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Chapter 21: Drugs Affecting the Endocrine System
Bisphosphonates
• Drugs: etidronate (Didronel), pamidronate (Aredia), risedronate (Actonel)
alendronate (Fosamax), tiludronate (Skelid), zoledronic acid (Zometa), ibandronate
(Boniva)
• Used for bone support, most commonly used
• Pharmacodynamics
▪ Adhere to bone, inhibit osteoclastic activity, potent inhibitors of both normal
and abnormal bone resorption
o Etidronate (Didronel): reduces both bone resorption and bone formation
because formation is coupled with resorption
o Pamidronate (Aredia) (available as IV only)
o and risedronate (Actonel): inhibit bone resorption with out inhibiting bone
formation and mineralization
o Alendronate (Fosamax): highly selective inhibitor of bone resorption 1
▪ 100 to 500 time more potent than the other drugs
▪ Does not interfere with osteoclastic recruitment or attachment but does
inhibit osteoclastic activity
o Tiludronate (Skelid): inhibits protein-tyrosine-phosphatease, results in detachment
of osteoclasts from the bone surface
▪ Inhibits the osteoclastic proton pump
o Zoledronic acid (Zometa): inhibits osteoclastic activity and induces osteoclast
apoptosis
▪ Also inhibits the increased osteoclastic activity and skeletal calcium
release induced by various stimulatory factors release by tumors
▪ Only available as IV formulation
o Ibandronate (Boniva): inhibits osteoclast activity and reduces bone resorption and
turnover based
on its affinity for hydroxyapatite (part of the bone matrix)
• All drugs in this class reduce vertebral fracture however,
o Only alendronate, risedronate, and zoledronic acid have demonstrated nonvertebral
fracture
reduction
o Pamidronate and zoledronic acid: only for parenteral use
• Pharmacotherapeutics
o Contraindication: uncorrected hypocalcemia, documented Barrett’s
esophagus, and renal insufficiency
o Caution: patient with GI disorders
o R/F severe esophageal adverse reactions is greater in patients who lie down after
taking these drugs or fail to take with a full glass of water
,o Etidronate has been withheld from patients with enterocolitis r/t diarrhea particularly at
high doses
▪ Associated with fracture in patients with Paget’s disease when given high
doses or when therapy lasted longer than 6 months
• Monitor with x-rays and lab work to assess for lesions
• Rare femur fracture in non-Paget’s patients using bisphosphonates
o IV formulations associated with higher renal toxicity risk especially with rapid infusion
▪ Check crt prior to every dose is required, force fluids before and after infusion
,• Clinical Use (Page 546 Dosing Chart)
o Osteoporosis
▪ Prevention and treatment of osteoporosis and its risk for fracture in men and
postmenopausal women (especially vertebral fractures)
▪ First line drugs: Alendronate, risedronate, and zolendronic acid with hip
fracture reductions, FDA approved for this indication
▪ Second-line drug: Ibandronate
▪ Ibandronate and zoledronic acid come in IV form
▪ Alendronate PO solution (Binosto) and PO tablets
▪ Zoledronic acid: only alternative form that shows evidence of hip fracture
reduction
▪ Prophylactic use in patients with early osteopenia r/t long term use of
medications that contribute to bone loss
• Includes (thyroid hormone, aromatase inhibitors, and glucocorticoids,
PPIs, SSRIs)
▪ It is recommended that all adults taking more than 7.5 mg of prednisone or its
equivalent for more than 3 weeks be given alendronate or risedrone
▪ In very high risk patients, maximum 2-year use of teriparatide (Forteo) (bone
mass benefit disappears after d/c) a parathyroid hormone, may be more
efficacious
• Bisphosphonates: bone mass benefit does not decline for 5 years
▪ Alendronate and risedronate initial doses for prevention of bone loss: 5mg/day or
35mg/week
▪ For existing osteoporosis: alendronate 10mg/day or 70mg/week
▪ Risedronate: 75mg for 2 days or 150mg once a month
o Paget’s Disease (Osteitis Deformans)
▪ All bisphosphonates are used to treat Paget’s disease when the alkaline
phosphatase is at least twice the upper limit of normal
▪ Asymptomatic or at risk for future complications from their disease
▪ Symptomatic Paget’s best treated with etidronate
▪ Etidronate slows accelerated bone turnover in pagetic lesions and to a lesser
extend in normal bone
▪ Reduced turnover causes symptomatic improvement: less bone pain and
decreased fractures
▪ 5-10 mg/kg daily for up to 6 months or 11 to 20 mg/kg daily for 3 months
▪ For all drugs indications for retreatment are evidence of active disease or failure
to normalize alkaline phosphatase levels
▪ Supplemental calcium and vitamin D if dietary intake is not adequate
▪ Space calcium supplements and bisphosphonates to prevent reduced
bioavailability
o Heterotopic Ossification
▪ Complications of THR
▪ Etidronate: first line
, ▪ Heterotopic ossification r/t spinal cord injury
▪ Use as soon as possible after injury
• Drug Interactions
o Adverse GI reactions, interact with drugs that affect the GI tract
▪ Histamine 2 blocking agents double alendronate bioavailability but the impact with unknow
o Calcium supplements and antacids interfere with bisphosphonate absorption when
taken within 1 hr
o R/F GI bleeding is increased when ASA and NSAIDs are concomitantly taken
o ASA may decrease the bioavailability of tiludronate by up to 50% when taken
2 hrs after the tiludronate