Treatment
Emergency Treatment
Rapid institution of treatment is vital for the dog presented in an acute Addisonian crisis. Initial treatment is directed at correcting hypovolemia and electrolyte∕acid- base abnormalities, and at glucocorticoid supplementation.
Adequate intravenous fluid therapy is the most important part of the treatment. Traditionally NaCl 0.9% has been recommended as the fluid of choice because of its high sodium concentration and lack of potassium. A lactated Ringer's solution is also adequate as it might correct the acidosis more rapidly and its potassium content is low. Fluid therapy is usually required for only a few days and can be withdrawn when the dog is eating well and major laboratory abnormalities are corrected. Electrolyte abnormalities usually resolve after adequate fluid therapy has been instituted. With life threatening hyperkalemia (K > 9 mEq/L and∕or ECG abnormalities) further specific therapy is needed. Hypoglycemia can be addressed by adding dextrose to the isotonic fluid bag in order to make a 2.5 or 5% solution. If clinical signs related to hypoglycemia are present boluses of 25% dextrose solution, 1mL∕kg in 0.9% saline may be administered (Lathan 2015).
Administration of glucocorticoids should also be started without delay if a patient is highly suspected of Addison's. Ideally dexamethasone sodium phosphate is used as it will not interfere with the cortisol measurement performed with the ACTH stimulation test and therefore does not delay performing the diagnostic test. Initial recommended dosages vary from 0.1 to 2 mg∕kg IV once and is followed by 0.05-0.1 mg/kg q12 h (Scott-Moncrieff 2015). Alternatively prednisone sodium succinate can be used but only after finalising the ACTH stimulation test.
Urine production, electrolytes, and glycemia should be monitored closely - shortly after initiating therapy and thereafter q 812 hours, until these parameters normalize.
The clinical response to emergency therapy in a dog presenting in an acute hypoadrenal crisis is usually excellent and maintenance oral therapy with mineralocorticoid and glucocorticoid supplementation should be started as soon as tolerated by the patient (usually when starting to eat).Maintenance Therapy
Mineralocorticoid supplementation is possible with oral fludrocortisone acetate or with injectable desoxycorticosterone pivalate (DOCP). The choice between both mineralocorticoids is mainly based on product availability, cost price, and personal preference of both veterinarian and owner. Some studies suggest that DOCP leads to a better suppression of plasma renin activity and therefore could be the mineralocorticoid of choice when both are available (Baumstark et al. 2014a).
Fludrocortisone Acetate (Florinef®)
Oral fludrocortisone acetate should be started at 0.01 mg/kg twice daily. Initially, serum sodium and potassium concentrations should be monitored every 1 to 2 weeks and the fludrocortisone dosage adjusted as needed. The dosage of fludrocortisone required typically increases during the initial 6-18 months. Therefore, monitoring is important and once stable, twice-yearly evaluation of the patient and electrolytes is essential. Fludrocortisone possesses a small degree of glucocorticoid activity, therefore over time; many dogs do not require extra glucocorticoid supplementation except in periods of stress. Besides traditional electrolyte monitoring, plasma renin activity seems a reliable tool to monitor treatment of hypoadrenocorticism (Baumstark et al. 2014a).
Desoxycorticosterone Pivalate (DOCP, Percorten®)
DOCP is administered SQ or IM at an initial dosage of approximately 1.5 mg/kg and this provides mineralocorticoid activity for an average of 28 days. Traditionally monitoring is also based on blood electrolyte measurements performed 14 and 28 days after the injection. If hyperkalemia and hyponatremia are observed on day 14, the next dosage should be increased by 5-10%.
If electrolytes are within normal range at day 14 but are abnormal at day 28, the dosing interval should be shortened by 48 hours. Once the injection schedule is stable, owners can be instructed to administer DOCP at home.Oral glucocorticoid therapy should also be instituted as soon as the patient has been stabilized. Initial therapy with prednisolone is initiated at 0.25-0.5 mg/kg q 12 h, however, this dosage should be tapered to 0.1-0.25 mg∕ kg q 24 h. Adjustments in the dose should be based on clinical response and the presence of side effects. In half ofthe dogs administered fludrocortisone, the prednisolone therapy can eventually be stopped except at times of stress. However, some dogs will permanently require a low maintenance dose. Dogs treated with DOCP always require daily oral glucocorticoid supplementation.
Other
In situations of stress, (sickness, travelling, surgery, boarding) it is recommended to administer prednisolone at a supra-physiologic dosage (2 to 5 times physiologic dose). Therefore, owners should have prednisolone available at home.
Salt supplementation can occasionally be helpful in maintaining serum sodium concentrations when high dosages of fludrocortisone are needed to obtain normal or almost normal sodium concentrations.
Treatment of 'Atypical' Hypoadrenocorticism
Currently oral glucocorticoid therapy is probably the only drug required to treat secondary and atypical cases. Further studies should clarify if dogs with atypical primary hypoadrenocorticism would benefit from mineralocorticoid therapy. Anyways, monitoring is advised with atypical cases as mineralocorticoid deficiency may also develop with time.