The Effect of Scheduling and Withdrawal of Carisoprodol on Prevalence of Intoxications with the Drug

Hospital admissions for paracetamol poisoning declined following codeine re-scheduling in Australia

BACKGROUND

Codeine was restricted to prescription only in Australia in 2018. This intervention aimed to reduce harms from codeine dependance and use, including toxicity from co-formulated paracetamol. We aimed to quantify the impact of this intervention on paracetamol poisoning hospital admissions in a national hospital admissions database.

METHODS

We analyzed the number of paracetamol overdoses resulting in hospital admissions from the Australian Institute of Health and Welfare National Hospital Morbidity Database, January 2011 to June 2020. We used interrupted time series analysis to quantify the effect of codeine re-scheduling on the monthly number of paracetamol poisoning-related hospital admissions in Australia. We compared paracetamol poisonings with no opioid combinations, and poisonings with probable paracetamol-codeine combinations.

RESULTS

There was an immediate and sustained decrease (level shift) in the number of paracetamol poisoning-related hospital admissions following codeine re-scheduling (RR=0.85; 95% CI 0.80-0.89). This reduction was due to the decrease in poisonings with likely paracetamol-codeine combinations (RR=0.62; 95% CI 0.57-0.67) while there was no change in other paracetamol poisonings (RR=0.91; 95% CI 0.96-1.01).

CONCLUSION

Codeine re-scheduling in Australia appears to have reduced paracetamol poisoning-related hospital admissions.

Outcomes associated with scheduling or up-scheduling controlled substances

BACKGROUND

Many nations place drugs into various "schedules" according to their risk of abuse and/or recognized medical value that vary in terms of their restrictions. To mitigate diversion or abuse, drugs sometimes get rescheduled or are scheduled for the first time. Until now, there have not been efforts to integrate lessons from across the range of such past events.

METHODS AND DATA

We searched for peer-reviewed evaluations of instances of (re-)scheduling drugs in the United States after 1969 and a comparably large set of instances from other countries. Those 109 articles were supplemented by 30 others found in other ways but not meeting those search criteria (e.g., because the information on rescheduling was a minor part of a more general article).

FINDINGS

Findings are reported for many outcomes and with diverse measures over different timelines, making standardization of outcomes difficult. For more than half of the events for which quantitative outcomes were reported, there were declines in use-related measures by at least 40 percent. It is common for there to be reports of increases in indicators pertaining to other substances, sometimes more dangerous but sometimes less dangerous; overall, substitution appears to occur, but be partial.

CONCLUSION

Scheduling and up-scheduling can - though does not always - have substantial effects on a range of outcomes. Substitution to other substances is a possibility and so should be anticipated.

Codeine use and harms in Australia: evaluating the effects of re-scheduling

BACKGROUND AND AIMS

Globally, codeine is the most-used opioid. In December 2016, Australia announced that low-strength codeine (≤ 15 mg) would be re-scheduled and no longer available for purchase over-the-counter; this was implemented in February 2018. We aimed to evaluate the effect of this scheduling change on codeine misuse and use and misuse of other opioids.

DESIGN AND SETTING

Interrupted time-series analysis of monthly opioid exposure calls to New South Wales Poisons Information Centre (NSWPIC, captures 50% of Australia's poisoning calls), January 2015- January 2019 and monthly national codeine sales, March 2015-March 2019. We incorporated a washout period (January 2017 - January 2018) between the announcement and implementation, when prescriber/consumer behaviour may have been influenced.

PARTICIPANTS

Intentional opioid overdoses resulting in a call to NSWPIC.

MEASUREMENTS

We used linear segmented regression to identify abrupt changes in level and slope of fitted lines. Codeine poisonings and sales were stratified into high strength (> 15 mg per dose unit) and low strength (≤ 15 mg). Only low-strength formulations were re-scheduled.

FINDINGS

We observed an abrupt -50.8 percentage [95% confidence interval (CI) = -79.0 to -22.6%] level change in monthly codeine-related poisonings and no change in slope in the 12 months after February 2018. There was no increase in calls to the NSWPIC for high-strength products, level change: -37.2% (95% CI = -82.3 to 8%) or non-codeine opioids, level change: -4.4% (95% CI = -33.3 to 24.4%). Overall, the re-scheduling resulted in a level change in opioid calls of -35.8% calls/month (95% CI = -51.2 to -20.4%). Low-strength codeine sales decreased by 87.3% (95% CI = -88.5 to -85.9%), with no increase in high-strength codeine sales in the 14 months following re-scheduling, -4.0% (95% CI = -19.6 to 14.6%).

CONCLUSIONS

Codeine re-scheduling in Australia appears to have reduced codeine misuse and sales.

Impact of Schedule IV controlled substance classification on carisoprodol utilization in the United States: An interrupted time series analysis

BACKGROUND

In January 2012, the Drug Enforcement Agency (DEA) classified carisoprodol as a Schedule IV controlled substance at the US federal level. We aimed to examine the effect of this policy on the use of carisoprodol in a commercially-insured population.

METHODS

This interrupted time series study included individuals with musculoskeletal disorders in the IBM MarketScan Commercial Database between December 2009 and February 2014. We used comparative segmented linear regression to assess changes in the proportions of patients who filled/newly filled carisoprodol each month.

RESULTS

A total of 13.3 million patients were included. 29 states with no scheduling prior to the DEA classification had lower baseline prevalence of carisoprodol use compared to 17 states that had scheduled carisoprodol individually before 2010 (11.0 vs. 21.1 patients with fills per 1000 patients). The federal scheduling was associated with an immediate decline (-1.12 per 1000 patients, p < 0.01) and decreasing trend in prevalence (-0.07 per 1000 patients per month, p = 0.02). This effect was not modified by existing state-level scheduling status. During the first, second, third, and fourth 6-month periods after federal scheduling, the relative difference between observed and predicted prevalence was 7.8%, 10.5%, 13.4%, and 19.8%. Similar patterns were observed for carisoprodol initiation. Overall, declining use was more pronounced among younger age groups and patients with injury.

CONCLUSIONS

Schedule IV controlled substance classification at the federal level was associated with a moderate reduction in the dispensing of carisoprodol regardless of whether scheduling was already present at the state level.

Pharmacokinetic modeling of carisoprodol and meprobamate disposition in adults

Carisoprodol is a widely prescribed muscle relaxant and is also a drug known to be a subject to abuse. Despite the fact that carisoprodol has been available for prescription since 1959, a number of gaps in our knowledge of the toxicokinetics of this common drug exist. For example, the volume of distribution (Vd) for carisoprodol in humans has not been reported. A two-compartment pharmacokinetic model describing carisoprodol metabolism and that of the primary metabolite, meprobamate, was developed to better understand the pharmacokinetics of this drug. The model accounts for first pass metabolism of carisoprodol and was able to replicate the data from several previously reported data sets. Based on an analysis of four different data sets, the Vd for carisoprodol ranged from 0.93 to 1.3 L/kg, while that for meprobamate ranged from 1.4 to 1.6 L/kg. The model was also used to estimate the probable dose of this drug in an individual where questions concerning the drug's role in her death had been posed. The model may, therefore, have significant utility for estimating doses of carisoprodol in medicolegal cases.

Severe Carisoprodol Withdrawal After a 14-Year Addiction and Acute Overdose

BACKGROUND

Carisoprodol, a centrally acting muscle relaxant with a high abuse potential, has barbiturate-like properties at the GABA-A receptor, leading to central nervous system depression and desired effects. Its tolerance and dependence has been previously demonstrated in an animal model, and withdrawal has been described in several recent case reports. Many cases can be effectively managed with a short course of benzodiazepines or antipsychotic agents. However, abrupt cessation in a patient with a history of long-term and high-dose carisoprodol abuse may result in symptoms that are more difficult for providers to treat.

CASE REPORT

We present a case of a 34-year-old man with a long history of carisoprodol abuse who was found unresponsive after having ingested 7.5 grams of carisoprodol. He was intubated and admitted to the intensive care unit. He was given propofol, dexmedetomidine, fentanyl, ketamine, lorazepam, midazolam, quetiapine, and haloperidol, some at high-dose infusions, before his agitation and ventilator asynchrony could be controlled. His improvement coincided with the addition of carisoprodol and phenobarbital to his treatment regimen. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Trends show increasing emergency department presentations for drug-related disorders and treatment. This case highlights an uncommon case of carisoprodol withdrawal that may be encountered by emergency physicians, and demonstrates that benzodiazepines may not be sufficient to suppress severe withdrawal symptoms. Treatment with carisoprodol and phenobarbital provided additional benefit and can be considered in cases of severe carisoprodol withdrawal.

The total sale of prescription drugs with an abuse potential predicts the number of excessive users: a national prescription database study

BACKGROUND

Prescription drug sales may vary considerably across regions and over time. This study aimed to assess whether there is an association between mean drug sales and prevalence of excessive use in a range of psychotropic prescription drugs with an abuse potential, and if so, whether the variation in mean drug sales mostly reflects variation in the prevalence of excessive use or mostly reflects variation in non-excessive use.

METHODS

Data on all filled prescriptions taken from the Norwegian prescription database for 10 drugs with an abuse potential (pain relievers, anxiolytics, and hypnotics) during one calendar year (2005) in Norway (n = 4,053,624) included number of defined daily doses (DDD). These were aggregated to individual level (n = 815,836) and county level (n = 19).

RESULTS

Analyses of individual level data showed that the distribution of drug use was skewed; those who used more than 365 DDD per year accounted for almost half of the sales of both anxiolytics and hypnotics. At the county level, the mean sales per inhabitant and the prevalence of excessive users were closely correlated, but both prevalence of non-excessive use and prevalence of excessive drug use were associated with the county-wise variation in mean drug sales.

CONCLUSION

Despite a strong individual control of access to psychotropic drugs through health personnel' prescribing, a small proportion of users account for a large fraction of the sales of these drugs. The sales vary significantly between regions and this variation is closely associated with the prevalence of excessive users. This suggests that sales figures as such may be used as an indicator to monitor variations in excessive use between regions and over time, and to evaluate interventions targeting over-prescription and excessive use.

Has Previous Abuse of Flunitrazepam Been Replaced by Clonazepam?

BACKGROUND AND AIMS

For many years, flunitrazepam was the benzodiazepine of choice among users of illegal drugs. The aim of this study was to investigate to which extent clonazepam use has increased in this population, and whether this was related to increased prescription or because of illegal availability.

METHODS

We used data from three sources to study the changes in the use of clonazepam: (1) Presence and concentrations of clonazepam and flunitrazepam in blood samples collected from Norwegian drugged drivers; (2) Sales numbers (legal market) for clonazepam, extracted from the Norwegian prescription database (NorPD), and (3) Specific seizures (illegal market) for clonazepam in Norway.

RESULTS

In 2004, 13.0% of the analysed blood samples from drugged drivers contained clonazepam, whereas this proportion had increased to 27.7% in 2013. In the same period, the frequency of flunitrazepam in drugged drivers decreased from 16.6% in 2004 to 3.2% in 2013. The number of clonazepam prescriptions decreased, while the number of seized tablets containing clonazepam increased considerably from 2004 to 2013.

CONCLUSIONS

For the last 10 years, a significant increase in the illegal use of clonazepam has been seen, now replacing flunitrazepam as the most used illegal benzodiazepine in Norway.

Factors affecting carisoprodol metabolism in pain patients using urinary excretion data

Carisoprodol is a skeletal muscle relaxant prescribed to treat pain. Carisoprodol is metabolized to meprobamate, an active metabolite with anxiolytic effects, by the genetically polymorphic CYP2C19 enzyme. Concomitant use of CYP2C19 substrates or inhibitors may alter carisoprodol metabolism, with therapeutic and/or toxic implications for effectively treating patients with pain. This was a retrospective analysis of urinary excretion data collected from patients with pain from March 2008 to May 2011. Carisoprodol and meprobamate urine concentrations were measured by liquid chromatography-tandem mass spectrometry, and the metabolic ratio (MR) of meprobamate to carisoprodol concentrations was determined in 14,965 subjects. The MR geometric mean and 95% confidence interval (95% CI) of the young group (105, 95% CI = 99.1-113) were ∼47.4% higher than the middle-aged group (71.9, 95% CI = 70-73.8) and nearly two times higher than the elderly group (54.4, 95% CI = 51.3-57.6). Females had a 20.7% higher MR compared with males. No significant change in the MR was observed with overall CYP2C19 inhibitor or substrate use. However, evaluation of individual inhibitors showed co-administration with esomeprazole or fluoxetine was associated with a 31.8 and 24.6% reduction in MR, respectively, compared with controls (P < 0.05). Omeprazole did not significantly affect the MR. Patient-specific factors such as age, sex and co-medications may be important considerations for effective carisoprodol therapy.

Carisoprodol tolerance and precipitated withdrawal

AIMS

Carisoprodol is a muscle relaxant that acts at the GABA(A) receptor. Concerns about the abuse liability of carisoprodol are increasing, but evidence that carisoprodol produces tolerance and a significant withdrawal syndrome has yet to be established. The purpose of the current study was to determine if repeated administration of carisoprodol produces tolerance and withdrawal signs in a mouse model.

METHODS

Carisoprodol (0, 100, 200, 300, or 500 mg/kg bid, i.p.) was administered to Swiss-Webster mice for 4 days and loss-of-righting reflex was measured 20-30 min following each administration. On the fourth day, bemegride (20 mg/kg), flumazenil (20 mg/kg), or vehicle was administered following carisoprodol and withdrawal signs were measured. Separate groups of mice receiving the same treatment regimen and dose range were tested for spontaneous withdrawal at 6, 12 and 24 h after the last dose of carisoprodol.

RESULTS

The righting reflex was dose-dependently impaired following the first administration of carisoprodol. A 75-100% decrease in the magnitude of the impairment occurred over the four days of exposure, indicating the development of tolerance to the carisoprodol-elicited loss-of-righting reflex. Withdrawal signs were not observed within 24h following spontaneous withdrawal; however, bemegride and flumazenil each precipitated withdrawal within 15-30 min of administration.

CONCLUSIONS

Carisoprodol treatment resulted in tolerance and antagonist-precipitated withdrawal, suggesting it may have an addiction potential similar to that of other long-acting benzodiazepine or barbiturate compounds.

Characterizing the subjective and psychomotor effects of carisoprodol in healthy volunteers

Carisoprodol is a centrally acting drug used to relieve skeletal muscle spasms and associated pain in acute musculoskeletal conditions. There is evidence from different sources that this oral muscle relaxant is abused and that it is associated with impairment leading to arrests for "driving under the influence" as well as increased risk of automobile accidents. Its subjective and psychomotor effects in healthy volunteers at therapeutic and supratherapeutic doses have not been well-characterized, and form the basis of this report. Fifteen healthy volunteers (8 males, 7 females) were administered 0, 350, and 700 mg of carisoprodol in separate sessions and for 6h afterwards they completed a battery of tests at fixed time intervals so as to assess the subjective and psychomotor effects of the drug. The supratherapeutic dose, 700 mg, increased visual analog scale ratings of terms that were more reflective of sedation (e.g., "sleepy," "heavy, sluggish feeling") than those of abuse liability, and produced impaired performance on several psychomotor tests. The therapeutic dose, 350 mg, while producing few and mild subjective effects, still produced psychomotor impairment. The fact that the therapeutic dose of carisoprodol produced minimal subjective effects while adversely affecting performance is of concern in that patients prescribed this drug may feel relatively normal and engage in tasks (driving) that could put themselves and others at risk.

Carisoprodol Legal Status and Patterns of Abuse

Objective:

To review the current legal status and patterns of abuse of carisoprodol.

Data Sources:

A literature search was conducted through MEDLINE (1950-August 2010), PubMed (1966-August 2010), EMBASE (1966-August 2010), and International Pharmaceutical Abstracts (1970-August 2010) using the search terms carisoprodol and abuse. In addition, reference citations from publications identified were reviewed. State laws and regulations were accessed through NABP LAW Online (2010) using the search term carisoprodol. Federal proposed rules were accessed through the Federal Register (1995 Volume 59-2010 Volume 75) using the search term carisoprodol.

Study Selection and Data Extraction:

State laws and federal proposed rules regarding carisoprodol were examined. Case reports and studies involving carisoprodol abuse were evaluated.

Data Synthesis:

Carisoprodol is not federally scheduled under the Controlled Substances Act (CSA). However, carisoprodol is scheduled in 36% (n = 18) of states of the US. The Drug Enforcement Administration issued a Notice of Proposed Rulemaking in the Federal Register on November 17, 2009, to place carisoprodol into schedule IV of the CSA, with a deadline to submit written comments by December 17, 2009. Case reports, retrospective studies, and national reports, including reports from the American Association of Poison Control Centers and results from the Monitoring the Future national survey on drug use, have identified carisoprodol's abuse potential.

Conclusions:

Carisoprodol should be placed in schedule IV of the CSA based on its abuse potential and current state laws and regulations. Federally scheduling carisoprodol would lead to uniformity among the states and hopefully assist in preventing prescription drug abuse. Larger, well-designed studies evaluating carisoprodol abuse should be performed.