Pamidronate

INDICATIONS AND USAGE Hypercalcemia of Malignancy Pamidronate disodium, in conjunction with adequate hydration, is indicated for the treatment of moderate or severe hypercalcemia associated with malignancy, with or without bone metastases. Patients who have either epidermoid or non-epidermoid tumors respond to treatment with pamidronate disodium. Vigorous saline hydration, an integral part of hypercalcemia therapy, should be initiated promptly and an attempt should be made to restore the urine output to about 2 L/day throughout treatment. Mild or asymptomatic hypercalcemia may be treated with conservative measures (i.e., saline hydration, with or without loop diuretics). Patients should be hydrated adequately throughout the treatment, but overhydration, especially in those patients who have cardiac failure, must be avoided. Diuretic therapy should not be employed prior to correction of hypovolemia. The safety and efficacy of pamidronate disodium in the treatment of hypercalcemia associated with hyperparathyroidism or with other non-tumor-related conditions has not been established. Paget’s Disease Pamidronate disodium is indicated for the treatment of patients with moderate to severe Paget’s disease of bone. The effectiveness of pamidronate disodium was demonstrated primarily in patients with serum alkaline phosphatase ≥ 3 times the upper limit of normal. Pamidronate disodium therapy in patients with Paget’s disease has been effective in reducing serum alkaline phosphatase and urinary hydroxyproline levels by ≥ 50% in at least 50% of patients, and by ≥ 30% in at least 80% of patients. Pamidronate disodium therapy has also been effective in reducing these biochemical markers in patients with Paget’s disease who failed to respond, or no longer responded to other treatments. Osteolytic Bone Metastases of Breast Cancer and Osteolytic Lesions of Multiple Myeloma Pamidronate disodium is indicated, in conjunction with standard antineoplastic therapy, for the treatment of osteolytic bone metastases of breast cancer and osteolytic lesions of multiple myeloma. The pamidronate disodium treatment effect appeared to be smaller in the study of breast cancer patients receiving hormonal therapy than in the study of those receiving chemotherapy, however, overall evidence of clinical benefit has been demonstrated (see CLINICAL PHARMACOLOGY , Osteolytic Bone Metastases of Breast Cancer and Osteolytic Lesions of Multiple Myeloma, Clinical Trials section).

DOSAGE AND ADMINISTRATION Hypercalcemia of Malignancy Consideration should be given to the severity of as well as the symptoms of hypercalcemia. Vigorous saline hydration alone may be sufficient for treating mild, asymptomatic hypercalcemia. Overhydration should be avoided in patients who have potential for cardiac failure. In hypercalcemia associated with hematologic malignancies, the use of glucocorticoid therapy may be helpful. Moderate Hypercalcemia The recommended dose of pamidronate disodium in moderate hypercalcemia (corrected serum calcium* of approximately 12 to 13.5 mg/dL) is 60 to 90 mg given as a SINGLE DOSE, intravenous infusion over 2 to 24 hours. Longer infusions (i.e., >2 hours) may reduce the risk for renal toxicity, particularly in patients with preexisting renal insufficiency. Severe Hypercalcemia The recommended dose of pamidronate disodium in severe hypercalcemia (corrected serum calcium* >13.5 mg/dL) is 90 mg given as a SINGLE DOSE, intravenous infusion over 2 to 24 hours. Longer infusions (i.e., >2 hours) may reduce the risk for renal toxicity, particularly in patients with preexisting renal insufficiency. * Albumin-corrected serum calcium (CCa, mg/dL) = serum calcium, mg/dL + 0.8 (4.0-serum albumin, g/dL). Retreatment A limited number of patients have received more than one treatment with pamidronate disodium for hypercalcemia. Retreatment with pamidronate disodium, in patients who show complete or partial response initially, may be carried out if serum calcium does not return to normal or remain normal after initial treatment. It is recommended that a minimum of 7 days elapse before retreatment, to allow for full response to the initial dose . The dose and manner of retreatment is identical to that of the initial therapy. Paget’s Disease The recommended dose of pamidronate disodium in patients with moderate to severe Paget’s disease of bone is 30 mg daily, administered as a 4-hour infusion on 3 consecutive days for a total dose of 90 mg. Retreatment A limited number of patients with Paget’s disease have received more than one treatment of pamidronate disodium in clinical trials. When clinically indicated, patients should be retreated at the dose of initial therapy. Osteolytic Bone Lesions of Multiple Myeloma The recommended dose of pamidronate disodium in patients with osteolytic bone lesions of multiple myeloma is 90 mg administered as a 4-hour infusion given on a monthly basis. Patients with marked Bence-Jones proteinuria and dehydration should receive adequate hydration prior to pamidronate disodium infusion. Limited information is available on the use of pamidronate disodium in multiple myeloma patients with a serum creatinine ≥ 3.0 mg/dL. Patients who receive pamidronate disodium should have serum creatinine assessed prior to each treatment. Treatment should be withheld for renal deterioration. In a clinical study, renal deterioration was defined as follows: For patients with normal baseline creatinine, increase of 0.5 mg/dL. For patients with abnormal baseline creatinine, increase of 1.0 mg/dL. In this clinical study, pamidronate disodium treatment was resumed only when the creatinine returned to within 10% of the baseline value. The optimal duration of therapy is not yet known, however, in a study of patients with myeloma, final analysis after 21 months demonstrated overall benefits (see Clinical Trials section). Osteolytic Bone Metastases of Breast Cancer The recommended dose of pamidronate disodium in patients with osteolytic bone metastases is 90 mg administered over a 2-hour infusion given every 3 to 4 weeks. Pamidronate disodium has been frequently used with doxorubicin, fluorouracil, cyclophosphamide, methotrexate, mitoxantrone, vinblastine, dexamethasone, prednisone, melphalan, vincristine, megesterol, and tamoxifen. It has been given less frequently with etoposide, cisplatin, cytarabine, paclitaxel, and aminoglutethimide. Patients who receive pamidronate disodium should have serum creatinine assessed prior to each treatment. Treatment should be withheld for renal deterioration. In a clinical study, renal deterioration was defined as follows: For patients with normal baseline creatinine, increase of 0.5 mg/dL. For patients with abnormal baseline creatinine, increase of 1.0 mg/dL. In this clinical study, pamidronate disodium treatment was resumed only when the creatinine returned to within 10% of the baseline value. The optimal duration of therapy is not known, however, in two breast cancer studies, final analyses performed after 24 months of therapy demonstrated overall benefits (see Clinical Trials section). Calcium and Vitamin D Supplementation In the absence of hypercalcemia, patients with predominantly lytic bone metastases or multiple myeloma, who are at risk of calcium or vitamin D deficiency, and patients with Paget’s disease of the bone, should be given oral calcium and vitamin D supplementation in order to minimize the risk of hypocalcemia. Method of Administration DUE TO THE RISK OF CLINICALLY SIGNIFICANT DETERIORATION IN RENAL FUNCTION, WHICH MAY PROGRESS TO RENAL FAILURE, SINGLE DOSES OF PAMIDRONATE DISODIUM SHOULD NOT EXCEED 90 MG (SEE WARNINGS ). There must be strict adherence to the intravenous administration recommendations for pamidronate disodium in order to decrease the risk of deterioration in renal function. Hypercalcemia of Malignancy The daily dose must be administered as an intravenous infusion over at least 2 to 24 hours for the 60 mg and 90-mg doses. The recommended dose should be diluted in 1000 mL of sterile 0.45% or 0.9% Sodium Chloride, USP, or 5% Dextrose Injection, USP. This infusion solution is stable for up to 24 hours at room temperature. Paget’s Disease The recommended daily dose of 30 mg should be diluted in 500 mL of sterile 0.45% or 0.9% Sodium Chloride, USP, or 5% Dextrose Injection, USP, and administered over a 4-hour period for 3 consecutive days. Osteolytic Bone Metastases of Breast Cancer The recommended dose of 90 mg should be diluted in 250 mL of sterile 0.45% or 0.9% Sodium Chloride, USP, or 5% Dextrose Injection, USP, and administered over a 2-hour period every 3 to 4 weeks. Osteolytic Bone Lesions of Multiple Myeloma The recommended dose of 90 mg should be diluted in 500 mL of sterile 0.45% or 0.9% Sodium Chloride, USP, or 5% Dextrose Injection, USP, and administered over a 4-hour period on a monthly basis. Pamidronate disodium must not be mixed with calcium-containing infusion solutions, such as Ringer’s solution, and should be given in a single intravenous solution and line separate from all other drugs. Note: Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.

WARNINGS Deterioration in Renal Function Bisphosphonates, including pamidronate disodium, have been associated with renal toxicity manifested as deterioration of renal function and potential renal failure. DUE TO THE RISK OF CLINICALLY SIGNIFICANT DETERIORATION IN RENAL FUNCTION, WHICH MAY PROGRESS TO RENAL FAILURE, SINGLE DOSES OF PAMIDRONATE DISODIUM SHOULD NOT EXCEED 90 MG (see DOSAGE AND ADMINISTRATION for appropriate infusion durations). Renal deterioration, progression to renal failure, and dialysis have been reported in patients after the initial or a single dose of pamidronate disodium. Focal segmental glomerulosclerosis (including the collapsing variant) with or without nephrotic syndrome, which may lead to renal failure, has been reported in pamidronate disodium-treated patients, particularly in the setting of multiple myeloma and breast cancer. Some of these patients had gradual improvement in renal status after pamidronate disodium was discontinued. Patients who receive pamidronate disodium should have serum creatinine assessed prior to each treatment. Patients treated with pamidronate disodium for bone metastases should have the dose withheld if renal function has deteriorated (see DOSAGE AND ADMINISTRATION ). PREGNANCY: Bisphosphonates, such as pamidronate disodium, are incorporated into the bone matrix, from where they are gradually released over periods of weeks to years. Pamidronate disodium may cause fetal harm when administered to a pregnant woman. In reproductive studies in rats and rabbits, pamidronate doses equivalent to 0.6 to 8.3 times the highest human recommended dose resulted in maternal toxicity and embryo/fetal effects. There are no adequate and well-controlled studies of pamidronate disodium in pregnant women. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, apprise the patient of the potential hazard to the fetus (See PRECAUTIONS ).

CONTRAINDICATIONS Pamidronate disodium is contraindicated in patients with clinically significant hypersensitivity to pamidronate disodium or other bisphosphonates.

ADVERSE REACTIONS Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Clinical Studies Hypercalcemia of Malignancy Transient mild elevation of temperature by at least 1°C was noted 24 to 48 hours after administration of pamidronate disodium in 34% of patients in clinical trials. In the saline trial, 18% of patients had a temperature elevation of at least 1°C 24 to 48 hours after treatment. Drug-related local soft-tissue symptoms (redness, swelling or induration and pain on palpation) at the site of catheter insertion were most common in patients treated with 90 mg of pamidronate disodium. Symptomatic treatment resulted in rapid resolution in all patients. Rare cases of uveitis, iritis, scleritis, and episcleritis have been reported, including one case of scleritis, and one case of uveitis upon separate rechallenges. Five of 231 patients (2%) who received pamidronate disodium during the four U.S. controlled hypercalcemia clinical studies were reported to have had seizures, 2 of whom had preexisting seizure disorders. None of the seizures were considered to be drug-related by the investigators. However, a possible relationship between the drug and the occurrence of seizures cannot be ruled out. It should be noted that in the saline arm 1 patient (4%) had a seizure. There are no controlled clinical trials comparing the efficacy and safety of 90 mg pamidronate disodium over 24 hours to 2 hours in patients with hypercalcemia of malignancy. However, a comparison of data from separate clinical trials suggests that the overall safety profile in patients who received 90 mg pamidronate disodium over 24 hours is similar to those who received 90 mg pamidronate disodium over 2 hours. The only notable differences observed were an increase in the proportion of patients in the pamidronate disodium 24-hour group who experienced fluid overload and electrolyte/mineral abnormalities. At least 15% of patients treated with pamidronate disodium for hypercalcemia of malignancy also experienced the following adverse events during a clinical trial: General: Fluid overload, generalized pain Cardiovascular: Hypertension Gastrointestinal: Abdominal pain, anorexia, constipation, nausea, vomiting Genitourinary: Urinary tract infection Musculoskeletal: Bone pain Laboratory Abnormality: Anemia, hypokalemia, hypomagnesemia, hypophosphatemia. Many of these adverse experiences may have been related to the underlying disease state. The following table lists the adverse experiences considered to be treatment-related during comparative, controlled U.S. trials. Treatment-Related Adverse Experiences Reported in Three U.S. Controlled Clinical Trials Percent of Patients Pamidronate Disodium Etidronate Disodium Saline 60 mg over 4 hr 60 mg over 24 hr 90 mg over 24 hr 7.5 mg/kg × 3 days n=23 n=73 n=17 n=35 n=23 General Edema 0 1 0 0 0 Fatigue 0 0 12 0 0 Fever 26 19 18 9 0 Fluid overload 0 0 0 6 0 Infusion-site reaction 0 4 18 0 0 Moniliasis 0 0 6 0 0 Rigors 0 0 0 0 4 Gastrointestinal Abdominal pain 0 1 0 0 0 Anorexia 4 1 12 0 0 Constipation 4 0 6 3 0 Diarrhea 0 1 0 0 0 Dyspepsia 4 0 0 0 0 Gastrointestinal hemorrhage 0 0 6 0 0 Nausea 4 0 18 6 0 Stomatitis 0 1 0 3 0 Vomiting 4 0 0 0 0 Respiratory Dyspnea 0 0 0 3 0 Rales 0 0 6 0 0 Rhinitis 0 0 6 0 0 Upper respiratory infection 0 3 0 0 0 CNS Anxiety 0 0 0 0 4 Convulsions 0 0 0 3 0 Insomnia 0 1 0 0 0 Nervousness 0 0 0 0 4 Psychosis 4 0 0 0 0 Somnolence 0 1 6 0 0 Taste perversion 0 0 0 3 0 Cardiovascular Atrial fibrillation 0 0 6 0 4 Atrial flutter 0 1 0 0 0 Cardiac failure 0 1 0 0 0 Hypertension 0 0 6 0 4 Syncope 0 0 6 0 0 Tachycardia 0 0 6 0 4 Endocrine Hypothyroidism 0 0 6 0 0 Hemic and Lymphatic Anemia 0 0 6 0 0 Leukopenia 4 0 0 0 0 Neutropenia 0 1 0 0 0 Thrombocytopenia 0 1 0 0 0 Musculoskeletal Myalgia 0 1 0 0 0 Urogenital Uremia 4 0 0 0 0 Laboratory Abnormalities Hypocalcemia 0 1 12 0 0 Hypokalemia 4 4 18 0 0 Hypomagnesemia 4 10 12 3 4 Hypophosphatemia 0 9 18 3 0 Abnormal liver function 0 0 0 3 0 Paget’s Disease Transient mild elevation of temperature >1°C above pretreatment baseline was noted within 48 hours after completion of treatment in 21% of the patients treated with 90 mg of pamidronate disodium in clinical trials. Drug-related musculoskeletal pain and nervous system symptoms (dizziness, headache, paresthesia, increased sweating) were more common in patients with Paget’s disease treated with 90 mg of pamidronate disodium than in patients with hypercalcemia of malignancy treated with the same dose. Adverse experiences considered to be related to trial drug, which occurred in at least 5% of patients with Paget’s disease treated with 90 mg of pamidronate disodium in two U.S. clinical trials, were fever, nausea, back pain, and bone pain. At least 10% of all pamidronate disodium-treated patients with Paget’s disease also experienced the following adverse experiences during clinical trials: Cardiovascular: Hypertension Musculoskeletal: Arthrosis, bone pain Nervous system: Headache Most of these adverse experiences may have been related to the underlying disease state. Osteolytic Bone Metastases of Breast Cancer and Osteolytic Lesions of Multiple Myeloma The most commonly reported (>15%) adverse experiences occurred with similar frequencies in the pamidronate disodium and placebo treatment groups, and most of these adverse experiences may have been related to the underlying disease state or cancer therapy. Commonly Reported Adverse Experiences in Three U.S. Controlled Clinical Trials Pamidronate Disodium 90 mg over 4 hours Placebo Pamidronate Disodium 90 mg over 2 hours Placebo All Pamidronate Disodium 90 mg Placebo N=205 N=187 N=367 N=386 N=572 N=573 General % % % % % % Asthenia 16.1 17.1 25.6 19.2 22.2 18.5 Fatigue 31.7 28.3 40.3 28.8 37.2 29.0 Fever 38.5 38 38.1 32.1 38.5 34 Metastases 1.0 3.0 31.3 24.4 20.5 17.5 Pain 13.2 11.8 15.0 18.1 14.3 16.1 Digestive System Anorexia 17.1 17.1 31.1 24.9 26.0 22.3 Constipation 28.3 31.7 36.0 38.6 33.2 35.1 Diarrhea 26.8 26.8 29.4 30.6 28.5 29.7 Dyspepsia 17.6 13.4 18.3 15.0 22.6 17.5 Nausea 35.6 37.4 63.5 59.1 53.5 51.8 Pain abdominal 19.5 16.0 24.3 18.1 22.6 17.5 Vomiting 16.6 19.8 46.3 39.1 35.7 32.8 Hemic and Lymphatic Anemia 47.8 41.7 39.5 36.8 42.5 38.4 Granulocytopenia 20.5 15.5 19.3 20.5 19.8 18.8 Thrombocytopenia 16.6 17.1 12.5 14.0 14.0 15.0 Musculoskeletal System Arthralgias 10.7 7.0 15.3 12.7 13.6 10.8 Myalgia 25.4 15.0 26.4 22.5 26 20.1 Skeletal Pain 61.0 71.7 70.0 75.4 66.8 74 CNS Anxiety 7.8 9.1 18.0 16.8 14.3 14.3 Headache 24.4 19.8 27.2 23.6 26.2 22.3 Insomnia 17.1 17.2 25.1 19.4 22.2 19.0 Respiratory System Coughing 26.3 22.5 25.3 19.7 25.7 20.6 Dyspnea 22.0 21.4 35.1 24.4 30.4 23.4 Pleural effusion 2.9 4.3 15.0 9.1 10.7 7.5 Sinusitis 14.6 16.6 16.1 10.4 15.6 12.0 Upper respiratory Tract Infection 32.2 28.3 19.6 20.2 24.1 22.9 Urogenital System Urinary Tract Infection 15.6 9.1 20.2 17.6 18.5 15.6 Of the toxicities commonly associated with chemotherapy, the frequency of vomiting, anorexia, and anemia were slightly more common in the pamidronate disodium patients whereas stomatitis and alopecia occurred at a frequency similar to that in placebo patients. In the breast cancer trials, mild elevations of serum creatinine occurred in 18.5% of pamidronate disodium patients and 12.3% of placebo patients. Mineral and electrolyte disturbances, including hypocalcemia, were reported rarely and in similar percentages of pamidronate disodium-treated patients compared with those in the placebo group. The reported frequencies of hypocalcemia, hypokalemia, hypophosphatemia, and hypomagnesemia for pamidronate disodium-treated patients were 3.3%, 10.5%, 1.7%, and 4.4%, respectively, and for placebo-treated patients were 1.2%, 12%, 1.7%, and 4.5%, respectively. In previous hypercalcemia of mali

CLINICAL PHARMACOLOGY The principal pharmacologic action of pamidronate disodium is inhibition of bone resorption. Although the mechanism of antiresorptive action is not completely understood, several factors are thought to contribute to this action. Pamidronate disodium adsorbs to calcium phosphate (hydroxyapatite) crystals in bone and may directly block dissolution of this mineral component of bone. In vitro studies also suggest that inhibition of osteoclast activity contributes to inhibition of bone resorption. In animal studies, at doses recommended for the treatment of hypercalcemia, pamidronate disodium inhibits bone resorption apparently without inhibiting bone formation and mineralization. Of relevance to the treatment of hypercalcemia of malignancy is the finding that pamidronate disodium inhibits the accelerated bone resorption that results from osteoclast hyperactivity induced by various tumors in animal studies. Pharmacokinetics Cancer patients (n=24) who had minimal or no bony involvement were given an intravenous infusion of 30, 60, or 90 mg of pamidronate disodium over 4 hours and 90 mg of pamidronate disodium over 24 hours (Table 1). Distribution The mean ± SD body retention of pamidronate was calculated to be 54 ± 16% of the dose over 120 hours. Metabolism Pamidronate is not metabolized and is exclusively eliminated by renal excretion. Excretion After administration of 30, 60, and 90 mg of pamidronate disodium over 4 hours, and 90 mg of pamidronate disodium over 24 hours, an overall mean ± SD of 46 ± 16% of the drug was excreted unchanged in the urine within 120 hours. Cumulative urinary excretion was linearly related to dose. The mean ± SD elimination half-life is 28 ± 7 hours. Mean ± SD total and renal clearances of pamidronate were 107 ± 50 mL/min and 49 ± 28 mL/min, respectively. The rate of elimination from bone has not been determined. Special Populations There are no data available on the effects of age, gender, or race on the pharmacokinetics of pamidronate. Pediatric Pamidronate is not labeled for use in the pediatric population. Renal Insufficiency The pharmacokinetics of pamidronate were studied in cancer patients (n=19) with normal and varying degrees of renal impairment. Each patient received a single 90 mg dose of pamidronate disodium infused over 4 hours. The renal clearance of pamidronate in patients was found to closely correlate with creatinine clearance (see Figure 1). A trend toward a lower percentage of drug excreted unchanged in urine was observed in renally impaired patients. Adverse experiences noted were not found to be related to changes in renal clearance of pamidronate. Given the recommended dose, 90 mg infused over 4 hours, excessive accumulation of pamidronate in renally impaired patients is not anticipated if pamidronate disodium is administered on a monthly basis. Figure 1: Pamidronate renal clearance as a function of creatinine clearance in patients with normal and impaired renal function. The lines are the mean prediction line and 95% confidence intervals. Hepatic Insufficiency The pharmacokinetics of pamidronate were studied in male cancer patients at risk for bone metastases with normal hepatic function (n=6) and mild to moderate hepatic dysfunction (n=7). Each patient received a single 90 mg dose of pamidronate disodium infused over 4 hours. Although there was a statistically significant difference in the pharmacokinetics between patients with normal and impaired hepatic function, the difference was not considered clinically relevant. Patients with hepatic impairment exhibited higher mean AUC (53%) and C max (29%), and decreased plasma clearance (33%) values. Nevertheless, pamidronate was still rapidly cleared from the plasma. Drug levels were not detectable in patients by 12 to 36 hours after drug infusion. Because pamidronate disodium is administered on a monthly basis, drug accumulation is not expected. No changes in pamidronate disodium dosing regimen are recommended for patients with mild to moderate abnormal hepatic function. Pamidronate disodium has not been studied in patients with severe hepatic impairment. Drug-Drug Interactions There are no human pharmacokinetic data for drug interactions with pamidronate disodium. Table 1 Mean (SD, CV%) Pamidronate Pharmacokinetic Parameters in Cancer Patients (n=6 for each group) Dose (infusion rate) Maximum Concentration (mcg/mL) Percent of dose excreted in urine Total Clearance (mL/min) Renal Clearance (mL/min) 30 mg (4 hrs) 0.73 (0.14, 19.1%) 43.9 (14.0, 31.9%) 136 (44, 32.4%) 58 (27, 46.5%) 60 mg (4 hrs) 1.44 (0.57, 39.6%) 47.4 (47.4, 54.4%) 88 (56, 63.6%) 42 (28, 66.7%) 90 mg (4 hrs) 2.61 (0.74, 28.3%) 45.3 (25.8, 56.9%) 103 (37, 35.9%) 44 (16, 36.4%) 90 mg (24 hrs) 1.38 (1.97, 142.7%) 47.5 (10.2, 21.5%) 101 (58, 57.4%) 52 (42, 80.8%) After intravenous administration of radiolabeled pamidronate in rats, approximately 50% to 60% of the compound was rapidly adsorbed by bone and slowly eliminated from the body by the kidneys. In rats given 10 mg/kg bolus injections of radiolabeled pamidronate disodium, approximately 30% of the compound was found in the liver shortly after administration and was then redistributed to bone or eliminated by the kidneys over 24 to 48 hours. Studies in rats injected with radiolabeled pamidronate disodium showed that the compound was rapidly cleared from the circulation and taken up mainly by bones, liver, spleen, teeth, and tracheal cartilage. Radioactivity was eliminated from most soft tissues within 1 to 4 days; was detectable in liver and spleen for 1 and 3 months, respectively; and remained high in bones, trachea, and teeth for 6 months after dosing. Bone uptake occurred preferentially in areas of high bone turnover. The terminal phase of elimination half-life in bone was estimated to be approximately 300 days. Pharmacodynamics Serum phosphate levels have been noted to decrease after administration of pamidronate disodium, presumably because of decreased release of phosphate from bone and increased renal excretion as parathyroid hormone levels, which are usually suppressed in hypercalcemia associated with malignancy, return toward normal. Phosphate therapy was administered in 30% of the patients in response to a decrease in serum phosphate levels. Phosphate levels usually returned toward normal within 7 to 10 days. Urinary calcium/creatinine and urinary hydroxyproline/creatinine ratios decrease and usually return to within or below normal after treatment with pamidronate disodium. These changes occur within the first week after treatment, as do decreases in serum calcium levels, and are consistent with an antiresorptive pharmacologic action. Hypercalcemia of Malignancy Osteoclastic hyperactivity resulting in excessive bone resorption is the underlying pathophysiologic derangement in metastatic bone disease and hypercalcemia of malignancy. Excessive release of calcium into the blood as bone is resorbed results in polyuria and gastrointestinal disturbances, with progressive dehydration and decreasing glomerular filtration rate. This, in turn, results in increased renal resorption of calcium, setting up a cycle of worsening systemic hypercalcemia. Correction of excessive bone resorption and adequate fluid administration to correct volume deficits are therefore essential to the management of hypercalcemia. Most cases of hypercalcemia associated with malignancy occur in patients who have breast cancer; squamous-cell tumors of the lung or head and neck; renal-cell carcinoma; and certain hematologic malignancies, such as multiple myeloma and some types of lymphomas. A few less-common malignancies, including vasoactive intestinal-peptide-producing tumors and cholangiocarcinoma, have a high incidence of hypercalcemia as a metabolic complication. Patients who have hypercalcemia of malignancy can generally be divided into two groups, according to the pathophysiologic mechanism involved. In humoral hypercalcemia, osteoclasts a