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Does the ionised form of a drug produce a pharmacological effect?

  1. Jul 10, 2013 #1
    Hi all,

    I was just wondering, does the ionised form of a drug produce a pharmacological effect? I know that an ionised drug is lipid-insoluble so it cannot traverse across the membrane. However, my question is, what happens to them if they remain in the gastrointestinal tract? Does it still have a function or is it eliminated from the system?

    Many thanks,
  2. jcsd
  3. Jul 10, 2013 #2

    jim mcnamara

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    Staff: Mentor

    Do you have a specific drug in mind? Consider one idea: suppose you as a company found a great new drug.
    Would you not want to manufacture the drug in a form that is readily absorbed? - you are assuming some type of pill or liquid I guess.

    A lot of drugs simply do not work via the alimentary canal. They are applied as creams or injections or IV's or whatever.

    Your question as posed is kinda hard to answer.

    Partial answer:
    In general "stuff" in the GI tract will move South if it is not absorbed. If you ever have children you will notice this effect in diapers when small children discover chewing gum.
  4. Jul 10, 2013 #3
    You're correct that ionized molecules are largely blocked from crossing lipid membranes. Most drugs are weak organic acids and or weak bases. Weak acids can be absorbed in both the stomach and small intestine because they are largely or almost completely unionized at each location. Weak bases are well absorbed in the small intestine where the pH is about 7.4.

    Ionized drugs require active transport to cross lipid membranes.

    Products that are intended to work in the GI tract are not absorbed such as antacids and cholestyramine which reduces the absorbtion of cholesterol.
    Last edited: Jul 10, 2013
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