NextDose: A web-based Bayesian dose forecasting tool

Last updated 19 June 2025

Observation Types

The NextDose Doses and Observations window is used to enter doses and individual observations such as weight. Observation types such as weight are associated with a date and time so that time varying changes in these observations may be used by the NextDose model. When MIC is used as an observation it is treated as a time varying observation. The new MIC value will be applied to observed doses and concentrations from the time of the MIC observation.

AUC T1

The AUC T1 observation calculates the area under the curve (~AUC) of the predicted individual concentration from the AUC starting time (h) entered in the measured value box. If the starting time is set to “.” the value will be calculated from the date and time of the observation. The time in hours is counted from the time of the first observation (dependent variable) or dose in the Doses and Observations window.

AUC T2

The AUC T2 observation calculates ~AUC from the AUC starting time in AUC T1 and ending at the time entered in the AUC T2 measured value box. If the starting time is set to “.” the value will be calculated from the date and time of the AUC T1 or AUC T2 observation. The time of AUC T2 should be set to a value greater than AUC T1, otherwise no value for AUC is generated. Multiple pairs if AUC T1 and AUC T2 may be specified. If an AUC T1 value is specified without an accompanying AUC T2 then ~AUC will be calculated up to the time of the last predicted concentration shown on the Results graph.

Hint: Use AUC occ to see the hours of doses as a guide for selection of AUC T1 and AUC T2. Both AUC occ and AUC T1 and AUC T2 observations may be used at the same time.

There are also observation types that are not time sensitive such as AUC occ. They can be associated with any date and time and have an effect across the full time sensitive dosing and observation history. This means you can add AUC occ as an observation at any date and time. The date and time will be set by default. You may change the date and time but this does not affect the behavior of AUC occ.

AUC Occ

The AUCocc observation is a signal to NextDose to generate a table of AUC values calculated after each dose. The date of this “observation” is unimportant. When present it applies to all doses shown on the Doses and Observations page. This table includes the area under the curve (~AUCocc) after each dose occasion until the time of the next dose based on the predicted individual concentration (Figure 1). The ~AUCocc following the last dose is calculated until the end of the predicted individual concentration display.

If you look at the AUCocc table (Table 1) you will see estimates of AUC after each dose (~AUCocc). These are numerical approximations to the true AUC after each dose. The “true” AUC can only be estimated (i.e. approximated) by numerical integration. The next column in the table shows AUCinf which is an exact calculation of the AUC from the dose on that occasion from 0 to infinity assuming the clearance estimated for that dose occasion (CL(T) had been constant with regular dosing long enough to reach steady state. The (occ/inf)% column is the % of the AUCinf achieved by each dose.

You may ignore the last dose (e.g. Table 1, Ndose=14) because the AUCocc includes the “tail” of concentrations predicted after the last dose so does not reflect a steady state dosing interval.

Figure 1 Predicted population and individual concentrations

Table 1 AUCocc Table

Note: The AUC estimates calculated from the predicted individual concentration time course use a simple integration method with an error of around 5%.