Drug Interactions between Actonel with Calcium and Uro-458

MONITOR CLOSELY: The following interaction applies only to products containing sodium biphosphate that are used for bowel cleansing. It does not apply to products containing sodium biphosphate that are used for other, non-laxative related purposes.

Coadministration with agents that affect renal function or perfusion such as diuretics, ACE inhibitors, angiotensin receptor blockers, and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the risk of acute phosphate nephropathy associated with the use of bowel-cleansing phosphate solutions. The risk and/or severity of fluid and electrolyte disturbances may also be increased, which can lead to serious adverse events including cardiac arrhythmias, seizures, and renal impairment. Acute phosphate nephropathy is a rare adverse event that presents as acute renal failure with minimal proteinuria and a bland urine sediment. Renal biopsy findings are consistent with nephrocalcinosis and include acute and/or chronic renal tubular injury, calcium-phosphate crystal deposition in the distal tubules and collecting ducts, and no other pattern of histological injury. The risk of acute phosphate nephropathy stems from the large phosphate load, fluid shifts, and decreased intravascular volume, which can be exacerbated in the presence of medications that affect renal perfusion or function. In reported cases, acute renal failure was typically diagnosed within two to five months of colonoscopy. These cases often resulted in permanent impairment of renal function, some requiring long-term dialysis.

MANAGEMENT: Caution is advised when bowel-cleansing phosphate preparations are prescribed in patients treated with agents that affect renal function or perfusion, particularly if they are frail or elderly. Bowel-cleansing phosphate preparations should not be used in patients who have impaired renal function or perfusion, dehydration, or uncorrected electrolyte abnormalities. In patients at risk for acute phosphate nephropathy, baseline and postprocedure labs including serum electrolytes, calcium, phosphate, BUN, and creatinine should be performed. Patients should be advised not to exceed the recommended dosage of their bowel-cleansing preparation and to drink sufficient quantities of clear fluids during before, during, and after bowel cleansing. Limited data suggest that administration of an electrolyte rehydration solution may attenuate the electrolyte abnormalities and hypovolemia. Hospitalization and intravenous fluid hydration may be appropriate for frail or elderly patients who may be unable to drink an adequate volume of fluid.

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GENERALLY AVOID: Agents that can alkalinize the urine such as thiazide diuretics, carbonic anhydrase inhibitors, and antacids may decrease the antibacterial effectiveness of methenamine by inhibiting its conversion to formaldehyde. Methenamine is most effectively converted in an acidic milieu of pH less than 5.5.

MANAGEMENT: Concomitant use of methenamine-containing preparations with thiazide diuretics, carbonic anhydrase inhibitors, or large doses of antacids should be avoided if possible. Otherwise, frequent urine pH testing may be considered. Some methenamine products may be used with antacids if dosing times are separated by at least one hour. Consult the manufacturer's product labeling for specific recommendations.

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MONITOR: Chronic administration of antacids may reduce serum salicylate concentrations in patients receiving large doses of aspirin or other salicylates. The mechanism involves reduction in salicylate renal tubular reabsorption due to urinary alkalinization by antacids, resulting in increased renal salicylate clearance. In three children treated with large doses of aspirin for rheumatic fever, serum salicylate levels declined 30% to 70% during coadministration with a magnesium and aluminum hydroxide antacid. Other studies have found similar, albeit less dramatic results. Antacids reportedly have no effect on the oral bioavailability of aspirin in healthy adults. However, administration of antacids containing either aluminum and magnesium hydroxide or calcium carbonate two hours before aspirin dosing led to reduced absorption of aspirin in uremic patients.

MANAGEMENT: Patients treated chronically with antacids (or oral medications that contain antacids such as didanosine buffered tablets or pediatric oral solution) and large doses of salicylates (i.e. 3 g/day or more) should be monitored for potentially diminished or inadequate analgesic and anti-inflammatory effects, and the salicylate dosage adjusted if necessary.

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ADJUST DOSING INTERVAL: Products containing aluminum, calcium, magnesium and other polyvalent cations such as antacids or vitamin with mineral supplements are likely to interfere with the gastrointestinal absorption of oral bisphosphonates. For example, the bioavailability of tiludronate has been shown to decrease 80% during simultaneous administration with calcium, and 60% when aluminum- or magnesium-containing antacids were administered one hour before tiludronate.

MANAGEMENT: Antacids or other oral medications containing aluminum, calcium, magnesium and other polyvalent cations should be administered at least 30 minutes after the bisphosphonate dose.

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MONITOR: Theoretical concerns exist regarding the potential for increased risk and severity of gastrointestinal toxicity during coadministration of oral bisphosphonates and nonsteroidal anti-inflammatory drugs (NSAIDs) due to additive or synergistic irritant effects on the gastrointestinal mucosa. Because NSAIDs reduce the rate of ulcer healing in the stomach and duodenum, it is also possible that NSAIDs may delay healing and exaggerate the mucosal injury caused by oral bisphosphonates. In a blinded, randomized, crossover study consisting of 26 healthy volunteers, investigators using endoscopic techniques reported a significantly higher incidence of gastric ulcers following combined treatment with alendronate 10 mg once a day and naproxen 500 mg twice a day for 14 days than after treatment with either alendronate or naproxen alone (38% vs. 8% and 12%, respectively). In contrast, a 3-year controlled clinical study found no significant difference in the incidence of upper gastrointestinal adverse events between alendronate 5 or 10 mg/day and placebo given to more than 2000 subjects, most of whom received concomitant NSAIDs. Likewise, the incidence of upper gastrointestinal adverse events was similar for risedronate (24.5%) and placebo (24.8%) among patients who were regular users (>= 3 days/week) of aspirin or NSAIDs in phase 3 osteoporosis studies, which enrolled a total of over 5700 patients. Aspirin use was reported by 31% of patients and NSAID use by 48% of patients, 24% and 21% of whom were regular users, respectively.

MONITOR: Theoretical concerns exist regarding the potential for increased risk and severity of renal impairment during coadministration of bisphosphonates with high dosages or chronic use of NSAIDs due to additive or synergistic nephrotoxic effects on the kidney. The use of bisphosphonates has been associated with nephrotoxicity manifested as deterioration of renal function and renal failure. Cases have primarily involved intravenous formulations of the drugs such as pamidronic acid and zoledronic acid, especially when they are administered too rapidly. The risk of hypocalcemia may also be increased, as drug-induced renal tubular damage can lead to renal loss of calcium and other electrolytes such as magnesium. Bisphosphonates alone often cause mild, asymptomatic hypocalcemia via inhibitive effects on bone resorption and possibly chelation of blood calcium. Chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs) may be associated with renal toxicities including elevations in serum creatinine and BUN, tubular necrosis, glomerulitis, renal papillary necrosis, acute interstitial nephritis, nephrotic syndrome, and renal failure.

MANAGEMENT: Caution is advised if bisphosphonates are prescribed in combination with NSAIDs. Patients receiving oral bisphosphonates should be closely monitored for the development of gastrointestinal toxicity and advised to immediately report potential signs and symptoms such as severe abdominal pain, nausea, vomiting, diarrhea, loss of appetite, dizziness, lightheadedness, and/or black, tarry stools. Patients receiving intravenous formulations of bisphosphonates should have renal function and serum electrolytes closely monitored. Serum creatinine should be assessed prior to each treatment, and treatment should be withheld in the presence of renal deterioration. In patients treated for bone metastases, treatment should not be resumed until renal function returns to baseline.

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