A whistleblower paramedic says he felt fobbed off when he took evidence of drug tampering to a manager at the Queensland Ambulance Service.

A paramedic turned whistleblower who uncovered evidence of drug tampering says the care of thousands of Queensland patients may have been compromised.

Tim Watkins has accused the Queensland Ambulance Service of ignoring evidence that drugs used by paramedics were tampered with over a much longer period of time than the four weeks the service had acknowledged.

Mr Watkins has told the ABC he felt "fobbed off" when he tried to raise concerns with managers after uncovering evidence including a broken morphine vial that had been refilled with water and glued back together.

Mr Watkins is the son-in-law of Brisbane woman Barbara Cook who was given a strong painkiller after breaking her leg in a fall in May 2013.

But she believes she was actually given water instead of the drug, and went on to develop an infection from a bacteria commonly found in water.

Mr Watkins says he became suspicious after his mother-in-law's experience, given he'd previously uncovered of drug tampering in the QAS Metro North region.

He says that when he raised his concerns about the broken morphine vial, his managers told him "faulty manufacturing" was to blame.

Ms Cook lodged a complaint about her care with the health ombudsman, but it wasn't upheld, partly because the QAS said there was no evidence of drug tampering at the time she was treated.

The QAS has said tampering only occurred over four weeks, spanning July and August 2013.

But Mr Watkins said he told a manager he knew of evidence that dated back to 2012, something that manager has said he does not remember.

QAS medical director Dr Stephen Rashford had denied there was a deliberate attempt to mislead the ombudsman after Ms Cook complained.

He told the ABC he wasn't made aware of a case that saw another paramedic plead guilty in a Brisbane court to a string of drug tampering offences that began in October, 2011.