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Energy Expenditure

EE: Medications/Drugs (2006)

INTRODUCTION

Determining energy needs is foundational for accurate nutrition assessment and intervention planning. Medications that alter various physiological processes occurring in the central nervous, neuromuscular, respiratory or cardiovascular systems may alter energy requirements.  Understanding the pharmacokinetic characteristics of medications, including the drug’s dosage, duration of therapy, dosing interval, and routes of administration help health professionals interpret the medication’s clinical relevance.

Medications were defined as having a “clinically relevant”, “potentially relevant” or “irrelevant” effect upon energy expenditure (as shown in definitions box).  When evaluating the influence of pharmacotherapy, it is important that steady state be achieved. Drug therapy may be considered at steady state when the duration of therapy is at least five times greater than the elimination half-life of the drug. Conversely, it will generally take at least five half-lives of the drug to be considered to potentially free of its metabolic effects.

Clinically-relevant effect is one which alters energy expenditure by at least 10% for a medication administered acutely or at least 5% if administered chronically. 

Potentially relevant alters energy expenditure by at least 5% when administered acutely or at least 3% if administered chronically

Irrelevant effect or “no effect” is if there is < 5% effect acutely or < 3% upon chronic administration of the medication. 

Acute administration of a medication would be if the duration of therapy is less than a month

Chronic administration of a medication would be if the duration of therapy is greater than a month

However, there are exceptions. For example, the elderly may have an altered volume of distribution, impaired hepatic metabolism, or reduced urinary clearance of numerous drugs.  Body fat can serve as a depot and increase the volume of distribution for some drugs so that extent of adiposity may influence drug distribution and elimination. Patients with end-stage liver or kidney disease may also have alterations in the elimination of medications. Certain ethnic groups have been classified as “fast metabolizers” or “slow metabolizers” for certain medications. Unfortunately, there are insufficient published data, particularly when addressing the effect of medications on energy expenditure, to make definitive recommendations for these sub-populations and it is recommended that the clinician consider these potential confounding factors when assessing the effect of pharmacotherapy upon energy expenditure. 

Overall, medications and diseases have an effect on individual energy expenditure and it is important to understand how and to quantify the effect.  The purpose of this systematic review was to answer the question, “What are the medication effects upon resting metabolic rate?”