Allowing Tmax in half-life

[billdenney]

I noticed several issues mentioning that Tmax should never be allowed in the half life, such as #220.

In most cases, this is the desired choice. But sometimes, mainly for IV bolus administration, you may want to allow it. The reason could be that in the case of IV bolus with either no distribution to tissues or where the distribution to tissues is the sole observed mechanism of central clearance (i.e. it looks like a theoretical one-compartment system), it is valid to allow Tmax in the half-life calculation.

It seems like you probably do allow it sometimes, and I wanted to make sure that you knew the rationale for including it.

[Gero1999]

This is actually a very good point . Disallowing TMAX will be risky for IV bolus studies if there are not enough points... We might need to open an issue and re-allow it, and perhaps make our own warning for profiles where TMAX is used for HL in non-IV bolus studies.

Actually on this direction there could be some nice ideas also for PKNCA. Perhaps would make sense either that:

• allow.tmax = FALSE do not affect IV bolus studies (when TMAX = 0). In the end, no one wants this to happen
• create a exclude function for profiles where TMAX != 0 & HL.start = TMAX

[js3110]

@billdenney good point , thanks! I would like to add that in #220 its not worded great, but the idea is that it is never calculated using tmax by default, not that its completely impossible. The user can still add a manual selection to include tmax.

In order to figure out the best solution, my question would be whether ALL IV bolus studies will want to include TMax, or just specific ones where there is not much data? because that will influence whether we make it a default or if we leave it as a manual option.