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Estimating Ideal Body Weight – A New Formula

Authors:

Abstract

A simple formula for estimating ideal body weight (IBW) in kilograms for both men and women is presented. The equation IBW = 22 x H2, where H is equal to patient height in meters, yields weight values midway within the range of weights obtained using published IBW formulae.
1082 Obesity Surgery, 15, 2005 © FD-Communications Inc.
Obesity Surgery, 15, 1082-1083
A simple formula for estimating ideal body weight
(IBW) in kilograms for both men and women is pre-
sented. The equation IBW = 22 x H2, where H is equal
to patient height in meters, yields weight values mid-
way within the range of weights obtained using pub-
lished IBW formulae.
Key words: Ideal body weight, obesity, drug dosage
Many medications are administered on the basis of
ideal body weight (IBW). This is especially impor-
tant in the morbidly obese patient because certain
classes of drugs with poor lipophilicity and narrow
therapeutic indexes, when administered on the basis
of total body weight (TBW), can lead to over-
dosage and drug toxicity.1For patients smaller than
IBW,simply scaling the dose of drug to TBW is
appropriate, because IBW and TBW approximate
each other. However, for morbidly obese patients
who are significantly larger than IBW, drug dosages
should be scaled to IBW, or IBW plus some fraction
of the difference between TBW and IBW.2How can
IBW be determined?
The concept of IBW was initially proposed by the
Metropolitan Insurance Company to describe a
range of weights associated with longevity for men
and women of different heights.3Although IBW
tables are available, few clinicians use them and
most rely on one of many complicated formulae to
estimate IBW.4-8 There is no absolute correct IBW
for any individual, and each IBW equation will give
a weight that differs for the same patient. IBW also
varies for different populations, and within the same
population at different times. For example, with
each new American generation, height-weight
tables have demonstrated a trend for adults to weigh
more than their predecessors while experiencing
similar or even greater longevity.3
We propose a simple approach to estimate IBW
based on the body mass index (BMI). BMI is calcu-
lated by dividing the patient's weight in kilograms
(kg) by the square of their height (H) in meters (m)
(BMI = kg / H2). A BMI between 20-25 is consid-
ered “normal” weight range. An equation, BMI =
IBW / H2or IBW = BMI x H2can be constructed to
reflect this. A similar concept was recently used to
estimate “normal weight” for fluid administration.9
Using a range of BMI values, we found that for
both men and women, IBW = 22 x H2yields weights
that fall midway within and “best fits” the range of
values obtained with accepted IBW formulae (Figure
1). We propose this formula as an extremely simple,
rapid, and reproducible means of estimating IBW.
References
1. Cheymol G. Effects of obesity on pharmacokinetics
implications for drug therapy. Clin Pharmacokinet
2000; 39: 215-31.
2. Bouillon T, Shafer SL. Does size matter? (Editorial).
Anesthesiology 1998; 89: 557-60.
3. Pai MP, Paloucek FP. The origin of the ‘ideal’ body
weight equations. Ann Pharmacother 2000; 34: 1066-9.
4. Broca PP. Memoires d'anthropologie. Paris 1871 / 1877.
5. Devine BJ. Gentamicin therapy. Drug Intell Clin
Pharm 1974; 8: 650-5.
6. Robinson JD, Lupkiewicz SM, Palenik L et al.
Brief Communication
Estimating Ideal Body Weight – A New Formula
Harry J. M. Lemmens, MD, PhD; Jay B. Brodsky, MD; Donald P. Bernstein, MD
Department of Anesthesia, Stanford University School of Medicine, Stanford, CA, USA
Reprint requests to: Jay Brodsky, MD, Department of Anesthesia,
H3580, Stanford University Medical Center, Stanford, CA, 94305,
USA. Fax: 650-725-8544; e-mail: Jbrodsky@stanford.edu
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Obesity Surgery, 15, 2005 1083
Estimating Ideal Body Weight – A New Formula
Determination of ideal body weight for drug dosage
calculations. Am J Hosp Pharm 1983; 40: 1016-9.
7. Miller DR, Carlson JD, Loyd BJ et al. Determining
ideal body weight. (Letter). Am J Hosp Pharm 1983;
40: 1622.
8. Deitel M, Greenstein RJ. Recommendations for report-
ing weight loss (Editorial). Obes Surg 2003; 13: 159-60.
9. Kabon B, Nagele A, Reddy D et al. Obesity decreases
perioperative tissue oxygenation. Anesthesiology
2004; 100: 274-80.
(Received April 12, 2005; accepted May 20, 2005)
Figure 1. Estimated values for ideal body weight (IBW) for both males (A) and females (B) are shown using a variety of
published formulae. The equation IBW = 22 x H2yields the best fit for both men and women.
Height (cm)
A Males
IBW (kg) Formulae:
56.2 kg (60 inch) + 1.41 kg/inch (ref. 7)
50 kg (60 inch) + 2.3 kg/inch (ref. 5)
52 kg (60 inch) + 1.9 kg/inch (ref. 6)
height (cm) - 100 (ref. 4)
(1 inch = 2.54 cm)
A = 23 x Height (m)2
B = 22 x Height (m)2
A = 21 x Height (m)2
Ideal Body Weight (kg)
120
100
80
60
Height (cm)
B Females
IBW (kg) Formulae:
53.1 kg (60 inch) + 1.36 kg/inch (ref.7)
45.5 kg (60 inch) + 2.3 kg/inch (ref. 5)
49 kg (60 inch) + 1.7 kg/inch (ref. 6)
height (cm) - 105 (ref. 4)
(1 inch = 2.54 cm)
A = 23 x Height (m)2
B = 22 x Height (m)2
A = 21 x Height (m)2
Ideal Body Weight (kg)
100
90
80
70
60
50
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The anesthetic management of obese patients differs from that of normal-weight patients. Obesity alters anatomy and physiology and is associated with numerous medical comorbidities. Obstructive sleep apnea (OSA) and obesity hypoventilation syndrome are common and fall under the umbrella of sleep-disordered breathing. OSA should be identified preoperatively and treated with continuous positive airway pressure. Morbidly obese (MO) patients should never be allowed to lie flat for induction of anesthesia. Obese patients should be positioned in the “ramped” or “head elevated laryngoscopy position.” Inadequate arm support can result in brachial plexus injury. The lateral position requires larger axillary rolls and beanbags. Obesity is a factor for a difficult airway but not a single study has demonstrated a direct relationship between increasing weight with increasing tracheal intubation difficulty. There is a subset of patients that often present with challenging airways. This group consists of MO men, often with OSA, who have thick necks and high Mallampati scores. Emergence from anesthesia should also be in an upper-body elevated position. MO patients can maintain adequate oxygenation during one-lung ventilation, but arterial oxygen tension remains significantly lower than in normal-weight patients. Postthoracotomy pain control in MO patients should include thoracic epidural or paravertebral regional anesthesia. Systemic opioids, in general, should be limited or avoided. This chapter considers the anesthetic management of the obese patient undergoing thoracic procedures with an emphasis on patients with sleep-disordered breathing.
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To provide a historical perspective on the origin and similarity of the "ideal" body weight (IBW) equations, and clarify the terms ideal and lean body weight (LBW). Primary and review literature were identified using MEDLINE (1966-November 1999) and International Pharmaceutical Abstracts (1970-November 1999) pertaining to ideal and lean weight, height-weight tables, and obesity. In addition, textbooks and relevant reference lists were reviewed. All articles identified through the data sources were evaluated. Information deemed to be relevant to the objectives of the review were included. Height-weight tables were generated to provide a means of comparing a population with respect to their relative weight. The weight data were found to correlate with mortality and resulted in the use of the terms desirable or ideal to describe these weights. Over the years, IBW was interpreted to represent a "fat-free" weight and thus was used as a surrogate for LBW. In addition, the pharmacokinetics of certain drugs were found to correlate with IBW and resulted in the use of IBW equations published by Devine. These equations were consistent with an old rule that was developed from height-weight tables to estimate IBW. Efforts to improve the IBW equations through regression analyses of height-weight data resulted in equations similar to those published by Devine. The similarity between the IBW equations was a result of the general agreement among the various height-weight tables from which they were derived. Therefore, any one of these equations may be used to estimate IBW.
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© FD-Communications Inc. Obesity Surgery, 13, 2003 159 Obesity Surgery, 13, 159-160 This Journal does not accept reports with the absolute weight loss (or the percent of weight lost) as the sole descriptive index – ie. operative weight minus the weight at a point in time, is not acceptable as the sole measure of weight loss. The initial weight in studies differs. Furthermore, after a bariatric operation in the super-obese, the number of kilograms lost tends to be greater, but the percent of excess weight loss tends to be less, than in the morbidly obese. For comparative bases, weight loss is preferred as percent of excess weight lost (%EWL) or change in body mass index (BMI). Metric units (ie. kg, meters, etc.) are necessary in this scientific journal. Ideal Body Weight Ideal Weight is derived from the 1983 Metropolitan insurance height and weight tables,1-7 and is the weight for each height at which mortality was lowest and longevity was highest. The Ideal Weight is less than the average weight for a specific height in the population. The Metropolitan Tables are based on the 1979 Build Study,8 which was the result of an 18-year mortality study derived from pooled data of 4.2 million individuals from 25 life-insurance companies in the USA and Canada. The Tables provide the weight that was found to be associated with maximum life expectancy. These weights are given in a range for body frame (small, medium and large), based on elbow width, measured with a calipers.1,2,9 The middle 50% of the elbow breadths (25th-75th percentiles) was designated as the medium frame, with 25% each falling within the small and large frames. Generally, the mid-point of the range of weights for medium frame is chosen as the “ideal” weight. Ideal weight may be calculated from the formula (Table 1) which gives values corresponding to the mid-point of the range for the medium frame on the Metropolitan Tables, with a margin of error <1%.10 There were a number of criticisms of the Metropolitan Tables:2 1) minorities were under-represented in the insurance-purchasing population; 2) 10% of the weights were self-reported; 3) the insured population was a higher economic group than the general population; 4) weights were performed wearing indoor clothing (allowing 5 lb for males and 3 lb for females, with 1” heels for both sexes); 5) applicants with major disease (eg. heart disease, cancer or diabetes at the time of insurance policy issuance) were excluded, to provide an indication of the sole effect of weight on mortality; 6) applicants were ages 25-59 years, although the ideal weight for survival increased up to age 50. However, there is no other study on weight survival based on so vast a sample. Excess Weight = Actual Weight - Ideal Weight Percent Excess Weight Loss = [(Operative Weight – Follow-up Weight) / Operative Excess Weight] X 100. The latter is the preferred means of reporting. Body Mass Index BMI is regarded as the most accurate method for comparing obesity and gives a number which indicates the degree of weight for all heights. It is calculated from the formula W/H2 for men and W/H1.5 for women, where the body weight is in kg and the height is in meters.11 However, the formula for women is somewhat difficult to use, so that the formula for men W/H2 is used for all patients. BMI has a very high correlation with body density and skinfold thickness measurements, and is the best indica- Editorial Recommendations for Reporting Weight Loss Table 1. Formula for calculation of Ideal Weight* Adult Female: 5 ft. tall = 119 lb. For each additional inch, add 3 lb. Adult Male: 5 ft. 3 inches tall = 135 lb. For each additional inch, add 3 lb. 1 foot=30.4 cm; 1 inch=2.54.cm. Divide lb. by 2.2 to change to kg. *Formula corresponds to mid-point of medium frame of the Metropolitan Tables, with accuracy within 1%. To convert to ideal weight for small or large frame, decrease or increase the result by 10%. Patients without shoes. tor for “fatness”.12,13 However, disease or mortality studies associated with BMI have generally been based on population studies of less than 30,000 individuals. Thus, BMI may actually have less accuracy in providing an ideal measure for survival than the 4.2 million people used in the Metropolitan study, from which the least mortality BMI was originally derived. BMI 20-25 kg/m2 is associated with least mortality, and mortality rises as the BMI rises or falls beyond the range of these numbers.14 BMI 20-25 indicates normal weight, >25-29.9 indicates overweight, ³30 indicates obesity, ³40 indicates morbid obesity, and ³50 has been designated as super-obesity. BMI <17.5 is among the criteria for anorexia nervosa, and is frequently seen in such malnutritions as cancer cachexia. Percent BMI Loss = [(Operative BMI - Follow-up BMI) / Operative BMI] X 100. Percent Excess BMI Loss (%EBMIL) Since the NIH/NIDDK defined excess weight as starting at a BMI>25,15 BMI units >25 have been defined as %EBMIL16 by the formula: %EBMIL = 100 - [(Follow-up BMI - 25 / Beginning BMI - 25) X 100] eg. If an individual has an initial BMI of 45, then the 20 BMI units above the upper limit of the normal of 25 BMI units, represents a %EBMIL of 100; a loss of 10 BMI units (to a BMI of 35) would be a %EBMIL of 50. It is possible that %EBMIL may become the standard to present weight loss data in clinical studies of the overweight and obese. Patient Follow-up Changes in %EWL, BMI, or %EBMIL are frequently shown in graphic form as a curve, with bars on one side of each time-point indicating the standard deviation (SD); the number of patients followed and the number eligible for follow-up at each time-point should be shown. However, a curve generally denotes longitudinal analysis which requires 100% follow-up at each time-point.17 Cross-sectional analysis is appropriate for studies of incomplete follow-up, using a table or bar-graph. The bar y-axis indicates the weight loss parameter chosen, with the time-points reported on the x-axis. Again, the number of patients followed and the number eligible for follow-up at each time-point should be indicated. SD may be indicated on top of each bar. Mervyn Deitel, MD; Robert J. Greenstein, MD We thank Kathleen Renquist, BS, IBSR Manager, Nicola Scopinaro and Horacio Oria, for review and suggestions. References 1. 1983 Metropolitan Height and Weight Tables. Metropolitan Life Foundation, Statistical Bulletin 1983; 64 (1): 2-9. 2. Deitel M. Indications for surgery for morbid obesity. In: Deitel M, ed. Surgery for the Morbidly Obese Patient. Toronto: FDCommunications 1989: 69-79. 3. Standards Committee, American Society for Bariatric Surgery. Guidelines for reporting results in bariatric surgery. Obes Surg 1997; 7: 521-2. 4. Cowan GSM, Hiler ML, Buffington CK. Criteria for selection of patients for bariatric surgery. In: Deitel M, Cowan GSM, eds. Update: Surgery for the Morbidly Obese Patient. Toronto: FDCommunications 2002: 76-9. 5. ASBS Standards Committee. Surgery for Morbid Obesity: What Patients Should Know, 2nd Edn. Toronto: FDCommunications, 2001: 27-8. (www.asbs.org) 6. NBSR Database Instructional Manual, Version 2.3, National Bariatric Surgery Registry, University of Iowa Hospital & Clinics, Department of Surgery, January 1987, P. 173 (E-mail: ibsr@uiowa.edu). 7. International Bariatric Surgery Registry, University of Iowa Hospitals, Iowa City, IA 52242, USA (www.surgery.uiowa.edu/ ibsr) 8. Build Study, 1979. Society of Actuaries and Association of Life Insurance Medical Directors of America. Chicago, 1980. 9. Frisancho AR, Flegel PN. Elbow breadth as a measure of frame size for US males and females. Am J Clin Nutr 1983; 37: 311- 4. 10. Miller MA. A calculated method for determination of ideal body weight. Nutritional Support Services 1985; 5 (3): 31-3. 11. White F, Pereira L. In search of the ideal body weight. Ann R Coll Phys Surg Can 1987; 20: 129-32. 12. Keys A, Fidanza F, Karvonen MJ et al. Indices of relative weight and obesity. J Chron Dis 1972; 25: 329-43. 13. Womersley J, Durnin JVGA. A comparison of the skinfold method with the extent of “overweight” and various weightheight relationships in the assessment of obesity. Br J Nutr 1977; 38: 271-84. 14. MacLean LD. Surgery for obesity: where do we go from here? Am Coll Surg Bull 1989; 74: 20-3. 15. Kuczmarski RJ, Flegal KM. Criteria for definition in overweight in transition: background and recommendations for the United States. Am J Clin Nutr 2000; 72: 1074-81. 16. Greenstein RJ, Belachew M. Implantable gastric stimulation (IGS™) as a therapy for human morbid obesity: report from the 2001 IFSO Symposium in Crete. Obes Surg 2002; 12 (Suppl): S3-S5. 17. Jeng G, Renquist K, Doherty C et al. A study on predicting weight loss following surgical treatment for obesity. Obes Surg 1994; 4: 29-36. Deitel and Greenstein 160 Obesity Surgery, 13, 2003
Article
Obesity is a worldwide problem, with major health, social and economic implications. The adaptation of drug dosages to obese patients is a subject of concern, particularly for drugs with a narrow therapeutic index. The main factors that affect the tissue distribution of drugs are body composition, regional blood flow and the affinity of the drug for plasma proteins and/or tissue components. Obese people have larger absolute lean body masses as well as fat masses than non-obese individuals of the same age, gender and height. However, the percentage of fat per kg of total bodyweight (TBW) is markedly increased, whereas that of lean tissue is reduced. Cardiac performance and adipose tissue blood flow may be altered in obesity. There is uncertainty about the binding of drugs to plasma proteins in obese patients. Some data suggest that the activities of hepatic cytochrome P450 isoforms are altered, but no clear overview of drug hepatic metabolism in obesity is currently available. Pharmacokinetic studies provide differing data on renal function in obese patients. This review analyses recent publications on several classes of drugs: antibacterials, anticancer drugs, psychotropic drugs, anticonvulsants, general anaesthetics, opioid analgesics, neuromuscular blockers, β-blockers and drugs commonly used in the management of obesity. Pharmacokinetic studies in obesity show that the behaviour of molecules with weak or moderate lipophilicity (e.g. lithium and vecuronium) is generally rather predictable, as these drugs are distributed mainly in lean tissues. The dosage of these drugs should be based on the ideal bodyweight (IBW). However, some of these drugs (e.g. antibacterials and some anticancer drugs) are partly distributed in adipose tissues, and their dosage is based on IBW plus a percentage of the patient’s excess bodyweight. There is no systematic relationship between the degree of lipophilicity of markedly lipophilic drugs (e.g. remifentanil and some β-blockers) and their distribution in obese individuals. The distribution of a drug between fat and lean tissues may influence its pharmacokinetics in obese patients. Thus, the loading dose should be adjusted to the TBW or IBW, according to data from studies carried out in obese individuals. Adjustment of the maintenance dosage depends on the observed modifications in clearance. Our present knowledge of the influence of obesity on drug pharmacokinetics is limited. Drugs with a small therapeutic index should be used prudently and the dosage adjusted with the help of drug plasma concentrations.
Article
Formulas for ideal body weight (IBW) in men and women were derived from the Metropolitan Life Insurance Company height and weight tables. Regression determinations of median weight versus height were performed for men and women. A program for a minicomputer was developed to generate plots for small, medium, and large frame sizes and for subjects of all frame sizes. Equations for ideal body weight were derived from the resulting data. For men of all frame sizes, IBW = 51.65 kg + 1.85 kg/inch of height >5 feet. For women of all frame sizes, IBW = 48.67 kg + 1.65 kg/inch of height > 5 feet. More accurate estimates of IBW by frame size can be obtained using equations derived from the plots for men and women of each frame size. Estimates of IBW obtained by the widely used empirical method probably contain only minor errors. However, formulas derived from actual height and weight data should be used in pharmacokinetic determination of dosage regimens for some drugs.
Article
Obesity is a worldwide problem, with major health, social and economic implications. The adaptation of drug dosages to obese patients is a subject of concern, particularly for drugs with a narrow therapeutic index. The main factors that affect the tissue distribution of drugs are body composition, regional blood flow and the affinity of the drug for plasma proteins and/or tissue components. Obese people have larger absolute lean body masses as well as fat masses than non-obese individuals of the same age, gender and height. However, the percentage of fat per kg of total bodyweight (TBW) is markedly increased, whereas that chrome P450 isoforms are altered, but no clear overview of drug hepatic metabolism in obesity is currently available. Pharmacokinetic studies provide differing data on renal function in obese patients. This review analyses recent publications on several classes of drugs: antibacterials, anticancer drugs, psychotropic drugs, anticonvulsants, general anaesthetics, opioid analgesics, neuromuscular blockers, beta-blockers and drugs commonly used in the management of obesity. Pharmacokinetic studies in obesity show that the behaviour of molecules with weak or moderate lipophilicity (e.g. lithium and vecuronium) is generally rather predictable, as these drugs are distributed mainly in lean tissues. The dosage of these drugs should be based on the ideal bodyweight (IBW). However, some of these drugs (e.g. antibacterials and some anticancer drugs) are partly distributed in adipose tissues, and their dosage is based on IBW plus a percentage of the patient's excess bodyweight. There is no systematic relationship between the degree of lipophilicity of markedly lipophilic drugs (e.g. remifentanil and some beta-blockers) and their distribution in obese individuals. The distribution of a drug between fat and lean tissues may influence its pharmacokinetics in obese patients. Thus, the loading dose should be adjusted to the TBW or IBW, according to data from studies carried out in obese individuals. Adjustment of the maintenance dosage depends on the observed modifications in clearance. Our present knowledge of the influence of obesity on drug pharmacokinetics is limited. Drugs with a small therapeutic index should be used prudently and the dosage adjusted with the help of drug plasma concentrations.
Article
Obesity is an important risk factor for surgical site infections. The incidence of surgical wound infections is directly related to tissue perfusion and oxygenation. Fat tissue mass expands without a concomitant increase in blood flow per cell, which might result in a relative hypoperfusion with decreased tissue oxygenation. Consequently, the authors tested the hypotheses that perioperative tissue oxygen tension is reduced in obese surgical patients. Furthermore, they compared the effect of supplemental oxygen administration on tissue oxygenation in obese and nonobese patients. Forty-six patients undergoing major abdominal surgery were assigned to one of two groups according to their body mass index: body mass index less than 30 kg/m2 (nonobese) or 30 kg/m2 or greater (obese). Intraoperative oxygen administration was adjusted to arterial oxygen tensions of approximately 150 mmHg and approximately 300 mmHg in random order. Anesthesia technique and perioperative fluid management were standardized. Subcutaneous tissue oxygen tension was measured with a polarographic electrode positioned within a subcutaneous tonometer in the lateral upper arm during surgery, in the recovery room, and on the first postoperative day. Postoperative tissue oxygen was also measured adjacent to the wound. Data were compared with unpaired two-tailed t tests and Wilcoxon rank sum test; P < 0.05 was considered statistically significant. Intraoperative subcutaneous tissue oxygen tension was significantly less in the obese patients at baseline (36 vs. 57 mmHg; P = 0.002) and with supplemental oxygen administration (47 vs. 76 mmHg; P = 0.014). Immediate postoperative tissue oxygen tension was also significantly less in subcutaneous tissue of the upper arm (43 vs. 54 mmHg; P = 0.011) as well as near the incision (42 vs. 62 mmHg; P = 0.012) in obese patients. In contrast, tissue oxygen tension was comparable in each group on the first postoperative morning. Wound and tissue hypoxia were common in obese patients in the perioperative period and most pronounced during surgery. Even with supplemental oxygen tissue, oxygen tension in obese patients was reduced to levels that are associated with a substantial increase in infection risk.
Determining ideal body weight. (Letter)
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Miller DR, Carlson JD, Loyd BJ et al. Determining ideal body weight. (Letter). Am J Hosp Pharm 1983; 40: 1622.
Brief Communication Estimating Ideal Body Weight – A New Formula Fax: 650-725-8544; e-mail: Jbrodsky@stanford 1083 Estimating Ideal Body Weight – A New Formula Determination of ideal body weight for drug dosage calculations
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Robinson JD, Lupkiewicz SM, Palenik L et al. Brief Communication Estimating Ideal Body Weight – A New Formula Harry J. M. Lemmens, MD, PhD; Jay B. Brodsky, MD; Donald P. Bernstein, MD Department of Anesthesia, Stanford University School of Medicine, Stanford, CA, USA Reprint requests to: Jay Brodsky, MD, Department of Anesthesia, H3580, Stanford University Medical Center, Stanford, CA, 94305, USA. Fax: 650-725-8544; e-mail: Jbrodsky@stanford.edu Obesity Surgery, 15, 2005 1083 Estimating Ideal Body Weight – A New Formula Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm 1983; 40: 1016-9.