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Variable furosemide absorption and poor predictability of response in elderly patients
M D Murray1, K M Haag, P K Black
1Department of Medicine, Indiana University School of Medicine, Indianapolis, USA.
Pharmacotherapy
|January 1, 1997
Summary
Extensive patient variability in furosemide absorption significantly impacts its bioavailability and natriuretic response. This variability overwhelms any minor differences between oral furosemide products, making formulation switching unlikely to alter patient outcomes.
Area of Science:
- Pharmacology
- Clinical Pharmacy
- Drug Bioavailability
Background:
- Furosemide is a widely prescribed diuretic for hypertension and heart failure.
- Understanding the variability in furosemide's bioavailability and its impact on natriuretic response is crucial for optimizing patient treatment.
- Marketed oral formulations of furosemide are assumed to have comparable efficacy, but inter- and intra-patient variability may influence this.
Purpose of the Study:
- To quantify the between- and within-patient variability of furosemide bioavailability and its natriuretic effect.
- To compare the bioavailability and natriuretic response across four different oral furosemide tablet formulations.
- To determine if product differences are significant given the inherent variability in patient response.
Main Methods:
- An open-label, crossover study was conducted in a general clinical research center.
- Seventeen patients (mean age 65 years) receiving diuretics for hypertension or heart failure participated.
- Each patient received five furosemide products (one IV, four oral) twice in a randomized order, totaling 10 treatments.
Main Results:
- Extensive between- and within-patient variability was observed in all measured parameters, including furosemide bioavailability and natriuretic response.
- Mean furosemide bioavailability was 49% (±17%), with coefficients of variation ranging from 25-43% across products.
- Multivariate analyses showed no statistically significant differences among the furosemide products for bioavailability, urinary furosemide excretion, or urinary sodium excretion.
Conclusions:
- Significant variability in furosemide absorption among and within individual patients greatly influences drug bioavailability and urinary excretion.
- This high degree of patient-specific variability masks any potential differences between approved oral furosemide formulations.
- Switching between different furosemide products is unlikely to result in predictable changes in patient response due to overwhelming inter- and intra-patient variability.