Etidronate

INTRODUCTION

Indications

Treatment of Paget's disease of bone. Treatment and prophylaxis of heterotopic calcification associated with total hip replacement or spinal cord injury. Used with other agents (saline diuresis) in the management of hypercalcemia associated with malignancies.

Action

Blocks the growth of calcium hydroxyapatite crystals by binding to calcium phosphate. Therapeutic Effects: Decreased bone resorption and turnover.

Adverse Reactions/Side Effects

GI: diarrhea, nausea IV: loss of taste, metallic taste. GU: nephrotoxicity. Derm: rash. MS: musculoskeletal pain, microfractures, osteonecrosis (primarily of jaw).

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Assess any muscle or joint pain. Report persistent or increased musculoskeletal pain to determine presence of bone or joint pathology, including fracture. Be especially aware of possible mouth and jaw pain due to osteonecrosis of the jaw. Bone pain may persist or increase in patients with Paget's disease, but usually subsides days to months after therapy is discontinued.

• Assess changes in pain and inflammation at heterotopic ossification site(s) to help document drug effectiveness. Assess range of motion if ossification occurs near a joint, and document any changes in joint function.

• Monitor and report signs of abnormal calcium levels. Signs of high calcium levels (hypercalcemia) include nausea, vomiting, anorexia, weakness, constipation, thirst, and cardiac arrhythmias. Low calcium levels (hypocalcemia) are indicated by paresthesia, muscle twitching, laryngospasm, colic, cardiac arrhythmias, Chvostek's sign (facial muscle twitching when the facial nerve is tapped), or Trousseau's sign (finger and wrist flexion during temporary occlusion of the brachial artery).

• Watch for signs of nephrotoxicity, including hematuria, increased urinary frequency, cloudy urine, and decreased urine output. Report these signs to the physician.

Interventions

• Protect against falls and fractures (See Appendix E). Modify home environment (remove throw rugs, improve lighting, etc.), and provide assistive devices (cane, walker) or other protective devices as needed to improve balance and prevent falls.

Patient/Client-Related Instruction

• Advise patient about the benefits of proper diet in sustaining bone mineralization. If necessary, refer patient for nutritional counseling about supplemental calcium and vitamin D.

• Instruct patient to report other troublesome side effects such as severe or prolonged skin rash, change in taste, or GI problems (diarrhea, nausea).

Pharmacokinetics

Absorption: Absorption is generally poor (1–6%) after oral administration.

Distribution: Half of the absorbed dose is bound to hydroxyapatite crystals in areas of increased osteogenesis.

Metabolism and Excretion: Unabsorbed drug is eliminated in the feces; 50% of the absorbed dose is excreted unchanged by the kidneys.

Half-life: 5–7 hr.