This looked interesting, so decided to look more into it (mostly Benzocaine).
Mechanism (Source 1):
Acquired Methemoglobinemia, or MetHB:
"Acquired methemoglobinemia may arise from exposure to direct oxidizing agents (eg, benzocaine, prilocaine), indirect oxidants (eg, nitrates)...."
Higher methemoglobin levels result in more severe symptoms, >70% methemoglobin out of total hemoglobin is often fatal.
Overview of acquired methemoglobinemia (Source 2):
Interesting to see that Dapsone was the most common cause of methemoglobinemia, a couple of cases from other commonly used drugs/anesthetics, and a couple cases of intentional sodium nitrite ingestion.
Benzocaine (Source 3, 4)
Benzocaine: oral anesthetic commonly applied before endoscopy, usually in the form of a spray.
Benzocaine Hydrochloride: water soluble salt form of benzocaine, in contrast to the nonsoluble base form.
Cases: Able to find a couple cases reports that mostly involve use of some brand of Benzocaine spray (usually 20%) during medical procedures. Recommended dosage of these sprays seems to be 1 sec, which is 200mg. Couldn't find cases of intentional overdoses on Benzocaine.
300mg for Benzocaine/500mg for prilocaine are some estimates for amounts that can induce methemoglobinemia.
FDA (Source 5):
Estimate at least 400 cases of benzocaine induced methemoglobinemia, and of 119 cases recently reviewed, found 4 deaths.
"We also conducted a study comparing the relative ability of the two local anesthetics benzocaine and lidocaine to make methemoglobin. The study showed that benzocaine generated much more methemoglobin than lidocaine in a red blood cell model." I think this is also the study Lilithium referenced in their post.
This got me really curious about the lethality of benzocaine, and compared to other drugs. (Personally, as long as a lethal dose is possible, relative comparisons is irrelevant).
So I followed references and found studies where animals were fed a variety of things that could kill them.
Keep in mind, there is often species difference in response and tolerance to any anything will be vastly different, take it with a HUGE grain of salt. I just looked these up out of curiousity.
https://cdn.caymanchem.com/cdn/msds/20132m.pdf
So apparently LD50 for rats is 3042 mg/kg, 2500 mg/kg for mouse?
For comparison, it seems to be 180 mg/kg for Sodium Nitrite.
https://www.chemtradelogistics.com/...ite_High_Purity_Special_Granular_Grade-EN.pdf
Benzocaine Rat Study (Source 6):
Rats were fed benzocaine hydrochloride in various doses (0, 2, 4, 8, 16...256, 512, 1024 mg/kg body weight) . Don't want to misinterpret the results, but using a benchmark of >70% methemoglobin being lethal, 512 mg/kg reaches that level in male and female rats.
Other interesting parts: "Applying a 10-fold safety factor for extrapolating these values from rats to humans implies that a single oral dose of 1.6–4.9 mg benzocaine hydrochloride per kg body weight would not induce methemoglobin in humans. A 1-s application of a 20% benzocaine spray (i.e., HurricaineÒ) delivers approximately 200 mg benzocaine or 3.3 mg benzocaine per kg body weight for a 60 kg individual (Novaro et al., 2003)." Again, don't trust "extrapolating these values from rats to humans".....
PAPP Review (Source 7):
While researching, came across this chemical...
PAPP is another chemical that can cause methemoglobinemia, commonly used as a pesticide so research on its lethality is pretty extensive.
Super lethal to cats and canids it seems, but less lethal to humans?
"The toxicity of PAPP (LD50) via the oral route is characterized by the relative sensitivity of mammals and birds which fall into three general groups:
1. LD50 <50mg/kg, with cats the most sensitive followed by stoats>coyote,
bobcats>kit foxes, ferrets, ducks and dogs;
2. LD50 100-500mg/kg, encompassing the majority of species tested; and
3. LD50 >1000mg/kg, represented by female mice and female guinea pigs and
magpies."
"..LD50 data is not available for humans, but in sub-lethal studies oral doses of up to 10mg/kg of mass have been administered with few if any side-effects other than methaemoglobinaemia."
Observed behavior prior to death: "One of the key drivers for developing PAPP has been animal welfare. When delivered at a lethal dose, rapid induction of high levels of methaemoglobin can quickly induce death with minimal symptoms of distress. Rapidly induced anoxia is the cause of death and appears to be without appreciable pain or discomfort....There were no signs of discomfort, stress or vomiting associated with poisoning; animals became quiet, lethargic, and then unconscious for a short period before death."
Conclusion:
There are many different chemicals that can cause methemoglobinemia, and SN is only one. However, given the general lack of testing on humans, it can be hard to have definitive conclusions of their effects, lethality, side effects, when overdosed on, factors that determine their suitability for suicide.
Also, why is everyone hung up on Benzocaine not being water soluble? Surely you can still drink it with water, or just eat it, bake it into a pie, I think. Much more concerning is the lack of cases, compared to SN.
Final thoughts/questions:
- How badly did doctors fuck up, did they keep spraying for a whole minute or something?
- Of the cases studies I looked at, none seemed to note side effects of benzocaine overdose beyond those expected from methemoglobinemia.
- Who was the first "lab rat" for SN, and why was it first chosen? Maybe other things were tried, didn't work so were forgotten..
- More research into the toxicology of PPAP, which you expect because its a pesticide.
Sources:
Overview:
1.
https://www.ncbi.nlm.nih.gov/books/NBK537317/
2.
https://www.sciencedirect.com/science/article/pii/S2214750024000283
Benzocaine:
3.
https://sci-hub.ru/10.1381/0960892053723376
4.
https://www.masimo.co.jp/pdf/whitepaper/LAB4280B.pdf
FDA:
5.
https://www.fda.gov/drugs/drug-safe...ompts-fda-action-oral-over-counter-benzocaine
Rat Study:
6.
https://sci-hub.ru/10.1016/j.fct.2011.06.048
PAPP:
7.
https://www.envirolink.govt.nz/asse...use-as-a-new-predator-control-tool-in-NZ2.pdf