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The Pill and Antibiotics question

  • 03-10-2008 10:18am
    #1
    helimachoptor
    Moderators, Science, Health & Environment Moderators Posts: 21,693 Mod ✭✭✭✭


    Something I've always wanted to know,
    Why do antibiotics stop the contraceptive pill from working?


Comments

  • #2
    Malari
    Registered Users, Registered Users 2 Posts: 18,150 ✭✭✭✭Malari


    helimachoptor wrote: »
    Something I've always wanted to know,
    Why do antibiotics stop the contraceptive pill from working?

    Isn't it something to do with it not being absorbed by the body properly? I'm not sure how though. Maybe if the antibiotic has killed some stomach bacteria this affects how oestrogen is taken in?

    Good question...


  • #3
    Ausone
    Registered Users, Registered Users 2 Posts: 124 ✭✭Ausone


    Malari wrote: »
    Isn't it something to do with it not being absorbed by the body properly? I'm not sure how though. Maybe if the antibiotic has killed some stomach bacteria this affects how oestrogen is taken in?

    Good question...

    That's it in a nutshell.
    Broad spectrum antibiotics knock out GIT flora which aid the absorption of hormones.


  • #4
    helimachoptor
    Moderators, Science, Health & Environment Moderators Posts: 21,693 Mod ✭✭✭✭helimachoptor


    Thanks for the answers lads!


  • #5
    tallaght01
    Closed Accounts Posts: 5,778 ✭✭✭tallaght01


    I'm pretty sure the evidence is pretty weak for antibiotics actually stopping the pill working.

    But i guess most peope won't take the risk. Pretty sensible approach in fairness.


  • #6
    Malari
    Registered Users, Registered Users 2 Posts: 18,150 ✭✭✭✭Malari


    So how long does the GI tract flora get knocked out for? It would presumably longer than the 5 days most antibiotics are prescribed for?


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  • #7
    helimachoptor
    Moderators, Science, Health & Environment Moderators Posts: 21,693 Mod ✭✭✭✭helimachoptor


    tallaght01 wrote: »
    I'm pretty sure the evidence is pretty weak for antibiotics actually stopping the pill working.

    But i guess most peope won't take the risk. Pretty sensible approach in fairness.

    Nope we wont be taking any risks!

    But is something I've always wanted to know the answer to.


  • #8
    Ausone
    Registered Users, Registered Users 2 Posts: 124 ✭✭Ausone


    Malari wrote: »
    So how long does the GI tract flora get knocked out for? It would presumably longer than the 5 days most antibiotics are prescribed for?

    It can take up to 14 days for the flora to recolonise.
    So adequate precautions for 14 days from when you start the antibiotics.


  • #9
    SomeDose
    Registered Users, Registered Users 2 Posts: 252 ✭✭SomeDose


    The combined contraceptive pill works most effectively when the normal gut bacteria are allowed to metabolise and recycle the oestrogens. In theory, all antibiotics can reduce the effectiveness of this pill by interfering with the balance of normal flora, but whether or not this actually happens in practice is debatable. Nevertheless, extra precautions are required during and after the course of therapy as mentioned above. This is not the case with progestogen-only pills, which are not metabolised in this manner and therefore are unaffected.

    One class of antibiotics (rifamycins) most definitely do interfere with all contraceptive pills, not because they interfere with your normal flora but due to the fact that they are potent inducers of liver enzymes. Strict additional precautions are necessary for up to 2 months after finishing these eantibiotics.


  • #10
    DrIndy
    Registered Users, Registered Users 2 Posts: 3,461 ✭✭✭DrIndy


    the COCP is a steroid hormone which is maintained in the body via enterohepatic circulation - this means it is excreted and dossolved in the bile and reabsorbed from the colon when the gut bacteria breakdown the bile into more basic salts - this recycles bile salts 20 times or so if i remember.

    Taking any antibiotic with broad spectrum (really anything but penicillin) will disrupt the normal gut flora, reducing the circulation, maybe giving some diaorrhea and effectively dropping the recycling rate of the bile salts.

    This means that the COCP is less absorbed and blood levels are effectively less, this in turn reduces the suppresion of the pituatory and ovulation can restart.

    Rifampicin is a unique drug used to treat TB and in combination, other severe infections - it is such a potent enzyme inducer that for all intents and purposes - the COCP is completely neutralised.


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