Table 2.

Urinary sampling methods in pharmacokinetic (PK) studies

Methods	Pros and cons
Midstream urine sample	Feasible for older children who can follow instructions. Not suitable for young children.
Urinary catheter sampling	This method is generally limited to children with indwelling urinary catheters (IDC) for clinical care, since IDC insertion purely for research is unacceptable in most jurisdictions.
Urinary adhesive bags	These bags may seem more practical (than awkward time collection periods), but this method is notoriously unreliable. The adhesive often comes loose and urine leaks in the diaper. Repeated urine bag adhesion may damage the vulnerable skin in young infants.
Gauze-diaper methods	Urine can be collected in cotton balls or gauzes separated from the diaper interior by a plastic film. By weighing the diaper at each time interval, the total urine volume can be deduced and urine for PK analyses can be expressed from the cotton. Care must be taken to ensure that the drug is fully recovered from the urine. Also, frequent diaper changes may not be allowed in very young infants, where minimal handling and procedures are standard of care.