Continuing Education Activity

Denosumab is a bone anti-resorptive drug used for the treatment of osteoporosis and other bone-related disorders. FDA-approved indications include prevention of skeletal-related events (e.g., bone pain and fractures) secondary to multiple myeloma or bone metastases from solid tumors, giant cell tumor of the bone, hypercalcemia of malignancy, osteoporosis in postmenopausal women with osteoporosis at high risk for fracture as well as men with osteoporosis at high risk of fracture, glucocorticoid-induced osteoporosis, and bone loss. This activity reviews the mechanism of action, adverse event profile, toxicity, dosing, pharmacodynamics, and monitoring of denosumab pertinent for interprofessional team members when denosumab therapy is appropriate to achieve optimal patient outcomes.

Objectives:

• Identify the mechanism of action of denosumab.
• Summarize the FDA-approved and other indications for therapy with denosumab.
• Outline the adverse event profile of denosumab.
• Explain the importance of improving care coordination among the interprofessional team to enhance the delivery of care for patients when using denosumab therapy.

Indications

Denosumab is a bone anti-resorptive drug used for the treatment of the following: 

FDA-approved Indications

1. Prevention of skeletal-related events (e.g., bone pain and fractures) secondary to multiple myeloma or bone metastases from solid tumors. Used in conjunction with treatments for primary malignancy[1]
2. Giant cell tumor of the bone. Indicated in adults and skeletally mature adolescents with an unresectable tumor or when surgical resection would likely cause severe morbidity.[2]
3. Hypercalcemia of malignancy. This drug is indicated when hypercalcemia is refractory to bisphosphonate therapy.
4. Osteoporosis. Indicated as therapy for postmenopausal women with osteoporosis at high risk for fracture. Indications also include the treatment of men with osteoporosis at high risk of fracture. A high risk for fracture is defined as those with multiple risk factors for fracture, a known history of an osteoporotic fracture,  or those who have failed prior osteoporosis treatment (e.g., bisphosphonates).[3]
5. Glucocorticoid-induced osteoporosis. Indicated for treatment in patients of both sexes at high risk for fracture who are initiating or continuing systemic glucocorticoids at a dose greater than or equal to 7.5 mg of prednisone daily for an expected duration of at least six months.[4]
6. Bone loss. Indicated for the treatment of androgen deprivation-induced bone loss and aromatase inhibitor-induced bone loss. The goal of therapy is to increase bone mass in men with prostate cancer receiving androgen deprivation therapy. In women, the treatment goal is to increase bone mass when receiving aromatase inhibitor therapy for breast cancer.[5]

Mechanism of Action

Denosumab is a total human IgG2 monoclonal antibody that binds to receptor activator of NF kappa B ligand (RANKL) and competitively inhibits its binding to receptor activator of NF kappa B (RANK). Soluble RANKL is a trimer and a member of the tumor necrosis factor (TNF) family of ligands. Each RANKL trimer can bind and oligomerize up to three receptors. When bound to RANK, RANKL potentiates osteoclast differentiation from hematopoietic stem cells and activates and prolongs the survival of mature osteoclasts. Osteoclasts' primary function then is to promote bone resorption. Denosumab binds to RANKL with high affinity and blocks it from binding to and oligomerizing its receptor RANK, thus inhibiting osteoclast maturation and bone resorption. 

Administration

The administration of denosumab should be via subcutaneous injection only and should not be administered intravenously or intramuscularly. Injection sites include the upper arm, upper thigh, or abdomen. No observation or premedication is required. Dosing is prescribed as 120 mg/1.7 mL (70 mg/mL) solution in a single-dose vial or as a single-use pre-filled syringe containing 60 mg in a 1 mL solution. Administer vitamin D and calcium as necessary to treat or prevent hypocalcemia — no dosing adjustments required for hepatic or renal impairment. The distribution and timing of doses depend on the pathology, as shown below. 

• Skeletal-related events secondary to multiple myeloma or bone metastases from solid tumors: administer 120 mg injection every four weeks
• Giant cell tumor of bone: 120 mg injection administered every four weeks with supplementary doses of 120 mg on the 8th and 15th day during the first month of treatment
• Hypercalcemia of malignancy: administer 120 mg injection every four weeks with supplemental doses of 120 mg on the 8th and 15th day during the first month of treatment
• Osteoporosis/bone loss: administer 60 mg every six months

Adverse Effects

Adverse effects include the following based on body systems:

Cardiovascular

• Peripheral edema (4% to 20%)
• Hypertension (5%)
• Angina pectoris (4%)

Central Nervous System

• Fatigue (45% or less)
• Headache (18%)
• Sciatica (6%)

Dermatologic

• Skin rash (14% or less)
• Dermatitis (11% or less)
• Eczema (11% or less)

Endocrine

• Hypophosphatemia (32%)
• Severe hypophosphatemia (15%)
• Hypocalcemia (3% to 10%)
• Hypercholesterolemia (8%)
• Grade 3 hypokalemia (4%)
• Grade 3 hypomagnesemia (4%)
• Severe (symptomatic) hypocalcemia (<1% to 3%)

Gastrointestinal

• Diarrhea (34%)
• Nausea (31%)
• Decreased appetite (25%)
• Vomiting (25%)
• Constipation (22%)
• Flatulence (3%)

Hematologic and Oncologic

• Anemia (22%)
• Thrombocytopenia (20%)
• New malignant neoplasm (4%)

Infection

• Serious infection (5%)

Neuromuscular and Skeletal

• Weakness (45% or less)
• Back pain (15%)
• Arthralgia (11%)
• Limb pain (11%)
• Musculoskeletal pain (7%)
• Ostealgia (5%)
• Myalgia (4%)
• Osteonecrosis of the jaw (1% to 4%)[6]

Ophthalmic

• Cataract (5% or less)

Respiratory

• Dyspnea (24%)
• Cough (16%)
• Upper respiratory tract infection (6% to 16%)
• Pneumonia (9%)
• Nasopharyngitis (8%)

Contraindications

• Known severe hypersensitivity to denosumab or any component of the formulation 
• Preexisting hypocalcemia 
• Pregnancy 

Monitoring

Clinicians should evaluate possible pregnancy before initiation of treatment. Obtaining vitamin D level and clearance from a dentist is suggested before the initiation of therapy. Within the first few weeks of treatment, recommended monitoring of serum creatinine, calcium, phosphorus, and magnesium. Monitor for signs and symptoms of hypocalcemia as well as hypercalcemia upon discontinuation of denosumab. A dental exam is a recommendation if osteonecrosis of the jaw is suspected. The evaluation of bone mineral density should occur anywhere between one to two years after initiating treatment. The recommendation is for periodic monitoring of vitamin D and serum calcium throughout the treatment duration.[7][8]

Toxicity

Atypical bone fractures: Although the incidence remains low, an association with atypical bone fractures exists with prolonged bisphosphonate therapy. However, clinicians have also observed these fractures in those receiving denosumab for osteoporosis or metastatic bone disease. These fractures are usually located in the subtrochanteric region or along the shaft of the femur. Patients tend to feel prodromal pain from weeks to months leading up to the fracture. Fractures commonly occur with little to no trauma in the area. Experts are unsure at this time if the atypical fractures occur secondary to denosumab toxicity or the patient’s underlying osteoporosis. Patients should receive counseling regarding the potential for new hip or thigh pain and the contralateral limb examined if an atypical fracture is suspected. Upon diagnosis of an atypical fracture, possible discontinuation of denosumab is an option. If discontinued, consider initiating a different osteoporosis therapy due to an increased risk of fracture.[9]

Hypersensitivity: Reports exist of clinically severe and anaphylactic reactions. Symptoms may include rash, pruritus, urticaria, facial edema, airway edema, and possibly hypotension. If these symptoms occur, initiate appropriate treatment and subsequently discontinue denosumab. 

Hypocalcemia: Due to its anti-resorptive effects, denosumab has the potential to cause hypocalcemia. There is documentation of severe, even fatal, cases of denosumab-induced hypocalcemia. Those with severe renal dysfunction may have an increased risk of developing hypocalcemia. Clinicians should obtain serum calcium and preexisting hypocalcemia corrected at the initiation of treatment. In patients with preexisting hypocalcemia, serum calcium requires frequent monitoring. Use denosumab with caution in those who have predisposing conditions to hypocalcemia.[10]

Osteonecrosis of the jaw (ONJ): Reports of ONJ have been observed in those receiving denosumab. Symptoms may include jaw pain, tooth infection, bone, and gingival erosion, toothache. An increased risk of being diagnosed with ONJ correlates directly to the duration of denosumab exposure. Those with predisposing factors, such as poor dentition and recent tooth extraction, are at a higher risk. If ONJ is suspected, make arrangements for a thorough dental exam. The risk of ONJ is considerably higher in patients with malignancy receiving denosumab than in patients with osteoporosis receiving denosumab. Denosumab should not be initiated until dental health is optimized. While on denosumab for cancer therapy, dental procedures are contraindicated. If ONJ is suspected, discontinue denosumab.[6]

Dermatologic reactions: Reports of dermatitis, eczema, and rash have been observed. If symptoms are severe, consider discontinuation of denosumab.

Enhancing Healthcare Team Outcomes

Healthcare workers, including primary care physicians and nurse practitioners who prescribe denosumab, should monitor the patients. Pharmacists should assist in monitoring for side effects. The patient should get a baseline evaluation from the dentist before initiating treatment. At regular intervals, the patient's electrolytes and renal function also require monitoring. The most severe complication of therapy is osteonecrosis of the jaw, and thus an oral exam is necessary at each visit. Periodic bone density evaluation every 1 to 2 years is the recommended interval for follow-up. Only through close monitoring of the patient can the morbidity of this agent be decreased.