Mechanism of action of phenytoin and its side effects
Hi everyone my name is peter welcome to my youtube tutorial in this section i’m going to to discussing our body anti-seizure drugs and specifically we shall look at the group called a high tones so under this group we have drugs such as furniture enforce penny turn those are the mostly used drugs right now in a as far as in tunisia drug management is concerned so
I am i gonna take you look up the mechanic of action of a finitary they would look at the pile equivalency then the side effects about this drug so therefore it has jumped into the first objective before that i have a structure here called the eridium structure so we shall refer to this structure more as we go on in anti-seizure drugs because most of these drugs
Have this structure so in phenytoin the other one and other two are what we call two benzene rings and then the x is a has a nitrogen and hydrogen are on it so therefore this structure is very important as far as discussing in texas event is concerned so therefore let me go to straight to the first objective which is the mechanism action so we see that finish to
It inhibits what we call the sodium channels this jump sodium channels are very potent in the propagation of that impulses that we see in the neurons so therefore this highly frequent firing neurons in the focal area in the brain where we have a serial point usually reduced oh because phenytoin is has what we call a huge dependent mechanism so it inhibits more of
Those highly firing neurons so therefore as the effect it will lead to the progression of the inactivated state of that sodium channels so there are four to drop to the second objective which is the equivalency of a finito so if anytime has what you call very poor solubility so therefore we see that we do not usually give 2010 as an iv because we need to exist as a
Sodium salt at a ph of 11 to 12 so therefore will inject this salt into the blood it will form a precipitate because blood has a low ph of about seven so therefore that drop in ph was up to the precipitation of our fan attorney and the site of injection and this will need to add damage to that that site of injection so that is a by a point to not forgiving veneto
So this poor solubility a problem was solved by international another new drug code forcefully turing which is basically the first spirited filtering whereby they request this hydrogen with a phosphate group so this phosphate group improved the episode veto of vengeance so we can give phenytoin in a status epilepticus we can give it in partial scissors and complex
Partial seizures so and another important factor about the phenytoin capsules is that the usually absorb carbon dioxide so when they do that codex i remember like i said finishing salt exists at a ph of 11 to 12 so in carbon dioxide is absorbed by this one is going to lead to the drop in ph so when the ph drops will precipitate out thus the phenytoin salts so this
Results in a very poor poor bioavailability so that is all about thereby equivalency of the drug so let us go to the side effects of the drug so one of the side effects that we know that the literal neuropathies these are very common when we check the dog for a long time then another a side effect to note is mr. keema’s usually this is a vertical nystagmus which
Involves the movement of eyes up in another side effects in here is the ataxia unable to balance and studies show that a person who has taken fainted by a long time has been reduced say villain then another side effect is a gingival hyperplasia so come on then another is that this area which is slurred speech so this is due to the action of this in activating
Sodium channels so any propagation in it neurons may be effective especially the neurons that serve the muscles for us i will use for speech then we shall look at what we call the drug-induced hypersensitivity so they said that since been fenton has to automatic benzene rings so during the metabolism of this drug this benzene rings produced what we call a immune
Induce us so this immunity nuisance i say to have to have an effect on causing these hypersensitivities then another side effect to note is that differently deficiency caused by filtering so now since phenytoin because causes foreign deficiency it is contraindicated in pregnancy because we know that folate is very important in a formation of the nucleic materials
So we do not give phenytoin in our pregnancy so that is a big point to note so another bye-bye you got the covariance point that i had forward to talk about is that that it’s phenytoin has it’s very hard to do it because any slight increment in it does merely two toxicity so as you know it does is phenytoin you will exhibit what we call our first-order kinetics
Whereby any increase in a concentration sorry any increase in those leads to an increase in position in blood so if i double the concentration then sorry if i’m done with the doors are also double the concentration in the blood then there is what we call a v-max at a point where the maximum dose that i i can give any patient so if i exit that maximum dose any
Slight milligram that i add on on that might lead to to exist is only to precipitate all these side effects that we’ve seen here so in the last point to note here i have what we call phenytoin has what we call ice i need user of the site cytochrome you for a enzymes so this any drug which any drug which is metabolized by this enzyme would have will be metabolized
Very faster compared to to the normal the normal mechanism so the cytochrome b 3 4 k inducer effects drugs such as done compositing for a permit we have your filing we have one firing we have contraceptives and very many other drugs so therefore when you’re giving finish way together with these drugs you have to be cautious cause the furniture will induce these
Enzymes which will metabolize these drugs very fast and it might affect especially these can’t a seizure grants it may affect the management of seizures so therefore thank you very much for watching so this was just discussing i was only talking about the hydra tones in my next sections are be discussing mobile other anti-seizure drugs thank you very much bye for now
Transcribed from video
Phenytoin Pharmacokinetics and Pharmacodynamics By Peter de-chemist Galif