acidic drugs

[aspiringmd1015]

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so for acidic drugs, to be asborbed they require acidic mediums and their absorption will be enhanced, and vice versa with alkalkine drugs( bc they become lipid soluble and can cross through the membrane right?) so with renal stones, uric acid stones form in acidic ph's. Is that because uric acid within an acidic urine will cause it to become more liphophilic(which doesnt suit well within a liquid medium like urine) so it precipitates out? or does the mechanism behind renal stones simply have to be increase conccentration of the solute

 

[aspiringmd1015]

so for example, with uric acid stones, you give the pt K bicarb to alkanalize the urine, bc an alkaline urine will make uric acid more poler and thus more water soluble and can be urinated out right?

 

[aspiringmd1015]

anyone? dfib slim?

 

[sloop]

Charged solutes dissolve best in polar solvents like water. When there's lots of acid around, there's lots of protons. Lots of protons favors protonation of charged conjugate bases forming unionized acid. Unionized acid is uncharged and so a) does not form bonds with water well and precipitates and b) crosses the non-polar lipid portion of membranes better.

Similar thing with base. Basic environments do not have enough protons for bases to accept and become charged. As a result, they remain uncharged. In acidic environments, they become charged and can't cross membranes well (and bond with water better). This is a problem with local anesthetics, for instance. They are bases and need to cross through the myelin to work. Acidic tissue (inflamed tissue) will ionize these molecules and make them less effective. Solution is to inject with bicarb.

 

[sloop]

so for example, with uric acid stones, you give the pt K bicarb to alkanalize the urine, bc an alkaline urine will make uric acid more poler and thus more water soluble and can be urinated out right?

Yes.

 

[aspiringmd1015]

ok excellent, thanks. Can you also explain the role of hypocitraturia causing calcium stones? is it bc it increases the concentration of the solutes of ca oxalate bc theres less conc of citrate?

 

[sloop]

ok excellent, thanks. Can you also explain the role of hypocitraturia causing calcium stones? is it bc it increases the concentration of the solutes of ca oxalate bc theres less conc of citrate?

Citrate binds to calcium instead of oxalate. Calcium citrate is more soluble than calcium oxalate.

Citrate/oxalate ratio is important in stone formation. On a related note, high oxalate foods (spinach, etc.) can also tip this balance towards stone formation.

 

[aspiringmd1015]

cystine stones are radiopaque correct? FA says lucent but errata says opaque bc of their sulfur content

 

[scoKraz4]

yes, as a quick google search has shown, they are opaque

 

[aspiringmd1015]

^i googled it myself, but i wanted to make sure. Im not missing points on the exam bc of memorization details, getting info on it on a PUBLIC forum is what forums are made for. Thanks anyways.

 

[pd1112]

You trust forum word of mouth over medscape, uptodate, etc.?