Rasburicase vs. Allopurinol

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson is going to compare and contrast some of the more salient points between rasburicase and allopurinol. You'll learn about their major differences in terms of uses, side effects, and special considerations.

A Lost Super Power

This lesson is going to arm you with knowledge about an amazing superpower that many animals have but humans no longer do. Because we don't have this superpower anymore, we can develop a painful form of arthritis known as gout. Gout can develop as a result of high levels of uric acid in the body and blood, something we call hyperuricemia. But we can take a pill and actually get this super-power back to help manage hyperuricemia. Imagine that! You get a superpower just by taking a pill!

Let's find out how in this lesson that compares and contrasts rasburicase and allopurinol.

Names & Indications

Allopurinol is a medication that is the generic term for Aloprim and Zyloprim, the trade names of the same exact compound. Rasburicase is the generic term for Elitek, the brand name of the same compound.

Allopurinol is indicated to treat the following:

  • Recurrent calcium oxalate calculi (stone) formation
  • Hyperuricemia as a result of cancer therapy
  • Gout

Contrast this with rasburicase, which is only indicated to treat hyperuricemia associated with cancer treatment.

Pharmacology

Ok, now that you've got that down, let's get to the really cool stuff. How do these medications actually work?

Well, allopurinol is a xanthine oxidase inhibitor. It prevents an enzyme, called xanthine oxidase, from working well. Xanthine oxidase helps produce uric acid. This means allopurinol minimizes the formation of uric acid in the body and thus helps manage hyperuricemia that way.

Ok, now something even more exciting. How does rasburicase work? Well, rasburicase is a urate-oxidase enzyme. In other words, it works by converting the bad uric acid into allantoin. Allantoin is an inactive and very soluble (easily excretable) substance.

This is the superpower the introduction was talking about. A very long time ago, it's likely most mammals, including our very own early ancestors, naturally had the ability to form this allantoin. We didn't need a pill to manage hyperuricemia or gout as a result. But nowadays, humans and a few other mammals have lost this superpower as we evolved. As a result, we are prone to building up uric acid in our body and suffering from gout. But by taking rasburicase, you are taking a pill to restore the super-power we had long ago! How cool is that!?

Warnings & Side Effects

That being said, neither medication is very cool if it causes you more harm than good. That's why these medications should be taken with caution, or not at all, in the following instances.

Allopurinol and rasburicase shouldn't be taken if the person has a history of hypersensitivity (allergy) to the medication or any other ingredient in the formulation. People with any history of blood-based reactions to rasburicase, such as hemolysis (destruction of red blood cells), shouldn't take this rasburicase. Individuals with G6PD deficiency, an inherited deficiency of the enzyme glucose-6-phosphate dehydrogenase, shouldn't take rasburicase either.

Important potential adverse effects to keep in mind with allopurinol include:

  • Bone marrow suppression
  • Drowsiness
  • Nausea and diarrhea
  • Reversible liver damage
  • Increase gout attacks in the early stages of allopurinol administration
  • A skin rash, followed by a more severe allergic reaction

Important potential adverse effects to keep in mind with respect to rasburicase include:

  • Hemolysis, or the destruction of red blood cells. The chances of this are low, less than 1%, but need to be mentioned.
  • Methemoglobinemia, which is when a form of hemoglobin called methemoglobin is elevated in the blood. Hemoglobin is the oxygen-carrying protein found in red blood cells. It can be converted to methemoglobin, which doesn't carry oxygen. Obviously, that's a problem!
  • Headaches and anxiety
  • Swelling of the arms or legs
  • Nausea, vomiting, diarrhea, constipation, and abdominal pain
  • Fever

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