Medication Induced Hypercalcemia Screener

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name: medication-induced-hypercalcemia-screener
description: Screen a hypercalcemic patient for medication- and supplement-induced causes — thiazides, lithium, vitamin D, vitamin A/retinoids, antiestrogens, theophylline, milk-alkali, SGLT2 inhibitors, immune checkpoint inhibitors, denosumab rebound, teriparatide/abaloparatide, foscarnet, ketogenic diet, aluminium. Trigger when a clinician asks "is this hypercalcemia drug-induced", "thiazide hypercalcemia", "lithium hypercalcemia", "denosumab rebound hypercalcemia", "vitamin D toxicity", "milk-alkali syndrome", "SGLT2 hypercalcemia", or any new hypercalcemia where medication review is needed.
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# 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.

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## 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

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## 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.

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### 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.

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### 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.

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### 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.

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## 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.

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## 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.

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## 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).