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Drug Interaction Considerations

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    Drug Interaction Considerations

    For as many drugs there are on the market, there are even more drug interactions to consider. It is a subject far to complicated to cover on a web forum. However, I thought it might be helpful to have some general principles about drug interactions.

    Drug-drug interactions
    Drug A can interact with drug B. Better yet, drug A can interact with drug B and C. Drug A interacts with drug B which causes and interaction with drug D. The possibilities are endless, especially when multiple drugs are used.

    Sometimes a drug interaction is clinically significant and sometimes it isn't. Lamictal interacts with birth control pills. It is not clinically significant in terms of birth control effectiveness. It is clinically significant if the patient is bipolar.

    Sometimes drug interactions can be managed by adjusting doses, choosing alternatives, or in some cases stopping a drug temporarily.

    Warfarin (blood thinner) is notorious for interacting with other drugs. A patient may have to be put on a drug that interacts with Warfarin. This is managed by monitoring bleeding times and adjusting Warfarin doses as needed. This includes when starting, stopping or changing a dosage of a medication that interacts with Warfarin.

    Tegretol interacts with Erythromycin antibiotics. The best way to deal with this interaction is to avoid it by choosing an antibiotic that doesn't interact.

    Statins (cholesterol lowering drugs) interact with Erythromycin antibiotics. This can be managed by stopping the Statin drug for the course of antibiotic treatment.

    Some drug interactions are used in clinical practice, on purpose. Drug A will be given to increase concentrations of drug B in the body to make drug B more effective.

    Duplicate Therapy
    There can be issues with drugs from the same class (group) used at the same time. Naproxen and Diclofenac are both non-steroidal anti-inflammatory drugs. It is not wise to use them together because it can increase the incidence of irritation and bleeding in the stomach. If one drug is at the optimal dose and is not working, a switch to another anti inflammatory, rather than adding one to another is the best approach. There are however a few circumstances when using drugs from the same class is appropriate.

    Drug Disease Interactions
    Certain drug classes should be avoided when possible for patients with certain disease states. Beta blockers should be avoided in asthmatics when possible because they can make asthma worse.

    Other Patient Factors in drug treatment
    The young. Some drugs are not recommended in the young because they haven't been tested, they are ineffective, or known to be harmful.
    The elderly. Doses need to be adjusted because the elderly do not process drugs as efficiently as younger people do. Drugs that increase the risk of a fall, a broken hip, and complications from that, such as Benzodiazepines, should be used with extreme caution. The general rule is 'start low and go slow'.
    Ethnicity. Some drug classes (groups) are ineffective in certain ethnic groups.
    Organ function. Drugs that are processed by the kidneys may need to be avoided or have dosage adjustments for those with reduced kidney function.
    The same can be said for drugs processed by the liver in those with reduced liver function.
    GI Tube. Drugs are introduced to the body thru a tube rather than by mouth. The drug formulation is critical in this case.
    Pregnancy. Need I say more.

    This list is by no means exhaustive but it does give you an idea of how many factors that need to be considered when choosing appropriate drug therapy.

    Sometimes what is appropriate in one case, may not be in another. Sometimes what is appropriate for one person, may not be for another.
    Last edited by AJ; May 3, 2010, 11:41 AM.

    Humans punish themselves endlessly
    for not being what they believe they should be.
    -Don Miguel Ruiz-

    WOW that is a lot of things to take into consideration.


      Thank you AJ for such great info. It sure makes a person stop and think.

      I get concerned about taking several drugs at once. I checked out a couple of sites, which was reassuring. Unfortunately I forget their names, but one may have been webMD? I also am a great believer in asking a pharmacist. They've got lists upon lists.
      Last edited by uni; May 4, 2010, 02:18 AM.

      ~ it's always worth it ~


        Hello AJ. That's a great list thankyou for providing it.

        I will add that even cigarette smoking may cause a different reaction to your med. For example Olanzipine (Zyprexa) may requires 40% more med if you smoke. In fact a young smoking male eliminate it 3Xs as fast as a non smoking elderly female.(source Also tell your doc or ask your pharmicist if you are going to quit smoking about any meds you take as the reverse is also true.

        Your comment about kids is right on. Kids are not small adults, but are still developing. Test are often limited because a large difference in development may occur in the time for a study to be completed. However there is little difference in brain function as we age a couple of yrs while a test is being done as a mid 30's adult.

        Thx again for the list. Take Care. paul m
        "Alone we can do so little;
        Together we can do so much"
        Helen Keller


          Thanks AJ, you are the best...

          As I was reading through the complex post that you had written I couldn't help but smile to myself at your level of intelligence, clearly shown in your post, and your kindness to share it with us, as I thought back on the silly sentence building exercise.
          Take Care,

          Courage does not always roar. Sometimes it is a quiet voice at the end of the day, saying...
          "I will try again tomorrow."


            I'm glad you guys found it helpful. What else is a girl to do on a day off when up at the crack of dawn.

            Karen you made my laugh. I finally realized how silly that silly exercise was. Thanks!

            Humans punish themselves endlessly
            for not being what they believe they should be.
            -Don Miguel Ruiz-



              it's clean and it works.

              it tells you how high the risks are of interference.

              most of meds cause CNS problems, but it's a good one if the doc throws you a new med and doesn't even bother to check. I know the pharmacies do but some of us like checking again


                Hello Lyxia. Nice to hear from you again .

                ~ it's always worth it ~