Why do acidic drugs remain unionized in acidic environement?

Why do acidic drugs remain unionized in acidic environement, and become ionized in basic environment?

Similarly, why do basic drugs become ionized in acidic environment and remain unionized in basic environment?

It's all got to do with equilibria. In a basic environment, there are few H+ ions and many OH- ions, making the aqueous solution electrochemically negative. This means the drugs tend to dissociate (the positive H+'s get attracted off by the negative OH-s).
They remain unionized in an acidic environment because there are many H+s, and few OH-s, making the environment electrochemically positive. There's no attractive force to try to pull the H+ off.

Vice versa for basic drugs and the environments.

I assume it is related to "isoelectric points", which if I recall correctly was "the pH at which an amino acid is at equilibrium".


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Thank you very much for your answer. And sorry about the late reply as I was sick lately.

Is it possible to explain what you're saying in words that are easier to understand for a someone who is trying to learn chemistry? ( I know it sounds odd that I am studying pharmacology without having basic knowledge in chemistry. But unfortunately I didn't really like chemistry in high school, and I didn't learn much as a result. Now I'm trying to learn chemistry as I have recently got interested in it after beginning to read Asimov's ''A short history of chemistry.'' )

You're welcome, and I hope you get well soon

I have personally never heard of drugs being referred to as acidic or basic. But I assume them to consist of amino acids, as these can ionise. Could you give me some examples of acidic and basic drugs?

Asimov? Duno about him, but have a look at some Chemistry catch up books, which will be for people above a certain level who need to quickly self-teach some bits that they didn't cover previously - they may prove useful

OK, Isolectric points



Imagine this concept on a more complicated amino acid, such as arginine, which has an unequal number of carboxyl vs amine groups. The net charge could be more than or +1 in this case.

Now imagine this on a bigger scale - on the scale of a drug molecule, that is relatively huge, and has many amino acids, with varying numbers of amine and carboxyl groups. The pH would have ionic effects at various points in the molecule.

hope this helps

Thank you very much for your greatly helpful answer.

Examples of acidic drugs are: Aspirin, penicillin, loop diuretics, phenytoin etc.
Basic drugs: Benzodiazepines, Morphine etc.

I was talking about Isaac Asimov, the sci-fi writer. If you like sci-fi, you may give his Foundation series a read, if you haven't already. There's a movie based on his novel ''I, Robot.''

I don't really need to understand chemistry stuff quickly. I was just trying to understand this kind of stuff out of curiosity. Actually, recently, I have been amazed by the mechanisms of the body at the molecular level. It makes me wonder how just a bunch of chemical processes make up what we are. And then you wonder, what makes the molecules work in that way. That is purely chemistry between atoms. Of course, you can be amazed by how atoms work, too. But then you delve into the world of physics. Basically, I'm into the chemistry and physics of living things ( motion of cars, rockets, or electric mechanisms of a computer don't pull me at all. )

And again, sorry about my late reply. This time I was busy with a friend who is likely to undergo a surgery for liver disease within a few days.

you're welcome. Ah, I see. I like I. Robot

hmm..I've studied those drugs quite a bit, but never been told about their acidic/basic property. But eHow gives a brief definition, so s'cool.

Yup, amazing it is! Let alone the whole body or a whole organ, one is amazed at a mere cellular process.

no prob. I hope your friend gets better soon