FOSAMAX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FOSAMAX (FOSAMAX).
Bisphosphonate that inhibits osteoclast-mediated bone resorption by binding to hydroxyapatite in bone matrix and impairing osteoclast activity through inhibition of farnesyl pyrophosphate synthase.
| Metabolism | Not metabolized; excreted unchanged via renal secretion and glomerular filtration. |
| Excretion | Renal excretion of unchanged drug is the primary route (approximately 50% of absorbed dose). Unabsorbed drug is eliminated in feces. No biliary excretion. |
| Half-life | Terminal elimination half-life is approximately 10.5 years in bone, reflecting slow release from the skeleton. Plasma half-life after intravenous administration is about 1 hour. |
| Protein binding | Approximately 78% bound to human plasma proteins. |
| Volume of Distribution | Vd is approximately 28 L (excluding bone, which represents a large deep compartment). Clinical meaning: extensive distribution to bone, where it accumulates. |
| Bioavailability | Oral bioavailability is approximately 0.7% under fasting conditions with plain water; food, beverages, or other medications reduce bioavailability significantly. |
| Onset of Action | Within 1 month of oral dosing, as measured by reductions in bone turnover markers. |
| Duration of Action | Up to several years after discontinuation due to prolonged retention in bone, with sustained suppression of bone resorption. |
70 mg orally once weekly for osteoporosis; 10 mg orally once daily for Paget's disease.
| Dosage form | SOLUTION |
| Renal impairment | Contraindicated in GFR <35 mL/min; no adjustment needed for GFR ≥35 mL/min. |
| Liver impairment | No dose adjustment required for mild to moderate hepatic impairment; not studied in severe hepatic impairment. |
| Pediatric use | Not recommended for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | No dose adjustment required; ensure adequate calcium and vitamin D intake. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for FOSAMAX (FOSAMAX).
| Breastfeeding | Alendronate is excreted into human breast milk in unknown amounts, but due to its low oral bioavailability and high protein binding, the amount absorbed by the infant is likely negligible. The milk-to-plasma ratio (M/P) is not established. Caution is advised; consider discontinuing breastfeeding or the drug based on the importance of the drug to the mother. No adverse effects in nursing infants have been reported. |
| Teratogenic Risk | Alendronate, a bisphosphonate, is classified as FDA Pregnancy Category C. Based on animal studies and limited human data, there is a potential risk of fetal skeletal abnormalities and hypocalcemia when administered during pregnancy. Use during the first trimester is associated with minimal risk based on small cohort studies, but second and third trimester exposure may theoretically affect fetal bone development due to drug incorporation into the bone matrix. However, the magnitude of risk in humans is not well established. Alendronate is not recommended during pregnancy unless clearly needed. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypocalcemia","Inability to stand or sit upright for at least 30 minutes","Esophageal abnormalities that delay esophageal emptying (e.g., stricture, achalasia)","Severe renal impairment (CrCl <35 mL/min)"]
| Precautions | ["Severe musculoskeletal pain (bone, joint, or muscle pain rarely severe and disabling)","Osteonecrosis of the jaw (ONJ) especially with invasive dental procedures","Atypical femur fractures with long-term use","Gastrointestinal adverse reactions (esophagitis, esophageal ulcer, dysphagia); instruct patients to take with plain water and remain upright","Hypocalcemia must be corrected before initiation","Renal impairment (not recommended if CrCl <35 mL/min or severe renal insufficiency)"] |
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| Fetal Monitoring | Monitor serum calcium, phosphate, and magnesium levels periodically during therapy, especially if signs of hypocalcemia. Assess renal function before and during treatment due to risk of renal toxicity. In pregnant women, consider fetal ultrasound to assess bone development if prolonged exposure. Also monitor for gastrointestinal adverse effects. |
| Fertility Effects | In animal studies, alendronate did not impair fertility at doses up to 25 mg/kg/day. There are no adequate human data on fertility effects. Bisphosphonates have been associated with delayed bone healing after fractures, but no direct effect on human fertility has been reported. |