Question

For which of the following medications should a client undergo therapeutic drug monitoring? a. Penicillin (antibiotic) b. Propranolol (beta-blocker) c. Furosemide (diuretic) d. Digoxin (cardiac glycoside)

Short answer

Digoxin (cardiac glycoside) is the medication for which a client should undergo therapeutic drug monitoring.

Step-by-step solution

Understand Therapeutic Drug Monitoring

Therapeutic Drug Monitoring (TDM) is the practice of measuring a specific drug at timed intervals in order to maintain a relatively constant concentration of the medication in the bloodstream, thus optimizing its efficacy while minimizing toxicity. This is necessary for drugs that have a narrow therapeutic index, meaning the range of dosages that are effective without being toxic is very small.

Identify the Drugs' Therapeutic Indices

Research the therapeutic index of each listed drug. A drug with a narrow therapeutic index will likely require TDM to ensure safe and effective dosing.

Determine Which Drug Requires TDM

Among the options, digoxin is a medication with a narrow therapeutic index. It has a very small window between effective therapeutic levels and toxic levels, and because of this, it requires careful monitoring to avoid serious side effects.

Key concepts

Therapeutic Index

The therapeutic index (TI) is a critical concept in pharmacology that refers to the ratio between the toxic dose and the effective dose of a drug. In essence, it gauges the safety margin of a medication.

Drugs with a wide therapeutic index have a substantial safety buffer between the dose that produces therapeutic effects and the dose that could cause toxicity. This means patients have a lower risk of side effects as the range of safe dosage is broad. For example, penicillin has a wide therapeutic index.

On the other hand, drugs with a narrow therapeutic index have a very tight range between efficacious and harmful doses. For these medications, even small variances in dosage or blood levels can result in undermedication or, conversely, toxic effects. Therefore, such drugs require careful monitoring to ensure they stay within the therapeutic range. Digoxin, used to treat certain heart conditions, is a classic example with a narrow therapeutic index; hence, it requires diligent therapeutic drug monitoring (TDM).

Drug Efficacy

Drug efficacy refers to the ability of a drug to produce the desired therapeutic effect. It is a measure of the maximum effect a drug can achieve at its optimal dosage. Efficacy is influenced by various factors including the drug's mechanism of action, its affinity for binding to its target, and the individual patient's characteristics, like age, sex, and genetic makeup.

High efficacy is a desirable trait in a medication as it means the drug can achieve its intended effect at a potentially lower dose, which in turn could reduce the risk of side effects. Yet, this does not always correlate with a wide therapeutic index. High efficacy drugs with a narrow therapeutic index are challenging as the optimal dose is crucial, making TDM incredibly important to tailor the drug dose for each patient's needs. In clinical practice, ensuring appropriate drug efficacy while avoiding adverse effects often involves ongoing dosage adjustments and monitoring, especially for those taking medications like propranolol or digoxin.

Drug Toxicity

The term drug toxicity describes the harmful effects that can occur when a person has accumulated too high a level of a drug in their bloodstream, generally due to overdosing or because the drug's clearance from the body is impaired. Signs of toxicity can range from mild side effects to severe organ damage and can be life-threatening.

TDM helps to prevent toxicity by tracking the plasma levels of drugs, particularly those with narrow therapeutic indices. This allows healthcare providers to adjust dosages promptly before a patient reaches toxic levels. Monitoring is also crucial for drugs like furosemide, where the balance of electrolytes can be disturbed and lead to its own kind of toxicity even if the drug's main effect is still within therapeutic levels. The aim is to optimize therapeutic effects while minimizing the risks, achieving a balance of safety and efficacy in medication management.