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In Pagetic patients the physician should adhere to the recommended dose regimen in order to avoid over- treatment with Didronel. The response to therapy may be of slow onset and may continue even for months after treatment with the drug has been discontinued. Dosage should not be increased prematurely nor should treatment be resumed before there is clear evidence of reactivation of the disease process. Re-treatment should not be initiated until the patient has had at least a three-month drug-free interval.
Etidronate disodium is not metabolized and is excreted intact via the kidney. Due to the lack of clinical experience the treatment of patients with impaired renal function should be undertaken with due caution. The use of etidronate disodium is discouraged in patients with severely impaired kidney function.
Caution should be taken in patients with a history of renal stone formation. In patients with impaired renal function or a history of renal stone formation, serum and urinary calcium should be monitored regularly.
It is recommended that serum phosphate, serum alkaline phosphatase and urinary hydroxyproline be measured before commencing medication and at three month intervals during treatment. If after three months of medication the pre-treatment levels have not been reduced by at least 25%, the patient may be relatively resistant to therapy. If the serum phosphate level is unchanged in the "resistant" patient, consideration should be given to increasing the dose since the absorption of pharmacologically active amounts of Didronel is typically accompanied by a rise in serum phosphate. This rise usually correlates with reductions in the biochemical indices of disease activity. If after three or more months of medication elevations of serum phosphate above the upper limit of normal are not accompanied by clinical or biochemical evidence of reduced activity, resistance of the disease to the action of Didronel is probable and termination of Didronel medication should be considered. Etidronate disodium suppresses bone turnover and may retard mineralisation of osteoid laid down during the bone accretion process. These effects are dose and time dependent. Osteoid, which may accumulate noticeably at doses of 10-20 mg/kg/day, mineralises normally post-therapy. Patients in whom serum phosphate elevations are high and reductions of disease activity are low may be particularly prone to retarded mineralisation of new osteoid. In those cases where 200mg per day (a single tablet) may be excessive, doses may be administered less frequently.
Patients with Paget's disease of bone should maintain an adequate intake of calcium and vitamin D. Patients with low vitamin D and calcium intake may be particularly sensitive to drugs that affect calcium homeostasis and should be closely monitored during Didronel therapy.
Etidronate disodium does not adversely affect serum levels of parathyroid hormone or calcium.
Hyperphosphataemia has been observed in patients receiving etidronate disodium, usually in association with doses of 10-20mg/kg/day. No adverse effects have been traced to this, and it does not constitute grounds for discontinuing therapy. It is apparently due to a drug-related increase in renal tubular reabsorption of phosphate. Serum phosphate levels generally return to normal 2-4 weeks post therapy.
Patients with significant chronic diarrhoeal disease may experience increased frequency of bowel movements and diarrhoea, particularly at higher doses.
Increased or recurrent bone pain at existing Pagetic sites and/or the appearance of pain at sites previously asymptomatic have been reported at a dose of 5mg/kg/day.At higher doses, the incidence rises to approximately 20%. When therapy continues, pain resolves in some patients but persists in others.
Fractures are recognised as a common feature in patients with Paget's disease. There has been no evidence of increased risk of fractures at the recommended dose of 5mg/kg/day for six months. At doses of 20mg/kg/day in excess of three months' duration, mineralisation of newly formed osteoid may be impaired and the risk of fracture may be increased. The risk of fracture may also be greater in patients with extensive and severe disease, a history of multiple fractures, and/or rapidly advancing osteolytic lesions. It is therefore recommended that the drug is discontinued when fractures occur and therapy not reinstated until the fracture healing is complete.
Patients with predominantly lytic lesions should be monitored radiographically and biochemically to permit termination of etidronate disodium in those patients unresponsive to treatment.The incidence of osteogenic sarcoma is known to be increased in Paget's disease. Pagetic lesions, with or without therapy, may appear by X-ray to progress markedly, possibly with some loss of definition of periosteal margins. Such lesions should be eva luated carefully to differentiate these from osteogenic sarcoma.
Osteonecrosis of the jaw, generally associated with tooth extraction and/or local infection (including osteomyelitis) has been reported in patients with cancer receiving treatment regimens including primarily intravenously administered bisphosphonates. Many of these patients were also receiving chemotherapy and corticosteroids. Osteonecrosis of the jaw has also been reported in patients with osteoporosis receiving bisphosphonates.
A dental examination with appropriate preventive dentistry should be considered prior to treatment with bisphosphonates in patient with concominant risk factors (e.g. cancer, chemotherapy, radiotherapy, corticosteroids, poor oral hygiene).
While on treatment, these patients should avod invasive dental procedures if possible. For patients who develop osteonecrosis of the jaw while on bisphosphonate therapy, dental surgery may exacerbate the condition. For patients requiring dental procedures, there are no data available to suggest whether discontinuation of bisphosphonate treatment reduces risk of osteonecrosis of the jaw.
Clinical judgement of the treating physician should guide the management plan of each patient based on individual benefit/risk assessment.
Atypical fractures of the femur
Atypical subtrochanteric and diaphyseal femoral fractures have been reported with bisphosphonate therapy, primarily in patients receiving long-term treatment for osteoporosis. These transverse or short oblique fractures can occur anywhere along the femur from just below the lesser trochanter to just above the supracondylar flare. These fractures occur after minimal or no trauma and some patients experience thigh or groin pain, often associated with imaging features of stress fractures, weeks to months before presenting with a completed femoral fracture. Fractures are often bilateral; therefore the contralateral femur should be examined in bisphosphonate-treated patients who have sustained a femoral shaft fracture. Poor healing of these fractures has also been reported. Discontinuation of bisphosphonate therapy in patients suspected to have an atypical femur fracture should be considered pending eva luation of the patient, based on an individual benefit risk assessment.
During bisphosphonate treatment patients should be advised to report any thigh, hip or groin pain and any patient presenting with such symptoms should be eva luated for an incomplete femur fracture.
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