Hi, got a pharmacy/chemistry/ biology question here that really needs some answers.
So pH is important to understand, along with the degree of ionisation to determine whether or not a drug with precipitate out of the solution. So we would want to formulate an aqueous solution at a pH were the drugs solubility is highest or it completely ionizes. But then, unionized drugs can easily diffuse though, and passively through cell membranes, to be absorbed into the systemic circulation to get its desired therapeutic effect.

I see this trade off between the two so which is more important???

Question

Hi, got a pharmacy/chemistry/ biology question here that really needs some answers.
So pH is important to understand, along with the degree of ionisation to determine whether or not a drug with precipitate out of the solution. So we would want to formulate an aqueous solution at a pH were the drugs solubility is highest or it completely ionizes. But then, unionized drugs can easily diffuse though, and passively through cell membranes, to be absorbed into the systemic circulation to get its desired therapeutic effect.

I see this trade off between the two so which is more important???

abb0t · Answer

solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution and phase joining.

Also bare in mind that most drugs are either weakly acidic or weakly basic having poor solubility in aqueous solution. Hence, the main concern in drug production is the bioavailability, which is where pH comes into play since pH varies in out bodies.
For instance, pH of our saliva is about in the 6's range.
But as soon as our food mixes with our gastrointenstinal juices in our stomach and enters the duodenum (small intestine) the pH changes to 7 or 8 (which is basic).