Warning:
These calculations are based on a number of assumptions
that may not apply to particular clinical scenarios. The author makes no claim
that the drug dosing will achieve the predicted levels. Use
with extreme caution.
The Tab key can be used
to move from one cell to the next. The Clear button will clear only the
data from the preceding section. The Clear All button will clear all
the entered and calculated data. Use the Print button to print the form.
For an explanation of pharmacokinetics and the calculations used, click on the
Reference button.
Enter the Patient Weight.
Select the medication being measured so that default values for the
parameters in section 1 can be entered automatically. Select --Other-- if
not listed, and manually enter the other values. In particular, the Draw Delay,
Level Error, and Time Error must be entered. Draw Delay is the time
in hours from the initiation of dose administration to the time that the peak
level is drawn (infusion time plus time allowed for distribution). A typical
value is 1 hour for aminoglycosides, 2 hours for vancomycin. Level Error
is the estimated error in drug level measurement. Default values for some
of the medications listed is one standard deviation for measured values of
a reference sample in our laboratory. If unknown, 0.5 mg/L is a reasonable
estimate. That levels are not drawn at the exactly the ideal moment is reflected
in the Time Error. A value of 0.5 hrs is reasonable.
Enter the data in section
2. The Indexed Dose (mg/kg/dose) is calculated from the patient's Weight
and the absolute Dose (mg/dose). Alternatively, the Indexed Dose
can be entered directly. The Peak-Trough Interval is calculated by
subtracting the Draw Delay entered in section 1 from the Dosing
Interval. Enter the measured Peak and Trough levels. (If
the Half-Life and Volume of Distribution are known, this section
may be skipped.)
Once the above data are
entered, click on the Calculate button in section 3 and the parameters
in this section will be calculated along with the range based on the specified
error ranges. If the Volume of Distribution and the Half-Life
are known or estimated, they can be entered directly with the other parameters
calculated from the entered data.
Enter the new Dose
and Dosing Interval proposed. (The calculator will compute the Dose
in mg/kg if left blank.) In general, increase the dose if the peak is too
low, and increase the dosing interval if the trough is too high.
Click on the Calculate
button after filling the cells in sections 4 and 5. Use the Clear button
to empty the cells in section 4 only
Edited:
November 1, 2001