Propylene Glycol and Polyethylene Glycol are both used in e-juice for e-cigs, as a way of delivering nicotine
in a vapour. I don't want to break any rules about sources discussion, you can probably work out the most useful search terms anyway.
Pharmacopoeia grade products meet the standards used in the pharmaceutical industry. When you see the letters Ph.Eur. on the label of a medicine bottle, it means that the drug
meets industry standards for the EU.
You probably won't see that on the label for PG or PEG though, as it's not a medication itself. A good supplier will have a product specification sheet or certificate, and it will say Pharmacopoeia Grade on the product itself, and at least 99% of the contents will be PG. The label on my bottle of PG reads:
Diluting the PG before adding the diazepam
would make it a less effective solvent. The idea is just to make it less irritating to the bowels.
I don't really know how much PG to use. As little as possible, but sufficient to cover the powder. Crushing the pills exposes more of the surface area to the solvent. I also have no idea how long it would take for PG to absorb diazepam in tablet form, or even if diazepam tablets
are miscible in PG.
I have PG at home as I like to make my own e-juice, being a huge fan of vaping nicotine. It's also possible to prepare a vapable infusion of cannabis
I just came across this:
Solubility of Lamotrigine, Diazepam, Clonazepam, and Phenobarbital in Propylene Glycol + Water Mixtures at 298.15 K Ali Shayanfar, William E. Acree, Jr. and Abolghasem Jouyban.
Biotechnology Research Center and Faculty of Pharmacy and Drug Applied Research Center, Tabriz University (Medical Sciences), Tabriz 51664, Iran, and Department of Chemistry, University of North Texas, Denton, Texas 76203-5070
J. Chem. Eng. Data, 2009, 54 (3), pp 1153–1157
Publication Date (Web): February 9, 2009
Experimental solubilities of four antiepileptic drugs, that is, lamotrigine, diazepam, clonazepam, and phenobarbital in propylene glycol + water mixtures at 298.15 K were reported. The solubility of drugs was increased with the addition of propylene glycol, and the maximum values are observed in neat propylene glycol.
So heating the PG to 25 degrees centigrade might help. My Uncle Baldylocks tells me that the the power adapter for his laptop provides a gentle heat source when preparing a cannabis infusion in PG.
I can't find any references or citations regarding the effects on bioavailability of using PG to prepare a rectal diazepam solution. My impression is that it might improve bioavailability, as it at least seems to have been used effectively in a clinical setting.