis of the worm)

indication for pyrantel pamoate

broad-spectrum anthelmintic for roundworm, pinworm, and hookworm that is effective against mature and immature forms in GI tract

AE's of pyrantel pamoate

GI symptoms, headache, rash, fever, caution in patients with liver dysfxn (causes transient AST/ALT elevation)

MOA of piperazine

GABA-receptor agonist that causes hyperpolarization, muscle relaxation, and flaccid paralysis of ascaris (alternative treatment for ascariasis)

AE's of piperazine

N/V/D, caution in liver/renal disease, C/I in pts with epilepsy or chronic neurologic disease

MOA of diethylcarbamazine

immobilizes microfilaria and alters surface structure, displacing them from tissues and making them more susceptible to destruction by host immune system

AE's of diethylcarbamazine

headache, malaise, anorexia, weakness, nausea, caution in pts with HTN or renal disease

Mazzotti reaction

reaction to dying microfilariae

sx: fever, malaise, papular rash, cough, leukocytosis, muscle or joint pain

prevent by pretreating with glucocorticoids and antihistamines

MOA of ivermectin

intensifies GABA-mediated transmission of signals in peripheral nerves

indication for ivermectin

DOC for strongyloidiasis, onchocerciasis, also used for scabies, lice, cutaneous larva migrans, and ascaris worms

AE's of ivermectin

fatigue, dizziness, N/V, rash, Mazzotti rxn, C/I with use of barbiturates, BZDs, and valproate (same MOA)

MOA of praziquantel

increases permeability of trematode and cestode cell membranes to Ca 2+, leading to paralysis, dislodgement, and death of flukes

AE's of praziquantel

eosinophilia, headache, dizziness, N/V/D, myalgia, rash

MOA of metronidazole

binds proteins and DNA and is cytotoxic, prodrug that is activated by nitro group of parasite

drug interactions with metronidazole

CYP2A9 and CYP2A6 inhibitor (eg. warfarin, phenytoin, ritonavir)

indication for metronidazole

DOC for amebiasis, giardiasis, and trichomoniasis; 2nd line for C. diff

AE's of metronidazole

nausea, headache, metallic taste, paresthesias, disulfiram-like effect (no alcohol), C/I in pregnancy and nursing

tinidazole

safer alternative to metronidazole

MOA of paromomycin sulfate

binds to 30S ribosomal subunit that inhibits protein synthesis

indication for paromomycin sulfate

DOC for cryptosporidiosis, alternative for leishmaniasis

AE's of paromomycin sulfate

accumulate in patients with renal insufficiency and cause renal toxicity

iodoquinol

unknown MOA

used for luminal amebicide with metronidazole

AE's: N/V/D, anorexia, may increase protein-bound serum iodine

diloxanide furoate

unknown MOA

used for luminal amebicide, 2nd line after paromomycin

tx for ascariasis

1st line: literally any bendazole

alternative: pyrantel pamoate, piperazine

tx for filariasis

diethylcarbamazine

tx for loaisis

diethylcarbamazine

tx for tropical eosinophilia

diethylcarbamazine

tx for onchocerciasis

1st line: ivermectin

alternative: diethylcarbamazine

tx for strongyloidiasis

1st line: ivermectin

alternative: thiabendazole

tx for schistosomiasis

praziquantel

tx for amebiasis

asymptomatic: luminal amebicides

colitis + dysentery: metronidazole + luminal amebicide

extraintestinal infection: metronidazole/tinidazole + luminal amebicide

tx for giardia

metronidazole

tx for taenia solium

praziquantel

tx for diphyllobothrium latum

praziquantel

tx for toxoplasmosis

sulfadiazine + pyrimethamine

tx for parasitic necrotizing fasciitis

amphotericin B

tx for malaria

1st line: chloroquine

if resistant: mefloquine or atovaquone/proguanil

tx for babesiosis

atovaquone + azithromycin

tx for chagas disease

benznidazole or nifurtimox