Peak serum levels are recommended when monitoring patients because the level in the blood drops so rapidly that many negative results are found at the trough. the peak occurs at 40 to 90 minutes post dose.

Preferred specimen: 1mL serum collected in a red-top tube (no gel–alternate specimen plasma). Promptly centrifuge and separate serum or plasma into a plastic screw-cap vial.

**PLEASE INDICATE SERUM OR PLASMA ON SCREW CAPPED TRANSPORT TUBE**