Theophylline formulas

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The theophylline model is not hardcoded into the program. The parameters are found in the drug model database and are fully usereditable. You can tailor each drug model to fit your patient population, or you can create your own models. See the Edit drug models section of the help file for further information.
Initial dosing
1. Determine loading dose of IV aminophylline.
2. Determine initial maintenance dose of IV aminophylline
ko = 0.5 x LBW x Smoking x Age factor x CHF/Liver failure x Drug factor where factors are: • Smoking = 1.5 • Age > 70 = 0.8 • Acute CHF or Liver failure = 0.6 • Interacting drugs = 0.75 • If theophylline is selected, multiply by 0.8
Dosage adjustment before steady state
1. Calculate Clearance (CL) with Chiou Method Two serum levels are required, the first level drawn one hour after the constant infusion started, and the second drawn at least one halflife later. The rate of infusion must be constant during the time between the two levels and the patient should not have received any oral theophylline 6 to 12 hours prior to the IV dose.
CL = [(2 x ko) / (Cp1 + Cp2)] + [(2 x Vd x (Cp1  Cp2)) / (Cp1 + Cp2) x (t2 t1)]
where ko = administration rate (mg/hr) Cp1 = level (mg/l) drawn 1 hour after start of infusion Cp2 = level (mg/l) 6 hours later Vd = 0.5 l/kg LBW t1 = time Cp1 drawn t2 = time Cp2 drawn
2. Calculate Incremental Loading Dose or Temporary Interruption
ILD = (Cpdes  Cpmeas) x Vd
TI = [ln (Cpdes / Cpmeas )] / Ke
3. Determine new infusion rate (ko')
Ko' = Cpdes x CL where Cpdes = desired level (mg/l) CL = clearance (l/hr)
Dosage adjustment at steady state
1. Calculate Clearance (CL)
CL = ko / Cpss where ko = administration rate (mg/hr) Cpss = steady state level (mg/l)
2. Calculate Incremental Loading Dose (ILD) OR Temporary Interruption (TI) Same as above
3. Determine new infusion rate (ko') Same as above
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