General

Standard hypercalcemia-related metabolic parameters, such as serum levels of calcium, phosphate, magnesium, and potassium, should be carefully monitored following initiation of therapy with pamidronate disodium. Cases of asymptomatic hypophosphatemia (12%), hypokalemia (7%), hypomagnesemia (11%), and hypocalcemia (5% to 12%), were reported in pamidronate disodium-treated patients. Rare cases of symptomatic hypocalcemia (including tetany) have been reported in association with pamidronate therapy. If hypocalcemia occurs, short-term calcium therapy may be necessary. In Paget’s disease of bone, 17% of patients treated with 90 mg of pamidronate disodium showed serum calcium levels below 8 mg/dL.

Patients with a history of thyroid surgery may have relative hypoparathyroidism that may predispose to hypocalcemia with pamidronate disodium.

Renal Insufficiency

Pamidronate disodium is excreted intact primarily via the kidney, and the risk of renal adverse reactions may be greater in patients with impaired renal function. Patients who receive pamidronate disodium should have serum creatinine assessed prior to each treatment. In patients receiving pamidronate disodium for bone metastases, who show evidence of deterioration in renal function, pamidronate disodium treatment should be withheld until renal function returns to baseline (see WARNINGS and DOSAGE AND ADMINISTRATION).

In clinical trials, patients with renal impairment (serum creatinine >3.0 mg/dL) have not been studied. Limited pharmacokinetic data exist in patients with creatinine clearance <30 mL/min (See Clinical Pharmacology, Pharmacokinetics). For the treatment of bone metastases, the use of pamidronate disodium in patients with severe renal impairment is not recommended. In other indications, clinical judgment should determine whether the potential benefit outweighs the potential risk in such patients.

Osteonecrosis of the Jaw

Osteonecrosis of the jaw (ONJ) has been reported predominantly in cancer patients treated with intravenous bisphosphonates, including pamidronate disodium. Many of these patients were also receiving chemotherapy and corticosteroids which may be risk factors for ONJ. Post-marketing experience and the literature suggest a greater frequency of reports of ONJ based on tumor type (advanced breast cancer, multiple myeloma), and dental status (dental extraction, periodontal disease, local trauma including poorly fitting dentures). Many reports of ONJ involved patients with signs of local infection including osteomyelitis. 

Cancer patients should maintain good oral hygiene and should have a dental examination with preventive dentistry prior to treatment with bisphosphonates.

While on treatment, these patients should avoid invasive dental procedures if possible. For patients who develop ONJ 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 the risk of ONJ. Clinical judgment of the treating physician should guide the management plan of each patient based on individual benefit/risk assessment (see ADVERSE REACTIONS).

Musculoskeletal Pain

In post-marketing experience, severe and occasionally incapacitating bone, joint, and/or muscle pain has been reported in patients taking bisphosphonates. This category of drugs includes pamidronate disodium. The time to onset of symptoms varied from one day to several months after starting the drug. Most patients had relief of symptoms after stopping. A subset had recurrence of symptoms when rechallenged with the same drug or another bisphosphonate.

Atypical fractures of the femur 

Atypical subtrochanteric and diaphyseal femoral fractures have been reported in patients receiving bisphosphonate therapy, including pamidronate disodium. These fractures can occur anywhere in the femoral shaft from just below the lesser trochanter to just above the supracondylar flare and are transverse or short oblique in orientation without evidence of comminution. These fractures occur after minimal or no trauma. Patients may experience thigh or groin pain 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. A number of case reports noted that patients were also receiving treatment with glucocorticoids (such as prednisone or dexamethasone) at the time of fracture. Causality with bisphosphonate therapy has not been established. 

Any patient with a history of bisphosphonate exposure who presents with thigh or groin pain in the absence of trauma should be suspected of having an atypical fracture and should be evaluated. Discontinuation of pamidronate disodium therapy in patients suspected to have an atypical femur fracture should be considered pending evaluation of the patient, based on an individual benefit risk assessment. It is unknown whether the risk of atypical femur fracture continues after stopping therapy.

Laboratory Tests

Patients who receive pamidronate disodium should have serum creatinine assessed prior to each treatment. Serum calcium, electrolytes, phosphate, magnesium, and CBC, differential, and hematocrit/hemoglobin must be closely monitored in patients treated with pamidronate disodium. Patients who have preexisting anemia, leukopenia, or thrombocytopenia should be monitored carefully in the first 2 weeks following treatment. Patients receiving pamidronate disodium may be at risk for anemia, leukopenia or thrombocytopenia and should have regular hematology assessments.

Drug Interactions

Concomitant administration of a loop diuretic had no effect on the calcium-lowering action of pamidronate disodium.

Caution is indicated when pamidronate disodium is used with other potentially nephrotoxic drugs.

In multiple myeloma patients, the risk of renal function deterioration may be increased when pamidronate disodium is used in combination with thalidomide.

Carcinogenesis, Mutagenesis, Impairment of Fertility

In a 104-week carcinogenicity study with daily oral administration of pamidronate in rats, there was a positive dose response relationship for benign adrenal pheochromocytoma in males (P <0.00001). Although this condition was also observed in females, the incidence was not statistically significant. When the dose calculations were adjusted to account for the limited oral bioavailability of pamidronate in rats, systemic exposure with the lowest daily dose associated with adrenal pheochromocytoma resulted in systemic exposures that were similar to the systemic exposure achieved at the intended clinical dose.

Adrenal pheochromocytoma was also observed in low numbers in the control animals and is considered a relatively common spontaneous neoplasm in the rat. Pamidronate given daily by oral administration was not carcinogenic in an 80-week study in mice.

Pamidronate was nonmutagenic in six mutagenicity assays, including: Ames bacterial mutagenicity assay, (with and without metabolic activation), nucleus-anomaly test, sister-chromatid-exchange study, point-mutation test, and micronucleus test in the rat.

In rats, decreased fertility occurred in first-generation offspring of parents who had received 150 mg/kg of pamidronate orally; however, this occurred only when animals were mated with members of the same dose group. Pamidronate has not been administered intravenously in such a study.

Animal Toxicology

In both rats and dogs, nephropathy has been associated with intravenous (bolus and infusion) administration of pamidronate.

Two 7-day intravenous infusion studies were conducted in the dog wherein pamidronate was given for 1, 4, or 24 hours at doses of 1 to 20 mg/kg for up to 7 days. In the first study, the compound was well tolerated at 3 mg/kg (1.7 x highest recommended human dose [HRHD] for a single intravenous infusion) when administered for 4 or 24 hours, but renal findings such as elevated BUN and creatinine levels and renal tubular necrosis occurred when 3 mg/kg was infused for 1 hour and at doses of ≥10 mg/kg. In the second study, slight renal tubular necrosis was observed in 1 male at 1 mg/kg when infused for 4 hours. Additional findings included elevated BUN levels in several treated animals and renal tubular dilation and/or inflammation at ≥1 mg/kg after each infusion time.

Pamidronate was given to rats at doses of 2, 6, and 20 mg/kg and to dogs at doses of 2, 4, 6, and 20 mg/kg as a 1-hour infusion, once a week, for 3 months followed by a 1-month recovery period. In rats, nephrotoxicity was observed at ≥6 mg/kg and included increased BUN and creatinine levels and tubular degeneration and necrosis. These findings were still present at 20 mg/kg at the end of the recovery period. In dogs, moribundity/death and renal toxicity occurred at 20 mg/kg as did kidney findings of elevated BUN and creatinine levels at ≥6 mg/kg and renal tubular degeneration at ≥4 mg/kg. The kidney changes were partially reversible at 6 mg/kg. In both studies, the dose level that produced no adverse renal effects was considered to be 2 mg/kg (1.1 x HRHD for a single intravenous infusion).

Pregnancy (See WARNINGS)

There are no adequate and well-controlled studies in pregnant women. Pamidronate disodium may cause fetal harm when administered to a pregnant woman. Bisphosphonates, such as pamidronate disodium, are incorporated into the bone matrix, from where they are gradually released over periods of weeks to years. The extent of bisphosphonate incorporation into adult bone, and hence, the amount available for release back into the systemic circulation, is directly related to the total dose and duration of bisphosphonate use. Although there are no data on fetal risk in humans, bisphosphonates do cause fetal harm in animals, and animal data suggest that uptake of bisphosphonates into fetal bone is greater than into maternal bone. Therefore, there is a theoretical risk of fetal harm (e.g. skeletal and other abnormalities) if a woman becomes pregnant after completing a course of bisphosphonate therapy. The impact of variables such as time between cessation of bisphosphonate therapy to conception, the particular bisphosphonate used, and the route of administration (intravenous versus oral) on this risk has not been established. If pamidronate disodium is used during pregnancy or if the patient becomes pregnant while taking or after taking this drug, the patient should be apprised of the potential hazard to the fetus.

Intravenous bolus dosing of pregnant rats and rabbits with pamidronate resulted in maternal toxicity and embryo/fetal effects when given during organogenesis at doses of 0.6 to 8.3 times the highest recommended human dose for a single intravenous infusion. Pamidronate can cross the placenta in rats and has produced marked maternal and nonteratogenic embryo/fetal effects in both rats and rabbits.

Nursing Mothers

It is not known whether pamidronate is excreted in human milk. Because many drugs are excreted in human milk, and because of the potential for serious adverse reactions in nursing infants from pamidronate disodium, a decision should be made to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

Safety and effectiveness of pamidronate disodium in pediatric patients have not been established.

Geriatric Use

Of the total number of subjects in clinical studies of pamidronate disodium, approximately 20% were 65 and over, while approximately 15% were 75 and over. No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.