Ph Scale of ketamine

[farmerwardy]

Just wondering if anybody knows where abouts on the ph scale ketamine sits?

and a link to some actual evidence would be good too,

[Paracelsus]

What do you mean by ketamine? pH can only be measured for solutions. Do you mean a standard 100 mg/mL injectable solution of ketamine HCl?

[farmerwardy]

Originally Posted by Paracelsus

What do you mean by ketamine? pH can only be measured for solutions. Do you mean a standard 100 mg/mL injectable solution of ketamine HCl?

yes. exactly that.
sorry for not being as clear as i could.

[Pondlife]

The Merck index says this about Ketamine: "pKa 7.5. pH of 10% aq soln 3.5"

Note that this is for Ketamine, not the hydrochloride salt. Merck lists the salt too, but does not give pKa or pH for it.

[rxbandit]

Heres an interesting paper... http://www.pubmedcentral.nih.gov/art...?artid=1181337

It is a study with rats, however I gleamed this tid bit, "Changing the level of positively charged ketamine (pKa 7.5) tenfold by changing pH from 6.5 to 8.5 caused a corresponding change in the forward rate while having no effect on the reverse rate."

further this makes sense due to this paper; http://jpet.aspetjournals.org/cgi/co...full/303/3/889

which in summary for our purposes says, "drug absorption is effected by; solubility, permeability, dipole moment, charge on cation, pH, molecule shape and physiology/enzyme availability"

which makes sense due to pH's effect on solubility for varying substances, and which also would pull at the Hydrochloride making its bond to the ketamine weaker and easier to break.

further, "When an amorphous suspension of the drug was dosed, absorption characteristics were similar to the solution, consistent with much more rapid dissolution and higher solubility of the amorphous material compared with the crystalline solid (Wald et al., 1995). "

So, it would appear putting a drug into solution first and altering the pH appropriately would increase onset and potentially get the drug absorbed quicker, which in turn could spare a fraction of the drug from bein metabolized or broken down.

You also need to remember the concentration gradient from biology to understand why a drug will be absorbed less as you do more, mainly for intranasal use. As a higher amount of the substance is absorbed their will be a lower propensity to absorb the substance subsequently as the concentration on the other side of the membrane is higher then it was at initial dosing.

I'll see what I can come up with in applicable terms.