Serum potassium influencing interacting drugs: risk-modifying strategies also needed at discontinuation.

BACKGROUND

Although the discontinuation of a medication may have important clinical consequences, there is generally much less attention given to medication surveillance when a drug is stopped than when it is started.

OBJECTIVE

To investigate the consequences on serum potassium levels of discontinuing a drug that increases the serum potassium level (PID↑) and a drug that decreases the serum potassium level (PLD↓) in patients taking both.

METHODS

Patients who were hospitalized in the University Medical Centre Utrecht in 2004-2009 and were using both a PID↑ and a PLD↓ were included when one of these drugs was discontinued during hospitalization. Serum potassium levels measured before (potassium(1)) and after (potassium(2)) discontinuation were compared in patients who stopped the PLD↓ and in patients who stopped the PID↑.

RESULTS

In the group of patients who stopped the PLD↓ (ie, continued the PID↑), mean serum potassium levels increased 0.19 mEq/L (range -0.9 to 1.8 mEq/L). After discontinuation of the PLD↓, serum potassium levels increased in 91 (59%) patients. Five patients (3.2%) developed hyperkalemia (potassium(2) >5.5 mEq/L). In the group of patients who stopped the PID↑ (ie, continued the PLD↓), mean serum potassium levels decreased 0.40 mEq/L (range -2.6 to 0.7 mEq/L). Serum potassium levels decreased in 61 (70%) patients after discontinuation of the PID↑. Fifteen patients (17%) developed hypokalemia (potassium(2) <3.5 mEq/L). Results were not influenced by length of stay, age, sex, renal function, and type of medication discontinued.

CONCLUSIONS

The effects of serum potassium-influencing drugs need to be monitored not only after starting but also after stopping the medication. The same may hold true for the effects of other drugs. Clinical risk management should therefore focus on the risks not only when new medication is prescribed, but also when medication is stopped.