What is the best course of action for an adult patient with a history of vitamin D deficiency, now presenting with hypercalcemia and an elevated intact PTH level of 14, after vitamin D supplementation has increased their vitamin D level to 65?

Stop Vitamin D Supplementation Immediately and Monitor for Resolution of Hypercalcemia

You should immediately discontinue all vitamin D supplementation because the patient has developed vitamin D-mediated hypercalcemia (calcium 10.7 mg/dL) with suppressed PTH (14 pg/mL), indicating excessive intestinal calcium absorption that will worsen with continued supplementation. 1

Understanding the Clinical Picture

Your patient has developed iatrogenic hypervitaminosis D with the following key features:

• Hypercalcemia (10.7 mg/dL, above the target range of 8.4-9.5 mg/dL) 1
• Suppressed PTH (14 pg/mL, below the normal range of 10-65 pg/mL in adults) 2
• Adequate vitamin D repletion (65 ng/mL, well above the target of 30 ng/mL) 1

This constellation indicates that vitamin D supplementation has overcorrected the deficiency and is now causing excessive calcium absorption from the gut, suppressing PTH appropriately in response to hypercalcemia. 1

Immediate Management Steps

Discontinue All Supplements

• Stop all vitamin D supplementation (cholecalciferol/ergocalciferol) immediately 1
• Stop all calcium-containing supplements and calcium-based products 1
• Total elemental calcium intake should not exceed 2,000 mg/day from all sources 1

Expected Timeline for Resolution

• Serum calcium should return to the target range of 8.4-9.5 mg/dL after discontinuation of supplements 1
• PTH should rise back into the normal range (10-65 pg/mL) as calcium normalizes 1
• Given vitamin D's long half-life, this process typically takes 4-8 weeks 1

Monitoring Protocol

Initial Phase (First 4 Weeks)

• Check serum calcium and PTH every 2 weeks for the first month after stopping supplementation 1
• Monitor for symptoms of hypercalcemia (confusion, fatigue, constipation, polyuria) 3

Ongoing Monitoring

• Continue checking calcium and PTH monthly until both normalize and remain stable for at least 4 weeks 1
• Once stable, monitor calcium and PTH every 3 months 1

When to Consider Resuming Vitamin D (If Needed)

Criteria for Restarting

• Do not restart vitamin D therapy until serum calcium returns to the target range (8.4-9.5 mg/dL) and remains stable for at least 4 weeks 1
• PTH must normalize (10-65 pg/mL) before considering any resumption 1

If Vitamin D Levels Drop Below 30 ng/mL

• If vitamin D levels eventually fall below 30 ng/mL after several months, consider restarting at a much lower maintenance dose of 800-1,000 IU daily (not the previous higher dose) 1
• Monitor calcium and PTH every 3 months during any future supplementation 1
• Target vitamin D level should be 30-40 ng/mL (not 65 ng/mL) 1

Critical Pitfalls to Avoid

Never Use Active Vitamin D Analogs

• Never use calcitriol, alfacalcidol, doxercalciferol, or paricalcitol to treat nutritional vitamin D deficiency, as they bypass normal regulatory mechanisms and dramatically increase hypercalcemia risk 1
• Active vitamin D sterols should only be used for advanced CKD with PTH >300 pg/mL 1

Avoid Ultra-High Doses

• Do not administer single ultra-high loading doses (>300,000-540,000 IU) as they have been shown to be inefficient or potentially harmful 1

Rule Out Primary Hyperparathyroidism

While your patient's current presentation shows suppressed PTH with hypercalcemia (consistent with vitamin D excess, not hyperparathyroidism), it's worth noting that:

• If PTH were elevated or inappropriately normal with hypercalcemia, this would suggest primary hyperparathyroidism 4
• In primary hyperparathyroidism with vitamin D deficiency, vitamin D repletion is generally safe and does not worsen hypercalcemia 5, 6, 7
• However, your patient's suppressed PTH rules out primary hyperparathyroidism and confirms vitamin D-mediated hypercalcemia 1

Safety Considerations

• Daily doses up to 4,000 IU are generally safe for adults, but individual responses vary significantly 1
• Toxicity can occur with prolonged high doses (typically >10,000 IU daily) or serum levels >100 ng/mL 1
• Your patient's level of 65 ng/mL is not toxic, but combined with the suppressed PTH and hypercalcemia, it indicates excessive vitamin D effect for this individual 1

Long-Term Management

• Once calcium and PTH normalize, recheck vitamin D levels annually 1
• If future supplementation is needed, use the lowest effective dose (800-1,000 IU daily) with close monitoring 1
• Some patients are more sensitive to vitamin D supplementation due to genetic variations in vitamin D metabolism 1