EtidronateRx

Trade Names: Didronel

Synonyms: Disodium etidronate, sodium etidronate

Drug Class: Bisphosphonate

Preparations
Tablets: 200- and 400 mg

Dose
Newer bisphosphonates are preferred (see Comments)
Paget’s disease: initially 5 mg/kg/day orally not to exceed 6 months
Heterotopic ossification with total hip replacement: 20 mg/kg/day for 1 month before and 3  months after surgery (4  months total)

Indications: Paget’s disease, prevention and treatment of heterotopic ossification (e.g., calcification after hip replacement)

Mechanism of Action: Adsorbs onto hydroxyapatite crystals and blocks their aggregation and growth

Contraindications: Hypersensitivity to bisphosphonates; severe renal impairment; osteomalacia; severe esophageal abnormalities, pregnancy

Precautions: Reduce dose in mild renal impairment. Avoid if possible if esophageal problems or renal impairment are present. Ensure that patient understands how the drug should be taken. A dental exam and preventive dental work should be performed before starting chronic bisphosphonate therapy. Paget’s disease with lytic lesions have a risk of fracture.

Monitoring: In Paget’s disease, alkaline phosphatase and markers of bone turnover are monitored as measures of response to treatment.

Pregnancy Risk: C

Adverse Effects
Common: Mild GI disturbance (i.e., nausea, dyspepsia, dysphagia), hypocalcemia (transient, mild), headache, increased bone pain in Paget’s
Less common: Severe erosive esophagitis, osteomalacia, osteonecrosis of the jaw, severe musculoskeletal pain, uveitis, altered taste, allergy

Drug Interactions
Antacids: Decreased bioavailability of etidronate
Calcium: If taken together, decreased bioavailability of etidronate

Patient Instructions: Take on an empty stomach (2 hours before meals). Should be taken with a full glass of water on arising in the morning. Nothing other than water should be taken for at least 30 minutes. Even coffee or fruit juice markedly reduce absorption. Delaying such intake for longer than 30 minutes (1–2 hours if possible) maximizes absorption. After taking, the patient must remain upright to reduce risk of esophageal irritation. Any other medications must be taken at least 30 minutes after bisphosphonate. Supplement calcium and vitamin D intake if required.

Comments: Etidronate should not be used for treatment of osteoporosis. Newer bisphosphonates are preferred for treatment of Paget’s as they are more potent and less likely to cause osteomalacia. Supplemental calcium and vitamin D are usually co-administered.

Clinical Pharmacology: Absorption 1%–5%; no metabolism; renal excretion. Half of absorbed dose is eliminated in 24 hours; the rest binds to calcium phosphate surfaces and is eliminated over months to years.

Cost: $$$

BIBLIOGRAPHY

Ralston SH. Clinical practice. Paget's disease of bone. N Engl J Med 2013;368:644-50. PMID: 23406029