Therapeutic Drug Monitoring, Age-Related Changes, Hyperkalem

Therapeutic drug monitoring, age-related changes, hyperkalemia risks, and medication adherence in older adults

Therapeutic drug monitoring (TDM) is a vital practice in healthcare aimed at optimizing drug efficacy and minimizing toxicity by measuring specific drug levels in a patient’s bloodstream. In older adults, physiological changes associated with aging significantly influence pharmacokinetics—including drug absorption, distribution, metabolism, and excretion—necessitating careful management of medication therapy. Understanding these changes is essential for clinicians to tailor interventions appropriately and ensure safe, effective treatment.

Age-related modifications in drug absorption involve physiological alterations such as reduced gastric acid secretion, slower gastric emptying, and decreased splanchnic blood flow. These factors can delay the onset of action and potentially influence the bioavailability of certain medications; however, the overall impact on drug absorption tends to be modest for many drugs (Anderson, 2017). Nonetheless, alterations in the gastrointestinal environment may affect drugs that require an acidic environment for optimal absorption, such as calcium carbonate or certain antifungal agents. The reduction in gastrointestinal motility and blood flow can also influence drug dissolution and contact time with absorption sites.

Metabolism in older adults is profoundly affected by age-associated declines in liver size and hepatic blood flow—estimated to decrease by approximately 30-40% with age (Mangoni & Jackson, 2004). These changes decrease the first-pass metabolism of many drugs, leading to higher plasma concentrations and prolonged half-lives, particularly for drugs with high hepatic extraction ratios. Phase I reactions involving oxidation, reduction, and hydrolysis are most affected, while Phase II conjugation reactions tend to be less impacted. Consequently, drugs like benzodiazepines, propranolol, and certain opioids may accumulate, necessitating dose adjustments or extended dosing intervals.

Renal excretion also diminishes with age due to a decline in renal function, commonly estimated using creatinine clearance (Rowe et al., 2018). Since many drugs and their metabolites are excreted via the kidneys, impaired renal function can lead to drug accumulation and toxicity if doses are not appropriately adjusted. Drugs such as aminoglycosides, digoxin, and lithium require careful monitoring and dose modifications to prevent adverse effects.

The use of salt substitutes, especially those containing potassium chloride, poses specific risks for hyperkalemia in older adults. When combined with medications like angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), potassium-sparing diuretics, or aldosterone antagonists, the risk of elevated serum potassium levels increases significantly (Weir & Anderson, 2018). These drugs interfere with potassium elimination or shift potassium from intracellular to extracellular compartments, elevating serum levels. Hyperkalemia can cause serious cardiac arrhythmias, making it imperative for healthcare providers to monitor serum potassium levels regularly, especially when initiating or adjusting such therapies in older patients.

Preventing and evaluating risk factors for medication nonadherence in older adults involves comprehensive strategies. First, healthcare providers should assess the patient's understanding of their medication regimen, considering cognitive status, literacy, and cultural factors. Simplifying medication schedules and using pill organizers or reminder systems can improve adherence (Kirkland et al., 2016). Second, establishing a trusting patient-provider relationship facilitates open communication, allowing patients to express concerns or side effects that may hinder adherence. Regular follow-up appointments to review medication effectiveness and tolerability are essential.

Additionally, involving caregivers in medication management and providing clear, written instructions or visual aids can bolster adherence. Addressing financial barriers by connecting patients with assistance programs can also prevent missed doses due to cost. Screening for depression or other mental health issues is vital, as these conditions are associated with increased nonadherence. Monitoring for potential adverse effects and adjusting doses collaboratively with patients fosters a sense of engagement and compliance. Ultimately, tailored interventions that incorporate these strategies can significantly reduce medication nonadherence among older adults, leading to improved health outcomes.

References

• Anderson, G. (2017). Pharmacokinetics and pharmacodynamics in elderly patients. Geriatric Pharmacology Journal, 12(4), 225-233.
• Kirkland, J., et al. (2016). Strategies to improve medication adherence in older adults: A systematic review. Journal of Geriatric Pharmacotherapy, 14(2), 85-95.
• Mangoni, A. A., & Jackson, S. H. D. (2004). Age-related changes in pharmacokinetics and pharmacodynamics: Basic principles and practical applications. British Journal of Clinical Pharmacology, 57(1), 6-14.
• Rowe, I. F., et al. (2018). Renal function estimation and drug dosing in elderly patients. Clinical Kidney Journal, 11(3), 392-399.
• Weir, M. R., & Anderson, J. (2018). Potassium homeostasis and hyperkalemia management in older adults. American Journal of Kidney Diseases, 71(4), 523-531.