What are the side effects of losartan and how should they be monitored and managed?

Losartan Side Effects: Monitoring and Management

Most Common Side Effects

The most frequently reported side effects of losartan are dizziness, upper respiratory tract infections (common cold symptoms), headache, back pain, and fatigue, though only dizziness occurs significantly more often than placebo. 1, 2, 3

Hypertension Patients

• Upper respiratory infection (stuffy nose, cold symptoms) 1
• Dizziness – the only adverse effect reported more frequently with losartan than placebo in clinical trials 4, 2
• Stuffy nose 1
• Back pain 1

Type 2 Diabetes with Diabetic Nephropathy

• Diarrhea 1
• Fatigue/tiredness 1, 2
• Low blood sugar (hypoglycemia) 1
• Chest pain 1
• High blood potassium (hyperkalemia) 1
• Low blood pressure (hypotension) 1

Serious Adverse Effects Requiring Immediate Action

Life-Threatening Reactions

• Angioedema – swelling of the face, lips, throat, or tongue requires immediate discontinuation and emergency medical attention 1, 4. Although less common than with ACE inhibitors, angioedema remains a documented serious adverse effect identified through postmarketing surveillance 4.

• Severe hypotension – may cause fainting or severe dizziness; patients should lie down if symptomatic and contact their physician immediately 1.

Pregnancy-Related Toxicity

• Absolute contraindication in pregnancy – losartan causes serious fetal toxicity including renal dysfunction, oligohydramnios, skull hypoplasia, and fetal death when used in the second and third trimesters 1, 5. Discontinue immediately upon pregnancy detection and switch to pregnancy-compatible alternatives (methyldopa, labetalol, or extended-release nifedipine) 6.

Metabolic and Laboratory Abnormalities

Hyperkalemia (Elevated Potassium)

• High-risk populations: patients with chronic kidney disease, diabetes, or those receiving potassium-sparing diuretics or potassium supplements 1, 6
• Monitoring schedule: check serum potassium and creatinine within 1–2 weeks after initiating therapy or dose changes, then at least annually during maintenance 6, 7
• Management: implement potassium-lowering strategies (dietary restriction, potassium binders) before discontinuing losartan 6

Renal Function Changes

• Expected finding: a modest, transient increase in serum creatinine of 0.1–0.3 mg/dL reflects hemodynamic changes rather than tubular injury and does not require discontinuation unless urinalysis shows acute tubular necrosis 6
• Worsening kidney function: monitor for swelling in feet, ankles, or hands, and unexplained weight gain 1
• Contraindication: severe bilateral renal artery stenosis due to risk of acute renal failure 6

Uric Acid Effects

• Losartan increases uric acid secretion and lowers plasma uric acid levels, which may benefit patients on thiazide diuretics but could potentially lead to uric acid stone formation 4

Rare Neurological Side Effects

• Tremors and dysarthria – one case report documented severe tremors and speech difficulty one hour after losartan administration, requiring hospitalization; symptoms resolved without treatment 8. This represents a potentially novel adverse effect requiring clinical attention.

Drug Interactions and Contraindications

Absolute Contraindications

• Dual RAAS blockade: never combine losartan with ACE inhibitors or direct renin inhibitors (aliskiren), especially in diabetic patients; this combination increases hyperkalemia, syncope, and acute kidney injury by 2–3-fold without cardiovascular benefit 6, 7, 1
• History of ARB-induced angioedema 6

Significant Drug Interactions

• NSAIDs – may blunt antihypertensive effect and worsen renal function 6
• Lithium – can precipitate lithium toxicity; monitor lithium levels closely 6
• Potassium supplements or potassium-sparing diuretics – markedly increase hyperkalemia risk 1, 6

Tolerability Profile

Losartan demonstrates superior tolerability compared to other antihypertensive classes, with a withdrawal rate of 2.3% versus 3.7% for placebo. 4

Key Tolerability Advantages

• Cough incidence: 3.1% with losartan versus 2.6% with placebo – significantly lower than ACE inhibitors 3, 2. This makes losartan particularly valuable for patients with ACE inhibitor-induced cough 2.
• First-dose hypotension: uncommon due to slower onset of action 4, 2
• Metabolic neutrality: no clinically relevant adverse metabolic effects or laboratory abnormalities documented 2

Monitoring Algorithm

Initial Phase (First 2–4 Weeks)

1. Baseline assessment: serum creatinine/eGFR, potassium, blood pressure (sitting and standing in elderly patients) 6, 7
2. Week 1–2 follow-up: recheck creatinine/eGFR and potassium, especially in patients with diabetes, CKD, or on potassium-affecting medications 6, 7
3. Week 2–4: reassess blood pressure; target <130/80 mmHg for most adults 6

Maintenance Phase

• Blood pressure: every 3–6 months once at target 6
• Renal function and electrolytes: at least annually, more frequently (every 3–6 months) in high-risk patients 6, 7
• Orthostatic blood pressure: measure in elderly (≥65 years) at each visit to detect postural hypotension 6

Special Population Considerations

Elderly Patients (≥75 Years)

• Initiate at low doses to reduce hypotension and renal insufficiency risk 6
• Monitor closely for dizziness, falls, and fatigue, which are more common in this age group 6
• Measure blood pressure in both sitting and standing positions at 1 and 3 minutes after standing 6

Hepatic Impairment

• Start at 25 mg once daily in mild-to-moderate hepatic impairment; plasma concentrations are approximately five-fold higher than in healthy individuals 6, 5

Renal Impairment

• No dosage adjustment necessary for various degrees of renal insufficiency 5, 7
• Losartan is not removed by hemodialysis 5
• Can be continued as eGFR declines to <30 mL/min/1.73 m² for cardiovascular benefit 6

Common Pitfalls to Avoid

1. Premature discontinuation for mild creatinine elevation – differentiate expected hemodynamic rises (0.1–0.3 mg/dL) from true acute tubular necrosis using urinalysis 6
2. Stopping losartan for hyperkalemia without attempting potassium-lowering strategies first – implement dietary restriction or potassium binders before discontinuation 6
3. Combining with ACE inhibitors – this is contraindicated and increases adverse events without improving outcomes 6, 7, 1
4. Assuming medication discontinuation was due to side effects – directly question patients about adherence, cost, and access issues before escalating therapy 6