Covariates

Covariates are patient-specific factors that a drug’s PK model uses to individualize its predictions — for example body weight or renal function. Which covariates are relevant depends entirely on the drug’s model, so the list you see is drawn from the drug used in this episode (administrators define this catalog — see Administration → Covariate catalog).

The Covariates tab is split into three sub-tabs by type.

Analytical

Laboratory values, such as creatinine or albumin.

Analytical (lab value) covariate entries.

Anthropometric

Body measurements, such as weight or height.

Anthropometric covariate entries.

Extracorporeal devices

Devices that affect drug clearance, such as dialysis or ECMO.

Extracorporeal device covariate entries.

Each entry is time-stamped, and its date cannot be earlier than the first recorded dose.

Tip

Creatinine clearance has special handling for some models — if a drug’s model expects a computed clearance rather than a raw lab value, a calculator asks for the values it needs (weight, height and serum creatinine, depending on the equation you pick) and calculates it for you. Every value it asks for must be greater than 0.

Note

Genetic (pharmacogenetic) covariates are recorded once per patient, not per episode — see the patient’s detail page in Patients.

Possible errors

Message	What it means	What to do
Date cannot be before the first dose	The covariate’s timestamp is earlier than the episode’s first dose.	Correct the date, or confirm the first dose’s own date/time is right.
Value is required	The measurement field was left blank, is not a number, or is negative.	Enter the measured value (0 or more).
Date is required	The date and time was left empty.	Enter when the value applied.
End date must be after the start date	An extracorporeal session ends at or before its start.	Correct the end, or leave it empty if the session is still running.
Weight must be greater than 0 / Height must be greater than 0 / Creatinine must be greater than 0	One of the fields used to calculate creatinine clearance is zero, negative, or missing.	Enter a real, positive value for every field the calculator shows.
Failed to add the record / Failed to update the record / Failed to delete the record	The request reached the server but failed.	Retry; if it persists, check your network connection or contact an administrator.

Next: Estimation.

Fields, checks and limits

Analytical and anthropometric records

Field	What to enter	Unit	Required	Minimum	Maximum	Message you see if it is wrong
Covariate	Which factor you are recording. You pick it from the list on the left; the record is added to the one selected.	None	Yes	None	None	None
Value	The measured value.	The unit set for that covariate in the catalog	Yes	0 (a negative value is refused)	No upper limit set in the form	Value is required.
Date and time	When the value applied.	Date and time	Yes	Not before the first dose	No upper limit set in the form	Date is required. Date cannot be before the first dose.

If you add a record at the same minute as an existing one for the same covariate, you see a caution (“A record already exists at {date} {time}.”), but you can still save it.

Extracorporeal device records

These records cover a period, such as a dialysis session.

Field	What to enter	Unit	Required	Minimum	Maximum	Message you see if it is wrong
Start	When the session began.	Date and time	Yes	Not before the first dose	None	Date is required. Date cannot be before the first dose.
End	When the session ended. Leave empty if it is still running.	Date and time	No	After the start (the same time is refused)	None	End date must be after the start date. Date cannot be before the first dose.
Value	The device setting, if the covariate has one.	The covariate’s unit	See the form	0 (a negative value is refused)	None	Value is required.

Two sessions of the same device can touch, but they cannot overlap. If they overlap, PKPDrugs tells you which session is in the way and what end time to use. A session that is still running must be ended before you add a new one that starts during it.

Creatinine clearance calculator

Some models need creatinine clearance (CLCR). The calculator offers three equations: Cockroft-Gault (adults), Schwartz (children) and Salazar-Corcoran (overweight patients). Age is taken from the patient’s birth date. You can tick Remember this choice for this patient.

Field	What to enter	Unit	Required	Minimum	Maximum	Message you see if it is wrong
Weight	Body weight. Not asked for with Schwartz.	kg	Yes, except with Schwartz	Greater than 0	None	Weight must be greater than 0
Height	Body height. Asked for with Schwartz and Salazar-Corcoran; not asked for with Cockroft-Gault.	cm	Yes, except with Cockroft-Gault	Greater than 0	None	Height must be greater than 0
Serum creatinine	Lab value.	mg/dL	Yes	Greater than 0	None	Creatinine must be greater than 0

Pharmacogenetic covariates (on the patient page)

Field	What to enter	Unit	Required	Minimum	Maximum	Message you see if it is wrong
Covariate	Which genetic factor.	None	Yes	None	None	Please select a covariate
Value	The result.	Shown in the Units column	Yes	Greater than 0	None	Value must be a number greater than 0

These values are kept once per patient and are used in every episode of that patient.