Background and aims Dexamethasone is a widely used adjuvant to local anesthetics for acute pain management. Though previous studies have compared the analgesic efficacy of i/v and perineural Dexamethasone, however none have evaluated systemic absorption of perineurally administered Dexamethasone. With the idea of finding some clarification of mechanism of action of Dexamethasone, we compared systemic levels of perineurally administered Dexamethasone with that given intravenously. Our primary outcome was to evaluate the blood levels of dexamethasone after its administration either perineurally or intravenously.

Methods After ethics committee approval, we included 30 patients undergoing unilateral upper limb surgery under ultrasound-guided supraclavicular brachial plexus block. Subjects were randomized to receive ultrasound-guided supraclavicular brachial plexus block using 0.375% Bupivacaine (25ml) with Dexamethasone (8mg) given either perineurally (group I) or intravenously (group II). Blood Dexamethasone levels were measured before drug administration, at 20, 40, 60 min, 2, 4, 8 and 12 hours after Dexamethasone administration. Postoperatively, patients were monitored for pain for 24 hours. Patients with NRS≥4 received i/v tramadol 2mg/kg.

Results The groups had comparable average maximum serum concentrations (Cmax) of Dexamethasone (Average Cmax=11403.61±4876.52ng/ml in group I and 12418.59±2414.92ng/ml in group II; p value=0.48), with average time until achieving Cmax of Dexamethasone being 20minutes. Area under the concentration curve (AUC(0-t)) was comparable between the two groups (59632.34±30769.74nghr/ml in group I and 61718.41±19479.34nghr/ml in group II; p value=0.83).

Conclusions Most of perineurally administered Dexamethasone was absorbed systemically. Thus, the possible mechanism of action of perineurally administered Dexamethasone could be similar to that administered intravenously, with most of its effect being due to its systemic absorption.