Autacoids are biologically active substances that are produced and released locally by cells in response to injury or inflammation. They play a crucial role in regulating the local physiological responses to injury or inflammation. In pharmacology, the study of autacoids is important as autacoids are involved in a number of pathological processes such as inflammation, pain, and fever. Understanding the role of autacoids in these processes is crucial in the development of effective treatments for a wide range of diseases.
Thus, studying autacoids is crucial in the field of pharmacology and is an important topic for NEET PG exams, as it forms the foundation for understanding the mechanism of action of various drugs and their use in the treatment of different diseases.
Histamine is a hormone which acts through various receptors:
Responsible for causing allergies.Promote wakefulness.
Secretes acid in the stomach
They are presynaptic auto-receptors. Hence, they inhibit the release of histamine. (Hence, drugs that block H3 can be used in narcolepsy, as it promotes wakefulness by blocking histamine release).
The most important drugs are the ones which block H1 receptors. They are known as antihistamines. They are divided into first-and second-generation drugs.
First generation antihistamines
They can cross the blood-brain barrier. Hence, they will block H1 in the brain and cause sedation.
They have additional anticholinergic property.
They cause minimal/no sedation.
They do not have additional anticholinergic property.
FIRST GENERATION ANTIHISTAMINES USES
Drugs that can be used in drug-induced Parkinsonism: Promethazine.
Acute muscular dystonia, Akathisia
Prophylaxis of motion sickness
Second generation drugs have only anti-allergic properties. Examples of some second-generation antihistamines are as follows:
Astemizole and terfenadine are now withdrawn as both of them have QT prolongation which can lead to Torsades de Pointes.
Serotonin can act on various receptors. They are classified as follows:
5HT1A is used to treat Anxiety. The drug used is Buspirone. (Bupropion has a very similar name to that of buspirone. They should not be confused with each other as Bupropion is used to support smoking cessation). 5HT1B are the receptors which are present in the Brain. They cause vasoconstriction. Hence, these drugs are used in the case of Migraine.
A unilateral, pulsatile headache is suggestive of migraine. Symptoms like photophobia, phonophobia etc. are seen in individuals suffering from migraine. For acute migraine attacks, the drugs of choice are Triptans if NSAIDs do not work.
Triptans are the drug of choice for cluster headache also. Another drug of choice other than Triptans is Ergotamine. But Ergotamine causes severe vasoconstriction in the periphery which can lead to gangrene. Hence, triptans are preferred to ergotamine for acute migraine. Whenever used, they should not be given together. Both these drugs act by stimulating 5HT1B/1D receptors.
The drug of choice for Prophylaxis is propranolol. New theories suggest that migraine is due to calcitonin gene related peptide (CGRP). Hence, it has to be decreased to treat migraines.
New Drugs in Migraine
Drugs blocking 5HT1 receptors
5HT1F agonist: This drug group is known as Ditans
CGRP antagonists (↓Release of CGRP): The drug group is called gepants.
Oral - e.g. Ubrogepant, olcegepant, Rimegepant
Monoclonal Antibodies (CGRP antagonists). These are injectable drugs. They are long acting. Hence, they are used for prophylaxis of migraine. Examples for this group of drugs are
Drugs blocking 5HT2 receptors
Drugs blocking 5HT3 receptors
Used for the treatment of vomiting. Setron group of drugs are the drug of choice for chemotherapy induced nausea vomiting.
Drugs blocking 5HT4 receptors
They are present in the GIT and they increase peristalsis. The drugs that stimulate them are prokinetic drugs. Examples are:
Cisapride (is withdrawn because of QT prolongation)
Prostaglandins are formed from the phospho-lipids of the membrane.
Phospho-lipids are converted to Arachidonic acid by PLPA2. Arachidonic acid is affected by COX producing prostaglandin (PG). Arachidonic acid affected by LOX produces leukotrienes (LT). Drugs that inhibit COX are known as non-steroidal anti-inflammatory drugs (NSAIDs).
Non-Steroidal Anti-Inflammatory Drugs
Their mechanism is that they inhibit COX.
There are two types of COX inhibitors.
Non-selective COX inhibitors (the ones that inhibit COX- 1 and COX – 2)
Selective COX inhibitors (The ones that primarily inhibit COX – 2 only)
Difference b/w Selective and Non-Selective Inhibitors
Less risk of causing peptic ulcer disease.
They increase the risk of Thromboembolism like myocardial infarction/stroke.
Most of the NSAIDs are used to treat fever, pain and inflammation. Aspirin is used for these purposes. In addition to that, aspirin is also used for anti-platelet action. The dose required for antiplatelet use of aspirin is <325 mg. It can be used for prophylaxis, myocardial infarction or stroke. At low dose (<325 mg), aspirin primarily inhibits the formation of Thromboxane A2. Hence, platelet aggregation will not take place.
Aspirin is contraindicated in gout, because it can cause hyperuricemia. Aspirin is contraindicated in children with viral illness because of the risk of Reye’s syndrome. Overdose of aspirin causes aspirin toxicity. The only antidote is to make the urine alkaline by giving sodium bicarbonate. This will help the excretion of aspirin through the urine.
The other name of paracetamol is acetaminophen. The exception associated with paracetamol is the fact that it has no anti-inflammatory property. This might be because of the fact that it only inhibits COX- 3 in the brain.
Paracetamol has lesser nephrotoxicity. Hence, it is preferred in a patient suffering from any sort of renal disease. On metabolism, it produces a compound called NAPQI which can cause liver damage. The antidote for paracetamol is N-acetyl cysteine.
Part of its analgesic metabolism is contributed by its action on a vanilloid receptor called TRPV (Transient Receptor Potential Vanilloid). A metabolite of paracetamol is assumed to be acting on these receptors.
It was considered as the drug of choice for Patent Ductus Arteriosus (PDA). But nowadays ibuprofen has become the drug of choice. Ibuprofen is the only anti-inflammatory drug that is preferred in children.
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