Drug Interactions between aspirin / caffeine / salicylamide and tobramycin

MONITOR: The nephrotoxic effect of aminoglycosides may be potentiated by nonsteroidal anti-inflammatory drugs (NSAIDs), particularly if the latter had been given in high dosages for prolonged periods. Four children with cystic fibrosis who had been receiving chronic ibuprofen developed acute renal insufficiency shortly after initiation of IV aminoglycoside therapy for pulmonary exacerbations. An adolescent with CF who received intermittent, standard-dose ibuprofen during treatment with IV gentamicin also developed renal failure in addition to severe vestibular toxicity. Animal models suggest that renal prostaglandins may play a role in maintaining normal renal blood flow and glomerular filtration rate during the development of aminoglycoside nephrotoxicity, thus inhibition of their production by NSAIDs may worsen the renal damage.

MANAGEMENT: Whenever feasible, NSAID use should preferably be discontinued prior to initiating IV aminoglycoside therapy. If concomitant administration is necessary, hydration status as well as renal and vestibular functions should be closely monitored.

MONITOR: In premature infants, NSAIDs may increase the plasma concentrations of aminoglycosides. The proposed mechanism is decreased aminoglycoside clearance due to NSAID reduction of glomerular filtration rate, which is already low in premature infants. In a study of 20 preterm infants who had been given at least three days of amikacin or gentamicin therapy, mean peak plasma concentration increased by 17% and 33%, and mean trough concentration increased by 29% and 48%, respectively, on day 1 following administration of IV indomethacin for patent ductus arteriosus. Serum creatinine increased by 17%, while urine output and serum sodium decreased. Six patients developed hyponatremia.

MANAGEMENT: It may be advisable to consider reducing the dosage of aminoglycoside prior to initiation of NSAID therapy in infants. During coadministration, plasma antibiotic concentrations and renal function should be closely monitored, and the antibiotic dosage further adjusted as necessary.

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MONITOR: The nephrotoxic effect of aminoglycosides may be potentiated by nonsteroidal anti-inflammatory drugs (NSAIDs), particularly if the latter had been given in high dosages for prolonged periods. Four children with cystic fibrosis who had been receiving chronic ibuprofen developed acute renal insufficiency shortly after initiation of IV aminoglycoside therapy for pulmonary exacerbations. An adolescent with CF who received intermittent, standard-dose ibuprofen during treatment with IV gentamicin also developed renal failure in addition to severe vestibular toxicity. Animal models suggest that renal prostaglandins may play a role in maintaining normal renal blood flow and glomerular filtration rate during the development of aminoglycoside nephrotoxicity, thus inhibition of their production by NSAIDs may worsen the renal damage.

MANAGEMENT: Whenever feasible, NSAID use should preferably be discontinued prior to initiating IV aminoglycoside therapy. If concomitant administration is necessary, hydration status as well as renal and vestibular functions should be closely monitored.

MONITOR: In premature infants, NSAIDs may increase the plasma concentrations of aminoglycosides. The proposed mechanism is decreased aminoglycoside clearance due to NSAID reduction of glomerular filtration rate, which is already low in premature infants. In a study of 20 preterm infants who had been given at least three days of amikacin or gentamicin therapy, mean peak plasma concentration increased by 17% and 33%, and mean trough concentration increased by 29% and 48%, respectively, on day 1 following administration of IV indomethacin for patent ductus arteriosus. Serum creatinine increased by 17%, while urine output and serum sodium decreased. Six patients developed hyponatremia.

MANAGEMENT: It may be advisable to consider reducing the dosage of aminoglycoside prior to initiation of NSAID therapy in infants. During coadministration, plasma antibiotic concentrations and renal function should be closely monitored, and the antibiotic dosage further adjusted as necessary.

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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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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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