I was told the same for syringes, use once only. A nurse in hospital tried to enforce this rule on me. At the time, I really put the 'multiple' in mdi, over 20 shots a day, and the nurse still tried to insist on one syringe per injection.
The doc walking past over-ruled the nurse. He said they have to give the one injection one needle advice because that's the nhs advice, and otherwise they are medically negligent. Practically, be sensible about reuse and its not a problem.
( Or at least, not as big a problem as supplying me with 20+ syringes every day. )