Medication-Induced Hypercalcemia — Screener

Run this skill on every new hypercalcemic patient before diagnosing PHPT or MAH. Drug- and supplement-induced hypercalcemia is reversible and easily missed.

---

STEP 1 — Take the medication & supplement history

Ask explicitly about:

• Prescription drugs — diuretics, mood stabilisers, oncology drugs, antivirals, osteoporosis injections
• OTC supplements — vitamin D, vitamin A, calcium, multivitamins, "bone health" preparations
• Antacids — calcium carbonate, milk-of-magnesia
• Recent injections — denosumab, teriparatide, abaloparatide, ICIs
• Recently stopped — denosumab discontinuation can cause rebound hypercalcemia
• Diet — ketogenic diet, large dairy intake, large vitamin D supplementation

---

STEP 2 — Match to the agent and act

Group A — Diuretics & mood stabilisers (PTH-dependent picture, mimics PHPT)

Thiazides

• Reduces renal Ca clearance. Typically only causes hypercalcemia in pre-existing PHPT or anephric patients.
• Action: stop the thiazide. Recheck Ca in 1–2 weeks. If still elevated → workup for PHPT.

Lithium

• 5% of users develop hypercalcemia. Shifts CaSR set-point upward + reduces renal Ca clearance.
• Action: stop or switch lithium if clinically possible (psychiatric collaboration). If lithium must continue and Ca is sustained high → consider PHPT workup; cinacalcet may be useful.

---

Group B — Vitamin / mineral excess

Vitamin D (D2, D3, 25(OH)D, calcitriol)

• Long half-life of cholecalciferol → hypercalcemia can persist weeks to months.
• Action: stop vitamin D. Hydration, calciuresis. Glucocorticoids + antiresorptive if severe. Restrict dietary calcium. Avoid sun.

Vitamin A / retinoids (cis-retinoic acid, ATRA) — >50,000 IU/day

• Mechanism: enhanced bone resorption.
• Action: stop, hydrate, antiresorptive if severe.

Milk-alkali syndrome — Ca carbonate ≥3 g/d + alkali (often modern OTC use)

• Triad: hypercalcemia + metabolic alkalosis + AKI / nephrocalcinosis.
• Action: stop calcium and antacid, rehydrate. Hemodialysis rarely.

---

Group C — Antiresorptive / anabolic bone agents

Denosumab — rebound hypercalcemia after discontinuation

• Most cases: children with bone tumours / fibrous dysplasia, occasionally adults with osteoporosis.
• Action: do not stop denosumab abruptly without bridging (bisphosphonate). If rebound has occurred → IV bisphosphonate, hydration.

Teriparatide [PTH(1-34)] / Abaloparatide [PTHrP analog]

• Transient hypercalcemia post-injection, resolves ~16 h.
• Action: confirm timing. If sustained → stop and reassess.

---

Group D — Oncology / antiviral / metabolic drugs

Antiestrogens (tamoxifen) — "tumour flare" hypercalcemia in breast cancer with bone mets

• Self-limiting; may need acute treatment (hydration, antiresorptive).

Theophylline / aminophylline

• Reversible on stopping; β-blockers can also help.

Foscarnet (antiviral, CMV)

• Rare; reversible on cessation.

Aluminum intoxication

• Setting: CKD on aluminium-containing phosphate binders, or contaminated dialysate / TPN.
• Action: stop aluminium source; chelate with desferrioxamine.

SGLT2 inhibitors

• Mechanism: osmotic diuresis + volume contraction, especially with co-existing risk factors (dehydration, thiazide, acidosis, undiagnosed PHPT).
• Action: hold drug, rehydrate, screen for PHPT.

Immune checkpoint inhibitors (ICIs)

• Mechanisms: ICI-induced hyperthyroidism / adrenal insufficiency / sarcoid-like granulomatosis / PTHrP / hyperprogression.
• Action: full workup including TSH, cortisol, PTHrP, imaging for new granulomas. Manage cause-specifically; glucocorticoids if granulomatous or adrenal.

Ketogenic diet (children with epilepsy)

• Mechanism: impaired osteoblast activity, reduced bone formation.
• Action: dietitian review; consider modifying ratio.

---

STEP 3 — Confirm reversibility

After stopping the suspected agent:

• Recheck corrected calcium at 1–2 weeks (longer for vitamin D — up to 8 weeks).
• If calcium normalises → diagnosis confirmed.
• If calcium remains elevated → return to the hypercalcemia-diagnostic-algorithm for PHPT, FHH, or MAH workup.

---

CLINICAL GUARDRAILS

• Drug-induced hypercalcemia can coexist with PHPT. Thiazide and lithium often unmask mild PHPT — recheck calcium after a 2–4 week washout before booking surgery.
• Vitamin D toxicity is long-lived. Cholecalciferol persists for weeks-to-months. Do not assume rapid resolution.
• Don't abruptly stop denosumab. Bridge with a bisphosphonate to prevent rebound resorption and hypercalcemia (especially in patients with high bone turnover).
• Lithium can't always be stopped. Coordinate with psychiatry; cinacalcet is an option in lithium-induced hypercalcemia who must continue lithium.
• OTC supplement load is often hidden. Ask about gummies, "bone-health" multivitamins, fish liver oil. Patients don't always volunteer these.
• ICIs cause endocrine mimics. A patient on pembrolizumab/nivolumab with hypercalcemia needs TSH, cortisol, ACTH, and chest imaging — not just a calcium recheck.

---

SOURCE

Bilezikian JP, Endotext. Approach to Hypercalcemia. NCBI Bookshelf NBK279129. Section: Medication-Induced Hypercalcemia (Thiazides, Lithium, Vitamin D, Vitamin A, Antiestrogens, Theophylline, Aluminum, Milk-Alkali, SGLT2i, ICIs, Denosumab, Teriparatide/Abaloparatide, Foscarnet, Ketogenic diet).