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A WHO document, contains the statement

[Melarsoprol] injections must be performed using glass syringes.

Why is this the case?

  • 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 1 at 6:06
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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".

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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 at 7:22
  • Answers here require supporting references, so @BarryHarrison is correct that you need to supply a citation. – Carey Gregory Mar 24 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 at 20:21
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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 1 at 5:46
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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 1 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.

  • Thanks for the answer! Should no better or more complete answer arise, this answer will be awarded the bounty. – Barry Harrison Apr 2 at 15:50
  • Would you have an alternate theory? Or is this the only one you have right now? – Barry Harrison Apr 7 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 7 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 8 at 0:27

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