Peak and Trough Levels

Shagce1 · Nov 13, 2014

Some drugs have a narrow therapeutic index. That means that too much of it could easily cause toxicity. Peak and trough blood levels need to be drawn to make sure levels in the blood are at an adequate range to not cause toxicity. Trough (or the low amount) is drawn prior (? 30 min or so, depends on facility policy) to administering the drug. A peak (or the high amount) is drawn approx 30 min (again according to facility policy) after administering drug. This way subsequent dosages can be adjusted accordingly to prevent toxicity. Someone correct me if I have not explained it well!

akulahawkRN, ADN, RN, EMT-P · Nov 13, 2014

I suppose that one way you could think about peak and trough is to use a rocket plane analogy. The rocket engine is the drug you infuse and the altitude it flies (or falls to) is the drug level. At first the rocket plane is just sitting on the pad, ready for flight. Then it takes off and it's engine burns for quite a while and the engine cuts off. The rocket plane continues to soar skyward but eventually it's altitude peaks and it begins to fall. (That's your loading dose.) After a certain amount of time, the rocket plane has fallen pretty far but hasn't hit the ground. The flight engineers want to keep the rocket plane above a certain minimum altitude (that's your trough), they figure how long to burn the engine again to increase the altitude up to a certain point (but not too high) and then determine about when the next burn should be. At first they're working from theoretical numbers because they need to wait for the rocket plane to settle down into a steady state. Then at some per-determined point, they measure the actual minimum altitude and compare that with what they calculated it should be. (That's your measured trough level) and then they adjust the next engine burn accordingly and they'll re-check periodically to ensure that the minimum altitude is still OK at the specified time. When they figure there has been enough flight time, they just allow the rocket plane to land...

ChooSoul · Nov 13, 2014

is there a set amount of time required to take labs for peak and trough levels?

like for antibiotics? when to take labs for these?

akulahawkRN, ADN, RN, EMT-P · Nov 13, 2014

The amount of time between draws depends upon the drug. Different rocket planes of different designs with different engines require different calculations specific to each rocket plane. This is because different drugs clear from the body at different rates.

mrsboots87 · Nov 14, 2014

Another way to think of it like this. You would draw a peak level lab when the drug should peak in the patient's system. This amount of time will vary depending on the drug. Could be 30 minutes, could be a couple hours. The peak is not when the drug takes affect, it is when the drug has reached its maximum effect and is at its highest concentration in the blood. A lab will be drawn at that time to see if the amount of drug in the body at its peak was high enough to be within therapeutic range for the drug and to ensure it didn't reach a toxic level. The trough is usually measuring a baseline. It would be measuring how much drug is in the system at the time the next dose is due. This will be when the drug is least effective. So this lab will be drawn right before administering the next dose of the drug. When that is will also vary by drug. The hope is that the trough level is still within therapeutic range. With the results, the dr will know if the dose is good, or if the dose needs to be decreased/increased, or if how many doses a day needs to be increased/decreased. Because if the peak is very high, but the trough is below therapeutic, we dont want to give them a higher dose or it could be toxic, we just want to give them the drug more often to keep it therapeutic. If the peak is below therapeutic or just barely above and the trough is low, then we would probably want to increase the dose per administration. PEak and trough usually only matters with drugs that have a very small therapeutic window, or when the patient has a potential or actual sensitivity to a drug.

mrsboots87 · Nov 14, 2014

is there a set amount of time required to take labs for peak and trough levels?
like for antibiotics? when to take labs for these?

When you look in your drug book, there will be a peak time listed for each drug. That is the timeframe in which you want to draw the lab for peak. So if the drug book says that a drug takes effect in 10-15 minutes, and it peaks at 4-6 hours, you want to have the peak lab drawn in that 4-6 hour window. Trough will be drawn before your next dose as determined by the physician.

KelRN215, BSN, RN · Nov 15, 2014

is there a set amount of time required to take labs for peak and trough levels?
like for antibiotics? when to take labs for these?

Trough is drawn just prior to the next dose (within 30 min or so), peak is drawn when the drug peaks in the patient's system. It varies by drug. Some might peak almost immediately and others several hours later.

SierraBravo · Nov 17, 2014

Actually, the peak and trough levels aren't drawn according to the time of the drug peak according to a drug reference. To completely understand this concept, you need to have a working knowledge of advanced pharmacology, pharmacokinetics, and pharmacodynamics (which is clearly outside the scope of this discussion). One of the main purposes of doing PK on certain drugs is to ensure that a steady state serum level is obtained and maintained and, as someone else said, to avoid toxicity.

IVRUS, BSN, RN · Nov 19, 2014

In actuality,

Peak levels are drawn 30-60 minutes post Aminoglycoside administration and with the Antibacterial Vancomycin, Peaks are drawn 1-1.5 hours post infusion completion. Always follow your institutional policies regarding therapeutic drug monitoring. And remember, Peaks are 'normally' not drawn for Vanc any more.

Here.I.Stand, BSN, RN · Nov 19, 2014

To completely understand this concept, you need to have a working knowledge of advanced pharmacology, pharmacokinetics, and pharmacodynamics (which is clearly outside the scope of this discussion).

Which is why these labs are usually timed by the pharmacist :yes:

SierraBravo · Nov 19, 2014

Which is why these labs are usually timed by the pharmacist

Exactly! I have completed graduate work in cellular and molecular physiology and pharmacology so I fundamentally understand the theory and application, but obviously not at the level of a Pharm.D. :)