Pharmacodynamic and pharmacokinetic principles

According to this units reading, pharmacodynamics is how drugs interact with the body and pharmacokinetics is the study of how medications move around the body (Chan, Ng, & Sim, 2015). Pharmacokinetics encompasses how the medication enters, gets distributed and metabolized, and is eliminated (Woo & Robinson, 2016). Pharmacodynamic factors that impact the functionality of a medication includes; level of function of the organs, receptor status, tolerance, and interaction (Woo & Robinson, 2016). These two concepts are important for providers to understand so that they can better treat and manage patients. Too often providers just focus on the end result of prescribing, rather than completely understanding the process that medications go through to achieve the desired outcome. Intravenous (IV) morphine sulfate is an opioid analgesic I recently used to treat neoplasm related pain. Whenever oral narcotics are given for inpatient cancer patients, it is important to consider the option of giving them an IV narcotic for breakthrough pain not relieved by an oral regimen. This can be done for a couple reasons; including first pass effect, absorption issues, inability to swallow, and why the patient may be in the hospital. For the average adult, the half-life of morphine is approximately 2 to 4 hours, and it is metabolized in the liver and excreted in the urine. The primary metabolism of morphine is by glucuronidation to morphine-3-glucuronide (DePriest et al, 2015). Since some oral opioids are metabolized in the liver by cytochrome P450, there is a risk of drug-drug interactions. IV morphine allows for no first pass effect and has 100% bioavailability. Considering that most medications require careful monitoring in the elderly, morphine can cause increased sensitivity and initial doses should be reduced (Adkinson, 2016). Since the kidneys clear the active metabolites, in patients with a GFR < 30, morphine should be avoided (Adkinson, 2016). Morphine has also been known to affect the central nervous system, the GI tract, and the respiratory system. Providers must assess for delirium, gait imbalances, constipation, and/or respiratory depression. It is also common practice for providers in palliative care to initiate a laxative for those on opioids in the hospital. Patients with cancer can suffer from symptoms related to the cancer or to the side effects of the oncology treatments. These symptoms can include nausea, vomiting, dysphagia from thrush, diarrhea, dehydration, and impaired liver and kidney function. Sometimes choosing an oral regimen can be counterintuitive if the patient is unable to absorb the medication due to vomiting. Cancer pain can be very difficult to treat and honing in on the type of pain (neuropathic, somatic, or visceral) is imperative for choosing the right medication and administration route. Morphine administered IV, enters the body directly into the circulatory system and gets distributed to the cells of the body, including crossing the blood brain barrier, placenta, and breast milk for those that may be pregnant or post partem. More specifically, it binds with Mu, Kappa, and delta receptors in the central and peripheral nervous system in an agonist manner (Pathan & Williams, 2012). This effect helps minimize the perception of the patients pain by blocking pain impulses. Atkinson, S. (2016). Geriatric Pharmacology?: The Principles of Practice & Clinical Recommendation, Second Edition. Eau Claire, WI: PESI Publishing & Media. Chan, Y. K., Ng, K. P., & Sim, D. S. (2015). Pharmacological Basis of Acute Care (4th ed.).Switzerland: Springer International Publishing. Deglin, J. H., & Vallerand, A. H. (2009). Daviss Drug Guide for Nurses (Vol. 11th ed). Philadelphia, Penn: F.A. Davis Company. Retrieved from DePriest, A. Z., Puet, B. L., Holt, A. C., Roberts, A., & Cone, E. J. (2015). Metabolism and Disposition of Prescription Opioids: A Review. Forensic Science Review, 27(2), 115145. Retrieved from Woo, T. M., & Robinson, M. V. (2016). Pharmacotherapeutics for Advanced Practice Nurse Prescribers (4th ed.). Philadelphia, PA: F.A. Davis Company. Critical thinking is not repetition of assigned reading material. Outside research of the literature is a vital part of the DB. Posts need to be substantive. This means that responses such as "I agree" or "great post" do not meet grading rubric requirements. Hide