Hello /sci/ looking for someone with some (bio)chem knowledge to explain me something. I'm an anesthetist in training and my reading about propofol injection pain led me down a path reading and thinking about acids and bases. Now here's what I'm wondering about:
lidocaine is a weak base, its generally seen as a 1% or 2% solution, this solution however is acidic because of the added HCl, its described as having a pH of 6.09 and 6.0 respectively. I assume (after reading pubchem section on lidocaine) this is because the solubility of lidocaine is not sufficient to reach these concentrations without ionising it. on Pubchem it is stated that lidocaine solubility is 410mg/L in water at 30C so far off from the needed 20mg/mL used for injection. I've come across an article (PMC3383550) in which they add sodium bicarbonate to change the pH towards 7.4 however what I dont get is what would happen on a chemical level. at a pH of 7.4 ive read that about 25% of lidocaine is in nonionozed form but wouldn't this mean that the concentration at 5mg/mL nonionized start precipitating out of solution?
Am I understanding it correctly or which steps in my thought process are wrong?