Therapeutic level can mean either of two concepts, both referring to the amount of pharmaceutical compound in the bloodstream of a patient. In scientific studies, therapeutic level, also known as the therapeutic ratio, refers to the difference between the amount of compound needed to produce a beneficial effect and how much will kill a patient. During routine medical treatment, therapeutic level refers to monitoring the amount of medication in a patient's bloodstream. The purpose of such testing is to ensure a pharmaceutical compound is present in the blood and that it is at a high enough concentration to offer effective treatment without causing harm.
Context is the most important clue in determining which definition applies, although professionals often use slightly different terminology to further prevent confusion. Typically, scientific studies refer to therapeutic level as the therapeutic ratio or the therapeutic index. Testing facilities and medical professionals typically refer to laboratory testing of therapeutic levels as therapeutic drug monitoring or therapeutic drug level. Specifically, therapeutic drug monitoring refers to the actual blood tests, while therapeutic drug level refers to the test results.
Although the two concepts differ slightly, both relate to the effective level of medication in the bloodstream of a patient. One merely focuses on the most extreme negative result, while the other focuses on avoiding harm to the patient during treatment. Scientists must first determine the therapeutic ratio so that doctors and testing facilities have the information necessary to determine initial dosing.
Ideally, doctors begin with a small initial dose of a compound, gradually increasing the dose until it becomes effective. Monitoring helps physicians to measure when the proper dosage is reach for a particular patient without reaching harmful levels. For example, medications used in the treatment of mental health disorders can be ineffective at low levels, but toxic at high levels. Finding the therapeutic level, or level at which the medication is effective without being toxic, requires monitoring of the concentrations in a patient's bloodstream.
Whether used in scientific research studies or routine patient care, therapeutic level is tested the same way. A small amount of blood is drawn and analyzed. Depending on the specific test and compound being tested, the exact amount of medication or other compound concentrated in the blood is measured first. Additional tests to check various organ functions may also be performed to compare against medication levels. Medications known to affect liver function, for example, may require a liver function test in additional to medication level tests.
Numerous factors can influence the correct therapeutic levels needed for various medications and compounds. Body size, ailment severity, and other medical conditions can change the recommended therapeutic level of a particular compound. Likewise, when used in scientific studies, the level of compound that produces death can also vary, depending on size and other factors. As such, recommended therapeutic levels are often represented as a range, such as 50-100 micrograms per milliliter or greater than .01 micromoles.