The long half-life of triamcinolone and its cortisol-suppressing effects may increase the risk for serious drug-drug interactions in patients treated with facet joint steroid injections for chronic low back pain who take medications with an inhibitory effect on corticosteroid metabolism, according to a study published in Pain Practice.

In this small cohort study, investigators evaluated 5 patients who were referred for bilateral L4-L5 and L5-S1 intra-articular lumbar facet joint injections at a pain medicine specialty clinic. To measure serum triamcinolone acetonide and serum cortisol levels, 5-mL blood samples were collected prior to and at several time points from 1 to 42 days after injection.

In addition, investigators used a software program to analyze triamcinolone serum concentration time data in these patients to determine terminal elimination half-life rates.

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The baseline average age of study participants was 42 years. All patients had a history of chronic low back pain and had not been treated with opioid medications. Within 24 hours of injection, the peak median triamcinolone concentration was 3.6 ng/mL. In a noncompartmental analysis, the terminal elimination half-life of triamcinolone was found to be 213 hours.

Triamcinolone treatment was found to result in reduced cortisol levels. Baseline cortisol levels ranged from 29 ng/mL to 87 ng/mL (nadir range, 4.2 ng/mL-16 ng/mL). Serum cortisol levels were <30 ng/mL for an average of 4.4 days after triamcinolone injection. Triamcinolone serum concentrations >1.9 ng/mL were associated with maximal cortisol-suppressing effects of the drug.

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Because of the study’s small patient population, the findings should be considered preliminary and not conclusive. In addition, because cortisol levels fluctuate throughout the day, the variable timing of blood draws in this study could have affected cortisol measurements.

”From a clinical perspective, the prolonged half-life and endocrine effects of triamcinolone could increase the risk of serious drug-drug interactions in subgroups of patients taking medications that inhibit the metabolism of corticosteroids,” concluded the authors.

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Dickson RR, Reid JM, Nicholson WT, Lamer TJ, Hooten WM. Corticosteroid and cortisol serum levels following intra-articular triamcinolone acetonide lumbar facet joint injections [published online February 12, 2018]. Pain Pract. doi: 10.1111/papr.12686