I wonder how real the "not relieved by morphine is", or what that means exactly. Looked into this a while back and only found this source [1]:

> Intravenous access was obtained and 15 mg of morphine was given slowly. Over the next five minutes very little pain relief occurred.

> [...]

> A further 7.5 mg of morphine was given intravenously 15 minutes after the first dose, but again this produced little relief. Over the ensuing 15 minutes a further 7.5 mg of morphine was injected intravenously, which eventually reduced the pain to a tolerable level.

[1] https://onlinelibrary.wiley.com/doi/abs/10.5694/j.1326-5377....