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Peaks and Troughs

What Are They, and More

Author: Corinne Tarantino, MPH

Editors: Alyssa Haag, Emily Miao, PharmD

Illustrator: Jillian Dunbar

Copyeditor: Joy Mapes


What are peaks and troughs?

Peaks and troughs are the highest and lowest concentrations of a medication in an individual’s body. They are used to determine dosing intervals, or how much time should pass between each new administration of the drug. Peak and trough levels are particularly useful for therapeutic drug monitoring, which is the process of measuring drug concentrations at intervals to ensure a consistent concentration of a medication remains in an individual. Therapeutic drug monitoring can also be used to maintain a steady, medicated state in an individual.  Therapeutic drug monitoring is important for medications with a narrow therapeutic index (i.e., are effective and nontoxic only in a small range of concentration levels), high variability, or adverse effects. Drugs commonly monitored include anti-seizure and psychotic medications (e.g., phenytoin, lithium), antibiotics (e.g., vancomycin, aminoglycosides), and immunosuppressants (e.g., tacrolimus, cyclosporine).

What do peak and trough levels indicate?

Peak and trough levels indicate drug levels in an individual’s body. A peak is the highest level of a medication in the blood, while a trough level indicates the lowest concentration. Troughs of medication concentration occur after the drug has been broken down and metabolized by the body.

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When do you take peak and trough levels?

The time to take peak levels depends on the route of administration. The peak level is taken about 15 to 30 minutes after intravenous injections or infusions, 30 minutes to 1 hour after intramuscular injections, and about 1 hour after a drug is taken orally. Peak levels are delayed in order to allow the medication to distribute throughout the body. In contrast, the trough level is measured immediately before the next administration of the medication. For therapeutic drug monitoring, peak and trough levels are often taken after the second or third dose.

What are the most important facts to know about peaks and troughs?

Peaks and troughs are the highest and lowest concentrations, respectively, of a medication in an individual’s body. They are used to determine dosing intervals, especially during therapeutic drug monitoring. The time the peak level is taken depends on the medication’s route of administration, while the trough level is taken just before the next dose is given.

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Related links

Drug administration and dosing regimens
Pharmacokinetics: Drug elimination and clearance
Pharmacokinetics: Drug metabolism

Resources for research and reference

Kang, J.-S., & Lee, M.-H. (2009). Overview of therapeutic drug monitoring. The Korean Journal of Internal Medicine, 24(1): 1-10. DOI: 10.3904/kjim.2009.24.1.1

Lipicky, R. J. (1994). Trough: peak ratio: the rationale behind the United States Food and Drug Administration recommendations. Journal of Hypertension. Supplement: Official Journal of the International Society of Hypertension, 12(8): S17-S19.

Thummel, K. E., Shen, D. D., & Isoherranen, N. (2017). Design and optimization of dosage regimens: Pharmacokinetic data. In L. Brunton, R. Hilal-Dandan, & B. Knollmann (Eds.), Goodman & Gilman's: The pharmacological basis of therapeutics (13th ed.). McGraw-Hill Education.