Drug Interactions between Flo-Pred and Phosphasal

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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MONITOR: The overuse or abuse of laxatives can cause significant loss of electrolytes and potentiate the risk of hypokalemia associated with corticosteroid therapy. Corticosteroids promote the retention of sodium and water and the excretion of potassium. Although these effects are primarily associated with mineralocorticoids like fludrocortisone, they may also occur with higher dosages of glucocorticoids or adrenocorticotropic agents, particularly if given systemically for longer than brief periods.

MANAGEMENT: In general, laxatives should only be used on a short-term, intermittent basis in recommended dosages. During concomitant therapy with corticosteroids, particularly if fludrocortisone or large doses of a glucocorticoid or adrenocorticotropic agent is given, patients should be counseled to recognize potential signs and symptoms of hypokalemia such as fatigue, myalgia, and muscle weakness. If maintenance of bowel regularity is required, patients should be advised to exercise and increase fiber in the diet and/or consider the use of bulk-forming laxatives.

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MONITOR: Coadministration with corticosteroids may decrease the serum concentrations and therapeutic effects of salicylates. Likewise, serum salicylate levels may increase following withdrawal of corticosteroid therapy, potentially resulting in salicylate toxicity. This interaction has been reported in patients receiving intra-articular as well as oral corticosteroids. One or more mechanisms may be involved, including an increase in the renal clearance and/or an induction of hepatic metabolism of salicylates caused by corticosteroids. Pharmacologically, the potential for increased gastrointestinal (GI) toxicity, including inflammation, bleeding, ulceration and perforation, should be considered due to additive ulcerogenic effects of these agents (especially aspirin) on the GI mucosa.

MANAGEMENT: Patients treated concomitantly with a corticosteroid may require higher dosages of salicylates or salicylate-like drugs. Pharmacologic response to these agents should be monitored more closely whenever a corticosteroid is added to or withdrawn from therapy in patients stabilized on their existing salicylate regimen, and the salicylate dosage adjusted as necessary. 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 severe abdominal pain, dizziness, lightheadedness, and the appearance of black, tarry stools. The selective use of prophylactic anti-ulcer therapy (e.g., antacids, H2-antagonists) may be appropriate, particularly in patients with a prior history of peptic ulcer disease or GI bleeding and in elderly and debilitated patients.

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