Lesson 4.4: Prescribing in Special Populations

Introduction

In clinical practice, healthcare providers frequently encounter patients who are part of special populations, including pregnant individuals, children, older adults, and those with renal or hepatic impairments. Prescribing medications for these groups requires an understanding of the unique physiological changes and risks involved. This lesson aims to equip students with the knowledge necessary to adjust prescribing practices for these populations, ensuring safe and effective management of medications.

Learning Objectives

• Understand dosing and safety considerations in pregnancy and lactation, pediatrics, older adults, and patients with renal or hepatic impairment.
• Learn about polypharmacy reduction and the principles of deprescribing in complex patients.
• Adjust prescribing based on special population needs and organ impairments.
• Apply deprescribing principles to minimize polypharmacy risks.
• Explain key concepts and terminology related to prescribing in special populations.

Special Populations and Dosing Considerations

1. Prescribing in Pregnancy and Lactation

Physiological Changes in Pregnancy

During pregnancy, considerable physiological changes may affect drug pharmacokinetics, such as altered absorption, distribution, metabolism, and excretion (ADME). For example:

• Absorption: Increased gastric pH and delayed gastric emptying may alter the absorption of medications.
• Distribution: Increased blood volume and body fat can change the volume of distribution for lipophilic and hydrophilic drugs.
• Metabolism: Hormonal changes may affect liver enzyme activity, altering drug metabolism.
• Excretion: Increased renal blood flow can enhance clearance of renally-excreted medications.

Safety in Prescribing

When prescribing during pregnancy, it is essential to consider the FDA's pregnancy categories. For example:

• Category A: Controlled studies show no risk in the first trimester.
• Category B: No evidence of risk in humans.
• Category C: Risk cannot be ruled out; use only if the benefits outweigh potential risks.

Example:

Consider prescribing an analgesic for a pregnant patient. Acetaminophen is classified as Category B, making it a safer choice compared to NSAIDs, which may carry risks especially in the third trimester due to the potential for premature closure of the ductus arteriosus.

2. Pediatric Considerations

Developmental Pharmacokinetics

In pediatrics, pharmacokinetics can vary significantly based on age. Infants and children metabolize drugs differently compared to adults, necessitating careful dosing adjustments.

• Neonates: Reduced renal and liver function; medications may require lower doses or adjustments in frequency.
• Children: Often require weight-based dosing, usually calculated as mg/kg.

Common Dosing Calculations

A common way to determine pediatric doses is through the following formula:

$$\text{Dose (mg)} = \frac{\text{Child's weight (kg)}}{70 \text{ kg}} \times \text{Adult dose (mg)}$$

Example:

If the adult dose of a medication is 500 mg and the child weighs 14 kg:

$$\text{Dose} = \frac{14}{70} \times 500 = 100 \text{ mg}$$

3. Older Adults

Pharmacokinetic Changes

Older adults often present pharmacokinetic changes that affect drug efficacy and safety. Changes in body composition, reduced renal and hepatic function, and polypharmacy are all critical considerations.

• Increased susceptibility to effects: Due to age-related physiological changes, older adults may be more sensitive to certain medications.

4. Renal and Hepatic Impairment

Dosing in Renal Impairment

For drugs eliminated primarily through the kidneys, it is vital to assess renal function, usually using the creatinine clearance formula:

$$\text{CrCl} = \frac{(140 - \text{age}) \times \text{weight (kg)} \times (0.85 \text{ if female})}{72 \times \text{serum creatinine (mg/dL)}}$$

Adjustments based on CrCl are essential, especially for medications with narrow therapeutic indices, such as digoxin or aminoglycosides.

Dosing in Hepatic Impairment

For hepatic impairment, consider using the Child-Pugh score to assess liver function and adjust dosing based on the classification (A, B, or C).

Polypharmacy and Deprescribing

Understanding Polypharmacy

Polypharmacy refers to the concurrent use of multiple medications, which can increase the risk of adverse drug events (ADEs). As patients age or accumulate comorbidities, they are more likely to experience polypharmacy.

Principles of Deprescribing

Deprescribing involves systematically stopping medications that may no longer be of benefit or may pose risks. Consider the following strategies:

1. Review all medications: Regularly assess the necessity of each medication.
2. Identify candidates for deprescribing: Look for medications that have limited benefit for the patient’s current state.
3. Create a tapering plan: For medications that require gradual withdrawal.

Example:

An older adult on multiple antihypertensives may only need one agent if they are well-controlled. A review might reveal that stopping the diuretic decreases risk for falls and dehydration without losing blood pressure control.

Conclusion

Prescribing in special populations necessitates a comprehensive understanding of the physiological changes and challenges that impact medication safety and effectiveness. By incorporating knowledge of pharmacokinetics, renal and hepatic function, and applying deprescribing principles, students can improve medication management and outcomes in these vulnerable groups.

Study Notes

• Understand pharmacokinetics and pharmacodynamics in special populations.
• Review the FDA pregnancy categories and their significance in prescribing.
• Calculate pediatric doses based on weight.
• Monitor renal and hepatic function when prescribing medications.
• Recognize the implications of polypharmacy and the principles of deprescribing.