Principles of Pharmacokinetics and Pharmacodynamics
Pharmacokinetics and pharmacodynamics are the main branches of pharmacology that are closely interconnected. Pharmacokinetics is defined in the following way – it is “the study of the time course of drug absorption, distribution, metabolism, and excretion” (Spruill et al., 2014, p.1). Therefore, clinical pharmacokinetics is the application of its principles to the management of drugs in an individual patient. Pharmacodynamics “refers to the relationship between drug concentration at the site of action and the resulting effect, including the time course and intensity of therapeutic and adverse effects” (Spruill et al., 2014, p.2). Understanding pharmacokinetics and pharmacodynamics is vital for any work related to drug management and administration.
Experiences, Observations, and/or Clinical Practices
My experience regarding pharmacokinetic and pharmacodynamic factors and their influence on patients’ anticipated responses is connected to palliative care. As a result of physiological shifts that happen in the organism of people receiving palliative care, the pharmacokinetics of applied drugs can be altered (Franken et al., 2016). Unfortunately, sufficient evidence regarding the exact mechanisms and processes has not yet been gathered and analyzed, and the issue was researched only partially. Nevertheless, various practices employed in palliative care take into account some of the known factors that may influence a patient’s response to certain drugs.
Pharmacokinetic and Pharmacodynamic Influence Factors
Regarding terminally ill patients, there are numerous factors that can be different for them in comparison to average patients; these factors can seriously influence pharmacokinetics and pharmacodynamics. The main areas of influence include absorption, distribution, and metabolism of drugs in patients’ organisms. Considering absorption, one main problem with it is that terminally ill patients often have gastrointestinal problems. For instance, “untreated, nausea and/or vomiting occur in 21-68% of all advanced cancer patients and in 70-80% of cancer patients receiving chemotherapy” (Abernethy et al., 2010). As a result of gastrointestinal problems, the absorption and subsequent bioavailability of drugs can decrease significantly.
The distribution of drugs in the bodies of terminally ill people can also be affected in various ways. Some of the common problems that terminally ill people experience are fluid deficit and body weight loss (Cooper et al., 2015). This issue causes various subsequent problems; for instance, the volume of distribution of lipophilic drugs may be lowered, therefore leading to higher peak concentrations. On the other hand, a fluid deficit can both decrease and increase the volume of distribution of hydrophilic drugs, depending on particular circumstances (Franken et al., 2016).
The liver is the main organ that influences the metabolism regarding drugs in the human organism. Terminally ill patients can experience reduced liver blood flow due to their age, as they are typically older than the population average, and due to dehydration (Cheeti et al., 2013). Consequently, patients’ drug metabolism can decrease; this is especially noticeable in the case of drugs with a high extraction ratio.
Personalized Plan of Care
Palliative care considers all of the mentioned factors and incorporates responses to most of those factors into the treatment patterns. For instance, to address gastrointestinal problems, it is recommended to constantly monitor the issue and use alternative routes to administer drugs, such as subcutaneous administration. To solve the problem with increased volume of distribution, it is common to raise an initial dose of a medicine. Metabolism is one of the issues for which no particular recommendations have been created so far; thus, the best response, in that case, is the increased level of attention and care. Overall, depending on the specific instances, a personalized plan of care for terminally ill patients should consider the mentioned recommendations and practices.
References
Abernethy, A. P., Wheeler, J. L., & Zafar, S. Y. (2010). Management of gastrointestinal symptoms in advanced cancer patients: the rapid learning cancer clinic model. Current opinion in supportive and palliative care, 4(1), 36–45. Web.
Cheeti, S., Budha, N. R., Rajan, S., Dresser, M. J., & Jin, J. Y. (2013). A physiologically based pharmacokinetic (PBPK) approach to evaluate pharmacokinetics in patients with cancer. Biopharmaceutics & drug disposition, 34(3), 141–154. Web.
Cooper, C., Burden, S. T., Cheng, H., & Molassiotis, A. (2015). Understanding and managing cancer-related weight loss and anorexia: insights from a systematic review of qualitative research. Journal of cachexia, sarcopenia and muscle, 6(1), 99–111. Web.
Franken, L. G., de Winter, B. C., van Esch, H. J., van Zuylen, L., Baar, F. P., Tibboel, D., MathĂ´t, R. A., van Gelder, T., & Koch, B. C. (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. Web.
Spruill, W.J., Wade, W.E., DiPiro, J.T., Blouin, R.A., & Pruemer, J.M. (2014). Concepts in clinical pharmacokinetics. American Society of Health-System Pharmacists.