What are the common and serious side effects of ertapenem?

Ertapenem Side Effects

Ertapenem is generally well tolerated, with the most common side effects being diarrhea (5-5.6%), nausea (2.5-3.4%), headache, and infused vein complications (3.2-4.5%), while serious but rare neurological toxicity including seizures and encephalopathy can occur, particularly in patients with renal impairment. 1, 2

Common Side Effects (≥5% incidence)

According to the FDA label and clinical trials, the most frequently reported adverse reactions in adults include 1:

• Diarrhea (5.0-5.6% incidence) 1, 2
• Nausea (2.5-3.4% incidence) 2
• Headache 1
• Infused vein complications (3.2-4.5% incidence) 2

In pediatric patients (≥3 months), the most common adverse reactions (≥5%) were 1:

• Diarrhea 1
• Vomiting 1
• Infusion site pain 1

Serious Neurological Side Effects

Central nervous system toxicity represents the most concerning adverse effect of ertapenem, particularly in vulnerable populations. 1, 3, 4

Seizures and Encephalopathy

• Seizures and other CNS adverse experiences have been reported during treatment, with the FDA label specifically warning about this risk 1
• Neurotoxicity most commonly presents as seizures, encephalopathy, and hallucinations, particularly in patients with end-stage renal disease (eGFR <30 mL/min/1.73 m²) 4
• Non-seizure neurotoxicity can manifest as delirium, altered mentation, visual hallucinations, vocal tremor, garbled speech, and progressive obtundation 3, 4, 5
• Symptoms typically appear 5-7 days after starting therapy and resolve within 24-48 hours of discontinuation 4, 5

High-Risk Populations for Neurotoxicity

Particular caution is warranted in 3, 4, 5, 6:

• Patients with renal impairment (eGFR <30 mL/min/1.73 m²) 4
• Elderly patients (≥70 years of age) 5
• Patients on hemodialysis or renal replacement therapy (seizure incidence 2.5% in this population) 3, 6
• Cachectic patients with acute kidney injury 5

Hepatic Effects

• Elevations in alanine aminotransferase (ALT) occurred in 8.3-8.8% of patients, comparable to comparator agents 2
• Most hepatic effects were mild-to-moderate in severity 2

Hematologic Effects

• Thrombocytosis is a rare but documented side effect that resolves upon discontinuation 7
• Other rare hematologic complications include hemolysis, anemia, and neutropenia 7

Local Injection Site Reactions

• Infused vein complications and phlebitis/thrombophlebitis are common with intravenous administration 2, 8
• Local reactions of moderate-to-severe intensity at the infusion site were infrequent and occurred with similar frequency to comparator agents 2
• When administered intramuscularly, caution should be taken to avoid inadvertent injection into a blood vessel 1

Drug Interaction Warnings

Critical Interaction with Valproic Acid

Co-administration of ertapenem with valproic acid or divalproex sodium reduces serum valproic acid concentrations, potentially increasing the risk of breakthrough seizures. 1

• The concomitant use is generally not recommended 1
• Alternative antibacterials other than carbapenems should be considered for patients whose seizures are well controlled on valproic acid 1

Probenecid Interaction

• Co-administration with probenecid inhibits renal excretion of ertapenem and is therefore not recommended 1

Hypersensitivity Reactions

• Serious hypersensitivity (anaphylactic) reactions have been reported in patients receiving β-lactams 1
• Ertapenem is contraindicated in patients with known hypersensitivity to product components or anaphylactic reactions to β-lactams 1

Clostridioides difficile-Associated Diarrhea

• C. difficile-associated diarrhea (ranging from mild diarrhea to fatal colitis) can occur 1
• Evaluate patients if diarrhea develops during or after treatment 1

Special Considerations for Intramuscular Administration

When ertapenem is administered intramuscularly using lidocaine HCl as a diluent 1:

• Contraindicated in patients with known hypersensitivity to local anesthetics of the amide type 1

Clinical Pitfalls to Avoid

1. Do not dismiss altered mental status as unrelated to ertapenem in elderly or renally impaired patients—consider drug-induced encephalopathy early, as extensive medical workup may delay recognition 5

2. Monitor for neurological symptoms starting around day 5-7 of therapy, particularly in high-risk populations 4, 5

3. Avoid using ertapenem in patients on valproic acid for seizure control unless absolutely necessary, as breakthrough seizures may occur 1

4. Dose adjustment is mandatory in patients with creatinine clearance ≤30 mL/min/1.73 m² to reduce neurotoxicity risk 1