TY for the details happydaysover.
I am not sure if that value of Quinine in his system is significant or not, I don't know how to extrapolate those figures to how much was ingested but...
Adding to what Hammilton said above about the blood brain barrier and ethanol ... if he took a significant amount of Quinine and/or Quinidine that also is a potent drug that also inhibits the BBB's function so... combining two BBB inhibitors would certainly allow more Loperamide into the CNS. I never inhibit mine intentionally for the reason that Loperamide would be too potent if even 1% entered the CNS from a mere 2mg.
I am not a professional, but my educated guess is the Quinine is the most dangerous factor in your son's case.
Add to that the fact he was a non-tolerant opioid user and it is clear how even a small dose of Loperamide could cause opioid overdose via hypoxia and respiratory failure
And of course ethanol is always a dangerous drug to combine with anything that slows respiration. I have consumed ethanol while on Lope twice and I can say I readied my naltrexone and had a stimulant because it did slow me down to levels that gave me cause for concern -- thus I never repeated it. Had I combined it with Quinine and/or Quinidine... I probably would've suffered the same fate.
Thanks for posting this information, I have been thinking awhile about the potential your son's case was related to the possibility of QTc interval / cardiovascular issues so while it is still a tragedy I am relieved that it wasnt related to cardio because that would make Lope unsafe even as an antidiarrheal if it interfered with heart function like that.
So to anyone else reading this.. take note that its NOT safe at all to deliberately interfere with BBB function by using drugs like Quinine to potentiate a drug that already can enter the BBB alone. Unless directed to for a specific medical reason - I think one application used is certain kinds of parasitical infections.
EDIT- Specifically, Quinine/Quinidine inhibits BBB function by interfering with p-Glycoprotein which is a substance used to prevent many kinds of molecules from entering the brain.
And the other danger here is never mix OTC or Rx depressants, including things like Diphenhydramine aka Benadryl with things like opioids.