The nurse is to administer vancomycin to the client diagnosed with sepsis. The client is to have a peak and trough level completed on this dose of vancomycin. Which action should the nurse initiate first?

A: A trough level must be drawn before vancomycin (Vancocin) is administered. This is the first action because if the trough level has not been drawn, it will delay the vancomycin dose and could result in a medication error. B: Checking medication compatibilities is important, but this can be completed while the laboratory is obtaining the trough level. C: Checking C&S report results is important, but this can be completed while the laboratory is obtaining the trough level. D: Calculating the administration rate is important, but this can be completed while the laboratory is obtaining the trough level.