Reflect on your experiences, observations, and/or clinical practices from the last 5 years and think about how pharmacokinetic and pharmacodynamic factors altered his or her anticipated response to a drug. Consider factors that might have influenced the patient’s pharmacokinetic and pharmacodynamic processes, such as genetics (including pharmacogenetics), gender, ethnicity, age, behavior, and/or possible pathophysiological changes due to disease.

Pharmacokinetics and Pharmacodynamics

Pharmacokinetics and pharmacodynamics processes affect a patient’s response to their treatment plan. I have witnessed a scenario where a patient’s expected reaction to a drug was altered. The patient was an 80-year-old male African American diagnosed with heart failure. The patient was prescribed digoxin for two weeks. During the patient’s scheduled review, he showed no improvement and complained of vision problems, loss of appetite, vomiting, nausea, diarrhea, and confusion. He reported that he began experiencing these symptoms when he started taking digoxin. After a review, the signs were diagnosed as digoxin toxicity (Cummings & Swoboda, 2022).

Factors affecting the patient’s response to medication include age. An 80-year-old individual is considered geriatric. Pharmacokinetic changes experienced in the elderly include decreased liver function (Thürmann, 2020). Notably, digoxin is metabolized in the liver to form digoxigenin monodigitoxoside as an active metabolite and digoxigenin bisdigitoxoside (David & Shetty, 2022). Decreased liver function in the patient causes a decrease in the metabolism of digoxin. The unmetabolized drug accumulates in the body in increased concentrations; hence, a patient experiences unexpected side effects and toxicity. Essentially, elderly patients have decreased renal function (Thürmann, 2020). Digoxin is mainly excreted through urine, and a decrease in renal function leads to a decreased elimination rate and digoxin accumulation in the body. Consequently, increased accumulation of digoxin causes increased side effects and toxicity.

Consistently, the patient’s care plan should consider his age when selecting a drug and determining the dose. The digoxin dose is adjusted using the patient’s liver function tests, kidney function tests, serum levels, and creatinine clearance. In addition, the dose for geriatric patients is calculated using their lean body weight. It is crucial to remember that higher doses of digoxin in elderly patients do not have any additional therapeutic benefit and increase the risk of digoxin toxicity.

References

Cummings, E. D., & Swoboda, H. D. (2022). Digoxin Toxicity. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470568/