The term 'opiate' is usually reserved for naturally-occurring opioid drugs such as morphine. 'Opioid' is a more generic term that includes the synthetic drugs such as fentanyl.

Syringes containing opioid drugs are identified by blue labels.

Fentanyl is about 100 times more potent than morphine and is presented for intravenous use in a solution containing 50 µg/ml.

An initial bolus dose of 1-3 µg/kg is usually given at induction, often before the intravenous induction agent, as it takes about 5 min to have an effect. One of fentanyl's effects is to reduce the response to laryngoscopy. It is therefore important to give fentanyl early, in a dose of 2-3 µg/kg, if the anaesthetic plan includes endotracheal intubation.

Repeated doses of fentanyl may be given intraoperatively, usually 50-100 µg, depending on the duration of surgery and analgesic plans. The duration of analgesic effects of fentanyl depend on the dose given and the level of surgical stimulation, but for the doses described above analgesia lasts about 15-30 min.