Useful Pharmacy Formulas 

Formula Name 
Formula 
Absolute Neutrophil Count (ANC) 
ANC = WBC X Percent of neutrophils 
Aminoglycoside Pharmacokinetics 
VD = 0.25 X IBW (unless ABW > 25% of IBW), then use VD = 0.25
X (IBW + 0.4 X (ABW  IBW)); Cl = CrCl; Ke = Cl / VD 


Expected level = ((S)(F) dose / VD / 1  e^{(kT)}) X e ^{(kt)} 

T = dosing interval, t = time (for peak t = 1; for trough t = T) 
Body Mass Index (BMI) 
Weight (lbs) X 703 / height (inches) 

Acceptable: < 25; Overweight: 2529; Obese => 30 
Body Surface Area (BSA) 
BSA (m_{2}) =
(Height (inches) X Weight (lbs) / 3131) ^{1/2} 
Centimeters to Inches (Height) 
Height (inches) = Height (cm) / 2.54 
Creatinine Clearance (CrCl) 
CrCl = (140  age X IBW (kg)) / (72 X SCr) 

for females: multiply above by 0.85 
Corrected Albumin (for Phenytoin levels) 
Corrected level = Phenytoin level / 0.2 X (Albumin + 0.1) 
Digibind Dosing 
Dose (vials) = serum digoxin (ng/ml) X weight (kg) / 100 

Each vial contains 38mg and binds
to approximately 0.5mg of digoxin; dispense with 0.22 micron filter and
dilute in 50100 normal saline 

Digoxin Pharmacokinetics 
VD = (3.8 X IBW) + (3.1 X CrCl); Cl = (0.8 X IBW) + CrCl; Ke = Cl / VD 

Expected level = (S)(F) dose / dosing interval / Cl 

(S = 1; F = 0.7 for tablet, 0.8 for elixir, and 1 for capsule and IV) 
Ideal Body Weight (IBW) 
Male: 106 lbs for first 5 feet, then 6 lbs for each inch over 5 feet 

Female: 100 lbs for first 5 feet, then 5 lbs for each inch over 5 feet 

OR 

Adults (18 y/o+): IBW (male) (kg) = 50 + (2.3 X height in inches over 5
feet) 

IBW (female) (kg) = 45.5 + (2.3 X height in inches over 5 feet) 

Children (IBW is in kg, height in cm) 

118 y/o: IBW = (height^{2} X 1.65) X 1000 

5 feet and taller: IBW (male) = 39 + (2.27 X height in inches over 5
feet) 

IBW (female) = 42.2 + (2.27 X height in inches over 5 feet) 
Phenytoin Pharmacokinetics 
VD = 0.65 X ABW; Vm = 7 X ABW; Km = 4 

Expected level = 4 X (S)(F) dose / Vm  dose 
Valproic Acid Pharmacokinetics 
VD = 0.14 X IBW; Cl (children) = 13 ml/kg/hr; Cl (adults) = 8 ml/kg/hr 

Expected level = ((S)(F) dose / VD / 1  e^{(kT)}) X e ^{(kt)} 
Vancomycin Pharmacokinetics 
VD = 0.7 X ABW; Cl = CrCl; Ke = Cl / VD 

Expected level = ((S)(F) dose / VD / 1  e^{(kT)}) X e ^{(kt)} 

(T = dosing interval, t = time (for peak t = 2; for trough t = T) 


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