Pharmacology - Antiemetics

hello in this video we're going to talk about the physiology of vomiting the vomiting is also known as emesis and throwing up amongst many other terms and it is a involuntary forceful expulsion of the contents of one stomach essentially through the mouth we will look at the so called emetic reflex which is the vomiting reflex and in order to understand the vomiting reflex we need to talk about the brain so here is the brain and the brain stem there's an area of the brain stem called the medulla oblongata where we find what's called the vomiting Center the vomiting Center contains essentially muscarinic receptors types of receptors and when these receptors are stimulated within the vomiting center this will trigger the vomiting reflex so the process of vomiting close to the vomiting center also near the medulla oblongata of the brainstem is another area called the chemoreceptor trigger zone or ctz for short now the CT zid as the name suggests gets triggered by chemicals and the ctz contains a few types of receptors and these are the dopamine to receptors and the 5-htt receptors 5-ht essentially is serotonin so these are serotonin receptors it's easy to remember ctz because we know that chemotherapy stimulates this chemoreceptor trigger zone so when the chemoreceptor trigger zone the CTS that is stimulated it will then stimulate the muscarinic receptors of the vomiting Center and when the master Inuk receptors of the vomiting Center are stimulated this will cause the vomiting reflex the emetic reflex though the chemoreceptor trigger zone is located in the medulla like the vomiting center the chemoreceptor trigger zone is located conveniently outside the blood brain barrier now the blood-brain barrier is a barrier preventing circulating substances in the blood from making contact with the brain and areas of the brain stem because the chemoreceptor trigger zone is situated outside the blood-brain barrier it is thus more permeable to circulating substances such as cytotoxic agents chemotherapy motion sickness is a very common thing people experience and the cause of motion sickness actually comes from the inner ear a bony structure called the labyrinth the labyrinth is made up of many areas one of which is called the vestibule a structure important for balance in space problems here will send electrical signals to the brainstem be at the vestibular cochlear nerve and the signals will get sent to an area specifically in the brainstem called the vestibular nuclei which is located in the pons of the brainstem the vestibular nuclei contain histamine 1 receptors and also muscarinic receptors so when the vestibular nuclei is stimulated during let's say motion sickness or during also morning sickness these signals will then be passed on to the chemoreceptor trigger zone and from here the chemoreceptor trigger zone will then send signals to the vomiting center in the medulla oblongata to trigger the vomiting reflex another cause of vomiting are things that occur from the cerebrum or the brain after it has processed all this sensory information so what I mean is that for example when people are emotionally overwhelmed or when people are in severe pain or when they smell something really bad or they see something repulsive something really bad essentially all this stuff will get sensed by the brain by the highest centers of the brain and from the higher brain centers this will then this signal then travel down to the vomiting center to stimulate the vomiting center to initiate the vomiting reflex this makes sense because some people get really nauseous when they see blood or guts or they smell something like a type of food that just smells horrible again the higher brain centers stimulate the vomiting Center through muscular neck receptors other causes of vomiting occur in the stomach so let's just recap some anatomy here so we have the mouth which connects to the esophagus which will travel down through the diaphragm which is the muscle muscular structure the esophagus will then join onto the stomach and the stomach joins onto the small intestine if we were to zoom into the stomach we can see they form deep pits deep pits and glands and these are lined up by many different types of cells one of which are called enteric chromatin cells the entire chromatin cells release serotonin in response to cytotoxic agents which is also which is thought to stimulate then 5-ht 3 receptors on sensory nerve fibers around the area and stimulation of this sensory nerve fiber which is actually the vagal nerve will bring this information to the vomiting center to trigger the vomiting reflex in summary all the causes of vomiting we talked about essentially will stimulate the vomiting center which is the output from which the vomiting reflex or the emetic reflex is initiated let's focus on what the vomiting reflex is and actually what happens during the process first it actually causes the lower esophageal sphincter to relax which makes sense because we need food to come up towards the mouth when we vomit we also need a diaphragm to contract and also the abdominal muscles to contract so that it will help push the food back up and this happens because we are increasing intra-abdominal pressure when we contract our muscles there are also autonomic changes such as tachycardia which is increase in heart rate and we also increase salvation as well as peristalsis the vomiting reflux also causes the epiglottis to close on at the top part because we don't want food to travel down to the lungs and once the vomiting reflux does all these things then the vomit or the food expulsion of food can happen so that was the physiology of vomiting the emetic reflux the vomiting reflux now let's talk about the medications that are used to treat manage and prevent nausea and vomiting in an acute as well as chronic situations these medications are also known as anti emetics basically preventing emesis preventing vomiting and the different classes of antiemetics include histamine one receptor antagonists histamine one antagonists are also called the histamine blockers which include promethazine so they're also called antihistamines and these class of medications actually just as a name suggests block histamine specifically histamine one receptors and these medications are actually commonly used to help relieve allergic reactions but they are also effective in nausea and vomiting specifically nausea vomiting to do with motion sickness or morning sickness as this diagram depicts then there is the 5-htt 3 receptors antagonists remember these because they end in Citrone so and they include ondansetron 5-ht as we mentioned earlier in the video is serotonin so 5-htt three receptors are serotonin receptors and therefore 5-htt three receptor antagonists are certain and receptor antagonists and these medications are used to control nausea and vomiting by working at the chemoreceptor trigger zone but also possibly in gastrointestinal tract which we'll talk about dopamine two receptor antagonists work on the chemoreceptor trigger zone and include a variety of subclasses you can say it's easy to remember this one concept that dopamine 2 receptor antagonists are also same or similar drugs that are used to treat schizophrenia or psychosis so these dopamine 2 receptor antagonists can be subdivided into a few groups the first group are at our the antipsychotics that ended as beans so for example for quote Paradine and chlorpromazine and the second group is meta Club bromide which actually inhibits dopamine 2 receptors but are thought to also stimulate gastrointestinal tract activity the final group is droperidol which also inhibits dopamine 2 receptors similar similar to Harrow impaler paradol and these guys are also used to treat schizophrenia so those were the drug linked to receptor antagonist class the fourth class are the muscarinic receptor antagonists such as higher sin with a h these guys block the receptors in the vomiting center inhibiting the vomiting reflex so let's look now at each of the antiemetic classes in a bit more detail and see what they're good for and see what the side effects are let's begin by looking at the histamine 1 receptor antagonists such as promethazine and these guys are good for motion sickness and morning sickness the side effects of these drugs include drowsiness and sedation the serotonin receptor antagonists ending in sec tron such as ondansetron are good antiemetics for patients undergoing chemotherapy radiation but also patients post-surgery as well the side effects of these drugs include headache as well as gastrointestinal upset remember that these drugs can also work locally at the gastrointestinal tract which we'll talk about the next class is your doubling to receptor antagonist which are your antipsychotics essentially the first group are your antipsychotic groups that end in a scenes such as prochlorperazine and chlorpromazine and they are good antiemetic drugs for chemotherapy and radiation patients they also block histamine and muscarinic receptors as well which may be useful in certain situations the side effects include sedation hypotension and extrapyramidal side effects it's important to mention extrapyramidal side effects here because this is a Sativex shared by a lot of antipsychotic medications and we'll talk a little bit more about that when we get into metoclopramide which is your next essentially group so metoclopramide are is good for chemo chemotherapy radiation patients who have nausea and vomiting as well as patients with reflux and hepatobiliary disorders the mechanism of action of metoclopramide not only does it work as a dopamine - receptor antagonist but it also works in the gut increasing gut motility the side effects of metoclopramide other than our gastrointestinal upset include extrapyramidal side effects extrapyramidal side effects as mentioned is a common side effect in antipsychotic medications and these extrapyramidal side effects include a test easier which is a restlessness tardive dyskinesia spasmodic torticollis ocular gyrus crisis and also it can also increase prolactin levels which can result in flack Turia menstrual problems as well as more lactation droperidol is your sort of other group of dopamine to receptor antagonists and these are also antipsychotics as well and they these drugs are good for acute chemotherapy induced vomiting though para dal is also used in surgery for post-operative nausea and vomiting so now focusing on the stomach area remember that we talked about the serotonin receptor antagonists the 5-htt 3 receptor antagonists well they can also work locally in the gut because there are serotonin receptors on sensory nerve fibers here and so what happens is that ondansetron for example can work locally here thus ondansetron is often used in pregnancy for those with bad nausea and vomiting although it is not recommended in the first trimester and there are some conflicting sort of evidence you can say finally the muscarinic receptor antagonists or anticholinergic such as hey listen with a h or good as prophylaxis for certain conditions and situations as well as for motion sickness side effects of these medications include having a dry mouth blurry vision and drowsiness it's easy to remember these side effects because they are anticholinergic side effects and remember Alice in Wonderland for the anticholinergic syndrome the muscarinic receptor antagonists are good as prophylaxis and for treating motion sickness because they also work at the vestibular nuclei which is where the whole process is if you remember so now that can including the video on the pharmacology of vomiting so that concludes the video on the pharmacology of antiemetics there are obviously other antiemetics used which I have not mentioned but this is the overall group and classes thank you for watching I hope you enjoyed this video

Channel: Armando Hasudungan

Views: 540,709

Keywords: antiemetics, pharmacology, pharmacotherapy, anti vomiting medication, drugs for vomiting, antivomiting, vomiting reflex, medications for vomiting, mechanism of action of antiemetics, metachlopramide, medicine, MOA, antiemetic agents, vomiting and nausea medicaiton, how do they work, animation

Id: zD_CWMlrb5s

Length: 15min 53sec (953 seconds)

Published: Sun Aug 13 2017