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Step I Cytochrome P450
Started by w a n g
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you have to know what's in wikipedia plus all the drugs that inhibit or induce p450 and what effects this will have on other drugs.
I can you the basic jist in a few lines. basically the cyp450 enzymes are a group of enzymes that exist in the smooth endoplasmic reticulum of your liver that primarily function to detoxify substances in your body. Basically what they do, is they chemically modify a substance so it becomes more water soluble allowing it to cross the basement membrane of the glomerulus and you urinate it out.
Now, like any enzyme, the intrinsic activity of these enzymes can be modified by certain substances/drugs. For example drugs like alcohol, rifampin, and phenobarbital induce CYP 450. What does this mean? Well, it revs up the activity of these enzymes, which in effect, will cause all other drugs in your body that are hepatically eliminated to be metabolized much quicker. The classic example exists when someone is taking rifampin for tuberculosis and is also on the birth control pill. If the physician doesn't account for this, and warn the patient, and the patient continues to have unprotected sex, rifampin will "rev up" cyp450 and cause the break down of the OCP, and walllah, your patient's pregnant.
this also works the other way around, where certain drugs such as cimetidine inhibit cyp450, and increase the half life of other drugs in your system.
hope that helps....
Now, like any enzyme, the intrinsic activity of these enzymes can be modified by certain substances/drugs. For example drugs like alcohol, rifampin, and phenobarbital induce CYP 450. What does this mean? Well, it revs up the activity of these enzymes, which in effect, will cause all other drugs in your body that are hepatically eliminated to be metabolized much quicker. The classic example exists when someone is taking rifampin for tuberculosis and is also on the birth control pill. If the physician doesn't account for this, and warn the patient, and the patient continues to have unprotected sex, rifampin will "rev up" cyp450 and cause the break down of the OCP, and walllah, your patient's pregnant.
this also works the other way around, where certain drugs such as cimetidine inhibit cyp450, and increase the half life of other drugs in your system.
hope that helps....
Some classic drugs that induce: phenytoin, carbamazapine, phenobarbital
Inhibitor: Valproic acid
Bottom line these drugs will either lower or increase the potency of an adjunct drug..so an inducer will fasten the breakdown of other drugs while an inhibitor will slow the breakdown process. Always watch out for a trick question like something that's eliminated extra-hepatically like in this class of drugs one might throw in lorazepam, oxazepam, temazepam..you should know they have no effects on cytochrome 450.
Inhibitor: Valproic acid
Bottom line these drugs will either lower or increase the potency of an adjunct drug..so an inducer will fasten the breakdown of other drugs while an inhibitor will slow the breakdown process. Always watch out for a trick question like something that's eliminated extra-hepatically like in this class of drugs one might throw in lorazepam, oxazepam, temazepam..you should know they have no effects on cytochrome 450.
Know the short portion in FA on it, then do lots of practice questions. You'll encounter quite a few that test your knowledge of it, and you'll realize they're actually the easiest questions.
