module 7- methods of calculation for individualized drug dosing

individualized drug dosing

the two methods for calculating this are body weight (BW) and body surface area (BSA). Other formulas that are associated with it, especially in bariatrics, are ideal body weight (IBW) and lean body weight (LBW)

square root method (BSA)

can be calculated by using the square root and fractional formula of height and weight divided by a constant, one for the metric system and another for inches and pounds. square root ( [height (in/cm) X weight (lb, kg)] / 3131)

body weight (BW)

drug dosing but this is the primary way medication is individualized for adults and children -manufacturers supply dosing info in the package insert - the insert data provide the dosage based on the patients weight in kg -the first step is to convert pounds to kilograms, if necessary. -the second step os to determine the drug dose by their weight by multiplying drug dose X body weight X frequency (day or per day in divided doses) -third step is to choose one of the four methods of drug calculation for the amount of drug to be given

ideal body weight

drug dosing by this is used for when medications that are poorly absorbed and distributed throughout the body fat. -formula is based on height and can be adjusted for weight and is used for nutritional assessment Male: 50kg + 2.3kg for EACH inch over 5 ft. female: 45.5kg + 2.3kg for EACH inch over 5 ft

nomogram

in square meters, is determined by the persons height and weight and where these points intersect on the nomogram scale. -these charts were developed from the square root formula and were correlated with heights and weights to provide a quick and simple method for drug dosing before calculators were available

lean body weight

is based upon height and weight but it is less frequently used because it may predict insufficient doses in obese patients Male: (0.32810 x (weight in kilograms) + (0.33929 x height in centimeters)) — 29.5336 (over age 16) Female: (0.29569 x (weight in kilograms) + (0.41813 x height in centimeters)) — 43.2933 (over age 30)

adjusted body weight

is used for dosing some medication for obese individuals or pregnant women. is better for nutritional assessment of obese individuals because it prevents overfeeding. IBW + 0.4(ABW (kg) - IBW (kg) ) =ABW

body surface area

this is an estimated mathematical function of height and weight. it is considered to be the most accurate way to calculate drug dosages in that the correct dosage is more proportional to the surface area -commonly used in chemotherapy and some drug dosages used for infants and children -there are two methods for calculating this- square root formula and the nomogram