Diphenhydramine dose-response: a novel approach to determine triage thresholds.

CONTEXT: It is unclear how much diphenhydramine (DPH) is toxic in humans. Previous dose-response studies have had conflicting results. Objective. We sought to evaluate DPH dose-response using a unique method that utilizes acetaminophen (APAP) serum concentrations to estimate DPH doses in patients ingesting APAP/DPH in a fixed-combination product. METHODS: We retrospectively analyzed APAP/DPH-only exposures in patients 2-80 years of age using case data from 15 U.S. poison centers. DPH dose was extrapolated from measured serum APAP concentrations. A clinically significant response (CSR) was predefined in terms of eight specific manifestations (e.g., coma) that would warrant emergency department intervention. Nominal logistic regression was used to model the probability of each recorded manifestation across DPH dose ranges examining fits for mg, mg/kg, log10 mg, and log10 mg/kg DPH doses. The threshold value where patients reliably became symptomatic was determined by further examining receiver operating characteristic curves. RESULTS: There were 509 cases that met inclusion criteria. Forty-five patients (9%) developed CSRs. A higher percentage of patients developed CSR at ≥ 7.5 mg/kg DPH and ≥1 g total DPH cutoff points (p < 0.05, Fisher's exact test). The best model for predicting the probability of CSR was a logistic fit of log(10) mg/kg dose (p < 0.05). By this model, for every 1 log(10) unit increase of mg/kg DPH dose, the odds of developing a CSR increased 47-fold (95% CI 17, 154). Receiver operating characteristic analyses showed a dose-related progression of symptoms. The cut-point with greatest sensitivity (98%) versus 1-specificity (57%) corresponded to an extrapolated mg/kg DPH dose of 8.2 mg/kg (95% CI 5.6, 10.5). CONCLUSION: Our findings support the current American Association of Poison Control Centers' guideline recommendation to refer patients to the hospital for evaluation if they have ingested greater than or equal to 7.5 mg/kg of DPH.

Toxicity from a clonidine suspension.

BACKGROUND: Clonidine is frequently prescribed to children. Clonidine overdose in children has resulted in major clinical effects and deaths. CASE REPORT: A 3.5-year-old male with a history of a seizure disorder and night terrors presented following difficulty walking, excessive sleeping, agitation when awake, and possible seizure activity. Chronic medications were valproic acid (VPA) and clonidine. On presentation, he alternated between poor responsiveness and agitation, with initial vitals: blood pressure, BP 144/76 mmHg; heart rate, 65 bpm; respiratory rate, 18 bpm; temperature 99.5 degrees F; and pulse oximetry 96% on room air. VPA level was 35 microg/mL. A toxicology consult the next day noted a dry mouth, 2-mm pupils, intermittent gasping, and central nervous system (CNS) depression, with a diagnostic impression of clonidine overdose. The caregiver had been giving 1 mL (0.1 mg) qd of a pharmacy-compounded clonidine suspension by a provided syringe. The pharmacy procedure record agreed with the physicians order. The amount dispensed was a 30-day supply but the bottle was empty on day 19, leading us to suspect a possible accelerated dosing error. The concentration in the bottle thus could not be confirmed. The child slowly returned to his baseline state over 48 hours. A serum clonidine level drawn approximately 18 hours after his last dose later returned at 300 ng/mL (reference range = 0.5-4.5 ng/mL). CASE DISCUSSION: Compounding and liquid dosing errors are common in children and may result in massive overdoses. There was an accelerated dosing error, but whether a compounding or suspension error or even an acute overdose occurred as well is unknown. CONCLUSION: Particular care should be taken with medications that have low therapeutic indices, that are extemporaneously compounded, and are prepared as liquids, where medication errors are more likely.