Drug Interactions between HalfLytely and Bisacodyl and trandolapril

MONITOR CLOSELY: Concomitant use of angiotensin converting enzyme (ACE) inhibitors and potassium salts may increase the risk of hyperkalemia. Inhibition of ACE results in decreased aldosterone secretion, which in turn causes potassium retention. In one report, a significant increase in serum potassium level (3.88 +/- 0.41 to 4.84 +/- 0.45 mEq/L) was observed within one or two days following the addition of captopril in five patients who were treated with regimens that included potassium supplements or potassium-sparing diuretics. Three patients had laboratory-diagnosed hyperkalemia, including one patient receiving potassium supplementation who had a 66% increase in serum potassium. Levels remained elevated until potassium supplementation or captopril therapy was reduced or discontinued. In a postmarketing survey of patients who were prescribed enalapril in England between April and December 1985, researchers identified ten cases where enalapril appeared to have contributed to a deterioration in renal function and subsequent death. All ten patients had hyperkalemia, and seven were also receiving moderate to high dosages of potassium-sparing diuretics and/or potassium supplements. Hyperkalemia was felt to be the immediate cause of death in two of them. Risk factors for developing severe or life-threatening hyperkalemia may include renal impairment, diabetes, old age, severe or worsening heart failure, dehydration, and concomitant use of other agents that block the renin-angiotensin-aldosterone system or otherwise increase serum potassium levels.

MANAGEMENT: Caution is advised if ACE inhibitors must be used concurrently with potassium salts, particularly in patients with renal impairment, diabetes, old age, severe or worsening heart failure, dehydration, or concomitant therapy with other agents that increase serum potassium such as nonsteroidal anti-inflammatory drugs, beta-blockers, cyclosporine, heparin, tacrolimus, trimethoprim, and licorice. The combination should generally be avoided in these patients unless absolutely necessary and the benefits outweigh the potential risks. Serum potassium and renal function should be checked prior to initiating therapy and regularly thereafter. Patients should be given counseling on the appropriate levels of potassium and fluid intake, and advised to seek medical attention if they experience signs and symptoms of hyperkalemia such as nausea, vomiting, weakness, listlessness, tingling of the extremities, paralysis, confusion, weak pulse, and a slow or irregular heartbeat.

ADJUST DOSING INTERVAL: By increasing gastric pH, antacids may reduce the resistance of the enteric coating of bisacodyl tablets, resulting in earlier release of bisacodyl and gastric irritation and dyspepsia.

MANAGEMENT: The administration of antacids and bisacodyl should be separated by at least one hour.

GENERALLY AVOID: Concomitant use of stimulant laxatives (e.g., bisacodyl, sodium picosulfate) may increase the risk of serious gastrointestinal adverse effects associated with certain osmotic laxatives (e.g., polyethylene glycol (PEG), oral sulfate solution), such as colonic mucosal ulcerations or ischemic colitis. There have been isolated case reports of ischemic colitis occurring with the use of PEG-based bowel cleansing products in combination with higher dosages of bisacodyl (usually greater than 10 mg). Bisacodyl can cause colonic ischemia due to transient reduction in splanchnic blood flow. When administered in conjunction with an osmotic laxative such as PEG, increased intramural pressure secondary to increased peristalsis may lead to ischemic colitis and perforation.

MANAGEMENT: The manufacturers for some osmotic bowel cleansing products recommend avoiding the concurrent use of stimulant laxatives. However, stimulant laxatives, in particular bisacodyl and sodium picosulfate, are sometimes used with PEG in certain bowel cleansing regimens to help reduce dose volume and improve patient tolerability and acceptance. Please consult individual product labeling for specific recommendations and guidance. Patients using osmotic bowel cleansing products and stimulant laxatives who present with sudden abdominal pain, rectal bleeding, or other symptoms of ischemic colitis should be evaluated promptly.

Coadministration with antacids may decrease the oral bioavailability of captopril and other angiotensin converting enzyme (ACE) inhibitors due to delayed gastric emptying and/or elevated gastric pH. In 10 healthy volunteers, 50 mL of an antacid suspension decreased the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of captopril (50 mg single oral dose) by 50% and 42%, respectively, compared to administration after fasting. The relative bioavailability of captopril was 0.66 with antacid, although its hypotensive activity did not seem to be affected. Based on available data, the clinical significance of this interaction appears to be minor. As a precaution, patients may want to consider separating the administration times of ACE inhibitors and antacids or oral medications that contain antacids (e.g., didanosine buffered tablets or pediatric oral solution) by 1 to 2 hours.