The trajectory of serum salicylate concentrations after ingestion of medicinal oil containing methyl salicylate.

Introduction: The toxicokinetics of methyl salicylate after unintentional or intentional ingestion of medicinal oil containing methyl salicylate has not been well studied. We aimed to characterize the trajectory of serum salicylate concentrations and to evaluate factors associated with the peak serum salicylate concentration and the time from ingestion to peak concentration.

Methods: This was a retrospective cohort study of consecutive patients reported to the Hong Kong Poison Control Centre for laboratory-confirmed methyl salicylate poisoning by all local public emergency departments between 1 July 2008 and 30 June 2023. We analyzed cases with at least three serum salicylate concentrations. Multivariable generalized linear regression was used to identify factors significantly associated with the peak serum concentration and the time from ingestion to peak concentration.

Results: We included 41 patients (median age 81.0 years; 32 women and nine men). The median time from ingestion to the first peak serum salicylate concentration was 5.6 h (IQR: 3.2-10.8 h). Multiple regression showed that gastric aspiration (adjusted regression coefficient [β] - 2.50; 95% CI: -3.93 to -1.08;  = 0.001) and single-dose activated charcoal (adjusted β - 1.22; 95% CI: -2.02 to -0.42;  = 0.003) were significantly associated with a lower peak concentration, after adjusting for patient age, sex, exposure due to intentional self-harm, reported ingested dose, time from ingestion to emergency department presentation, vomiting, concurrent use of aspirin (acetylsalicylic acid) and other medications that affect gastric emptying or gastric acid secretion, blood pH, serum albumin concentration, and creatinine clearance.

Discussion: The serum salicylate concentration did not peak as quickly as generally believed, highlighting the importance of continued monitoring. Gastric aspiration and single-dose activated charcoal may help reduce gastrointestinal absorption, but their impact on clinical outcomes remains unclear.

Conclusions: Given the median time of 5.6 h (IQR: 3.2-10.8 h) from ingestion to the peak salicylate concentration, gastric aspiration and single-dose activated charcoal can be considered in patients up to a few hours after medicinal oil ingestion when the airway is protected.