What laboratory tests should be drawn when increasing the dose of Losartan (losartan)?

From the Guidelines

When increasing losartan dosage, it is crucial to monitor serum potassium and creatinine levels 7-14 days after initiation or dose change, as recommended by the most recent guidelines. This is because losartan, an angiotensin II receptor blocker (ARB), can affect kidney function and electrolyte balance, particularly potassium levels. The medication works by blocking the renin-angiotensin-aldosterone system, which can lead to increased potassium retention and potential changes in renal function 1.

Some key laboratory tests to consider when increasing losartan dosage include:

• Serum potassium
• Creatinine
• Estimated glomerular filtration rate (eGFR) may also be useful in assessing renal function These tests should be performed within 1-2 weeks after dose adjustment and then periodically thereafter. Patients with pre-existing kidney disease, those taking potassium supplements, or those on other medications that can increase potassium (like potassium-sparing diuretics or NSAIDs) require especially careful monitoring 1.

It is also important to note that liver function tests may be considered in patients with liver disease or those experiencing symptoms of liver dysfunction. Blood pressure should also be monitored regularly to ensure the medication is effectively controlling hypertension without causing hypotension. However, the most critical consideration is the monitoring of serum potassium and creatinine levels, as emphasized by the latest guidelines 1.

From the FDA Drug Label

7.1 Agents Increasing Serum Potassium Coadministration of losartan with other drugs that raise serum potassium levels may result in hyperkalemia. Monitor serum potassium in such patients. 7. 2 Lithium Increases in serum lithium concentrations and lithium toxicity have been reported during concomitant administration of lithium with angiotensin II receptor antagonists. Monitor serum lithium levels during concomitant use. 7. 3 Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) Including Selective Cyclooxygenase-2 Inhibitors (COX-2 Inhibitors) In patients who are elderly, volume-depleted (including those on diuretic therapy), or with compromised renal function, coadministration of NSAIDs, including selective COX-2 inhibitors, with angiotensin II receptor antagonists (including losartan) may result in deterioration of renal function, including possible acute renal failure. These effects are usually reversible. Monitor renal function periodically in patients receiving losartan and NSAID therapy. 7. 4 Dual Blockade of the Renin-Angiotensin System (RAS) Dual blockade of the RAS with angiotensin receptor blockers, ACE inhibitors, or aliskiren is associated with increased risks of hypotension, syncope, hyperkalemia, and changes in renal function (including acute renal failure) compared to monotherapy

When increasing losartan, the following labs should be drawn:

• Serum potassium levels to monitor for hyperkalemia, especially in patients taking other drugs that raise serum potassium levels 2
• Serum lithium levels in patients taking lithium concomitantly with losartan 2
• Renal function tests, such as estimated glomerular filtration rate (GFR), to monitor for deterioration of renal function, especially in patients taking NSAIDs or with compromised renal function 2
• Electrolytes in patients on losartan and other agents that affect the RAS, such as ACE inhibitors or aliskiren 2

From the Research

Laboratory Tests to Monitor When Increasing Losartan

When increasing the dose of losartan, it is essential to monitor certain laboratory tests to ensure the patient's safety and adjust the treatment plan as needed. The following laboratory tests should be considered:

• Serum creatinine (Cr) levels: to assess renal function and monitor for potential kidney damage 3, 4, 5, 6
• Potassium (K) levels: to monitor for potential hyperkalemia, a common side effect of angiotensin-receptor antagonists 3
• Uric acid levels: to assess for potential changes in uric acid metabolism 3
• Estimated glomerular filtration rate (eGFR): to evaluate renal function and monitor for potential declines in kidney function 5
• Proteinuria: to assess the level of protein in the urine and monitor for potential changes in kidney function 4, 6

Rationale for Monitoring

The rationale for monitoring these laboratory tests is based on the potential effects of losartan on renal function and electrolyte balance. Losartan has been shown to reduce the progression of renal disease in patients with type 2 diabetes and nephropathy 4, 6, but it can also cause changes in renal function, particularly at high doses 5. Additionally, losartan can cause hyperkalemia, particularly in patients with renal impairment 3. Therefore, regular monitoring of these laboratory tests is essential to ensure the safe and effective use of losartan.

Key Findings

Key findings from the studies include:

• Losartan reduces the progression of renal disease in patients with type 2 diabetes and nephropathy 4, 6
• High-dose losartan (150 mg) is associated with a greater reduction in eGFR compared to low-dose losartan (50 mg) 5
• Losartan causes a significant reduction in proteinuria in patients with type 2 diabetes and nephropathy 4, 6
• Losartan is generally well-tolerated, but it can cause hyperkalemia and changes in renal function 3, 4, 5, 6