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The therapeutic index (TI; also referred to as therapeutic ratio) is a quantitative measurement of the relative safety of a drug with regard to risk of overdose.It is a comparison of the amount of a therapeutic agent that causes toxicity to the amount that causes the therapeutic effect. [1]
Another use is in the therapeutic drug monitoring of drugs with a narrow therapeutic index. For example, gentamicin is an antibiotic that can be nephrotoxic (kidney damaging) and ototoxic (hearing damaging); measurement of gentamicin through concentrations in a patient's plasma and calculation of the AUC is used to guide the dosage of this drug ...
The therapeutic index (TI) is used to quantify the risks and benefits of a certain drug. It describes the relationship between toxic dose and minimum effective dose, thus providing an important insight into the safety of a drug. [35] The Therapeutic Index is calculated using the following equation:
Tricyclics have a narrow therapeutic index, i.e., the therapeutic dose is close to the toxic dose. [7] Factors that increase the risk of toxicity include advancing age, cardiac status, and concomitant use of other drugs. [8] However, serum drug levels are not useful for evaluating risk of arrhythmia or seizure in tricyclic overdose. [9]
Population pharmacokinetics seeks to identify the measurable pathophysiologic factors and explain sources of variability that cause changes in the dose-concentration relationship and the extent of these changes so that, if such changes are associated with clinically relevant and significant shifts in exposures that impact the therapeutic index ...
The protective index is similar to the therapeutic index, but concerns toxicity (TD 50) rather than lethality (LD 50); thus, the protective index is a smaller ratio. Toxicity can take many forms, as drugs typically have multiple side effects of varying severity, so a specific criterion of toxicity must be specified for the protective index to ...
When a drug has a narrow therapeutic index, titration is especially important, because the range between the dose at which a drug is effective and the dose at which side effects occur is small. [2] Some examples of the types of drugs commonly requiring titration include insulin, anticonvulsants, blood thinners, anti-depressants, and sedatives.
This relationship, termed the therapeutic index, is defined as the ratio TD 50:ED 50. In general, the narrower this margin, the more likely it is that the drug will produce unwanted effects. The therapeutic index emphasizes the importance of the margin of safety, as distinct from the potency, in determining the usefulness of a drug.