Bone Health: Denosumab, Calcium & Vitamin D

Urology owns bone health more than many realize: androgen deprivation therapy in men and aromatase inhibitors in women both accelerate bone loss dramatically, and fragility fractures carry real morbidity and mortality (a hip fracture in an elderly man carries a one-year mortality approaching 30%). ADT causes bone loss faster than natural menopause — up to 4–5% of bone mineral density per year in the first years. This chapter covers who to assess, the universal foundation, and the drugs — including the important distinction between osteoporosis dosing and bone-metastasis dosing of denosumab.

23.1 Who to assess

• Postmenopausal women and men aged ≥ 70; anyone with a prior fragility fracture (a fracture from a fall from standing height IS osteoporosis until proven otherwise, regardless of the DEXA).

• Treatment-induced bone loss — high-yield in urology: men starting or continuing ADT for prostate cancer; women on aromatase inhibitors for breast cancer. Screen these patients at treatment initiation, not years later.

• Chronic glucocorticoids, hypogonadism, smoking, excess alcohol, low body weight, rheumatoid arthritis, and malabsorption.

• Tools: DEXA bone density (T-score) plus the FRAX 10-year fracture-risk estimate (FRAX has a checkbox for secondary osteoporosis — use it for ADT patients). Osteoporosis = T-score ≤ −2.5 OR a fragility fracture; osteopenia = −1.0 to −2.5.

23.2 The universal foundation — for everyone

• Calcium: OTC calcium citrate + vitamin D3 gummies providing 1,200 mg calcium daily.

• Vitamin D: typically 800–1,000+ IU/day; target a 25-hydroxy-vitamin D level ≥ 30 ng/mL. Check the level in anyone starting bone therapy — you cannot correct calcium without adequate vitamin D.

• Lifestyle: weight-bearing and RESISTANCE exercise (the most underprescribed intervention in men on ADT), fall-prevention (vision, footwear, home hazards, medication review), smoking cessation, and limiting alcohol.

23.3 Denosumab is our drug of choice

Advanced Urology's bone-protection strategy is simple and deliberate: calcium and vitamin D as the foundation, and denosumab as the antiresorptive of choice. Denosumab is a fully human monoclonal antibody against RANKL — it prevents RANKL from activating osteoclasts, shutting down bone resorption at its source. It reliably increases bone density and reduces vertebral, non-vertebral, and hip fractures. We use denosumab BIOSIMILARS (the identical molecule at lower cost), not the brand.

Every denosumab patient needs calcium and vitamin D levels checked, abnormalities corrected, and OTC calcium citrate + vitamin D3 gummies providing 1,200 mg calcium daily. This is not optional — it prevents hypocalcemia and is required for the drug to work safely.

23.4 The anabolic exception — severe osteoporosis in women

Denosumab and the other antiresorptives STOP bone from being lost. An anabolic agent does something different — it BUILDS new bone. For a woman whose skeleton is already severely depleted, preventing further loss is not enough; she needs bone back. That is the patient in whom we use an anabolic.

Who qualifies (very high fracture risk) — consider an anabolic first-line when any of the following are present: a T-score ≤ −3.0; a recent (within ~12 months) fragility fracture; multiple fragility fractures; a fracture while already on an antiresorptive; or a very high FRAX 10-year risk (roughly > 30% major osteoporotic or > 4.5% hip).

23.5 ADT bone-health protocol (men on androgen deprivation)

1. At ADT initiation: baseline DEXA and FRAX; check vitamin D; start calcium and vitamin D; counsel on exercise and falls.

2. Treat EVERY patient starting or receiving ADT with denosumab. Use 60 mg every 6 months when there are no bone metastases. If bone metastases are present, use 120 mg every 12 weeks instead — do not give both regimens.

3. Reassess bone density periodically (typically every 1–2 years) while on ADT; keep doses on schedule and supplementation consistent.

4. Do not forget that ADT bone loss begins immediately — the first year is the steepest. Intervene early rather than after the first fracture.

23.6 Denosumab 120 mg every 12 weeks for bone metastases

Bone-metastasis dosing is different from osteoporosis dosing — a higher dose given more often — and is aimed at protecting the skeleton in metastatic disease (most often advanced prostate cancer; see Chapter 20). This is a different clinical goal: not preventing osteoporotic fractures, but preventing the catastrophic complications of bone metastases.

• Universal baseline: every patient with bone metastases gets a baseline DEXA and denosumab.

• Dose: denosumab 120 mg subcutaneously every 12 weeks. That is twice the dose of the osteoporosis regimen given about twice as often (roughly 4 doses a year versus 2), which works out to about four times the annual exposure. Confirm the indication before every order: 60 mg every 6 months is osteoporosis and ADT bone protection; 120 mg every 12 weeks is bone metastases.

• Why every 12 weeks, and not monthly: the FDA label and long-standing practice are 120 mg every 4 weeks. We dose every 12 weeks to reduce osteonecrosis of the jaw, on the strength of the REDUSE trial (SAKK 96/12) — a randomised phase III non-inferiority study of 1,380 patients with bone metastases from breast or castration-resistant prostate cancer, median follow-up 37 months. Twelve-weekly dosing was non-inferior to four-weekly for time to first symptomatic skeletal event (HR 1.023, 90% CI 0.874–1.197; median 56.5 vs 56.6 months), with less hypocalcaemia (30% vs 46%) and less ONJ (6.9% vs 8.5%).

• Two honest caveats. First, REDUSE's reduced arm gave four loading doses every 4 weeks before switching to every 12 weeks; our protocol goes to every 12 weeks from the first dose, which is a step beyond what the trial tested. Second, this is a deliberate departure from the product label. Both are reasons to state the schedule explicitly when you communicate with oncology, the infusion suite, or an outside provider — do not assume they are expecting a 12-weekly patient.

• Why we use it: it prevents and delays SKELETAL-RELATED EVENTS (SREs) — pathologic fractures, spinal cord compression, and the need for radiation or surgery to bone. In head-to-head data it delays SREs more effectively than the bisphosphonate alternative, which is one reason it is our agent of choice.

• Practical advantages: subcutaneous administration (no infusion chair, no IV access), and no renal dose adjustment — though note that hypocalcemia risk is actually HIGHER in renal impairment, so calcium status matters even more, not less.

• Calcium + vitamin D are mandatory: check calcium and vitamin D levels, correct abnormalities BEFORE starting, and use OTC calcium citrate + vitamin D3 gummies providing 1,200 mg calcium daily. Monitor calcium during therapy.

• ONJ risk is meaningfully higher at this dose and frequency than at the osteoporosis dose — obtain dental clearance before initiation and avoid invasive dental procedures while on therapy. Counsel the patient to tell every dentist they are on it.

• Keep it on schedule: as with the lower dose, do not interrupt without a managed plan. If denosumab is stopped, the patient must be transitioned to zoledronic acid (Zometa); coordinate with the treating physician/oncology.