Pharmacology of Codeine
Codeine is one of the drugs within the opiate family that is medically used to relieve pain especially due to its antitussive effect (Kane & Triggle, 2007). However, this drug has minute analgesic effects and as a result does not lead to considerable levels of respiratory depressions as compared to other opiates such as morphine. Its analgesic effect largely depends on the method in which it is metabolized. Individuals who do not have CYP2DC are poor metabolizers and therefore suffer from low analgesia (Kirchheiner, et al., 2007). On the other hand, its concentration in relation to that of the brain is affected by other factors such as age and medical condition of an individual. This paper will analyze how pharmacological aspects of codeine relate to various facets such as half-life, side effects, and receptors; in terms of psychiatric disorders.
Before a physician administers Codeine sulfate to a patient, they must consider certain factors. Some of these factors include; characteristics of the opioid that the patient previously took, patients ability to tolerate opioids and medical conditions of the patient (Kane & Triggle, 2007). However, it is important to note that tolerance can improve with the continued usage of the drug. Adult dosage should range between 15-60mg based on the considered factors. This dosage should be taken after every four hours (Holzer, 2014). Once the medical objective is attained, dosage should be stopped immediately to avoid either addiction or withdrawal symptoms.
Codeine is usually absorbed along the gastrointestinal tract whereby maximum concentration takes place approximately one hour after the drug has been administered. But comparing this drug to other opiates, it is known to have an apparent distribution level within the tissues (Kane & Triggle, 2007). Approximately seventy-five percent of every codeine dose is metabolized together with glucuronic acid to form codeine-6-glucunoric while the rest is converted to morphine. These conversions are enhanced by UDP-glucuronosyltransferase and cytochrome P4502D6 enzymes respectively (Kirchheiner, et al., 2007). Norcodeine and morphine are further conjugated with glucuronic acid which metabolizes them to morphine-3-glucuronide and morphine-6-glucuronide (Kirchheiner, et al., 2007). These two compounds are the ones which have an analgesic effect within the human body.
Neurotransmitters Affected and Receptors
All opiate receptors have a specific component known as G-receptor (Holzer, 2014). It functions as both positive and negative controller in synaptic transmission, thereby activating the effector proteins. The effector system, on the other hand, stimulates the release of nociceptive neurotransmitters such as dopamine and noradrenaline (Holzer, 2014). Subsequently, these compounds inhibit release of insulin and glucagon thereby resulting to the analgesic effect. Therefore, we can argue that the most prevalent therapeutic action of codeine is analgesia. Scientific evidence has proved that there are various opiate receptors and endogenous compounds within the central nervous system, which play a crucial role in the perception of analgesic effects (Holzer, 2014). Other effects of codeine within the central nervous system are the direct causation of respiratory depression in the brainstem respiratory centers, cough reflex along the medulla and partial meiosis.
Codeine Sulfate is usually contraindicated in a number of cases. For instance, it is contraindicated as a postoperative pain management drug especially among children who have gone through surgical procedures such as tonsillectomy (Haidon & Cunliffe, 2010). In addition, it is critically used for patients who have been medically proved to be hypertensive to other opioids such as morphine. This drug has equally found application in other medical cases such as among patients with acute bronchial asthma or those who have been suspected to have paralytic ileus (Haidon & Cunliffe, 2010). However, before contraindication is done for pediatric purposes, clinicians must be cautious. This is because numerous cases of respiration depression or even death have been reported among children who were administered with codeine as a post-operation reliever yet they had obstructive sleep apnea or else if they are ultra-rapid metabolizers of the drug.
Research shows that codeine has a half-life of approximately three hours (Haidon & Cunliffe, 2010). This simply means that almost half of every dose that has been administered is either metabolized or eliminated within these hours. About ninety percent of the dose is usually excreted by the kidneys while the rest remained as codeine without necessarily being metabolized (Haidon & Cunliffe, 2010). This remaining percent is later eliminated from the body, after seven to ten hours.
Despite the fact that codeine is medically prescribed to relieve acute and chronic pain within the body, it is subject to abuse resulting in numerous side effects. Other than the common pain relief, excess doses of codeine are known to create a pleasurable euphoric feeling to the user and the end result is usually addiction (Holzer, 2014). When this drug is administered, it enters into the central nervous system and on reaching the brain, it enhances the release of pleasurable hormones and this feeling is the one behind this addiction. Many people who are fond of abusing codeine end up getting trapped into other related opiates such as heroin as they try to seek for more pleasure. Mental disorders are the most prevalent among codeine addicts. Some of these disorders include; schizophrenia, anxiety, alcoholism and bipolar disorder (Holzer, 2014). A codeine addict will most likely have the following physical symptoms; psychosis, hallucination, and delusion (Holzer, 2014). There are also long-term effects associated with codeine abuse and these includes; liver damage, respiratory depression, coma, and seizures (Holzer, 2014). A person willing to withdraw from codeine addiction should do so under medical precaution because there are equally withdrawal side effects such as; insomnia, stomach cramps, and nausea.
It is, therefore, clear that despite the medical benefits associated with codeine administration, precautions should be taken to avoid any effects that can result from its abuse. Its application should strictly be pain relief and once the patient achieves a stable health condition, no more dosage should be allowed especially by considering the side effects.
Haidon, J. L. & Cunliffe, M. (2010). Analgesia for Neonates. Continuing Education in Anaesthesia, Critical Pain, and Care, 10(4), 123-127.
Holzer, P. (2014). Pharmacology of Opioids and their Effects on Gastrointestinal Function. The American Journal of Gastroenterology Supplements, 2(1), 9-16.
Kane, B. M. & Triggle, D. J. (2007). Codeine Drugs: The Straight Fact Series. Infobase Publishing.
Kirchheiner, J., et al. (2007). Pharmacokinetics of Codeine and its Metabolite Morphine in Ultra- Rapid Metabolizers due to CYP2D6 Duplication. The Pharmacogenomics Journal, 7(1), 257-265.
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