Background and Importance CT-guided transforaminal epidural steroid injection (TFESI) has become increasingly used in the treatment of radicular pain. Choice of pharmacologic agents for this procedure faces several issues, one of them is compatibility of local anaesthetic and corticosteroid mixture.

Aim and Objectives We aimed to assess the compatibility of local anaesthetic and corticosteroid mixtures that are used in TFESI.

Materials and Methods First, we conducted a literature search. In the experimental part of our study, local anaesthetics (lidocaine, bupivacaine, levobupivacaine, trimecaine) and corticosteroids (particulate: betamethasone, methylprednisolone acetate; non-particulate: dexamethasone) for injection available in Slovakia were used. Each local anaesthetic was mixed with each corticosteroid in the syringe using 1:1 and 1:3 volume ratio at room temperature. Formation of crystals in the mixture was observed visually and was confirmed with a microscope. The size of the crystals was determined using a microscope slide with a micrometre scale.

Results Based on a literature search alone we could only identify incompatibility between betamethasone and levobupivacaine and compatibility of mixtures of lidocaine and dexamethasone. In vitro we observed a turbidity after mixing lidocaine with dexamethasone in 1:1 ratio, but it was only transient. Precipitation of crystals was observed after mixing dexamethasone with bupivacaine, levobupivacaine and trimecaine. After mixing particulate corticosteroids (betamethasone and methylprednisolone acetate) with local anaesthetic suspension, particles formed big clusters (>> 100 μm).

Conclusion and Relevance In our in vitro experiment we confirmed compatibility of the mixture of lidocaine and dexamethasone as described in literature. Incompatibility between dexamethasone and bupivacaine, levobupivacaine and trimecaine was identified in vitro, although not reported in literature. Mixtures of local anaesthetic and corticosteroid are potentially unsafe due to possible incompatibilities. Caution is warranted during their use in TFESI. Separate administration of these two drug classes as recommended by some experts would overcome the issues of possible incompatibility of the mixture.