NAPLEX Question of the Week: Conquering the Carbapenems

This week's question focuses on a very specific agent within the carbapenem class.
NAPLEX Question of the Week: Conquering the Carbapenems
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GB is a 62-year-old male presenting to the hospital with fever, abdominal pain, and distention. He is diagnosed with an intra-abdominal abscess with final culture growing Extended spectrum beta-lactamase (ESBL)-producing E. coli

PMH: Type 2 diabetes, COPD, Hypertension

Social History: Tobacco user, alcohol use (2 drinks/day)

Family History: Mother: Type 2 diabetes; Father: Hypertension

Medications: Trelegy Ellipta 100mcg/62.5mcg/25mcg 1 inhalation daily, Metformin 1g PO BID, Losartan 50mg PO daily

Notable Labs: WBC 15,000 cells/microL; FBG: 110mg/dL

Vitals: RR 20; HR 100 bpm; BP 138/87 mmHg, Temperature: 100.5 F

The surgical resident is asking you about the possibility of ertapenem therapy. Which of the following statements is true of ertapenem? Select all the apply.

A. Ertapenem is typically administered once daily.

B. Ertapenem could be used for P. aeruginosa if this had grown instead in GB's culture.

C. Ertapenem can cause seizures, especially if accumulated due to renal dysfunction.

D. Ertapenem can decrease the concentration of losartan when administered together.

E. Ertapenem's brand name is Invanz.

Rationale: Ertapenem is a carbapenem antibiotic with broad spectrum against multi-drug resistant gram-negative organisms including ESBL-producing organisms. Ertapenem is indicated for complicated intra-abdominal infections, complicated SSTIs, diabetic foot infections, CAP, complicated UTIs, and pelvic infections. Let's go through each answer and discuss rationale. 

Answer A is correct. The typical dosage for adults and children aged 13 and up is 1 gram once daily given IV or IM. If a patient has an estimated CrCl of 30ml/min or less, then the dose should be decreased to 500mg IV or IM once daily. 

Answer B is incorrect. Ertapenem has three major holes in coverage that the other carbapenems do not have. These are Enterococcus species, Acinetobacter baumannii, and Pseudomonas aeruginosa.

Answer C is correct. The carbapenems have a warning for potentially causing seizures in patients. This risk is increased when the drug is accumulated due to reduced renal excretion in patients with renal dysfunction. Imipenem/cilastatin (Primaxin) tends to have the highest risk. 

Answer D is incorrect. There is no impact of ertapenem on losartan. However, ertapenem and other carbapenems can abruptly decrease the level of valproic acid or divalproex, potentially causing seizures in patients maintained on this drug. This is because carbapenems inhibit acyl peptide hydrolase which is in the cells of the liver. This increases glucuronidation of valproic acid. Therefore, carbapenems should be avoided in patients on valproic acid, as giving more valproic acid will not overcome the decrease in concentrations. 

Answer E is correct. The brand name of ertapenem is Invanz.

Brand/Generic Used: Ertapenem/Invanz; Trelegy Ellipta/fluticasone-umeclidinium-vilanterol; Metformin/Glucophage; Losartan/Cozaar

References:

Ertapenem package insert - https://www.accessdata.fda.gov/drugsatfda_docs/label/2012/021337s038lbl.pdf

Ertapenem and valproic acid interaction - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2932497/#:~:text=They%20concluded%20that%20carbapenems%20increased,which%20thereby%20decreased%20valproate%20levels.

NAPLEX Competencies Covered:

1.1 From instruments, screening tools, laboratory, genomic or genetic information, or diagnostic findings

1.4 From medical records: treatment adherence, or medication-taking behavior; chief complaint, medication history, medical history, family history, social history, lifestyle habits, socioeconomic background

1.5 Signs or symptoms of medical conditions, healthy physiology, etiology of diseases, or pathophysiology

2.2 Commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names; physical descriptions; or how supplied

3.4 Drug dosing or dosing adjustments; duration of therapy

3.5 Drug route of administration, dosage forms, or delivery systems

3.6 Drug contraindications, allergies, or precautions

3.7 Adverse drug effects, toxicology, or overdose

3.8 Drug interactions

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