Hypercalcemia in Dogs and Cats: Treatment

The treatment of hypercalcemia depends on the severity of the abnormality, the presence of clinical signs, and the underlying cause. Have you not yet identified the cause of hypercalcemia in your patient? Then read our Vet Info on the pathophysiology and diagnosis of hypercalcemia in dogs and cats here. Not every patient with hypercalcemia requires immediate treatment, but increased ionized calcium accompanied by clinical signs should always be managed actively.

When to treat?

Not every patient with hypercalcemia requires immediate treatment. The decision to initiate therapy depends on both the severity of the hypercalcemia and the presence of clinical signs.

Treatment is indicated in patients with:

• Moderate to severe ↑ ionized calcium (iCa)
• Clinical signs (e.g. lethargy, vomiting, PU/PD)
• A rapid increase in calcium concentrations
• Increased risk of complications (chronic kidney disease, arrhythmias, urolithiasis)

In cases of very mild, asymptomatic hypercalcemia, particularly in cats with idiopathic hypercalcemia, careful monitoring may initially be sufficient.

First step: stabilization

Intravenous fluid therapy

Fluid therapy is the cornerstone of treatment and should ideally be initiated as soon as possible. Volume expansion increases the glomerular filtration rate and enhances renal calcium excretion.

Practical considerations:

• 0.9% NaCl is often the first choice
• Suggested dose: 80–180 mL/kg/day, adjusted based on hydration status

Important considerations:

• Start fluid therapy before administering other medications
• Monitor closely for overhydration, particularly in cardiac patients and cats
• Correction of dehydration alone may already result in a significant decrease in calcium concentrations

Furosemide

Furosemide can be used to further enhance renal calcium excretion, but should only be initiated once the patient is adequately rehydrated.

• Dose: 1–2 mg/kg q12h (IV, SC, or PO)
• Alternative: CRI administration is also possible

Important considerations:

• Never use in dehydrated patients
• Monitor electrolytes (Na, K, Ca) and hydration status closely
• Risk of hypovolemia

Calcitonin

Calcitonin has a relatively rapid onset of action and can be used as a bridging therapy until other treatments become effective.

• Dose: 4–6 U/kg q8–12h IM or SC

Characteristics:

• Rapid reduction in calcium concentrations
• Effect is often short-lived
• Can be combined with other therapies

Second step: targeted medical therapy

Glucocorticoids

Glucocorticoids lower calcium concentrations through several mechanisms, including reduced intestinal calcium absorption and decreased bone resorption.

• Prednisolone: 1–2 mg/kg/day
• Dexamethasone: alternative option for IV or SC administration

Important considerations:

• Do not initiate glucocorticoids before completing the diagnostic work-up
• They may mask the diagnosis of neoplastic disease (e.g. lymphoma)

Glucocorticoids are particularly useful in:

• Hypercalcemia of malignancy
• Idiopathic hypercalcemia
• Certain inflammatory diseases

Bisphosphonates

Bisphosphonates are the mainstay of therapy for persistent or severe hypercalcemia, particularly when increased bone resorption plays a role.

Mechanism of action:

• Inhibit osteoclast activity
• Result in a prolonged reduction in calcium concentrations

Main options for parenteral administration (oral options are discussed further below):

• Pamidronate: 1.3–2 mg/kg IV
• Zoledronate: 0.1–0.25 mg/kg IV (more potent, lower dose required)

Characteristics:

• Onset of effect within 1–3 days
• Duration of effect: weeks
• Repeat administration may be required if needed

Important considerations:

• Administer as a diluted solution over a slow intravenous infusion
• Monitor renal function closely
• Watch for electrolyte abnormalities

Specific approach in cats with idiopathic hypercalcemia

In cats with idiopathic hypercalcemia, management is often less aggressive and mainly focused on long-term control.

Initial approach:

• Dietary modification (should be assessed on an individual basis)
• Avoid acidifying diets
• Possible dietary options:
  • Renal diet:
    • Lower calcium content
    • However, also lower in protein and phosphorus → may potentially stimulate PTH production
    • Alkalinizing effect
  • High-fiber diet:
    • Less acidifying
    • May help bind calcium
    • However, often higher in calcium and lower in protein
  • Canned food:
    • Higher water intake
    • Promotes urinary calcium excretion and reduces the risk of urolithiasis
    • Monitoring alone may be sufficient in mild cases

If treatment is required:

• Glucocorticoids
• Bisphosphonates
  • Alendronate (PO):
    • Cat: 5–10 mg/cat once weekly
    • Practical administration guidelines:
      • Administer on an empty stomach
      • Give with water (approximately 5 mL)
      • Wait approximately 2 hours before feeding
    • Important considerations:
      • Risk of esophagitis and possible esophageal stricture formation (administer with butter and/or flush with water afterward)
      • Long-term effects are not yet fully understood
  • Monitoring:
    • Recheck ionized calcium (iCa) after one month
    • If insufficient improvement is seen, increase the dose by 5 mg/cat/week (up to a maximum dose of 30 mg/cat/week PO)
    • Add prednisolone if the response remains inadequate, and ensure that other causes of hypercalcemia have been thoroughly excluded

Monitoring during treatment

Careful monitoring during treatment is essential to evaluate therapeutic response and avoid complications.

Important parameters to monitor:

• Ionized calcium
• Hydration status
• Renal function
• Electrolytes

The frequency of monitoring depends on the severity of the hypercalcemia and the therapies being used.

Summary

The treatment of hypercalcemia follows a stepwise approach. Initial management focuses on stabilizing the patient with fluid therapy, potentially combined with furosemide and calcitonin. This is followed by a more targeted therapeutic approach using glucocorticoids or bisphosphonates, depending on the underlying cause.

In cats with idiopathic hypercalcemia, the focus is often placed more on long-term management than on acute intervention.