Benzimidazoles

Question 1

Benzimidazoles

Answer 1

Albendazole
Mebendazole
Thiabendazole

Primarily used for helminthes (worms)
Ranging from common pinworms in children to pathogens causing massive cystic lesions in brain

Most intestinal worms can be cured with a single dose
Tissue invasive diseases- prolonged courses

Mebendazole/thiabendazole no longer available in US

Question 2

Benzimidazoles MOA

Answer 2

Interfere with elongation of the microtubules that are responsible for parasitic cellular structure- leading to disruption of growth and division

Question 3

Benzimidazoles Spectrum

Answer 3

Nematodes (roundworms):
Ascaris lumbricoides (roundworm)
Enterobius vermicularis (pinworm)
Necator americanus (hookworm)
Strongyloides stercoralis (threadworm)

Cestodes (tapeworms)
Echinococcus (liver abscess)
Taenia solium (neurocysticercosis)

Question 4

Benzimidazoles Adverse Effects

Answer 4

Albendazole very well tolerated (especially as single dose)

Multi dose regimens- primarily GI; hepatotoxicity and neutropenia rare

Thiabendazole most toxic- CNS effects

Generally avoid them in pregnancy (some data- may be safe after first trimester)

Question 5

Benzimidazoles Important Facts

Answer 5

Appear to be C450 substrates 
Strong inducers (phenytoin/rifampin) may lower serum levels 

Oral absorption of albendazole is limited; not a problem for intestinal nematode infections; interactions would not be a concern
Be careful of interactions with treatment of systemic infections

For some parasitic infections, drug induced killing of the parasite releases antigens that can cause allergic reactions
Corticosteroids sometimes given to mitigate the effect

Question 6

Benzimidazoles Good For

Answer 6

Single dose- most intestinal nematode infections

Alternative for treatment of Strongyloides

Treatment for tissue invasive Echinococcus or Taenia infection