4.3 Scheduling Peak and Trough levels: A systematic approach

What are peak and trough levels used to maintain?

Plasma drug levels within a narrow therpeutic range

What are common drugs associated with weak trough levels?

Amino glycoside antibiotics and vancomycin

What is the lowest plasma concentration associated with an administered dose usually drawn 30-50 minutes before the scheduled dose?

Trough level

Why are trough levels drawn before the scheduled dose?

So the results are available before giving the next dose

What is the highest plasma concentration attained from a dose, drawn soon after the completion of a dose?

Peak level

If the order is: Gentamicin 375 mg IV q 8 h with P/T levels on the 5th dose and the first dose was hang at 2100 on Tuesday what time and on what day is the fifth dose due?

0500 on Thursday

Where would information about when the first dose was given be?

On the MAR

Why do we need to know the infusion time?

Because trough is before and peak is after so we need to know how long it runs for

Infusion times are

Unique for each drug and are not ordered by the physician (can vary from 30 minutes up to 2 hours or more)

Where can you find the infusion times?

Available via pharmacy instructions, drug guides or package inserts

In this example if the infusion time is 1 hour, when would you schedule the Trough labs or if the hospital dictates that you do it 30 minutes before?

0430 on thursday

When would you schedule the peak lab if it has to be 30 minutes after?

Dose will finish at 0600, so lab scheduled for 0630