Therapeutic drug monitoring is required for:
**Core Concept**
Therapeutic drug monitoring (TDM) is a clinical practice that involves measuring the concentration of a medication in the blood to ensure it falls within a therapeutic range, thereby maximizing efficacy while minimizing toxicity. This is particularly crucial for drugs with a narrow therapeutic index, where the difference between an effective dose and a toxic dose is small.
**Why the Correct Answer is Right**
The primary goal of TDM is to prevent adverse effects associated with drug toxicity. Drugs with a narrow therapeutic index, such as antiepileptics (e.g., phenytoin, carbamazepine), anticoagulants (e.g., warfarin), and certain antibiotics (e.g., aminoglycosides), require TDM to maintain therapeutic levels and prevent toxicity. TDM helps clinicians adjust doses and minimize the risk of adverse effects.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because TDM is not typically required for drugs with a wide therapeutic index, such as acetaminophen, where the difference between an effective dose and a toxic dose is large.
**Option B:** This option is incorrect because while monitoring of drug levels may be helpful, it is not always necessary for drugs with a relatively stable pharmacokinetic profile, such as metformin.
**Option C:** This option is incorrect because while TDM may be used in some cases for drugs with a narrow therapeutic index, it is not typically required for all patients taking these medications.
**Clinical Pearl / High-Yield Fact**
When interpreting TDM results, clinicians should be aware that peak and trough levels of a medication can provide different information, and trough levels may be more relevant for predicting toxicity.
**Correct Answer:** D.