Your dog has lived with the symptoms of Cushing's disease (hyperadrenocorticism)--excessive thirst or appetite, incontinence, weight gain, hair loss--that seemed like normal aging in a senior dog over 7 years of age. After a battery of tests, your dog has been diagnosed with an adrenal adenoma--a tumor on the adrenal gland above the kidney--which caused the hormone imbalance that led to Cushing's disease. Now you must embark on a lifelong regime of drug therapy to control the symptoms of your dog's incurable hyperadrenocorticism.
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Mitotane, o, p'-DDD (Lysodren)
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Marketed as Lysodren, mitotane is an adrenolytic drug--it inhibits the secretions of the adrenal gland including cortisol. Too much cortisol is the cause of Cushing's disease. In the case of adrenal adenomas, your veterinarian will administer mitotane as chemotherapy, to reduce cortisol levels and maintain them within a normal range. It starts with an induction dose--a week to 10 days at 25 to 50 mg/kg daily, followed by a less frequent maintenance dose for the rest of the dog's life. The goal is remission of the disease.
The Opposite Effect
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With mitotane, the trick for your veterinarian will be to prevent the onset of hypoadrenocorticism (also called Addison's disease)--loss of appetite, persistent vomiting and diarrhea caused by insufficient cortisol in the system. If this happens, your veterinarian will discontinue the mitotane and administer prednisone to help regulate cortisol levels for the short term. An expensive but safer alternative to mitotane is available, however, as detailed below.
Side Effects of Mitotane
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Side effects of mitotane include gastrointestinal upset such as vomiting and diarrhea, as well as central nervous system symptoms such as loss of coordination and seizures. If your dog develops side effects such as these, your veterinarian may divide the dose of the medication into two smaller doses to be given at 8-to-12-hour intervals.
Ketaconazole (Nizoral)
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Ketaconazole dosage begins at 5mg/kg twice a day for a week. Your veterinarian will check your dog's cortisol levels, and may increase the dose to 10mg/kg. If a further test at 14 days reveals an inadequate response, your vet can increase the dose to 15 mg/kg. This drug is safer than mitotane in terms of side effects but has a failure rate of 20 to 25 percent and is very expensive.
Side Effects of Ketaconazole
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Side effects include vomiting, diarrhea and injury to the liver. Ketaconazole may also inhibit the action of some medications. As always, let your veterinarian know what other medications and supplements your dog is taking.
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