Fexofenadine is well known as allegra which acts as a selective H1 antagonist and it belongs to second generation antihistamines. This drug chemically belongs to diphenylmethanes.
Hi everyone today in this video we are going to discuss how fexofinitine acts in allergy we will see the mechanism factions side effects and uses of phagophenine phagin is one of the drag which is well known by its brand name alegra this drug is an anti-istamine it can be used in the treatment of allergic rhinitis allergy granite is also called as hay fever and
This condition can produce few of the symptoms like the runny nose itching watery eyes sneezing and congestion which results in the difficulty in breathing all these are absurd because of the allergic reactions in the patients all these symptoms can be observed because of the release of one mediator that is the histamine now the actions of the histamine can be
Blocked by phagophenol which acts as an antihistamine and this drug can also be used in the under condition like the chronic idiopathic utic area which is again one of the allergy conditions which produce some skin irritation itching and allergy in such conditions we can use the phagophenol now today in this video let us see how this phageofinitine acts and how
It can block the actions of the histamine first of all let us see the structure of the fixofinadine we can observe one of the phenyl group here and another phenyl group here these two phenyl groups are attached to the methane group so physophenidine belongs to the chemical category of diphenyl methanes among the antihistamines we have several chemical categories
But the phagocytin belongs to that diphenyl methanes and we are well familiar with one of the first generation diphenyl methane drag that is the diphenhydramine diphenhydramine is present in many of these syrups as well as the tablets as an anti-ist mine and it is well known with the brand name benedryl but this drag is having so many side effects because it can
Easily enter into the cns thereby can produce the sedation drowsiness dizziness in the patients but the phagophenotin is a second generation diphenyl methane which is not entering into the cns thereby this drug shows less sedation let us see another structure this is not the fix of inaden this is the end the track terrafine adding terrafin adding is a related
Drug to the figsofinadine when this drug is administered within the body this drug can be converted into another structure like this and this is nothing but the phagophenol in this way terafin adin is metabolized to the phagophenol you can observe a small difference between the telephone adenine and exophinadine in the terrafin iodine methyl group is present
At this position but in the phagophenine we can observe a coh group carboxylic acid group is present in the effects of inadequate so simply in this reaction terrafinidine is converted into phagozophine by oxidation reaction but the terrafinidine is one of the drag which can increase the qt interval within the ecg which produce a fatal cardiac arrhythmias what we
Call point is this is a fatal side effect that’s why tefinitine is withdrawn from the market because of the torsion dependence but still fixofinadine is available in the market which is not having significant increase in the qt interval so it is not producing torsion d point is but still this drug should be carefully given in the patients who are at the risk
Of the increase in the qt intervals how it acts all we have seen the effects of united is an anti-strain or it is an anti-allergic drug so this drug is mainly reducing the allergic response allergens can act as antigens so that they are going to release the histamine from the masses basophils as well as snowfalls and this histamine can act on the h1 receptors
Which are responsible for the allergic response now the phagophenine can block this h1 receptor selectively thereby it can inhibit the actions of the histamine but now let us see how this allergen can release the histamine and how this histamine can act on the h1 receptors to produce the allergic response first of all let us see the release of the histamine the
Allergens can act as the antigens so that they can bind to the antigen presenting cells so when this antigen binds to this antigen presenting cells they will activate these cells and once they are going to be bound these antigens can be internalized within the antigen presenting cells and then they can undergo fragmentation such that they are going to release one
Of the complement related to the antigen now this complement can be recognized by mhc2 molecules which are expressed on the antigen presenting cells now this antigen fragment is going to be expressed with mhc2 molecules this fragment is recognized by cd4 t cells once the cd4 t cells recognize this antigen fragment they can stimulate the th2 lymphocytes these
Deh2 lymphocytes are mainly responsible for the release of the interleukins and by this they can convert the plasma cells into the b cells b cells are very important for release of the antibodies so because of the activation of the bcs they are going to release the antibodies and one of the important antibodies the ige antibody immunoglobulin e now this ig can
Act on the different types of cells like the muscles and isonophiles so that it can release the histamine now the muscles are equipped with the different types of mediators and one of the important mediator is the histamine and in order to degranulate the histamine they are going to express few of the binding proteins which are the fc sigma are binding proteins
On which the ig antibodies can act now this ig antibodies can bind to the mass cells now when this antigen is going to interact with these antibodies the mass cells can undergo the degranulation and they release the histamine this histamine is responsible for the allergic response histamine can act through the histamine receptors in order to show the allergic
Response but we have different types of histamine receptors they can be classified from h1 to h4 the important one are the h1 receptors and h2 receptors h1 receptors are mainly present in the lungs nasal mucosa endothelium neurons gastric mucosa lymphocytes at all of these locations the h1 receptors are present which are responsible for the itching bronchodilation
Vasodilation and salivation all these are the allergic response produced by histamine through the h1 receptors and his men can also act through the h2 receptors which are present at the gastric mucosa heart lungs and cns and when these receptors are activated they can increase the gastric acid secretion because the histamine can act through the gastric parietal
Cells as well as it can also produce a cardiac stimulation but here the allergic response is mediated by h1 receptors so now the phagophenine acts on the h1 receptors and many of the cells the h1 receptors are going to be expressed and these h1 receptors are the seven transmembrane g protein coupled receptors now when the histamine is going to acting on the
H1 receptors they are going to be activated and since they are the g protein coupled receptors they are going to activate the phospholipase system this phospholipid sees the cleavage enzyme which can cleave the phosphoridal inositol by phosphate into the two fragments one of the fragment is the ip3 inositol triphosphate and another fragment is the dag diacyl
Glycerol now this ip3 and dag are the two important secondary messengers which are which are released by action of the histamine ip3 can act on the sarcoplasmic reticulum sarcoplasmic reticulum express v of the ion channels which are the store-operated calcium channels these ion channels are the target for the ip3 so they can also be called as ip3 receptors
Now when this ip3 acts on this ip3 receptors it can cause the release of the calcium from the sarcoplasmic reticulum similarly the diesel reservoir can attach with the cell membrane and it can activate the one of the enzymes protein kinase c when this protein kinase c is going to be activated it can stimulate the entry of the calcium through the calcium channels
Expressed on the cell membrane now because of the protein kinase c the calcium can more enter into the cell so that the intracellular calcium levels are going to be increased in this way histamine can increase the intracellular calcium levels and as the calcium is going to be increased it can increase the contraction for example within the lungs it can produce
A bronchoconstriction which produce some congestion and difficulty in breathing at the same time the increased intracellular calcium can increase the release of the nitric oxide within the endothelium now this nitric oxide can produce a vasodilation within the vascular smooth muscle in this way histamine can produce the contraction of the bronchial smooth muscle
At the same time it can produce a relaxation of the vascular smooth muscle and this vasodilation can increase the allergic response by increasing the vascular permeability so so many mediators can enter into the blood vessels so that the inflammatory response can be increased now let’s see how phagophenoid in acts physophenidine is selectively blocking the h1
Receptors so that these receptors are going to be inhibited thereby histamine cannot produce any action through the h1 receptors in this way phagofine iodine is a select 2h1 antagonist thereby inhibits the allergic reactions mediated by histamine now let’s see the side effects of the phagoxofinitin the one of the important side effect is the headache that can be
Observed in many of the patients and apart from this side of egg fexofinadine can also produce dry mouth stomach pain and some dizziness in the patient and very rarely if exophanidine can also induce the fever in the patients drug interactions physophenidine undergoes somewhat less metabolism and its metabolism is going to be mediated by cytochrome p450 system
When the phagophenine is given with other drugs like the erythromycin ketoconazole these type of drugs can inhibit this metabolism of the phixophin aden thereby they can increase the levels of the phagocytin within the body this may lead to the toxicity of the phagophenine that’s why these type of drugs should be carefully given with the phagophenone and even
Antacids can decrease the absorption of the phagophenine interestingly one more food drug interactions with the grapefruit juice grapefruit juice can inhibit the metabolism of the phagophenol thereby can increase the levels of this drug which may increase the qt interval within the ecg that’s why this drug is not recommended along with the grapefruit use in order
To avoid this unwanted drug interaction how it is given exophenadine is given as a tablet form at a dose of 30 mg 60 mg and 180 mg and it is also available as a capsule and this capsule is available at the 60 mg dose and it can also given as a oral suspension this water suspension is available at a dose of 30 mg per 5 ml the dose of the physophanide depends on
The allergic condition and days of the patient it can be given as a twice daily formulation where it is given at a dose of 60 mg given twice daily so the maximum dose is 120 mg otherwise it can be given as single dose where 180 mg of the phase of an iodine is given and the suspension can be given at 30 mg dose twice daily so that the maximum dose is the 60 mg
So that’s about the effects of inadenium which is well known as alegra fixophenidine is a select two h1 antagonist with less sedation drowsiness compared with the first generation antihistamines so that’s for today if you like this video please subscribe to our channel share this video with your friends post your comments in the comment box thank you for watching this video
Transcribed from video
How Fexofenadine acts in allergy By egpat
