Another option to maintain steady extracellular calcium concentration is a CRI of 10% calcium gluconate at 2.5 to 10 mg/kg/hr
(or 60 to 90 mg/kg/day).1-3,10 Some authors recommend administering intravenous fluids at a maintenance rate (60 ml/kg/day) with 10, 20, or 30 ml of 10%
calcium gluconate added to a 250-ml fluid bag to create a 1-, 2-, or 3-mg/kg/hr elemental calcium infusion.1,2 The higher rate of infusion is used for more severely hypocalcemic patients.2 In patients receiving calcium as a CRI, measure the serum calcium concentration (either total or ionized) every eight to
12 hours to assess efficacy and avoid hypercalcemia.10 As the oral treatments begin to take effect, gradually withdraw CRI therapy similar to subcutaneous therapy.2 At this point, administering an oral vitamin D analogue and oral calcium salts should maintain serum calcium concentration.
Long-term management
Lifelong administration of a vitamin D analogue is the mainstay of treatment for primary hypoparathyroidism.1-4,9 In patients with primary hypoparathyroidism, the vitamin D concentration is also decreased. For the intestines to have normal
absorption of dietary and supplemental oral calcium, vitamin D must be present in sufficient quantity. The goal of oral supplementation
is to maintain the total serum calcium concentration between 8 and 9.5 mg/dl, which is just below the normal range, to avoid
signs of hypocalcemia yet minimize the risk of developing hypercalcemia.1-3,10 Initial supplementation with oral calcium salts is often required for the first few months.
Table 2: Vitamin D Analogues for Treating Hypoparathyroidism in Dogs and Cats*
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Several vitamin D analogues are available (Table 2). The most commonly prescribed are ergocalciferol (vitamin D2), dihydrotachysterol, and calcitriol (1,25-dihydroxycholecalciferol).1,2 The dosages of these analogues vary widely, and the onset of effect to increase serum calcium concentration varies by preparation.
A minimum of 24 to 96 hours of therapy is needed before there is an effect, and hypercalcemia commonly develops.1,2 Hypercalcemia causes serious and even fatal complications that include acute or chronic renal failure. Counsel owners regarding
the signs of hypercalcemia (polydipsia, anorexia, vomiting, and depression), and instruct owners to discontinue all supplementation
and seek veterinary care if these signs are noted.1,2,9,10 Furthermore, regular monitoring of the total serum calcium concentration is crucial for the management of hypoparathyroidism.
When the patient is stabilized, discharged from the hospital, and receiving oral medications, measure the total serum calcium
concentration at least weekly.2 When calcium concentrations remain consistently within the desired range, these re-evaluations may occur every three to
four months, though more frequent re-evaluation allows better control of the calcium concentration and minimizes the risk
of complications.1-3
Vitamin D dose increases of 10% to 20% are indicated when the total serum calcium concentration is below the ideal value.2 When the calcium concentration multiplied by the phosphorus concentration is > 60 to 70, there is an increased risk for
soft tissue mineralization. In growing animals, it is also prudent to monitor the serum phosphorus concentration to identify
and address a calcium-phosphorus product > 60 to 70.5 Treatment would involve medications to lower either the calcium concentration or phosphorus concentration or both. Additionally,
if the patient is an intact female, ovariohysterectomy is indicated because in people, estrogen, pregnancy, and lactation
complicate regulation of serum calcium concentration.9
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