Patient-Focused Medication Considerations: Pediatrics and Older Adults

1. Body Surface Area (BSA) Calculation

BSA-based formulas are considered the most accurate and are typically reserved for high-risk medications, such as chemotherapy. To use this method, clinicians often utilize a BSA nomogram, such as the West nomogram, which uses a child's height and weight to estimate surface area.

The formula for estimating a child's dose using BSA is: $\begin{aligned} \frac{\text{BSA of child}}{\text{BSA of adult}} \times \text{Adult dose} = \text{Estimated child's dose} \end{aligned}$ $\begin{aligned} \frac{\text{BSA of child (m}^2)}{\text{Manufacturer's recommended dose}} = \frac{\text{Estimated child's dose}}{\text{Adult dose}} \end{aligned}$

2. Weight-Based Dosage

The most common method in clinical practice is the weight-based approach, where doses are prescribed in milligrams per kilogram (mg/kg).

Exam Tip: Pediatric Safety When calculating weight-based doses, always ensure the patient's weight is converted to kilograms (kg) first ($1 \text{ kg} = 2.2 \text{ lbs}$). Confusing pounds with kilograms is a common source of medication error and potential toxicity.

Worked Example: A child weighs $12 \text{ kg}$. The prescribed dose of acetaminophen is $15 \text{ mg/kg}$. $\begin{aligned} 12 \text{ kg} \times 15 \text{ mg/kg} = 180 \text{ mg} \end{aligned}$ The child should receive $180 \text{ mg}$.

Older-Adult Medication Management

Older adults (defined as age 65 or older) face different risks, primarily stemming from the physiological decline of organ systems.

Physiological Changes and Pharmacokinetics

Aging causes a gradual decline in the function of the cardiovascular, gastrointestinal, hepatic, and renal systems.

• Absorption: Reduced gastric acid production and decreased gastrointestinal blood flow (which can drop by 40-50% by age 65) can impair drug absorption.
• Distribution: Older adults typically have increased body fat and decreased lean muscle mass. This can lead to the accumulation of fat-soluble (lipophilic) drugs, such as sedatives, resulting in prolonged effects. Furthermore, reduced protein (albumin) levels mean fewer protein-binding sites, increasing the amount of active, unbound drug in the system.
• Metabolism: Decreased liver mass and reduced blood flow to the liver (decreasing by about 1.5% per year after age 25) slow down drug metabolism.
• Excretion: A decline in the number of intact nephrons and a reduction in the glomerular filtration rate (GFR) by 40-50% can lead to delayed drug excretion and toxicity.

Polypharmacy and the Prescribing Cascade

Older adults often manage multiple chronic conditions, leading to polypharmacy—the use of many different drugs concurrently. As the number of medications increases, so does the risk of drug interactions. For a patient taking 10 or more medications, the risk of a drug interaction is estimated to be 100%.

This often leads to a prescribing cascade, where a new medication is prescribed specifically to treat the side effects of an existing drug, rather than treating a new medical condition.

Clinical Rule of Thumb: "Start Low and Go Slow" To minimize the risk of adverse effects in older adults, clinicians should start with the lowest possible dose and increase it slowly based on the patient's response.

Safety Tools and Nonadherence

To manage these risks, clinicians use tools like the Beers Criteria, which identifies medications that may be inappropriately prescribed or cause adverse reactions in older adults.

Additionally, medication nonadherence is a significant concern in this population. Factors contributing to nonadherence include declining cognition, reduced manual dexterity (making pill-splitting difficult), financial constraints, and complex dosing regimens.

Summary Table: Comparative Pharmacokinetics