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What Are Trough Levels?

A clinic visit may result in your doctor asking you to have your trough level checked. You may wonder why your doctor is asking you to have your blood checked for that. Going for that test and letting your doctor know your trough level can spell the difference between getting over- or under-medicated.

  1. Trough Level

    • When doctors and pharmacists say "trough level," it simply means the lowest amount of a drug present in the bloodstream that still exerts a therapeutic effect. Knowing the trough level of a drug allows your physician to determine how much of the drug is being eliminated from your bloodstream in a given time.

    Peak Level

    • The peak level, on the other hand, is the opposite of the trough level. A peak level is the highest concentration of a drug in the bloodstream that is capable of exerting a therapeutic event. Physicians take note of the peak level to determine how much of the drug is being absorbed by the body. Drugs given intravenously usually reach peak level the fastest, while drugs taken orally are the slowest.

    Importance of Monitoring Levels

    • When a doctor obtains information about the peak and trough levels of a drug in a patient's bloodstream, she is able to make appropriate decisions regarding administration of the next dose. Knowing the trough level, for example, allows a physician to determine whether the initial dosage given is enough to achieve the desired therapeutic effect. By making dosing adjustments based on the peak and trough levels, physicians and pharmacists can develop a dosing plan that will help a patient achieve a steady drug concentration within the bloodstream throughout the period of medication.

      This is especially important when patients are medicated for an extended period of time with such drugs as antibiotics, chemotherapy, methadone for opioid withdrawal and rehabilitation, digoxin therapy for heart failure, and steroid regimens for people with autoimmune disease.

    Narrow Therapeutic Index Drugs

    • A narrow therapeutic index drugs has a small difference between therapeutic and toxic levels. Some of these drugs are antibiotics, such as aminoglycosides and rifampicin; anti-epileptic medication, such as carbamazepine; mood-stabilizing drugs, such as lithium; and blood-thinning medication, such as warfarin. People under treatment with NTI drugs have to be carefully monitored by physicians and such monitoring would include periodic checks for trough levels to ensure that drug concentrations do not fluctuate toward toxic levels.

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