Plasma concentration monitoring of oral vancomycin

Letter

In the comprehensive review on therapeutic drug monitoring of vancomycin by Legg et al,¹ while not specifically stated, the article appears to refer to intravenous use of vancomycin.

Vancomycin can also be used via oral or enteral route for the treatment of Clostridioides difficile-related pseudomembranous colitis. Of interest is the following comment in Therapeutic Guidelines: Antibiotic: ‘Systemic absorption of vancomycin can occur with oral or enteral administration. If toxicity is suspected, consider measuring vancomycin plasma concentrations; otherwise, therapeutic drug monitoring is not required.’²

In contrast, the current C. difficile infection management guidelines from the Australasian Society of Infectious Diseases state: ‘Neither vancomycin nor fidaxomicin is absorbed systemically from the gastrointestinal system and achieves higher colonic levels and stool concentrations than metronidazole; this may explain their improved efficacy.’³

Although there are multiple case reports of enteric absorption of vancomycin in the critically ill,^4-6 it is uncommon to perform drug monitoring when using oral vancomycin to treat pseudomembranous colitis unless demonstrating drug toxicity.

Perhaps the authors can explain how measuring vancomycin plasma concentrations (as opposed to the area under the concentration–time curve over a 24-hour period [AUC₂₄]) can help in such rare cases, to complete the loop on its safe and effective use.

Shyan Goh
Orthopaedic Surgeon
Meadowbrook, Queensland

Conflicts of interest: none declared

 

References

1. Legg A, Devchand F, Gwee A, Sandaradura I, Lai T. Safe and effective use of vancomycin. Australian Prescriber 2025;48:54-9.
2. Clostridioides difficile infection. In: Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited; 2025. [cited 2025 Jun 19]
3. Longhitano A, Roder C, Blackmore T, Campbell A, May M, Athan E. Australasian Society of Infectious Diseases updated guidelines for the management of Clostridioides difficile infection in adults and children in Australia and New Zealand. Intern Med J 2025;55:503-13.
4. Rakocevic R, Guevarra K. Systemic Absorption of Oral and Rectal Vancomycin in a Critically Ill Patient: A Case Report. Cureus 2024;16:e76008.
5. Yamazaki S, Suzuki T, Suzuki T, Takatsuka H, Ishikawa M, Hattori N, et al. An extremely high bioavailability of orally administered vancomycin in a patient with severe colitis and renal insufficiency. J Infect Chemother 2017;23:848-51.
6. Coutsouvelis J, Witney KA, Corallo CE, Spelman D. Systemic Absorption from Oral Vancomycin: Check the Dose! Journal of Pharmacy Practice and Research 2011;41:225-6.

 

Authors’ response

Amy Legg, on behalf of the authors of the article, comments:

Thank you for your correspondence. Our article was focused on the use of parenteral vancomycin, but we appreciate the situation you describe also warrants consideration. Vancomycin therapeutic drug monitoring is not recommended for patients on oral vancomycin; however, in some very rare settings (e.g. severe or fulminant colitis, stage 5 chronic kidney disease, prolonged exposure to high oral vancomycin doses [2 g/day], concurrent vancomycin retention enema use), or if vancomycin toxicity is strongly suspected, checking a vancomycin plasma concentration may be appropriate.^1-5 In this setting, drug concentration is used only to monitor for toxicity (not effectiveness). If the vancomycin plasma concentration is detectable, clinical review is needed for dose reduction or a change in therapy. Thresholds for toxicity are as described in the main article – a spot concentration greater than 15 mg/L or an AUC₂₄ above 600 mg.hr/L (would need to be calculated manually). Serum creatinine should also be monitored if systemic absorption of vancomycin is suspected.

 

References 2

1. Clostridioides difficile infection. In: Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited; 2025. [cited 2025 Jun 19]
2. Kelly CP, Lamong JT, Bakken JS. Clostridioides difficile infection in adults: Treatment and prevention. In: UpToDate. Wolters Kluwer; 2025. [cited 2025 Jun 30]
3. Wilke K, Helbig S, de With K. Serum vancomycin concentrations after oral and intracolonic vancomycin administration in a patient with colonic discontinuity and severe Clostridium difficile infection. Am J Health Syst Pharm 2018;75:e189-e93.
4. Pettit NN, DePestel DD, Fohl AL, Eyler R, Carver PL. Risk factors for systemic vancomycin exposure following administration of oral vancomycin for the treatment of Clostridium difficile infection. Pharmacotherapy 2015;35:119-26.
5. Rakocevic R, Guevarra K. Systemic Absorption of Oral and Rectal Vancomycin in a Critically Ill Patient: A Case Report. Cureus 2024;16:e76008.

 

The Editorial Advisory Committee welcomes letters, which should be less than 250 words. Before a decision to publish is made, letters which refer to a published article may be sent to the author for a response. Any letter may be sent to an expert for comment. When letters are published, they are usually accompanied in the same issue by any responses or comments. The Committee screens out discourteous, inaccurate or libellous statements. The letters are subedited before publication. Authors are required to declare any conflicts of interest. The Committee's decision on publication is final.