Corticosteroid and Cortisol Serum Levels Following Intra-articular Triamcinolone Acetonide Lumbar Facet Joint Injections.

BACKGROUND: Facet joint steroid injections are used to treat chronic low back pain. However, little is known about the systemic absorption and serum levels of steroids following intra-articular facet joint injections. The primary objective of this preliminary study was to investigate the pharmacokinetics of triamcinolone acetonide following fluoroscopically guided intra-articular lumbar facet joint injections in a cohort of patients with chronic low back pain. A secondary aim was to investigate the effects of triamcinolone on serum cortisol levels following lumbar facet joint injections. METHODS: The study cohort included 5 patients undergoing fluoroscopically guided intra-articular lumbar facet joint injections at a pain medicine specialty clinic. Blood was collected prior to the injections and on days 1, 2, 4, 6, 8, 14, 21, 28, 35, and 42 following the injections. RESULTS: The terminal elimination half-life of triamcinolone in a noncompartmental analysis was 213 hours. The peak median triamcinolone concentration of 3.6 ng/mL was detected within 24 hours after the injections. Serum cortisol levels were < 30 ng/mL for an average of 4.4 days. The maximum effect of triamcinolone on cortisol suppression was observed with triamcinolone serum levels of > 1.9 ng/mL. CONCLUSIONS: The peak serum concentration of triamcinolone following intra-articular facet joint injections occurred within 24 hours. The median terminal elimination half-life was 213 hours, but baseline cortisol levels were suppressed for an average of 4.4 days. Clinically, the prolonged half-life and endocrine effects of triamcinolone could increase the risk for serious drug-drug interactions in patients taking medications that inhibit corticosteroid metabolism.