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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Osteosarcoma, Cisplatin and Magnesium

Updated: October 4th, 2018

Low magnesium may be a threat for dogs receiving chemotherapy.

Magnesium is a mineral in the body that is needed for proper functioning of over 300 different enzyme systems.  A study was done on critically ill dogs, and over half were found to have low magnesium.

Low magnesium levels increase the risk of toxic reactions to the chemotherapy drug cisplatin.

Cisplatin is one of the most common cancer medications used in dogs, most commonly for the bone cancer osteosarcoma.   Like most chemotherapy medications, there is toxicity to consider, and with this drug the kidneys are the most likely to be injured.  Other organs can also be affected (for more on cisplatin toxicity and what to do about it, see the Guide).

A new drug in the same class, carboplatin,  has a higher safety profile.  However, it is also more expensive than cisplatin, especially if your loved dog is a large breed.  In some cases we are cornered into using cisplatin and must do what we can to keep it as safe as possible.

This brings us back to the magnesium story.  Low magnesium levels increase the odds of cisplatin’s injury to the kidneys. Cisplatin also creates low magnesium levels in the dog body.  So the logical thought would be to simply measure magnesium and see what the level is, so we might supplement based on blood tests.

Here though, we have a problem.  Blood tests of magnesium are simply not very accurate.  Less than half a percent of magnesium in the body is found in the blood. This means that low blood levels don’t necessarily mean low body levels.  More than half of the magnesium in the body is found in the bones, and the rest in tissues and cells, but not really blood.

Since a large portion of dogs are known to have low magnesium levels when they are admitted to veterinary hospitals, and we know that low body magnesium increases the risk of cisplatin toxicity, and dogs with ostesarcoma often have lost the magnesium stored in their amputated limb bones…what do we do?

We can estimate the total body magnesium with a blood test called ionized magnesium, which is available at Michigan State Diagnostic Lab.  Many times however we need action today, instead of waiting for test results.

Supplement your loved dog with a little magnesium (under veterinary supervision of course) if cisplatin is in the future.  Apocaps contains magnesium for this reason.  Discuss dosing with your veterinarian as excessive supplementation can cause digestive upset.


Dr D



Leave a Comment

  1. Mariel on February 6, 2012 at 7:05 pm

    Why not apply magnesium oil to the skin where the dog can’t lick it? People absorb Mg poorly through supplements, and need baths with diluted Mg sulfate [Epsom salts] or transdermal Mg chloride, “Mg oil” from Swanson or Ancient Minerals.

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