Principles of Pharmacokinetics and Pharmacodynamics
Advanced practice nurses have the responsibility of understanding pharmacokinetics and pharmacodynamics of the medications they prescribe to their patients. Pharmacokinetics refer to the way drugs move throughout the body by means of absorption, distribution, metabolism, and excretion. Pharmacodynamics refer to the ways drugs physiologically impact the body as evident by drug responses, interpatient variability, dose-response relationships, drug receptor interactions and a drug’s therapeutic index. Pharmacokinetics and pharmacodynamics collectively impact the therapeutic response a drug has on a patient (Rosenthal and Burchum, 2021).
Professional Experience
My experience as a hospice nurse over the last 2 years has enlightened me on the challenges in managing symptoms of patients at the end of life. Opioids such as Morphine, Fentanyl, and Dilaudid are effective in reliving symptoms of pain and dyspnea that patients often experience in their last days of life due to terminal diagnoses such as cancer or end stage COPD. Although, opioids are very effective in reliving these symptoms not all opioids possess the same pharmacokinetics and pharmacodynamics (Franken et al., 2016)
For example, an internal medicine physician referred his patient to me who was a 65-year-old female with metastatic ovarian cancer. The patient was described to me as being cachectic, weak with severe protein calorie malnutrition, hypernatremia, and an acute kidney injury. The physician told me the patient was interested in enrolling in hospice. When I entered the patient’s hospital room for my initial visit it was apparent to me the patient was exhibiting myoclonus as evident by the involuntary muscle jerking of the arms she was experiencing while lying in bed along with nonverbal signs of pain. Upon chart review my attention was raised to the fact the patient had an elevated creatinine level and was recently started on IV Morphine Sulfate for symptom management of pain.
Factors that Influenced the Patient
When morphine sulfate is given intravenously it is absorbed in the blood. Then, it is distributed and metabolized by the kidneys where it is then eliminated (Rosenthal and Burchun, 2021). Since the patient’s renal function was impaired due to metastatic disease the body’s inability to metabolize and excrete morphine caused myoclonus. The complications of the patient’s metastatic disease including cachexia, severe protein calorie malnutrition, hypernatremia, and acute kidney injury may also contribute to the pharmacodynamics of morphine sulfate and its individual variation effect on the patient. Interestingly, Rosenthal and Burchum, 2021, share that some opioids are more effective in women versus men, therefore, women may require lower doses of opioids to reach pain relief (Rosenthal and Burchum, 2021, p 159).
Personalized Care Plan
As the hospice nurse I was responsible for collaborating with the hospice physician to develop personalized hospice plan of care. I paged the hospice physician to the bedside and reviewed the patient’s medical history, other medications prescribed as well as informing the physician of my assessment of the patient. The decisions was then made by the hospice physician to transition the patient from IV Morphine Sulfate to IV Fentanyl. The British journal of clinical pharmacology warns patients being transitioned off one opioid and on to another must be closely monitored because there is risk the patient maybe be either over medicated or under medicated (Kuip et al., 2017). In this case the patient’s myoclonus resolved after 24 hours of discontinuation of Morphine Sulfate and patient was able to verbally report adequate pain relief with the use of Fentanyl.
Resources
Rosenthal, L. D., & Burchum, J. R. (2021). Lehne’s pharmacotherapeutics for advanced practice
nurses and physician assistants (2nd ed.) St. Louis, MO: Elsevier.
Franken, L.G., De Winter, B.C.M., Van Esch, H.J., Van Zuylen, L., Baar, F. P. M., Tibboel, D.,
Mathôt, R.A.A., Van Gelder, T., and Koch, B.C.P. (2016). Pharmacokinetic considerations and recommendations in palliative care, with focus on morphine, midazolam and haloperidol. Expert Opinion on Drug Metabolism & Toxicology, 12(6), 669-680. https://doi.org/10.1080/17425255.2016.1179281
Kuip, E. J. M., Zandvliet, M. L., Koolen, S. L. W., Mathijssen, R. H. J., and van der Rijt, C. C.
D. (2017) A review of factors explaining variability in fentanyl pharmacokinetics; focus on implications for cancer patients. British Journal of Clinical Pharmacology, 83, 294– 313
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