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Cytochrome P450

Discussion in 'Step I' started by w a n g, May 8, 2008.

  1. w a n g

    w a n g blarg 7+ Year Member

    Apr 19, 2007
    What the heck is all this cytochrome stuff? Stuff inducts/inhibits it. Makes some stuff last longer or shorter. What is exactly needed to be learned for step 1 about this? Wikipedia is too long and complicated!
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  3. RussianJoo

    RussianJoo Useless Member 10+ Year Member

    Jun 7, 2004
    Rock City

    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.
  4. docmd2010

    docmd2010 Senior Member 7+ Year Member

    Apr 17, 2005
    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....
  5. w a n g

    w a n g blarg 7+ Year Member

    Apr 19, 2007
    awesome i am much smarter now! thanks!
  6. nightowl

    nightowl Senior Member 7+ Year Member

    Jun 9, 2004
    there's a list of drugs that induce/inhibit P450 in first aid in the pharm section, along with mnemonics... it's worth looking it up :)
  7. Lamborghini1315

    Lamborghini1315 Sleep deprived 7+ Year Member

    Jun 7, 2006
    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 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, should know they have no effects on cytochrome 450.
  8. osli

    osli Senior Member 5+ Year Member

    Oct 13, 2005
    I'd also know where the azoles belong, many antiretrovirals, and a host of herbal stuff. Seems like good USMLE fodder.
  9. Teufelhunden

    Teufelhunden 1K Member Physician 10+ Year Member

    Nov 7, 2000
    Avon, Ohio
    Good p450 interaction table here.
  10. jatt12


    Feb 21, 2012
  11. Phloston

    Phloston Physician Lifetime Donor Classifieds Approved 5+ Year Member

    Jan 17, 2012
    Osaka, Japan
    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.

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