Captain.Heroin said:
Due to methadone's high volume of distribution, it is not going to "rush" like most commonly abused opiates would when IV'd.
It's not always rush that makes i.v. a more economic solution to p.o. ingestion. Methadone is more effective peripherally taken no matter the high p.o. bioavailability. Anyhow, for maintenance purposes injecting methadone is pointless.
But certainly this thread doesn't really point out that using a PVC (peripheral venous catheter) requires knowledge and experience in this field. I don't think someone who cannot inject 5ml of solution without keeping the needle in the vein is experienced to put a catheter in his vein. BTW it won't change the "pressure thing"... If injecting the solution causes such pressure that the needle comes out of the vein, then the process of injecting is done wrong.
5ml of the methadone syrup contains 5mg of methadone hydrochloride, that's the most widespread concentration for easiness of dosing. It's a very low dose but taking how thick the syrup is, such injections aren't safe. Although I've heard of people injecting 40ml of methadone, I would never do such a thing. To the OP, you say you got small needles, actually for injection of such thick solutions you SHOULD use BIGGER needles. If you know how to inject properly, even injecting with a 0.7mm needle shouldn't leave a mark that wouldn't disappear after a day.
And let's be honest, a 5ml syringe isn't big. It's definitely used in medicine for i.v. injections. It may seem to be big for those who use exclusively insulin syringes because they shoot up heroin or for some other reason.
That's just about filling in missing holes in this thread. Too bad it's too late and you didn't come here to consult before doing all this because having 50ml of methadone syrup you would get high simply drinking it as advisable.
EDIT: Sorry, this was about butterfly needles... Yet, IMO this requires knowledge and experience as well.