A Pilot Study Exploring the Plasma Potassium Variation in Dogs Undergoing Steroid Therapy and Its Clinical Importance

In most situations in veterinary medicine, glucocorticoids are the drugs of choice used, that is, to reduce the inflammatory response or limit an inappropriate immune response. Their use in long-term therapy may cause side effects that may weaken the patient. The aim of the study was to evaluate possible variations in the plasma potassium concentrations and their clinical relevance in dogs undergoing steroid therapy with methylprednisolone in anti-inflammatory doses. The study used a sample of 21 dogs (n = 21) presented for consultation, with a clinical condition requiring a corticosteroid therapeutic protocol with an anti-inflammatory dose of methylprednisolone. All the individuals were submitted to a corticosteroid therapeutic protocol administered orally during 18 days. During this period, 3 time points were considered: T0 (the day the prescription was first given), T1 (3 days later), and T2 (8 days later). Blood samples were collected from a peripheral vein to measure plasma potassium concentrations in T0, T1, and T2. Corticosteroid therapy on an outpatient basis statistically significantly decreased plasma potassium levels, especially between T1 and T2 (P = .03). The plasma potassium levels decreased in 12.5% of the males, compared with a decrease of 23.1% in the females. No statistically significant relationships were observe between the decreased plasma potassium levels and age, clinical condition, and patient׳s body weight. However, we found a statistically significant association between decreased plasma potassium levels and sex. The study results may justify the need for the systematic prescription of potassium supplements in patients undergoing steroid therapy, similar to what already occurs in human medicine.

Introduction

In most situations in veterinary medicine, glucocorticoids are used to reduce the inflammatory response or limit an inappropriate immune response. Their effects vary with the type of glucocorticoid, its potency, the type of dosage form, the dose administered, the route of administration, the duration of treatment, and individual factors.¹ Depending on the biological half-life period, glucocorticoids can be divided into the following 3 groups: short-acting glucocorticoids with a half-life lower than 12 hours (hydrocortisone and cortisone); intermediate-acting glucocorticoids with a half-life between 12 and 36 hours (prednisone, prednisolone, triamcinolone, and methylprednisolone); or long-acting glucocorticoids with a half-life greater than 48 hours (betamethasone and dexamethasone).1, 2, 3 The anti-inflammatory potency of methylprednisolone is approximately 5 times higher than that of cortisol, and its mineralocorticoid activity is negligible.⁴ Although glucocorticoids are the drugs of choice, their use in long-term therapy may cause side effects that may weaken the animal or not be tolerated by owners. The most common side effects are polyuria, polydipsia, muscle weakness, skin changes, predisposition to infections, gastrointestinal ulcers, and muscle atrophy. They can also cause insulin resistance, hyperglycemia, and hepatic disease. Tolerance to side effects varies from patient to patient. Large dogs are particularly sensitive, and cats are more resistant to these effects than dogs.² At the kidney level, glucocorticoids may increase the glomerular filtration rate, excretion of water, sodium and chlorine retention, and the excretion of potassium and calcium.1, 3 This can lead to hypokalemia and hypocalcemia, which are described as rare.⁴ The poor preservation of potassium may be due to a decreased resorption at the ascending portion of Henle׳s loop level or an increase in secretions at the distal nephron level.⁵ These effects may result from glucocorticoids׳ interference with the actions of vasopressin, the renin-angiotensin system,3, 6, 7 the epithelial sodium channel,⁷ aquaporin-2 channels, prostaglandins, or Na+/K+ pumps either directly or through brokers.7, 8, 9, 10 Human patients receiving corticosteroid therapy rarely develop clinical hypokalemia. However, when this occurs, it may have serious effects on skeletal muscles and the myocardium. The increased risk of atrial fibrillation observed in patients undergoing corticosteroid treatment may be in part due to hypokalemia. To the authors׳ knowledge, no studies have been conducted to date with dogs to examine this issue. In prevention, this may justify the systematic prescription of potassium supplements to veterinary patients undergoing treatment with glucocorticoids, which is already practiced in human patients.¹¹ The present study aimed to evaluate possible variations in the plasma potassium concentrations and their clinical relevance in dogs undergoing steroid therapy with methylprednisolone in anti-inflammatory doses.