During the 6-year study period, the CPCS had 1411 reports coded as dextromethorphan abuse and all underwent manual case record review. Ultimately, 1382 dextromethorphan abuse cases were included in the final analysis. On review, 29 cases were excluded because of the following reasons: drug information cases (n=10), duplicate cases (n=2), product reported did not contain dextromethorphan (n=1), misclassified as abuse (n=14), and reported symptoms were unrelated to dextromethorphan ingestion (n=2). During the study, the CPCS received 1 336 475 human exposure calls.
From 1999 through 2004, the frequency of all dextromethorphan abuse cases reported to the CPCS increased 10-fold (). The average effect was an almost 50% increase in the frequency of reported cases each year compared with the previous year (odds ratio, 1.48; 95% confidence interval, 1.43–1.54). This increase in the number of dextromethorphan abuse cases () and the proportion of dextromethorphan cases among all exposures reported () was also seen in the data collected by the AAPCC (odds ratio, 1.31; 95% confidence interval, 1.29–1.33) and DAWN (through 2002) (odds ratio, 1.15; 95% confidence interval, 1.13–1.18). The CPCS dextromethorphan abuse reports are included in the cases reported to the AAPCC, but these alone would not account for the national AAPCC trend.
Dextromethorphan Abuse Cases Reported to the CPCS From 1999 Through 2004*
Figure 1 A comparison of California Poison Control System (CPCS), American Association of Poison Control Centers (AAPCC), and Drug Abuse Warning Network (DAWN)12 dextromethorphan abuse cases. Dextromethorphan DAWN data were unavailable for 2003 and 2004. Dextromethorphan (more ...)
Figure 2 The proportion of California Poison Control System (CPCS), American Association of Poison Control Centers (AAPCC), and Drug Abuse Warning Network (DAWN)12 dextromethorphan abuse cases compared with the total exposures reported to each database. Dextromethorphan (more ...)
The overall increase in the frequency of dextromethorphan abuse cases was paralleled by an increase in the frequency of dextromethorphan abuse cases reported in adolescents (defined as those aged 9–17 years). During the 6-year study period, 74.5% of all reported CPCS dextromethorphan abuse cases involved adolescents. The overall median age was 16 years. The proportion of all dextromethorphan abuse cases that occurred in adolescents increased over the duration of the study according to the CPCS (odds ratio, 1.25; 95% confidence interval, 1.15–1.36) and AAPCC (odds ratio, 1.03; 95% confidence interval, 1.01–1.05) databases. The largest proportional increase in adolescent abuse was seen from 1999 to 2000 (). The highest frequency of dextromethorphan abuse in the CPCS and AAPCC databases was among adolescents aged 15 and 16 years (). The younger adolescent age distribution is further underscored by the observation that in CPCS reporting the combined frequency among 12- to 13-year-old subjects exceeded that of 18-year-old subjects.
Figure 3 A comparison of the trends in abuse according to age for cases reported to the California Poison Control System (CPCS) and the American Association of Poison Control Centers (AAPCC) during the study. The age was not reported in 22 of the CPCS cases and (more ...)
Of the 1382 cases of dextromethorphan abuse included in our study, the most commonly abused product was Coricidin HBP Cough & Cold Tablets. This was followed by dextromethorphan-containing Robitussin products (Wyeth, Madison, NJ) (). The proportion of abused dextromethorphan products represented by Coricidin HBP Cough & Cold Tablets increased over the study period (odds ratio, 1.23; 95% confidence interval, 1.13–1.26). This increasing trend in abuse of Coricidin HBP Cough & Cold Tablets corresponded to an increase in the number of exposures that involved a solid dose form of dextromethorphan (odds ratio, 1.43; 95% confidence interval, 1.31–1.56). In contrast to the increase in acute cases of dextromethorphan abuse, long-term abuse reports to the CPCS were uncommon (n=32) and declined over the study period (odds ratio, 0.51; 95% confidence interval, 0.40–0.64).
Most dextromethorphan cases resulted in minor (636 cases [46.0%]) or moderate (578 cases [41.8%]) outcomes. Seven cases (0.5%) had major outcomes. For the remaining cases, either no symptoms were reported (94 cases [6.8%]) or the outcome was unknown (67 cases [4.8%]) (). There were no fatalities reported. All 7 major outcome cases involved serious pulmonary complications, such as respiratory depression or aspiration requiring intubation. Five of the major outcome cases involved coingestants, 3 of which involved ethanol. Among the major outcome cases, only 2 involved minors. There was an increase in combined moderate and major outcomes during the study (odds ratio, 1.09; 95% confidence interval, 1.01–1.17). A multivariate model incorporating study year, age, sex, presence of coingestants, and exposure to Coricidin HBP Cough & Cold Tablets showed an increased incidence of moderate and major outcomes among patients in later years (odds ratio, 1.09; 95% confidence interval, 1.01–1.18) and among male adolescents (odds ratio, 1.22; 95% confidence interval, 1.09–1.37).
Polysubstance use was reported by history in 278 (20.1%) of all subjects. The most common agents reported were ethanol (n=93), marijuana (n=40), opiates (n=23), acetaminophen (n=17), amphetamines (n=14), selective serotonin reuptake inhibitors (n=10), pseudoephedrine (n=10), and benzodiazepines (n=9). Self-reported ethanol coingestion was documented among 93 (6.7%) subjects; however, only 23 cases had laboratory confirmation. Three cases were coded as having major outcomes (levels ranged from 230–373 mg/dL), and 11 were coded as having moderate outcomes. Only 17 patients reported ingesting acetaminophen by history; however, there were 26 patients with confirmed laboratory acetaminophen levels (range, 9.1–111.0 μg/mL). More important, 8 patients had a delayed presentation to the hospital (range, 8 hours–4 days), and in 4 additional patients the time of ingestion was unknown. Sixteen patients received N-acetylcysteine therapy, of whom 7 experienced elevated transaminase levels. Of these 7 patients, 1 was a long-term alcohol user. Of the 26 subjects with acetaminophen involvement, 14 were coded as having a moderate outcome and 0 were coded as having a major outcome. There was no significant difference in the occurrence of the combined major and moderate outcomes between patients who did or did not have any coingestant (odds ratio, 0.96; 95% confidence interval, 0.83–1.14).
The most common adverse effects reported were tachycardia (n=593), lethargy (n=481), hypertension (n=289), confusion or altered mental status (n=277), mydriasis (n=251), agitation (n=171), gastrointestinal effects (n=159), dizziness (n=94), ataxia (n=83), hallucinations (n=80), slurred speech (n=77), nystagmus (n=75), fever (n=54), loss of consciousness (n=26), tachypnea (n=20), seizure (n=12), and hypotension (n=12).