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Effect of standard-dose trimethoprim/sulfamethoxazole on the serum potassium concentration in elderly men
J M Witt1, J M Koo, B D Danielson
1Trinity Hospital Pharmacy, Minot, ND 58702, USA.
Objective:
To determine the effect of standard-dose trimethoprim/sulfamethoxazole (TMP/SMX) (TMP 160 mg and SMX 800 mg q12h) on the serum potassium concentration.
Design:
Retrospective and concurrent study.
Setting:
A Veterans Affairs Medical Center.
Patients:
Fifty-three men hospitalized at the Fargo Veterans Affairs Medical Center. Thirty-three patients who received standard-dose TMP/SMX for 3 or more days comprised the study group. Twenty patients who received oral cephradine or amoxicillin for 3 or more days comprised the control group. Patients who received potassium supplements, potassium-sparing diuretics, angiotensin-converting enzyme inhibitors, nonsteroidal antiinflammatory drugs, beta-blockers, heparin, known nephrotoxic agents, patients with a serum creatinine concentration of more than 177 mumol/L, and patients with baseline hyperkalemia (serum potassium concentration > 5.1 mmol/L) were excluded.
Results:
The serum potassium concentration in the study group was 4.22 +/- 0.40 mmol/L and increased by 0.31 +/- 0.38 mmol/L at the end of therapy (p < 0.001). Twenty-six patients in the study group (78.8%) had an increase in the serum potassium concentration during TMP/SMX therapy. Fourteen of these patients had follow-up serum potassium concentrations obtained after completion of therapy. The serum potassium concentration returned to baseline in 10 of these patients. The serum creatinine concentration also increased during therapy. However, the correlation between the increase in the serum potassium concentration and the increase in the serum creatinine concentration was weak (Pearson r = 0.29). The serum potassium in the control group was 4.34 mmol/L and remained essentially unchanged during therapy.
Conclusions:
Therapy with standard-dose TMP/SMX is associated with a slight increase in the serum potassium concentration. Routine monitoring of the serum potassium concentration in patients who are treated with standard-dose TMP/SMX therapy is unnecessary. However, TMP/SMX should be considered as a possible cause of unexplained hyperkalemia in elderly patients receiving TMP/SMX therapy.
Insights
Standard-dose trimethoprim/sulfamethoxazole (TMP/SMX) therapy slightly increases serum potassium levels. Routine monitoring is not needed, but consider TMP/SMX for unexplained hyperkalemia in elderly patients.
Area of Science:
- Pharmacology
- Nephrology
- Internal Medicine
Background:
- Trimethoprim/sulfamethoxazole (TMP/SMX) is a commonly prescribed antibiotic.
- Potential effects of TMP/SMX on electrolyte balance, particularly serum potassium, require investigation.
Purpose of the Study:
- To evaluate the impact of standard-dose TMP/SMX on serum potassium concentrations in hospitalized patients.
Main Methods:
- Retrospective and concurrent study design involving 33 patients receiving standard-dose TMP/SMX and 20 controls.
- Exclusion criteria included potassium supplements, specific diuretics, ACE inhibitors, NSAIDs, beta-blockers, heparin, nephrotoxic agents, impaired renal function, and baseline hyperkalemia.
Main Results:
- TMP/SMX therapy led to a statistically significant increase in serum potassium (0.31 +/- 0.38 mmol/L, p < 0.001) in 78.8% of patients.
- Serum potassium normalized in 10 out of 14 patients after TMP/SMX discontinuation.
- A weak correlation was observed between increased serum potassium and increased serum creatinine.
Conclusions:
- Standard-dose TMP/SMX is associated with a mild elevation in serum potassium.
- Routine serum potassium monitoring during TMP/SMX therapy is generally not necessary.
- TMP/SMX should be considered in the differential diagnosis of unexplained hyperkalemia, especially in elderly patients.