July 4, 2015
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Albenza

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Albenza




CLINICAL PHARMACOLOGY

Mechanism Of Action

ALBENZA (albendazole) is a synthetic, antihelminthic drug of the class benzimidazole [see Microbiology].

Pharmacokinetics

Absorption

Albendazole is poorly absorbed from the gastrointestinal tract due to its low aqueous solubility. Albendazole concentrations are negligible or undetectable in plasma as it is rapidly converted to the sulfoxide metabolite prior to reaching the systemic circulation. The systemic anthelmintic activity has been attributed to the primary metabolite, albendazole sulfoxide. Oral bioavailability appears to be enhanced when albendazole is coadministered with a fatty meal (estimated fat content 40 grams) as evidenced by higher (up to 5-fold on average) plasma concentrations of albendazole sulfoxide as compared to the fasted state.

Maximal plasma concentrations of albendazole sulfoxide were achieved 2 hours to 5 hours after dosing and were on average 1310 ng/mL (range 460 ng/mL to 1580 ng/mL) following oral doses of albendazole (400 mg) in 6 hydatid disease patients, when administered with a fatty meal. Plasma concentrations of albendazole sulfoxide increased in a dose-proportional manner over the therapeutic dose range following ingestion of a high-fat meal (fat content 43.1 grams). The mean apparent terminal elimination half-life of albendazole sulfoxide ranged from 8 hours to 12 hours in 25 healthy subjects, as well as in 14 hydatid and 8 neurocysticercosis patients.

In a study conducted in 113 fed and 117 fasted healthy subjects, ALBENZA chewable tablets were bioequivalent to ALBENZA tablets following single 400 mg oral doses of albendazole. In this study, the average time to reach the maximal plasma concentrations of albendazole sulfoxide was 4.5 hours (range 2 to 10 hours) with a fatty meal (fat content 60 grams) and at 3 hours (range 1 to 5 hours) in the fasted state. Following administration of ALBENZA chewable tablets, average maximal plasma concentrations of albendazole sulfoxide were 804 ng/mL (range 202 to 2244 ng/mL) and 218 ng/mL (range 54 to 592 ng/mL) in the fed and fasted states, respectively. The apparent elimination half-life of albendazole sulfoxide was comparable between ALBENZA chewable tablets and ALBENZA tablets when both were given either under fed or fasted conditions.

Following 4 weeks of treatment with albendazole (200 mg three times daily), 12 patients' plasma concentrations of albendazole sulfoxide were approximately 20% lower than those observed during the first half of the treatment period, suggesting that albendazole may induce its own metabolism.

Distribution

Albendazole sulfoxide is 70% bound to plasma protein and is widely distributed throughout the body; it has been detected in urine, bile, liver, cyst wall, cyst fluid, and cerebrospinal fluid (CSF). Concentrations in plasma were 3-fold to 10-fold and 2-fold to 4-fold higher than those simultaneously determined in cyst fluid and CSF, respectively.

Metabolism and Excretion

Albendazole is rapidly converted in the liver to the primary metabolite, albendazole sulfoxide, which is further metabolized to albendazole sulfone and other primary oxidative metabolites that have been identified in human urine. Following oral administration, albendazole has not been detected in human urine. Urinary excretion of albendazole sulfoxide is a minor elimination pathway with less than 1% of the dose recovered in the urine. Biliary elimination presumably accounts for a portion of the elimination as evidenced by biliary concentrations of albendazole sulfoxide similar to those achieved in plasma.

Specific Populations

Pediatrics

Following single-dose administration of 200 mg to 300 mg (approximately 10 mg/kg) ALBENZA to 3 fasted and 2 fed pediatric patients with hydatid cyst disease (age range 6 to 13 years), albendazole sulfoxide pharmacokinetics were similar to those observed in fed adults.

Geriatrics

Although no studies have investigated the effect of age on albendazole sulfoxide pharmacokinetics, data in 26 hydatid cyst patients (up to 79 years) suggest pharmacokinetics similar to those in young healthy subjects.

Microbiology

Mechanism of Action

ALBENZA binds to the colchicine-sensitive site of β-tubulin inhibiting their polymerization into microtubules. The decrease in microtubules in the intestinal cells of the parasites decreases their absorptive function, especially the uptake of glucose by the adult and larval forms of the parasites, and also depletes glycogen storage. Insufficient glucose results in insufficient energy for the production of adenosine trisphosphate (ATP) and the parasite eventually dies.

Mechanism of Resistance

Parasitic resistance to albendazole is caused by changes in amino acids that result in changes in the β-tubulin protein. This causes reduced binding of the drug to β-tubulin.

In the specified treatment indications, albendazole appears to be active against the larval forms of the following organisms:

Echinococcus granulosus
Taenia solium

Last reviewed on RxList: 6/29/2015
This monograph has been modified to include the generic and brand name in many instances.

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