Drug Interactions between aspirin / caffeine / salicylamide and tiludronate

MONITOR: The combined use of low-dose or high-dose aspirin with other nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the potential for serious gastrointestinal (GI) toxicity, including inflammation, bleeding, ulceration, and perforation. Aspirin at anti-inflammatory dosages or higher may also decrease the plasma concentrations of many NSAIDs. The decreases have ranged from none or small (piroxicam, meloxicam, naproxen, tolmetin) to substantial (flurbiprofen, ibuprofen). However, the therapeutic response does not appear to be affected. Investigators theorize that aspirin may displace NSAIDs from plasma protein binding sites, resulting in increased concentration of unbound, or free, drug available for clearance. The increase in NSAID free fraction, and possibly some contributory anti-inflammatory effect from aspirin, may account for the lack of overall effect on therapeutic response.

MANAGEMENT: Caution is advised if aspirin, particularly at anti-inflammatory dosages, is used with other NSAIDs. Concomitant administration of NSAIDs is considered contraindicated or not recommended with aspirin at analgesic/anti-inflammatory dosages by many NSAID manufacturers. During concomitant therapy, patients should be advised to take the medications with food and to immediately report signs and symptoms of GI ulceration and bleeding such as abdominal pain, bloating, sudden dizziness or lightheadedness, nausea, vomiting, hematemesis, anorexia, and melena.

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ADJUST DOSING INTERVAL: Aspirin has been reported to decrease the bioavailability of tiludronate by up to 50% when taken two hours after tiludronate. The mechanism of the interaction is unknown.

MANAGEMENT: Aspirin should be taken two hours before or two hours after tiludronate.

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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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One study has reported that coadministration of caffeine and aspirin lead to a 25% increase in the rate of appearance and 17% increase in maximum concentration of salicylate in the plasma. A significantly higher area under the plasma concentration time curve of salicylate was also reported when both drugs were administered together. The exact mechanism of this interaction has not been specified. Physicians and patients should be aware that coadministration of aspirin and caffeine may lead to higher salicylate levels faster.

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