Here’s an interesting post by a relatively new rheumatologist-blogger. Apparently diclofenac, a non-steroidal anti-inflammatory drug (NSAID) also known as Voltaren – of the same class as ibuprofen, A.K.A. Motrin and Advil – is toxic in birds. How do birds ingest it? Well obviously they feed on dead cows!

Vulture populations crashed in the nineties and pathologists were able to show that they died of renal failure with secondary visceral gout. Surprisingly, the usual suspects, disease and human encroachment on habitat, were not involved directly. It turns out that the vultures were being poisoned by voltaren, which they ingested while feasting on deceased, voltaren-treated cattle. After their initial investigations, biologists undertook carefully contolled studies and were able to confirm the toxicity of voltaren to these birds, the high prevalence of voltaren in cattle, and that birds feeding on such cattle can easily ingest a lethal dose.

Why are cows fed diclofenac? I have no idea and 3+Speckled (nice one Doc!) doesn’t mention why either. We’ll have to look into it sometime.

Interestingly, 3+Speckled notes that another drug of the same class – meloxicam – does not seem to be toxic in birds.

We generally treat the NSAIDs as a class, except for the newer division into cox-1 and cox-2. It is hard to explain why one would have such a dramatically different effect here, but it does remind us of the possibility of drug specific, and species specific, rather than class specific effects of anti-inflammatories.

He’s absolutely correct. Interestingly, there are other areas where NSAIDs don’t appear to act the same way in the body. There’s evidence that in Alzheimer’s Disease some NSAIDs may slow the onset of the disease, at least in animals, while others don’t. Why is this? It appears that they don’t act just through the standard NSAID pathway. All NSAIDs block the expression of an enzyme called cyclo-oxygenase (COX) which is central in making prostaglandins, which in turn are key elements of inflammation.

In Alzheimer’s though, some NSAIDs also appear to block the synthesis of a substance called Aβ1-42, which is an important component of Alzheimer’s plaques in the brain. (Sorry, I don’t have any references that are in the public domain.)

It’s an important demonstration of the fact that drugs of same class do not necessarily have the exact same effects. Rofecoxib (Vioxx) was somehow different from many other NSAIDs in increasing the risk of heart disease. Why? That’s unclear at this point. But the general point is an important one: we can’t assume that all drugs that are similar in structure and function are identical.

Please check out Rheumination.

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