Incidence of rebound salicylate toxicity following cessation of urine alkalinization.

INTRODUCTION: Management of patients with salicylate toxicity frequently requires urine alkalinization to enhance excretion of salicylate. One strategy for determining when to stop urine alkalinization is to wait for two consecutive serum salicylate concentrations to be less than 300 mg/L (2.17 mmol/L) and declining. When alkalinization of the urine ceases, a rebound in serum salicylate concentration can occur from tissue redistribution or delayed gastrointestinal absorption. Whether this can lead to rebound toxicity is not well understood.

METHODS: This was a single-center, retrospective review of cases with a primary ingestion of acetylsalicylic acid reported to the local poison center over a five-year period. Cases were excluded if the product was not listed as the primary ingestion or if there was no serum salicylate concentration documented after discontinuation of intravenous sodium bicarbonate infusion. The primary outcome was the incidence of serum salicylate rebound to a concentration greater than 300 mg/L (2.17 mmol/L) after discontinuation of intravenous sodium bicarbonate infusion.

RESULTS: A total of 377 cases were included. Of these, eight (2.1%) had a serum salicylate concentration increase (rebound) after stopping the sodium bicarbonate infusion. All these cases were acute ingestions. Five of the eight cases had rebound serum salicylate concentrations that were greater than 300 mg/L (2.17 mmol/L). Of these five patients, only one reported recurrent symptoms (tinnitus). Prior to stopping urinary alkalinization, the last or the last two serum salicylate concentrations were less than 300 mg/L (2.17 mmol/L) in three and two cases, respectively.

CONCLUSIONS: In patients with salicylate toxicity, the incidence of rebound in serum salicylate concentration after cessation of urine alkalinization, is low. Even if serum salicylate rebounds to supratherapeutic concentrations, symptoms are often absent or mild. Routine repeat serum salicylate concentrations after urine alkalinization is stopped may be unnecessary unless symptoms recrudesce.