What to monitor when starting Cozaar (Losartan)?

Monitoring When Starting Cozaar (Losartan)

When initiating losartan, you must monitor renal function (serum creatinine) and serum potassium within 7-14 days after starting therapy, then periodically thereafter, as this is critical to prevent hyperkalemia and acute renal failure. 1, 2

Baseline Assessment (Before Starting)

Before initiating losartan, obtain the following:

• Serum creatinine and estimated GFR to assess baseline renal function 2
• Serum potassium to identify pre-existing hyperkalemia 2
• Blood pressure measurement 1
• Pregnancy test in women of childbearing potential (losartan is contraindicated in pregnancy) 2

Early Monitoring (First 1-2 Weeks)

Critical monitoring window at 7-14 days post-initiation:

• Serum potassium: Monitor for hyperkalemia, particularly in patients taking other drugs that increase potassium (potassium supplements, potassium-sparing diuretics, NSAIDs) 1, 2
• Serum creatinine/renal function: Watch for acute deterioration, especially in volume-depleted patients, those with renal artery stenosis, severe heart failure, or chronic kidney disease 2
• Blood pressure: Assess for symptomatic hypotension, particularly in volume- or salt-depleted patients 2

Ongoing Monitoring

Routine follow-up schedule:

• Blood pressure: Monitor regularly during treatment; patients with pre-existing hypertension should check weekly at home for the first month, then at 3 months and every 6 months thereafter 1
• Renal function and potassium: Recheck periodically, especially after dose adjustments 1, 2
• Clinical assessment: Monitor for signs of renal dysfunction or hyperkalemia at routine visits 1

High-Risk Populations Requiring Closer Monitoring

Patients at particular risk who need more frequent monitoring:

• Volume-depleted patients (on high-dose diuretics): Correct volume depletion before starting losartan to prevent symptomatic hypotension 2
• Renal artery stenosis or chronic kidney disease: These patients may experience acute renal failure as their renal function depends on the renin-angiotensin system 2
• Severe heart failure: Monitor closely for renal function deterioration 2
• Elderly patients: No dosage adjustment needed, but monitor renal function carefully 3, 4
• Patients on concomitant medications: Those taking potassium supplements, potassium-sparing diuretics, NSAIDs, or other drugs affecting potassium require more vigilant monitoring 1, 2

Critical Safety Considerations

Avoid these dangerous combinations:

• Never combine with ACE inhibitors or direct renin inhibitors: This increases risk of hyperkalemia and renal dysfunction 1, 5
• Avoid in pregnancy: Discontinue immediately if pregnancy is detected due to fetal toxicity 2
• Withhold or discontinue if clinically significant decrease in renal function occurs 2

Common Pitfalls to Avoid

• Failing to check potassium early: Hyperkalemia can develop rapidly, especially with concomitant medications 2
• Not correcting volume depletion first: This leads to symptomatic hypotension after the first dose 2
• Inadequate monitoring in CKD patients: These patients are at highest risk for acute renal failure 2
• Missing pregnancy screening: Losartan causes serious fetal harm in second and third trimesters 2