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Side Effects of the Drugs – Iatrogenic Cushing’s Syndrome
Iatrogenic Cushing’s syndrome is a side effect of high dose steroids and is caused by too much corticosteroid in the body. To a lesser extent, the immediate side effects observed when the dog initially goes on steroids eg., drinking, eating and urinating excessively is a mild example of Cushing’s syndrome. Personally I like to see dogs responding to high doses of prednisolone in this way, as it means that they are responding to the drugs as they should.
Usually, Cushing’s syndrome only becomes a real problem when exceptionally high doses, or prolonged high doses of steroids are administered, maybe due to a relapse, or in some cases where the vet is inexperienced in reducing steroid doses and keeps the dog on a high dose for longer than necessary; or when the dog is not responding to treatment and higher doses are necessary to control the disease. This is where the cytotoxic drug Azathioprine, and other more recently used, immunosuppressive drugs are very useful.
All drugs carry side effects and Azathioprine is no exception, but it does not carry the same side effects as prednisolone, therefore by using this drug in combination with prednisolone it reduces the risk of iatrogenic Cushing’s syndrome. As Azathioprine takes at least 10 days to take effect, starting the ‘combination’ therapy at the beginning of treatment may enable the prednisolone to be lowered within the 10-28 day band and still maintain a good level of immunosuppression. If your dog is not responding to treatment then your vet may consider changing his treatment to other immunosuppressive drugs.
How Can I Tell if My Dog Develops Iatrogenic Cushing’s Syndrome?
Iatrogenic means ‘drug induced’. Clinical signs of Iatrogenic Cushing’s syndrome are the same as primary Cushing’s syndrome but can present with acute clinical signs. It reflects the level of corticosteroid in the body.
The most notable side effects are, heavy panting, some hair loss, and an increase in drinking and urinating, excessive pigmentation. This is something everyone seems to be aware of and accepts as normal when a dog is on high dose steroids. Very often the dog will be weaned down to a low dose before any major problems arise.
Acute Cushing’s syndrome due to overdosing of corticoid steroids can be very serious. Blood results will reflect this, especially the liver enzymes which may be extremely high. Red blood cells and blood platelets may also be high and blood clotting may be a risk.
So when should you alert your vet to suspected, unacceptable level of corticosteroid? The owner should take note when other clinical signs occur, such as: Depression, anorexia, muscle wasting and extreme weakness, continuous panting, lethargy - unwillingness to exercise, skin lesions and thinning of the skin, excessive hair loss, pot-bellied appearance and sagging back, behavioural changes (aggression).
If your dog is showing these signs it will probably mean that the dose of steroids needs to be lowered. It is important that it is not confused with a relapse of the dog’s condition or an infection. The dilemma is that steroids must not be withdrawn too quickly otherwise the dog may go into an adrenal insufficiency crisis. If the clinical signs of iatrogenic Cushing’s syndrome is intolerable, it is hoped that the high dose of steroids that he has been on will have already done their job and that his autoimmune disease will be stable. As long as the steroids are lowered in a controlled manner and in time, all the symptoms of Cushing’s will subside and your dog will return to normal, but extreme signs must not be ignored.
Reducing the Tablets
When significant improvement in the dog’s condition is seen, usually between 10-28 days, the initial steroid dose is usually reduced by 25%. The dose is generally given for another 10 - 28 days and depending on the dog’s progress and clinical signs the dose is significantly reduced once more for a further 10-28 days; and again in another 10-28 days. Anecdotal evidence has shown that if at this stage the dose is lowered more slowly, or reduced to an every other day dose over a period of months rather than weeks, relapse are less likely to occur. It is always tempting to get your dog off steroids as soon as possible, but when treating autoimmune disease, as long as the dog is on a low, every other day dose then taking the last stage slowly seems to work best, depending, of course, on the severity of the disease and allowing for the difference in individual response - no two dogs reactions are exactly the same. With some autoimmune diseases such as SLE, the dog is likely to be on steroids for the rest of his life. Usually an every other day dose can be achieved, but you risk a relapse if you take the dose too low. Below is the best example of a reducing immunosuppressive protocol I have come across. It is an excellent guide and can be adjusted to the individual.
Example: Reduction Protocol for prednisolone:
Clinical Immunology of the Dog & Cat , 2nd Edition, by Michael J Day
Professor Michael DayBSc, BVMS(Hons), PhD, DSc, DiplECVP, FASM, FRCPath, FRCVS
Professor of Veterinary Pathology, University of Bristol, UK and WSAVA - Chairman of Scientific Advisory Committee.
This example is based on a dog receiving an induction dose of 1.0mg/kg/q 12hrs (q = every)
Dose Duration (based on clinical effect)
1.0mg/kg/q 12h 10-28 days
0.75mg/kg/q 12h 10-28 days
0.5mg/kg/q 12h 10-28 days
0.25mg/kg/q 12h 10-28 days
0.25mg/kg/q 24h 10-28 days
0.25-0.5mg/kg EOD at least 21 days
0.25-0.5 mg/kg every third day at least 21 days
Every reduction is made after consideration to improvement of clinical signs, blood results and side effects of the drugs.
Prednisolone: "Doses above 2.2mg/kg/day do not give more immunosuppression but do cause more side effects. Many internists believe that prednisolone doses should not exceed 80mg per day, regardless of the dog's weight." Plumb's Veterinary Drug Handbook Eight Edition.
The dose of azathioprine 2mg/kg/24 or 48 hrs, can be reduced initially by giving a lower dose tablet per day, or gradually reducing from daily dosing to every 2nd day, every 3rd day, every 4th day etc..... Remember, azathioprine tablets should not be broken or handled without gloves.
How Do I Know if My Dog Will Relapse?
Until you have attempted to wean your dog off of the tablets for the first time you will not know if he is likely to relapse or not. Sometimes during the weaning off process, before you even get down to an every other day dose, he may relapse. If this happens then the drug dosage has to be raised, probably up to the last dose before the relapse (maybe a little higher, depending on the severity of the relapse) and then start the weaning process again. If this happens again, then you and your vet may have to settle for keeping him on a low maintenance dose to achieve a good quality of life. A low, every other day maintenance dose of prednisolone is preferred to enable the dog’s liver to rest in between doses. There are many autoimmune diseases that carry a good, drug free prognosis. The more common, serious autoimmune diseases that may not need long term steroid therapy are: primary immune-mediated polyarthritis, autoimmune haemolytic anaemia and thrombocytopenia. However, as previously stated, all dogs are different and it very much depends on the individual dog, the severity of the disease, the experience of the vet and the vigilance and compliance of its owner.
If a relapse occurs whilst the dog is still being treated then true remission has not been achieved. If the dog has achieved remission and has enjoyed a period without drugs or is on EOD maintenance drugs, when a relapse occurs or he develops another autoimmune disease, he has encountered a ‘trigger factor’ which has induced this change.
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