Size and aggregation of corticosteroids used for epidural injections

The purpose of this study was to document particulate size in commonly used corticosteroid preparations. Inadvertent injection of particulate corticosteroids into a vertebral or foraminal artery can cause brain and spinal cord embolic infarcts and the size of the particles could be directly related to the chance that a clinically significant infarct would occur. One might assume that corticosteroids with particles significantly smaller than red blood cells might be safer.

The following four types of corticosteroid preparations were used in various solutions and evaluated under light microscopy: dexamethasone sodium phosphate injection, triamcinolone acetonide injectable suspension, betamethasone sodium phosphate and betamethasone acetate injectable suspension, and methylprednisolone acetate injectable suspension.

Dexamethasone sodium phosphate particle size was approximately 10 times smaller than red blood cells and the particles did not appear to aggregate; even mixed with 1% lidocaine HCl solution and with contrast dye, the size of the particles were unchanged. Triamcinolone acetonide and betamethasone sodium phosphate showed variable sizes; some particles were larger than red blood cells, and aggregation of particles was evident. Methylprednisolone acetate showed uniformity in size and the majority were smaller than red blood cells which were not aggregated, but the particles were densely packed.

Compared with the particulate steroid solutions, dexamethasone sodium phosphate had particles that were significantly smaller than red blood cells, had the least tendency to aggregation, and had the lowest density. These characteristics should significantly reduce the risk of embolic infarcts or prevent them from occurring after intra-arterial injection. Until shown otherwise in clinical studies, interventionalists might consider using dexamethasone or another corticosteroid preparation with similar high solubility and negligible particle size when performing epidural injections.