NAPLEX Question of the Week: Renal Dose Adjustments?

A common task among pharmacists is assessing renal function to dose medications. Are you up for the challenge?

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KL is a 68 yo male admitted to your hospital complaining of shortness of breath, fatigue, nausea and vomiting, and fever. He is 5 foot 8 inches, weighs 110 kg, and has no known drug allergies. A chest x-ray was performed, and patchy opacities were observed with a clinical diagnosis of community-acquired pneumonia. Past medical history includes CKD stage 3, GERD, depression, and hypertension. KL’s medication list includes ceftriaxone 2g IV q24h, azithromycin 500 mg IV q24h, famotidine 20 mg IV q12h, metoclopramide 10mg IV q6h, lisinopril 20mg PO daily, and Celexa 20 mg PO daily. Pertinent labs taken today are Scr 2.3 mg/dL (baseline 2.2 mg/dL), K 3.4 mEq/L, WBC 22K, and temperature of 101°F. Based on the patient’s current renal function, which medications would need to be renally dose adjusted?

 

A. Ceftriaxone

B. Lisinopril

C. Celexa

D. Metoclopramide

E. Famotidine

Answers with rationale.

The correct answers are D and E. 

First we need to calculate KL’s ideal body weight.
IBW for males = 50 + (2.3 X inches over 5ft)
50 kg + (2.3 X 8) = 68.4 kg
Since his actual body weight is greater than 20% of his ideal, we should use his 40% adjusted body weight.
Adjusted body weight = IBW + 0.4(Actual body weight – Ideal body weight)
68.4 kg + 0.4(110 kg – 68.4 kg) = 85.04 kg


We can now use this weight in the Cockcroft-gault equation:
 (140-age)(weight in kg)/(72*Serum creatinine (mg/dL))*0.85 if female

Therefore:
(140-68)(85.04 kg))/(72*2.3 mg/dL) = 36.9 mL/min 

Ceftriaxone does not need any dose adjusting because it is excreted primarily hepatobiliary. Ceftriaxone is the only cephalosporin that is excreted in this manner which makes it unique for renal dose adjustments. While lisinopril can cause acute kidney injury, it is often used in CKD patients for renal protection (his current SCr is near baseline) and therefore should be continued and not renally adjusted. Celexa (citalopram) also does not require renal dose adjustments. Famotidine would need to be renally dose adjusted since his creatine clearance is less than 50 mL/min.  Lastly, metoclopramide would also need to be renally dose adjusted because his creatinine clearance is less than 60 mL/min. Typically the dose is halved from 10mg to 5mg to limit accumulation which could potentially result in neurologic side effects (such as pseudoparkinsonism) due to dopamine blockade. 

Competency areas of note:

1.1: Obtain, interpret, or assess data, medical, or patient information from instruments, screening tools, laboratory, genomic or genetic information, or diagnostic findings

2.2: Identify drug characteristics from commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names; physical descriptions; or how supplied

4.1: Perform calculations based on patient parameters or laboratory measures

Christopher M. Bland

Clinical Professor, University of Georgia College of Pharmacy

Dr. Christopher M. Bland is a Clinical Professor at the University of Georgia College of Pharmacy at the Southeast GA campus in Savannah, GA. Dr. Bland has over 20 years of academic and clinical experience in a number of clinical areas. He is a Fellow of both the Infectious Diseases Society of America as well as the American College of Clinical Pharmacy. He is co-founder of the Southeastern Research Group Endeavor, SERGE-45, with over 80 practitioners across 14 states involved. Dr. Bland serves as Associate Editor for the NAPLEX Review Guide 4th edition as well as Editor-In-Chief for the Question of the Week. He has provided live, interactive reviews for more than 10 Colleges/Schools of Pharmacy over the course of his career.