Drug Interactions between chlorpheniramine / codeine / phenylephrine / potassium iodide and Trimpex

MONITOR CLOSELY: The use of trimethoprim in combination with other potassium-sparing drugs or potassium salts may increase the risk of hyperkalemia. Trimethoprim inhibits sodium reabsorption and potassium excretion by blocking sodium channels in the renal distal tubules. Studies of patients treated with standard and high dosages of trimethoprim-sulfamethoxazole compared to similar controls treated with other antibiotics indicate that reversible increases in serum potassium are fairly common with trimethoprim use. Although generally asymptomatic, severe hyperkalemia including metabolic acidosis, paralysis, nonoliguric renal failure, and ventricular arrhythmia have been reported. Risk factors for developing hyperkalemia include use of high dosages of trimethoprim (e.g., for the treatment of MRSA skin infections or Pneumocystis jiroveci pneumonia (PCP) in AIDS patients); renal impairment or age-related decline in renal function; aldosterone or adrenal insufficiency; concomitant use of drugs that increase the risk of hyperkalemia (e.g., ACE inhibitors, angiotensin II receptor blockers, aldosterone antagonists; potassium-sparing diuretics); diets with potassium-rich foods (e.g., tomatoes, raisins, figs, baked potatoes, bananas, papayas, pears, cantaloupe, mangoes); and use of potassium salt substitutes.

MANAGEMENT: Serum potassium and sodium levels as well as renal function should be closely monitored during coadministration of trimethoprim with other potassium-sparing drugs or potassium salts, particularly in patients receiving high-dose or long-term trimethoprim treatment and in patients with renal impairment, diabetes, old age, severe or worsening heart failure, or dehydration. A dosage reduction of trimethoprim is recommended in renal dysfunction (50% reduction for CrCl between 15 and 30 mL/min). Patients should be given dietary counseling to avoid excessive intake of potassium-rich foods and salt substitutes, 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. Trimethoprim should be discontinued if hyperkalemia occurs.

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MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients. Sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Cautious dosage titration may be required, particularly at treatment initiation. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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