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A WHO document, contains the statement

[Melarsoprol] injections must be performed using glass syringes.

Why is this the case?

Chris
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Barry Harrison
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  • I will NOT be accepting the answer by @ayush. As another answer on Chemistry.SE states, the claim that propylene glycol can dissolve plastic is "absurd," as evidenced by the sale of antifreeze in plastic). For now, I will keep searching for another answer. – Barry Harrison Apr 01 '19 at 06:06

2 Answers2

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Since Melarsoprol is insoluble in water, dosage occurs via a 3.6% propylene glycol intravenous injection.

As propylene glycol can dissolve plastic, the drug should preferably be administered using a glass syringe (only if sterilisation is reliable), otherwise inject immediately (but slowly) using a plastic syringe (Source).

Melarsoprol is sometimes colloquially referred to as "arsenic in antifreeze".

Chris Rogers
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ayush
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    Is there any citation that propylene glycol can dissolve in plastic? Can't we buy antifreeze in plastic? – Barry Harrison Mar 24 '19 at 07:22
  • Answers here require supporting references, so @BarryHarrison is correct that you need to supply a citation. – Carey Gregory Mar 24 '19 at 15:30
  • @BarryHarrison - There was a source linked but easily missed as it was provided via a superscript number 1. I have edited the answer to make it clearer – Chris Rogers Mar 24 '19 at 20:21
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    @ChrisRogers Thanks for the edit. I did see that source. I am hoping the answer can be improved by a reference for "arsenic in antifreeze" as well as "propylene glycol can dissolve plastic". I plan on accepting this answer after these edits are made. – Barry Harrison Mar 28 '19 at 05:23
  • @BarryHarrison - Like I said, there is a citation for disovjng plastic. I can see your point on the arsenic in antifreeze. A quick Google search on that gives https://doi.org/10.1016/j.pt.2018.04.002 which mentions the colloquialism. – Chris Rogers Mar 28 '19 at 08:28
  • @ChrisRogers I appreciate the fact that there is a source. I can accept the answer. Alternatively, I can wait for a second source that specifically mentions plastic and propylene glycol, rather than the already cited source that says it is true. Is a medical organization the best source for a chemical phenomenon? – Barry Harrison Mar 29 '19 at 22:33
  • @BarryHarrison - I would consider medical practice guidelines to be reputable enough. Why do you question its reputation? Médecins Sans Frontières, also known in English as Doctors Without Borders is a major medical non-government organisation. Maybe you could put it to a question in [meta] – Chris Rogers Mar 30 '19 at 09:28
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    @ChrisRogers Thank you for your time and the discussion. I will NOT be accepting this answer. As a brilliant answer on Chemistry.SE states, the claim that propylene glycol can dissolve plastic is "absurd," as I had hypothesized (see my above comment on antifreeze being sold in plastic). For now, I will keep searching for another answer. Thanks again! – Barry Harrison Apr 01 '19 at 05:46
  • @BarryHarrison - That is interesting when plastic syringes are made of polypropylene and the document they cited states that polypropylene is not compatible with antifreeze. The thing is that elsewhere in the data sheet it states that polypropylene is compatiblewith propylene glycol when it can be used as antifreeze as an alternative to ethylene glycol. – Chris Rogers Apr 01 '19 at 08:53
  • @ChrisRogers You bring up some very good points. – Barry Harrison Apr 01 '19 at 13:02
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    Could also be the stoppers which may not be made of the same material as the body, and could be only some plastic syringes but it's simplest to give directions to not use plastic. Also, note that it doesn't need to be a strong enough reaction to actually dissolve the syringe as in you see it melting before your eyes. It could be very subtle leaching out from the syringe into the injection that is nonetheless not desirable. – Bryan Krause Apr 01 '19 at 19:37
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The reason for it may not be the barrel of the syringe, but the rubber in the stopper which is of a different material. There was a study done on paraldehyde and the affect it had on the plastic in syringes and needle hubs. The pertinent part (Note the time, there was no effect until after at least 3 hours immersion) is below (Emphasis mine).

No measurable change in residue weight was noted in any syringes for up to three hours. Compared with the control, there was a significant increase in the average weight of residue in the Glaspak and in the Plastipak syringes at 6, 12, and 24 hours. There was no significant difference in the weight of residue between the Glaspak and Plastipak syringes at those times, however. The amount of residue for the plastic and metal needle hubs was not significantly different. The source of the extractive residue appeared to be the rubber plunger tip. Since the nature of the extractive material in the residue is not known, paraldehyde should be administered in all-glass syringes if possible; other syringe types can be used only if the drug is administered immediately.

So basically, it's possibly erring on the side of caution as they don't know how soon it might start dissolving stuff.

JohnP
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  • Thanks for the answer! Should no better or more complete answer arise, this answer will be awarded the bounty. – Barry Harrison Apr 02 '19 at 15:50
  • Would you have an alternate theory? Or is this the only one you have right now? – Barry Harrison Apr 07 '19 at 22:40
  • @BarryHarrison - It isn't really even a theory. It's just something I found that could account for it. I have no idea if the same restrictions apply for this medication, it was just another med that recommended glass syringes with a little more detail on why. – JohnP Apr 07 '19 at 23:38
  • The same user who addressed the original issue with propylene glycol dissolving plastic has also stated that propylene glycol doesn't dissolve (or otherwise leach) latex. See this question. Of course, he/she may be wrong. – Barry Harrison Apr 08 '19 at 00:27