medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...

and pharmacology, a trough level or trough concentration (C_trough) is the

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...

reached by a drug immediately before the next dose is administered,AGAH
working group Pharmacokinetics, 2004. often used in

therapeutic drug monitoring Therapeutic drug monitoring (TDM) is a branch of clinical chemistry and clinical pharmacology that specializes in the measurement of medication levels in blood. Its main focus is on drugs with a narrow therapeutic range, i.e. drugs that can easily ...

. The name comes from the idea that on a graph of concentration versus time, the line forms a U-shaped trough at the lowest region, before a new dose sends it higher again. The usual criterion is concentration in the blood serum, although in some instances local concentration within tissues is relevant. It is pharmacokinetically normal that over time, the drug

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

s are being

metabolized Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

or cleared by the body, so the concentration of drug that remains available is dropping. In a medicine that is administered periodically, the trough level should be measured just before the administration of the next dose in order to avoid overdosing.Archived version 2009-11-22
/ref> A trough level is contrasted with a "peak level" ( C_max), which is the highest level of the medicine in the body, and the "average level", which is the mean level over time. It is widely used in clinical trials for newer medicines to investigate therapeutic effectiveness and safety. C_trough is slightly different from C_min, the minimum concentration during the time interval between administration of two doses.

References

Pharmacokinetics {{pharma-stub