A Pharmacometric Method for Quantitative Determination of Improvement in Body Composition and Characterization of the Exposure–Response Relationship during Treatment of Obesity with Tirzepatide

Jun 25, 2025Clinical pharmacology and therapeutics

Measuring Body Composition Improvements and Drug Response in Obesity Treatment with Tirzepatide

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Abstract

A phase 3 clinical trial with 2,539 participants showed that tirzepatide led to a reduction of fat mass three times greater than that of .

An exposure-response model indicated that tirzepatide significantly improved body composition over time.
Females experienced greater weight reduction compared to males when treated with the same drug dose.
Participants with higher baseline weight or body mass index experienced a slower rate of weight reduction.
The model results were consistent with data from a subset of participants who underwent dual energy x-ray absorptiometry (DXA) measurements.
A pharmacometric-based body composition model is proposed for future clinical trials to evaluate similar drugs.

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About half of the world's population is living with overweight or obesity. Tirzepatide is an approved treatment for chronic weight management. We sought to characterize the for weight reduction in patients with overweight or obesity and quantify the associated changes in body composition. Monthly body weight measurements were available from 2,539 study participants in a phase 3 clinical trial investigating placebo, 5, 10, or 15 mg of tirzepatide administered once-weekly. The dependent variables used for modeling were (FFM) and fat mass. These FFM and fat mass values were calculated for each patient based on their total body weight, height, and sex. The exposure-response model revealed that administration of tirzepatide resulted in three times greater reduction of fat mass than that of FFM. This differential effect resulted in improved body composition over time. The model results showed good agreement with available data from a subset (10%) of clinical trial participants who had dual energy x-ray absorptiometry (DXA) measurements. For the same drug exposure, females achieved greater weight reduction than males. Study participants with higher baseline weight or body mass index at baseline had a slower rate of weight reduction and were expected to take longer to reach their nadir weight. We present and propose the use of a pharmacometric-based body composition model to describe weight reduction in future clinical trials investigating similar drugs in similar patient populations, in lieu of DXA scans. In such future trials, our approach can be used to describe exposure-response relationships, optimize doses, and investigate covariates, while considering potential differences in fat mass and FFM.

Key numbers

3×

Reduction Increase

Reduction in compared to .

31%

Female Baseline Decrease

Lower baseline in females compared to males.

longer time

Weight Loss Rate Delay

Participants with higher baseline weight take longer to reach weight loss goals.

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A Pharmacometric Method for Quantitative Determination of Improvement in Body Composition and Characterization of the Exposure–Response Relationship during Treatment of Obesity with Tirzepatide

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