1. Calculate lean body weight (LBW)
Devine method:
LBW (Males) = 50 + [ 2.3 x (60 - Height in inches) ]
LBW (Females) = 45.5 + [ 2.3 x (60 - Height in inches) ]
Hume method:
LBW (Males) = (0.3281 x Weight in kg) + (0.33939 x Height in cm) - 29.5336
LBW (Females) = (0.29569 x Weight in kg) + (0.41813 x Height in cm) - 43.2933
The Devine method is the default result. For short stature patients (less than 60 inches), the Hume method is utilized when its result is less than baseline LBW (50kg for males, 45.5kg for females) and greater than Devine.
Please note that neither of these method is valid in amputees.
2. Calculate adjusted body weight (ABW)
ABW = LBW + [CF x (WT-LBW)]
where CF = correction faction (usually 20 to 40%)
WT = actual body weight
LBW = lean body weight
3. Calculate body surface area (BSA)
Mosteller BSA = (HT X WT)^2 / 3600
where HT = height in centimeters
WT = weight in kilograms
DuBois BSA = 0.007184 x (HT^ 0.725 + WT^ 0.425)
where HT = height in centimeters
WT = weight in kilograms
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Since creatinine is produced by muscle, lean body weight (which estimates muscle mass) is usually recommended in creatinine clearance calculations, unless the patient is obese. The default definition of obese is BMI > 30, this is when the correction factor begins. However, you may adjust both of these determinants if your practice is different. To adjust the obesity correction factor, enter your Kinetics Setup dialog, then look under the creatinine clearance settings.
4. Calculate Creatinine Clearance per Jelliffe Multistep method
i. Estimate urinary creatinine excretion rate
E (males) = LBW x (29.305 -[0.203 x (age)])
E (females) = LBW x (25.3 -[0.18 x (age)])
ii. Correct for nonrenal creatinine excretion in chronic renal failure
E = E x [1.035 - 0.0377(SCr)]
where SCr is the latest serum creatinine
OR if SCr is rising, the average SCr
iii. Correct for rising serum creatinine
E = E - [4 x ABW x (Scr1-Scr2)] / D
where ABW= adjusted weight in kilograms
Scr1= the latest serum creatinine
Scr2= the earlier serum creatinine
D = the number of days between
iv. Calculate Corrected creatinine clearance (CrCl)
CrCl/1.73 m2 = (E * 0.12) / (SCr * BSA)
where SCr is the most recent serum creatinine
BSA = Body surface area
5. Calculate Creatinine Clearance per Cockroft and Gault equation
CRCL Males = ABW(140 - Age) / (SCr x 72)
CRCL Females = 85% of male value
where SCr is the most recent serum creatinine
ABW = adjusted body weight
5. Calculate dosage
Option 1 - Dosing table
Dosage tables are derived from either the FDA approved product labeling, Bennett's tables, AHFS Drug Information, or Medical Letter handbook of Antimicrobial Therapy.
Option 2 - One compartment model
For the antibiotics listed below and for user-added models, a dosage methodology utilizing a one compartment model may be used.
i. Determine model pk parameters, examples5:
Drug |
Peak/Trough |
A |
B |
C |
ACYCLOVIR |
40/10 |
0.035 |
0.002 |
0.217 |
AMPICILLIN |
50/ 5 |
0.058 |
0.0064 |
0.26 |
AZLOCILLIN |
250/25 |
0.116 |
0.0058 |
0.16 |
AZTREONAM |
100/10 |
0.116 |
0.0023 |
0.143 |
CARBENICILLIN |
200/20 |
0.046 |
0.0042 |
0.346 |
CEFAMANDOLE |
60/ 6 |
0.043 |
0.0065 |
0.216 |
CEFAZOLIN |
120/20 |
0.032 |
0.0026 |
0.15 |
CEFONICID |
150/25 |
0.014 |
0.0016 |
0.10 |
CEFORANIDE |
120/20 |
0.023 |
0.0021 |
0.132 |
CEFOTAXIME |
80/ 4 |
0.069 |
0.0056 |
0.159 |
CEFOTETAN |
120/20 |
0.02 |
0.00178 |
0.125 |
CEFOXITIN |
60/ 6 |
0.035 |
0.0066 |
0.216 |
CEFTAZIDIME |
60/ 6 |
0.028 |
0.0034 |
0.237 |
CEFTIZOXIME |
60/ 6 |
0.028 |
0.0046 |
0.229 |
CEFUROXIME |
60/ 8 |
0.041 |
0.0051 |
0.174 |
CEPHALOTHIN |
50/ 5 |
0.06 |
0.0114 |
0.26 |
CEPHAPIRIN |
50/ 5 |
0.06 |
0.0092 |
0.24 |
CEPHRADINE |
50/ 5 |
0.06 |
0.0065 |
0.26 |
IMIPENEM |
40/ 1 |
0.173 |
0.0052 |
0.162 |
METHICILLIN |
40/ 4 |
0.173 |
0.0075 |
0.305 |
METRONIDAZOLE |
25/ 8 |
0.053 |
0.0005 |
0.45 |
MEZLOCILLIN |
250/25 |
0.173 |
0.0052 |
0.155 |
PIPRACILLIN |
250/25 |
0.173 |
0.0052 |
0.156 |
TICARCILLIN |
200/20 |
0.043 |
0.0053 |
0.336 |
ii. Calculate rate constant (Kel) using A & B from Table 1.
Kel = A + (CrCl x B)
where CrCl = calculated creatinine clearance
iii. Calculate dosing weight (DW)
DW = LBW + CF x (ABW-LBW)
where ABW = actual body weight
LBW = lean body weight
CF = correction factor
iv. Calculate volume of distribution (Vd) using C from Table 1.
Vd = DW * C
v. Calculate ideal dosing interval (tau)
tau = tinf + [ (-1 / kel) x ln (Cpmax/Cpmin) ]
where Cpmin = Target trough
Cpmax = Target peak
vi. Calculate ideal maintenance dose
MD = kel x Vd x Cpmax x tinf x (1 - e-kel x tau / 1 - e-kel x tinf)
where tau = ideal dosing interval
vii. User selects practical dosage and interval
viii. Calculate expected peak & trough levels
Peak = [MD / (tinf x Vd x kel)] x [(1 - e-kel x tinf) / (1 - e-kel x tau)]
Trough = Peak x e-kel x (tau - tinf)
See also:
Other creatinine clearance methods