Hyperadrenocorticism Part 2: Treatment and Monitoring

Presenter: Dr Christopher Byers DVM,DA CVECC,DACVIM (SAIM), CVJ from criticalcaredvm.com

The medical treatment and monitoring of hyperadrenocorticism (HAC) was the subject matter for part two of the webinar series being led by Dr Christopher Byers. Memories were jogged by Dr Byers discussing the use of mitotane (Lysodren) as a treatment option for HAC, being the medical treatment of choice prior to the development of the licensed product , trilostane (Vetoryl). Due to the requirements of the cascade it is now this product we are most likely to be most familiar with.

There are many differences between trilostane and mitotane and having experienced the irreversible effects of mitotane on the adrenal cortex in an overdosed patient, I’ve always viewed trilostane as the safer option with its reversible mode of action. According to Dr Byers however, this is not necessarily the case with both products having benefits and side effects. After all trilostane does not have a perfect track record with Dr Byers citing an FDA trial where out of 107 dogs with either ACTH dependant and ACTH independent disease , 2 dogs on trilostane developed adrenal necrosis, one of which died.

Treatment and monitoring with both products were covered in depth by Dr Byers and the standard dosing of trilostane every 24hours featured within this discussion with Dr Byers explaining there may also be reasonable grounds to administer trilostane every 12hrs in certain cases. This could be considered when patients have concurrent diabetes mellitus, if clinical signs are NOT controlled despite monitoring test results being normal and if clinical signs are not apparent during the day but become evident at night.

Dr Byers also explained that mitotane and trilostane can also be used to medically treat occult HAC as well as ACTH independent disease. Studies looking at the treatment of ACTH independent disease with trilostane or mitotane showed no statistically significant difference in mean survival times between the use of either medication. Occult HAC was also discussed and covered those frustrating cases where the clinical signs of HAC appear to be staring us in the face yet all the screening tests for HAC are negative. As Dr Byers so aptly put it, if it walks like a duck and quacks like a duck then surely it is a duck?! Dr Byers explained there are some conditions where dogs produce an excess of the hormone 17 hydroxyprogesterone which will cause classic HAC signs and under these circumstances, this chemical would need to be measured instead of cortisol during an ACTH stimulation test. Once diagnosed, treatment may just involve giving supplements of melatonin and lignans. However in some cases they will also need treatment with either mitotane or trilostane.

Monitoring response to treatment also played a significant part within this veterinary webinar and one key element according to Dr Byers is ensuring the owners are well educated in the importance of medicating at a certain time so we can perform our monitoring tests at the optimum time (4-6 hours after trilostane). Dr Byers also emphasized the usefulness in asking clients to keep a journal of their treated pet, monitoring signs such as polyphagia and polydypsia which when resolve offer an indicator of a good response to treatment.

This veterinary webinar organised by ‘The Webinar Vet’ provided substantial information and advice on the medical treatment and monitoring of HAC. It also gives practical advice on what to do when cases don’t respond in quite the way one might expect, not an unusual scenario in the treatment of HAC, and will surely prove useful to any vet in practice today.

The Stethoscope (MRCVS)

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