Pharm help

[ant2cory]

I have my first pharm test coming up this week and I have gotten myself so confused. I am hoping someone can help me understand a concept. Please understand I am NOT asking to just be told the answer but to help me understand why the answer is what it is:

Are most drugs water soluble or lipid soluble? I have in my notes that most are water soluble so they can be excreted by the kidneys and so they don't cross the blood brain barrier (which only lipid soluble drugs can do). Then in the book(and another part of my notes) it says that more are lipid soluble so they can pass through cell membranes.

The part in the book says "most systemic drugs are formulated to be lipid soluble so they can move through the cell membrane, even oral tabs and capsules that must be sufficiently water soluble to dissolve in the aqueous fluid of the stomach and small intestines."

If they are lipid soluble, how are they stopped from going into the brain? And if they are water soluble, what is the liver doing since it doesn't need to change the composition for the kidneys? I can honestly see how it would make sense both ways, and for me to learn it, it has to make sense!!

[SierraBravo]

First of all, I wouldn't concern myself about whether most drugs are hydrophobic or hydrophilic; frankly at this point in your education it doesn't matter and you're not likely to get a question in nursing school asking about whether most drugs are hydrophobic or hydrophilic. Secondly, just because a drug is hydrophobic doesn't mean that it will necessarily cross the blood/brain barrier. The cellular physiology of how and when a drug is able to permeate the blood/brain barrier is outside the scope of this discussion, but if you are interested I would sit down with your Professor and discuss it.

Are you taking a pharmacology class? If so, I would go back and review the concept of ADME; absorption, distribution, metabolism, and excretion. I think you might need some reinforcement on those topics.