Concentrations

The Concentrations Observed tab records the patient’s measured drug levels — the samples PKPDrugs uses, together with the recorded doses, to estimate that patient’s individual PK parameters.

Caution

This tab stays disabled until the episode has at least one recorded dose.

Recorded concentration samples for an episode.

Adding a concentration

Add a row directly in the table with:

Field	Notes
Sample date and time	Must not be earlier than the first recorded dose.
Concentration type	Trough, Peak, or Other (Trough is pre-selected).
Observed concentration	The measured concentration, in the drug’s metric (e.g. mg/L). Zero is accepted; a negative value is not.

Adding a concentration sample.

Entries can be edited or deleted afterward, as long as the episode is still active.

Possible errors

Message	What it means	What to do
Date cannot be before the first dose	The concentration’s timestamp is earlier than the episode’s first dose.	A concentration can’t have been measured before the drug was administered — correct the date/time, or check you’re editing the right dose if the first dose’s timing was wrong.
Concentration must be a positive number	The measured value is negative, empty, or not a number.	Enter a value of 0 or more in the drug’s metric (e.g. mg/L).
Date is required	The sample date and time was left empty.	Enter when the sample was taken.
Failed to add concentration / Failed to update concentration / Failed to delete concentration / Failed to ignore the concentration / Failed to use the concentration again	The request reached the server but failed.	Retry; if it persists, check your network connection or contact an administrator.

Next: Covariates.

Fields, checks and limits

Add or edit a concentration

Field	What to enter	Unit	Required	Minimum	Maximum	Message you see if it is wrong
Sample date and time	Day and time the sample was taken. One field.	Date and time	Yes	Not before the first recorded dose	No upper limit set in the form	Date is required. Date cannot be before the first dose.
Concentration type	Trough, Peak or Other. Trough is pre-selected.	None	Yes	None	None	None (a type is always selected)
Observed concentration	The level the laboratory reported.	The drug’s concentration unit (shown on the episode)	Yes	0 (a negative value is refused)	1,000,000 (the database refuses a larger value; the form sets no limit)	Concentration must be a positive number.

A sample cannot be older than the first dose, because the drug was not in the body before that.

Ignore a sample

Use Ignore on a row to leave one sample out of the estimate without deleting it. The row shows an Ignored badge. Use Use again to put it back. The change appears in the activity feed.

The episode must always keep one sample that the estimate can use. If you try to ignore or delete the last usable sample, you see: “The episode must keep one concentration the estimation can use”.