Immediate-release (IR) fentanyl is used to treat breakthrough pain, a transient exacerbation of otherwise controlled chronic background pain.  The aim of this review is to evaluate the currently available IR fentanyl preparations (Abstral sublingual tablets, Actiq lozenges and Effentora buccal tablets) plus the newly licensed intranasal formulation (Instanyl), and to discuss whether the products are interchangeable and when it is most appropriate to use each one.  The review will not discuss the analgesic efficacy of fentanyl per se, as this is well established, or the use of strong opioids in palliative care, but will evaluate studies that compare the different fentanyl IR products.

No studies comparing the fentanyl products with each other were identified. The majority of trials were placebo controlled.  One mixed treatment comparison study compared the evidence from placebo-controlled trials of three formulations of fentanyl: fentanyl buccal tablets, orotransmucosal fentanyl citrate and intranasal fentanyl spray, and a trial comparing orotransmucocal fentanyl in patients already using immediate release morphine sulphate.  This has been published as a conference poster.

All three fentanyl products were more effective than placebo in treating breakthrough cancer pain.  Pain relief obtained with the morphine sulphate tablets was similar to that with placebo. Intranasal fentanyl provided a greater reduction in pain intensity than the buccal and orotransmucosal products at each time point assessed. Orotransmucosal fentanyl produced significantly lower pain intensity scores than morphine sulphate at all time points, as well as greater pain relief.   All immediate release fentanyl products gave pain relief within 10-15 minutes of administration.  Maximum plasma concentrations were reached faster with fentanyl nasal spray than 

The wide range of fentanyl products makes it easier to individualise treatment for each patient but can lead to errors in dosing due to differences in pharmacokinetic/dynamic profiles.  The products are not interchangeable.   Switching from one product to another must not be done at a 1:1 ratio due to differences in bioavailability and the absorption profiles: a new dose titration must be carried out.  This may result in insufficient pain control during the titration phase.