Albendazole is an effective anti-parasitic drug that works by inhibiting the polymerization of tubulin in parasitic worms, interfering with their cell division and glucose supply. Its pharmacokinetics show that absorptions vary based on whether it is taken with food, with the active metabolite, albendazole sulfoxide, having a half-life of approximately 8.5 hours. Generally well tolerated, albendazole has minimal side effects but is contraindicated in certain conditions, such as pregnancy and liver disease.

1. Albendazole Mechanism of Action &
Pharmacokinetics Explained: Key Insights for
Health Professionals
​
Introduction
Have you ever thought about how albendazole works in our body? Today, we will
discuss the albendazole mechanism of action (moa) and its pharmacokinetics.
We take albendazole medicine for deworming, get relief and forget. Many people
have a curiosity to know the fate of the drug.
Albendazole is a miracle drug because it uniquely kills parasitic worms.
Albendazole medicine is basically used for deworming, and it comes on the
essential drugs list of WHO (World Health Organisation).

2. Here, I have made an easy guide to understanding the albendazole mechanism of
action (moa), pharmacokinetics, side effects, and contraindications.
In this post, you will learn how albendazole works and how the body reacts in
response to albendazole.
How does albendazole work in the body?
Albendazole basically works on the genetic material of parasites. Let’s understand
the parasite’s genetic structure.
The genetic material of the parasite could be DNA or RNA, which depends on the
type of parasite.
Normally, parasites or helminths contain microtubules in the nucleus. These
microtubules are fundamental components of parasites.
Microtubules are basically polymers that are made up of tubulin protein subunits
such as alpha and beta tubulin.
These alpha and beta tubulins are monomers. During cell division, alpha and beta
subunits get polymerized which converts into dynamic structures called
Microtubules.
The principal mechanism of action of albendazole is inhibiting polymerization and
the cell division process of parasites. But it also depends on the types of parasitic
worms –
Albendazole mechanism of action for intestinal worms
When you take albendazole, it goes to your small intestine, which is directly active
against intestinal worms.
Albendazole strongly binds to the β-tubulin site of worm parasites. As a result, it
inhibits the polymerization process that destroys the assembly of the worm’s
microtubules.

3. In other words, it stops the cell division process. Moreover, albendazole stops egg
production and prevents the hatching of existing eggs.
Albendazole also stops the glucose supply for helminths.
You don’t need albendazole in your blood circulation for intestinal helminths (such
as hookworm, pinworm, roundworm).
In this condition, you have to take albendazole on an empty stomach so that it can
stay for a longer time in your intestine. Albendazole does not absorb on an empty
stomach but is rapidly absorbed with a fatty meal.
Albendazole mechanism of action for tissue worms
Sometimes, parasitic worms penetrate your blood circulation and tissues via
intestine to blood or skin to blood. In this condition, Albendazole acts as a prodrug.

4. Suppose you have a neurocysticercosis problem (worms in your brain). In this
condition, you need to take albendazole with a fatty meal because you want
albendazole in your blood.
When you take albendazole with a fatty meal (approximately 40 g fat), it increases
the absorption.
Firstly, it goes to your stomach and then the small intestine. From the small
intestine, albendazole is rapidly absorbed into your hepatic portal circulation via
the inferior mesenteric vein.
As soon as albendazole reaches the liver, it converts into albendazole sulfoxide by
first-pass- metabolism. Here, albendazole sulfoxide is a real anthelmintic for
systemic worm infections.
After reaching blood circulation, it easily crosses your blood-brain barrier (BBB)
and enters cerebrospinal fluid (CSF) because albendazole is a highly lipid-soluble
drug.
In your brain, albendazole accumulates in higher concentrations. It effectively kills
Taenia solium worms that cause neurocysticercosis.
Here, albendazole binds on the β-tubulin site of Taenia solium worms, inhibiting
polymerization and cell division.
Where is albendazole absorbed?
Albendazole is a weak base drug. Generally, weak base drugs have good
absorption in the basic medium because they remain unionized in an alkaline
medium.
So, albendazole is well absorbed in an alkaline medium like the small intestine.
Here, it would be best to take a fatty meal because albendazole dissolves better
with fatty substances.

5. In the influence of fatty meal, the albendazole drug readily crosses the bilayer lipid
membrane of the small intestine and enters the hepatic portal circulation. By this
hepatic portal vein, it goes to your liver for first-pass metabolism.
How is albendazole metabolized?
Albendazole is a prodrug that is inactive form. It gets activated after the
metabolism of albendazole in the liver.
When you take an albendazole tablet or suspension, it is rapidly absorbed with a
fatty meal.
After the absorption of albendazole, it goes to your liver for first-pass-metabolism
via the hepatic portal vein.
Here, albendazole gets rapidly metabolized in the liver and converts into an active
metabolite, i.e., albendazole sulfoxide (primary metabolite).
Albendazole sulfoxide is an active metabolite (anthelmintic action) that produces a
therapeutic or pharmacological effect.
Albendazole sulfoxide (ABZ sulfoxide) is widely distributed in your entire body. It
goes to the target site (like the brain, lungs, skin, etc.), where the parasitic worms
cause infestation.
The volume of distribution of ABZ sulfoxide is not much high because albendazole
sulfoxide is 70% bound to plasma protein. It means 70% bound drug and 30%
unbound drug (free drug).
This 30 % unbound drug goes to your target tissue for an anthelmintic effect. The
rest of the bound drug is slowly released from protein binding and provides a
therapeutic effect.
After the therapeutic effect, albendazole sulfoxide re-enters in your blood and goes
to the liver for biotransformation.

6. Here, albendazole sulfoxide converts from an active metabolite to an inactive one.
The main purpose of the biotransformation (or metabolism) of albendazole
sulfoxide is to eliminate the drug from your body. Albendazole sulfoxide can’t
excrete itself because it is a lipid-soluble drug.
Therefore, it has to metabolize from lipid-soluble to water-soluble.
In phase I reaction, albendazole sulfoxide gets destroyed (or breaks down) so that it
cannot go back to your tissue. Here, CYP3A4 P450 enzymes help to introduce
oxygen atoms in ABZ sulfoxide and decrease its pharmacological effects.
After that, ABZ sulfoxide gets conjugate with glucuronide in Phase 2 reaction that
makes the drug super polar (or water-soluble) – Albendazole sulfone.
Albendazole sulfoxide (primary metabolite or active metabolite or lipid soluble)
↓
Albendazole sulfone (secondary metabolite or inactive metabolite, or
water-soluble)
This ABZ sulfone goes to your kidney and eliminates quickly. But the maximum
proportion of albendazole sulfone is eliminated via bile.

7. What is the half-life of albendazole?
The half-life of albendazole sulfoxide is around 8.5 hours. This means 50% ABZ
sulfoxide will start eliminated from your body every 8.5 hours.
Suppose you have taken Albendazole tablet 400 mg. It will reach your bloodstream
in the form of albendazole sulfoxide 400 mg.
ABZ sulfoxide 400 mg (100%)
↓8.5 hrs
ABZ sulfoxide 200 mg (50%)
↓17 hrs
ABZ sulfoxide 100 mg (25%)

8. ↓25.5 hrs
ABZ sulfoxide 50 mg (12.5%)
↓34 hrs
ABZ sulfoxide 25 mg (6.25%)
↓42.5 hrs
ABZ sulfoxide 12.5 mg (3.125%)
↓51 hrs
ABZ sulfoxide 6.25 mg (1.562%)
↓59.5 hrs
ABZ sulfoxide 3.125 mg (0.781%)
It takes around 60 hours to wash out albendazole from your body thoroughly.
How often should albendazole be taken?
The albendazole dosage depends upon the type and severity of parasitic worms.
As per a study, each person should take albendazole a single dose every six
months.
Therefore, you should take the albendazole dose in kids and adults under proper
medical supervision.
To know albendazole dosage, click here
Are there any side effects of albendazole?

9. There are no significant side effects of albendazole in a single-dose therapy.
Although, some side effects have been reported as per duration of treatment –
Common (≥1%) side effects of albendazole
Abdominal pain is most frequently reported during short-dosing of albendazole.
Uncommon (>0.1% and <1%) side effects of albendazole
You may also have diarrhoea, nausea, vomiting, dizziness, itchiness and/or skin
rashes.
Rare (< 0.1%) side effects of albendazole
You might have life-threatening side effects but it rarely happens if you are on
long-term therapy of albendazole. It could be –
● Leukopenia
● Aplastic anemia
● Pancytopenia
● Agranulocytosis
● Thrombocytopenia
● Bone marrow suppression especially in liver disease (such as hepatic
echinococcosis) patients
● Hypersensitivity reactions including rash, pruritis and urticaria
● Severe hepatic abnormalities, including jaundice and hepatocellular damage

10. Who should not take albendazole?
Albendazole is contraindicated in certain conditions –
● Hypersensitivity to albendazole and other drugs related to benzimidazole
derivatives
● Liver disease
● Pregnancy
● Anemia or any blood disorder like leukopenia
Why is albendazole contraindicated in pregnancy?
Albendazole comes in Category C, which is not supposed to be safe in pregnancy.
Drugs in category C carry a risk that cannot be eliminated.
Animal (rat and rabbit) studies have shown that albendazole can cause teratogenic
effects (embryotoxicity and skeletal malformations) during pregnancy.
However, studies on pregnant women are not satisfactory.
Therefore, it would be better to stay away from albendazole during pregnancy
unless the potential benefit outweighs the potential risk to the fetus.
Is albendazole safe for humans?

11. Albendazole is a well-tolerated and safest drug for deworming. Using albendazole
improves the health of entire communities, including child nutrition and
development.
Albendazole does not cause any potential side effects if it is used in one-time
administration.
You might need to worry if you have systemic worm infestation.
Suppose you take an albendazole drug for systemic worms like hydatid disease and
neurocysticercosis. In this case, it may also elevate the level of your liver enzymes
as albendazole is metabolized by the liver.
During albendazole therapy for tissue parasites, you may also observe a less blood
cells count in your blood test report.
In this case, you may require regular blood monitoring during albendazole therapy.
What drugs interact with albendazole?
Albendazole does not cause any severe reaction to other drugs. However some
medicines may interfere with the efficacy of albendazole.
Drugs that decrease the efficacy of albendazole
Your doctor may increase the albendazole dose if you or your children are on
antiepileptic drugs like phenytoin, carbamazepine, and phenobarbital. These drugs
are enzyme inducers that decrease the efficacy of albendazole by increasing the
metabolism of albendazole.
Drugs that increase the efficacy of albendazole
Some drugs inhibit the metabolism of albendazole. So, your doctor may decrease
the dose of albendazole if you or your children are taking the following medicines
or foods –

12. ● Cimetidine
● Corticosteroids like dexamethasone,
● Antiparasitic drugs like praziquantel and levamisole
● Grapefruit (by inhibiting albendazole metabolism)
● Long-term administration of antiretroviral drug – ritonavir
Conclusion
We learned how albendazole works in the body (albendazole mechanism of action)
and how your body responds after taking albendazole (pharmacokinetics of
albendazole).
Albendazole medicine effectively works in intestinal and tissue helminths by
binding on the β-tubulin site of worm parasites.
It is the safest anthelmintic with minimal side effects.
We need to focus on the administration of albendazole – with food (for tissue
parasites) or without food (for intraluminal parasites). It is always best to take
albendazole under proper medical supervision.
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Have questions?
Let me know in the comments below. I will try my best to answer all of them.

13. FAQ
Q 1 How long does albendazole stay in your system?
The half-life of albendazole sulfoxide in your blood is 8.5 hours. So, it effectively
works for around 8.5 hours. But it stays in your blood for 2-3 days for a complete
washout.
Q 2 What is the mechanism of action of mebendazole?
Since mebendazole also belongs to the benzimidazole class of drugs. So, its
mechanism of action is similar to albendazole. Mebendazole is also bound to the
β-tubulin site of parasitic worms.
Q 3 What happens after taking albendazoles?
For tissue helminths, albendazole rapidly absorbs in your blood when it is taken
with a fatty meal. But for intestinal helminths, you don’t need to take it with a fatty
meal. You should take albendazole on an empty stomach, which stays in your
intestine and kills the worms.
Q 4. What is the bioavailability of albendazole?
The bioavailability of albendazole is less than 5%. You cannot get albendazole in
your blood because it is a prodrug. The bioavailability of albendazole gets
increased if you take it with a fatty meal. It converts into albendazole sulfoxide
(active metabolite) in your blood after first-pass metabolism in the liver.
Q 5. Does albendazole work immediately?
Although the onset of action of albendazole sulfoxide is 2 to 5 hours it typically
does not work immediately. Its effectiveness depends on various factors, including
the type of parasitic infection being treated, the severity of the infection, and
individual patient factors. The effects of albendazole are usually felt three days
after taking it.
Sources –

14. 1. KD Tripathi. Essentials of medical pharmacology, 7th edition. Jay Pee Brothers,
2013; Anthelmintic drugs, Chapter-61, Pages – 849 to 851.
2. Michelle A. Clark et al. Lippincott’s Illustrated reviews: Pharmacology, 5th
edition. Wolters Kluwer health, 2012. Anthelmintic drugs; Chapter-27; Pages 455
to 460.