**Question:** Therapeutic drug monitoring is advised in all except

A. Drugs with a narrow therapeutic index and high risk of toxicity
B. Drugs with a wide therapeutic index and low risk of toxicity
C. Drugs with a narrow therapeutic index and low risk of toxicity
D. Drugs with a wide therapeutic index and high risk of toxicity

**Correct Answer:** C. Drugs with a wide therapeutic index and low risk of toxicity

**Core Concept:** Therapeutic drug monitoring (TDM) is the process of measuring a patient's plasma concentration of a drug to ensure that it remains within the therapeutic range. This is essential for drugs with a narrow therapeutic index (NTI) and high risk of toxicity or drugs with a wide therapeutic index (WTI) and low risk of toxicity.

**Why the Correct Answer is Right:** Drugs with a narrow therapeutic index (NTI) have a small range of plasma concentrations that provide the desired therapeutic effect, while simultaneously avoiding adverse reactions. In such cases, TDM helps to ensure that the drug concentration remains within the therapeutic range, preventing toxicity and optimizing treatment outcomes.

**Why Each Wrong Option is Incorrect:**

A. Drugs with a wide therapeutic index (WTI) and high risk of toxicity: These drugs have a broad range of plasma concentrations that can produce the desired therapeutic effect without causing adverse reactions. While TDM can be useful in monitoring such drugs, it is less critical compared to drugs with NTI, as the risk of toxicity is relatively low.

B. Drugs with a wide therapeutic index (WTI) and low risk of toxicity: As mentioned above, TDM is still less critical for drugs with WTI and low toxicity risk. In this scenario, the risk of toxicity is low, and the therapeutic range is already wide, reducing the need for precise concentration measurements.

C. Drugs with a wide therapeutic index (WTI) and low risk of toxicity: Similar to option B, drugs with WTI and low toxicity risk do not require frequent monitoring or precise concentration measurements, as the therapeutic range is already wide, reducing the need for precise concentration measurements.

D. Drugs with a narrow therapeutic index (NTI) and low risk of toxicity: TDM is less critical for drugs with NTI and low toxicity risk. While TDM can help ensure optimal treatment outcomes, the risk of toxicity is already low due to the drug's narrow therapeutic range.

**Clinical Pearl:** TDM is crucial for NTI drugs and high-risk cases, such as pediatrics, renal or hepatic impairment, and drug interactions. In these situations, TDM can help optimize drug exposure, minimize toxicity, and improve treatment efficacy. It is less essential for drugs with a wide therapeutic index (WTI) and low risk of toxicity.