Navigating the impact of obesity on medication effectiveness requires pharmacists to devise evidence-based dosing strategies — and be willing to alter them if results aren’t optimal, said speakers at a Wednesday session of the 2025 Midyear Clinical Meeting & Exhibition.
Speakers Kyle Molina, Lisa Thompson, and Mitchell Buckley discussed the challenges in dosing antimicrobials, chemotherapy agents, and anticoagulants for obese patients in the session, The Weight Debate: Best Practices for High-Risk Medication Dosing Controversies in Extreme Weight Patients.
Molina, a pharmacist with Scripps Health, focused on vancomycin, which is used for serious infections, such as pneumonia and sepsis. Starting about 15 years ago, real-world evidence began to challenge the longtime use of total body weight in vancomycin dosing. Reports showed obese patients were receiving excessively high doses — putting them at risk of acute kidney injury.
He cited a study showing that the drug accumulated in the bodies of obese patients within the first 10 days of treatment. “Additionally, they linked that accumulation to clinical outcomes,” Molina said. “Fourteen percent of these patients suffered acute kidney injury during their course of therapy.”
Yet current guidelines continue to recommend actual body weight dosing based on other studies. “We want to make sure we’re individualizing all of our dosing strategies emphasizing actual body weight for our initial calculations,” he said, “[but] potentially performing dose capping and really monitoring these patients.”
Weight is a cornerstone of chemotherapy dosing, an especially relevant factor given that obesity-related cancers are on the rise, said Thompson, pharmacy clinical coordinator at Banner Health in Arizona.
A high weight can have an impact on pharmacokinetics, she said. Obese patients often have inflammation, accelerated gastric emptying, and dysregulated blood flow in adipose tissue — all of which change how the chemotherapy agents affect the body, said Thompson.
Clinical guidelines released in 2012 recommended capping doses at certain weights due to fears of toxicity. However, those guidelines were updated in 2020 to now recommend giving the full weight-based dose. Three of five solid tumor studies showed that reducing doses for obese patients resulted in worse outcomes, she said.
Thompson also described dosing strategies in newer cancer treatments, including targeted therapies and subcutaneous medications. She recommended the audience explore Project Optimus, an initiative by the Food and Drug Administration to reform dose optimization and selection in oncology drug development.
Buckley discussed what happened after his institution, Banner University Medical Center, began offering standard heparin protocol based on anti-Xa levels. Pharmacists noticed that obese patients’ anti-Xa levels were off, and Buckley decided to launch an audit.
The team’s findings showed obese and morbidly obese patients had levels that were too high, indicating excessive heparin effect and an increased risk of bleeding. Nursing staff were frequently being dispatched to shut off the infusion.
“Not only was it a risk to the patient, but it was intrusive to the workflow,” said Buckley.
Pharmacists decided to change the infusion protocol and use actual body weight to determine dose sizes. Patients who exceeded certain weight ranges saw their doses reduced. Buckley emphasized that pharmacy teams should find what works for their patients.
“If we had the right answer we wouldn’t be sitting in this session today,” said Buckley. “One of the things I’d emphasize is do a small sample and audit the protocol in obese populations.”
