Dosing Considerations for Obese Patients

Introduction to Weight-Based Dosing

For most medications in obese patients, the ideal body weight (IBW) or adjusted body weight (ABW) is more appropriate for dose calculation than the total body weight (TBW), according to the Anaesthesia guideline society 1
The American Society of Anaesthesiologists recommends using IBW for dose calculation of certain medications in obese patients, as it provides a more accurate estimate of the patient's lean body mass 1

The total body weight (TBW) is the patient's actual weight, which may not be suitable for dose calculation in obese patients, as stated by the Anaesthesia guideline society 1
The ideal body weight (IBW) is calculated using formulas based on the patient's height and sex, and is often used as a basis for dose calculation in obese patients, according to the Anaesthesia guideline society 1
The adjusted body weight (ABW) takes into account that obese patients have an increased lean body mass, and is calculated as: ABW (kg) = IBW (kg) + 0.4 × (TBW (kg) - IBW (kg)), as recommended by the Anaesthesia guideline society 1

For most anesthetic agents, the use of total body weight is rarely appropriate and increases the risk of relative overdosing, according to the Anaesthesia guideline society 1
For neuromuscular blocking agents (NMBAs), the ideal body weight is recommended for dose calculation, as stated by the Critical Care Medicine guideline society 2, 3
Randomized studies have demonstrated that using IBW for dosing of atracurium resulted in significantly shorter recovery times and less variability compared to dosing based on total body weight, according to the Critical Care Medicine guideline society 3

For cytotoxic chemotherapeutic agents, it is recommended to use the total body weight (TBW) regardless of obesity status, as stated by the Journal of Clinical Oncology guideline society 4, 5, 6
Studies have not shown an increase in hematologic or non-hematologic toxicity in obese patients receiving doses calculated based on total body weight, according to the Journal of Clinical Oncology guideline society 5
The probability of febrile neutropenia decreases as the body mass index (BMI) increases among patients receiving dose-based total weight, as stated by the Journal of Clinical Oncology guideline society 5

For obese children, it is recommended to use the actual body weight for initial dose calculation of resuscitation medications, according to the Circulation guideline society 7
For subsequent doses in obese pediatric patients, physicians may consider adjusting doses to achieve the desired therapeutic effect, as stated by the Circulation guideline society 7

The distribution of medications in obese patients is specific to each drug, making generalizations difficult, according to the Anaesthesia guideline society 1
The clearance of medications metabolized by oxidation, conjugation, or reduction is generally not decreased in obesity, as stated by the Anaesthesia guideline society 1

Use the ideal body weight (IBW), as recommended by the Anaesthesia guideline society 1
Consider the total body weight (TBW) or adjusted body weight (ABW), according to the Anaesthesia guideline society 1
Use the total body weight (TBW), as stated by the Journal of Clinical Oncology guideline society 4, 5, 6

Consistency in measuring weight and choosing the type of weight between patients and for a single patient is crucial when using weight-based dosing, according to the Critical Care Medicine guideline society 3
For medications with a narrow therapeutic index, therapeutic drug monitoring may be necessary to adjust doses appropriately, as stated by the Critical Care Medicine guideline society 3
In patients with morbid obesity, consider comorbidities that may affect the pharmacokinetics of medications, according to the Journal of Clinical Oncology guideline society 4
Remember that excess weight is primarily fat, which has relatively low blood flow, affecting medication distribution, as stated by the Anaesthesia guideline society 1

The Society of Critical Care Medicine recommends dosing benzodiazepines based on ideal body weight, rather than actual body weight, in obese patients to ensure more predictable clinical responses and fewer adverse effects 8, 9, 10
Using ideal body weight for dosing results in more predictable clinical responses and fewer adverse effects compared to dosing based on actual body weight, as demonstrated by studies 9

When prescribing benzodiazepines to obese patients, the Society of Critical Care Medicine recommends using ideal body weight (IBW) for initial dose calculations and considering adjusted body weight (ABW) as an alternative when appropriate 8, 9
Maintaining consistency in the weight measurement method used for a single patient throughout their treatment is crucial, as emphasized by the Society of Critical Care Medicine 9, 10

Using actual body weight for benzodiazepine dosing in obese patients can lead to prolonged sedation and recovery times, as well as greater variability in clinical response, according to the Society of Critical Care Medicine 9, 10
Prolonged sedation and recovery times are potential risks of incorrect dosing, highlighting the importance of using ideal body weight for dosing calculations 9, 10