The associations between central serous chorioretinopathy and muscle relaxants: A case-control study

PURPOSE

To evaluate the role of muscle-relaxants as risk factors for the development of central serous chorioretinopathy (CSC) - the second most common retinopathy in our settings; despite multiple risk factors seen in our patients, 21% were initially labelled as idiopathic.

MATERIALS AND METHODS

Retrospective case-control study at a tertiary hospital in the United Arab Emirates, where we reviewed the medical records of 273 patients with CSC examined between 2010 and 2019 for use of muscle-relaxants including tolperisone/eperisone, carisoprodol and gabapentin/pregabalin within a year of onset/recurrence of the disease. Intake of drugs with known association with CSC (including corticosteroids/sympathomimetics) was also recorded. Two hundred eighty-six subjects with adverse events seen at the same institute during the same study period served as controls. Odds ratios, Chi-Square tests and multivariate logistic regression were carried out to determine any associations with the muscle-relaxants and other pharmacological confounders - corticosteroids/sympathomimetics.

RESULTS

Muscle relaxants may increase the risk of CSC as evident on multivariate regression analysis (OR: 2.55; confidence interval [CI]: 1.208-5.413); the significance was retained on removing the 6 subjects who had corticosteroids/sympathomimetics (OR: 2.30; CI: 1.073-4.939). Univariate analysis yielded an OR of 2.52 for muscle relaxants (CI: 1.2149-5.2276), 2.96 for eperisone/tolperisone (CI: 1.3531-6.5038), and 6.26 for eperisone as an individual agent (CI: 1.8146-21.6252).

CONCLUSION

We found muscle relaxants to be associated factors of CSC regardless of inclusion of corticosteroids/sympathomimetics (P < 0.05). Among individual classes of muscle relaxants in this study, only eperisone/tolperisone posed a significant risk (P < 0.05). The vascular smooth muscle relaxation could be the possible mechanism that affects the choroidal blood flow and indirectly predisposes to CSC.

Toxicity of Somadril Compound on Fetal Ileum Tissues of Albino Rats

BACKGROUND AND OBJECTIVE

Carisoprodol is a relaxant muscular-skeleton associated with sore muscles and appropriate studies have not been performed on carisoprodol effects on fetuses and mothers. This study has been conducted to clarify the treatment with a high and low dosage of carisoprodol (Somadril) on the histopathological, histochemical changes in the fetal ileum of the Albino rats.

MATERIALS AND METHODS

In the present research 30 adult pregnant rats have been used and divided into three classes (10 pregnant rats in each group), the first group was the group of Control (C). The 2nd and 3rd groups (S1 and S2) were treated with carisoprodol oral doses equating to 10.8 and 21.6 mg/100 g b.wt. per day, respectively. For 15 days from day 6-20 of pregnancy, groups S1 and S2 are administered. On the 20th day of pregnancy, the pregnant rats were sacrificed and small parts of fetal ileum for histopathological and histochemical studies.

RESULTS

Diverse histopathological and histochemical alternations were detected in the fetal ileum tissue of the two groups S1 and S2 after maternal treatment with high and low doses of carisoprodol compared to the control set.

CONCLUSION

This study showed that several histopathological and histochemical deformities in the fetal ileum tissues were caused by the administration of carisoprodol.

Utilization Patterns of Skeletal Muscle Relaxants Among Commercially Insured Adults in the United States from 2006 to 2018

OBJECTIVE

To examine the prevalence and duration of skeletal muscle relaxant (SMR) treatment among commercially insured adults in the United States.

METHODS

We used the MarketScan Research Database to identify a cohort of adults 18 to 64 years who had ≥2-year continuous enrollment between 2005 and 2018. We estimated the prevalence of SMR treatment using a repeated cross-sectional design and derived treatment duration using the Kaplan-Meier method. Analyses were stratified by age group, sex, geographic region, individual SMR agent, and musculoskeletal disorder.

RESULTS

48.7 million individuals were included. Treatment prevalence ranged from 61.5 to 68.3 per 1,000. About one-third of users did not have a preceding musculoskeletal disorder diagnosis. Cyclobenzaprine was the dominant agent accounting for >50% of prescriptions. The considerable growth in the use of baclofen, tizanidine, and methocarbamol paralleled with a decline in carisoprodol and metaxalone use. The prevalence was highest in the South while lowest in the Northeast. The median treatment duration was 14 days with 4.0%, 1.9%, and 1.0% of individuals using SMRs for more than 90, 180, and 365 days, respectively. Compared with cyclobenzaprine, patients initiating baclofen, tizanidine, and carisoprodol had longer treatment duration.

CONCLUSIONS

SMRs are widely used in the United States. Their use slightly increased in recent years, but trends varied among individual agents, patient groups, and geographic regions. Despite limited evidence to support efficacy, a sizable number of U.S. adults used SMRs for long-term and off-label conditions. Further study is needed to understand determinants of treatment as well as outcomes associated with such use.

Houston Cocktail: Driving under influence of hydrocodone, alprazolam, and carisoprodol

Concurrent use of opioids, benzodiazepines, and skeletal muscle relaxants potentiates the drug effect and respiratory depression via interactions of μ-opioid and GABAA receptors. In the early 2000s when abuse of prescription drugs began to spike, a potent combination including hydrocodone, alprazolam, and carisoprodol, aka the "Houston Cocktail" or "Holy Trinity", emerged that may give users heroin-like euphoria. This research evaluated driving while intoxicated (DWI) cases that tested positive for hydrocodone, alprazolam, and carisoprodol, between 2015 and 2019. The blood samples were collected from drivers and submitted by the Houston Police Department (HPD). They were subsequently analyzed for alcohol and drugs by reference laboratories or Houston Forensic Science Center (HFSC). Toxicological findings, demographic information, and observed impairment were evaluated for the Houston Cocktail-positive DWI cases. A total of 80 DWI/DUID cases positive for hydrocodone, alprazolam, and carisoprodol in blood in which the traffic offense occurred between May 2015 and December 2019 were identified. Among these Houston Cocktail cases, the mean (median, range) concentrations were 75 (61, 6.9-322) ng/mL for hydrocodone, 58 (48, 5.8-180) ng/mL for alprazolam, and 3.9 (3.0, 0.3-14; n = 68) µg/mL for carisoprodol; 80 (100%) and 23 (29%) cases were also positive for meprobamate (mean 13; range 1.2-41 µg/mL) and hydromorphone (1.8; 1.0-3.3 ng/mL), respectively; carisoprodol and meprobamate in 12 of the cases were qualitatively detected. Forty six percent of those cases were females and 54% were males; 44% were Blacks, 46% were Whites, and 10% were other races as identified by the arresting officer. Mean (median) age of the drivers was 36 (34) years, ranged from 22 to 60 years. Twenty eight percent of the cases were positive for the Houston Cocktail only; 21% had one other drug/metabolite, 28% two, 14% three, and 10% had four or more additional drugs/metabolites. Of the 80 cases, cannabinoids were the most frequently detected analytes (35%), followed by codeine (11%). The drivers exhibited driving problems related to lane position, vigilance, judgment, speed, and/or braking. Many of the drivers (70-84%) had red/glassy eyes, slurred speed, poor balance, HGN and impaired divided attention. The present study showed that despite a traffic safety risk, drivers in Houston continue to use this dangerous drug combination. The risk is further exacerbated by the fact that the many drivers had yet other drugs in the system besides the three drugs.

Carisoprodol pharmacokinetics and distribution in the nucleus accumbens correlates with behavioral effects in rats independent from its metabolism to meprobamate

Carisoprodol (Soma®) is a centrally-acting skeletal-muscle relaxant frequently prescribed for treatment of acute musculoskeletal conditions. Carisoprodol's mechanism of action is unclear and is often ascribed to that of its active metabolite, meprobamate. The purpose of this study was to ascertain whether carisoprodol directly produces behavioral effects, or whether metabolism to meprobamate via cytochrome P450 (CYP450) enzymatic reaction is necessary. Rats were trained to discriminate carisoprodol (100 mg/kg) to assess time course and whether a CYP450 inhibitor (cimetidine) administered for 4 days would alter the discriminative effects of carisoprodol. Additionally, pharmacokinetics of carisoprodol and meprobamate with and without co-administration of cimetidine were assessed via in vivo microdialysis combined with liquid-chromatography-tandem mass spectrometry from blood and nucleus accumbens (NAc). The time course of the discriminative-stimulus effects of carisoprodol closely matched the time course of the levels of carisoprodol in blood and NAc, but did not match the time course of meprobamate. Administration of cimetidine increased levels of carisoprodol and decreased levels of meprobamate consistent with its interfering with metabolism of carisoprodol to meprobamate. However, cimetidine failed to alter the discriminative-stimulus effects of carisoprodol. Carisoprodol penetrated into brain tissue and directly produced behavioral effects without being metabolized to meprobamate. These findings indicate that understanding the mechanism of action of carisoprodol independently of meprobamate will be necessary to determine the validity of its clinical uses.

Overlapping prescriptions of opioids, benzodiazepines, and carisoprodol: "Holy Trinity" prescribing in the state of Florida

BACKGROUND

High-risk combinations of controlled medications, such as those involving opioid analgesics, are under increased scrutiny because of their contribution to the opioid epidemic in the United States. Responsible prescribing guidelines indicate that the triple drug combination--opioids, benzodiazepines and skeletal muscle relaxants, especially carisoprodol--should not be concurrently prescribed.

METHODS

This pharmacoepidemiologic study was designed to primarily examine the characteristics of patients receiving this triple combination compared to the group receiving only opioids and benzodiazepines.

RESULTS

Results show that, while the number of exposed patients has declined since 2012, approximately 17,000 Floridians were prescribed this combination in 2017 alone. Demographically, recipients of these prescriptions were younger, more likely to be female, and geographically-localized. Furthermore, these patients were more frequently associated with a prescriber in the top 1% of opioid and/or benzodiazepine prescribing, have more multiple provider episodes ("doctor shopping"), and receive higher mean daily opioid dosages.

CONCLUSIONS

These findings raise important questions as to how frequently prescribers are checking prescription drug monitoring programs, following US Centers for Disease Control and Prevention opioid prescribing guidelines, and/or handling the clinical challenges associated with pharmaceutical management of patients with complex, painful health conditions.

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.

Carisoprodol withdrawal syndrome resembling neuroleptic malignant syndrome: Diagnostic dilemma

Soma (Carisoprodol) is N-isopropyl-2 methyl-2-propyl-1,3-propanediol dicarbamate; a commonly prescribed, centrally acting skeletal muscle relaxant. Neuroleptic malignant syndrome (NMS) is a potentially life-threatening adverse effect of antipsychotic agents. Although diagnostic criteria for NMS have been established, it should be recognized that atypical presentations occur and more flexible diagnostic criteria than currently mandated, may be warranted. We wish to report a postoperative case of bilateral knee replacement who presented with carisoprodol (Soma) withdrawal resembling NMS that was a diagnostic dilemma. Subsequently, it was successfully treated with oral baclofen in absence of sodium dantrolene.

Assessment of direct gating and allosteric modulatory effects of meprobamate in recombinant GABA(A) receptors

Meprobamate is a schedule IV anxiolytic and the primary metabolite of the muscle relaxant carisoprodol. Meprobamate modulates GABAA (γ-aminobutyric acid Type A) receptors, and has barbiturate-like activity. To gain insight into its actions, we have conducted a series of studies using recombinant GABAA receptors. In αxβzγ2 GABAA receptors (where x=1-6 and z=1-3), the ability to enhance GABA-mediated current was evident for all α subunit isoforms, with the largest effect observed in α5-expressing receptors. Direct gating was present with all α subunits, although attenuated in α3-expressing receptors. Allosteric and direct effects were comparable in α1β1γ2 and α1β2γ2 receptors, whereas allosteric effects were enhanced in α1β2 compared to α1β2γ2 receptors. In "extrasynaptic" (α1β3δ and α4β3δ) receptors, meprobamate enhanced EC20 and saturating GABA currents, and directly activated these receptors. The barbiturate antagonist bemegride attenuated direct effects of meprobamate. Whereas pentobarbital directly gated homomeric β3 receptors, meprobamate did not, and instead blocked the spontaneously open current present in these receptors. In wild type homomeric ρ1 receptors, pentobarbital and meprobamate were ineffective in direct gating; a mutation known to confer sensitivity to pentobarbital did not confer sensitivity to meprobamate. Our results provide insight into the actions of meprobamate and parent therapeutic agents such as carisoprodol. Whereas in general actions of meprobamate were comparable to those of carisoprodol, differential effects of meprobamate at some receptor subtypes suggest potential advantages of meprobamate may be exploited. A re-assessment of previously synthesized meprobamate-related carbamate molecules for myorelaxant and other therapeutic indications is warranted.

Quantitation of Carisoprodol and Meprobamate in Urine and Plasma Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Carisoprodol and meprobamate are centrally acting muscle relaxant/anxiolytic drugs that can exist in a parent-metabolite relationship (carisoprodol → meprobamate) or as a separate pharmaceutical preparation (meprobamate aka Equanil, others). The monitoring of the use of these drugs has both clinical and forensic applications in pain management applications and in overdose situations. LC-MS/MS is used to analyze urine or plasma/serum extracts with deuterated analogs of each analyte as internal standards to ensure accurate quantitation and control for any potential matrix effects. Positive ion electrospray is used to introduce the analytes into the mass spectrometer. Selected reaction monitoring of two product ions for each analyte allows for the calculation of ion ratios which ensures correct identification of each analyte, while a matrix-matched calibration curve is used for quantitation.

Assessment of subunit-dependent direct gating and allosteric modulatory effects of carisoprodol at GABA(A) receptors

Carisoprodol is a widely prescribed muscle relaxant, abuse of which has grown considerably in recent years. It directly activates and allosterically modulates α1β2γ2 GABAARs, although the site(s) of action are unknown. To gain insight into the actions of carisoprodol, subunit-dependent effects of this drug were assessed. Whole-cell patch clamp recordings were obtained from HEK293 cells expressing α1β2, α1β3 or αxβzγ2 (where x = 1-6 and z = 1-3) GABAARs, and in receptors incorporating the δ subunit (modeling extrasynaptic receptors). The ability to directly gate and allosterically potentiate GABA-gated currents was observed for all configurations. Presence or absence of the γ2 subunit did not affect the ability of carisoprodol to directly gate or allosterically modulate the receptor. Presence of the β1 subunit conferred highest efficacy for direct activation relative to maximum GABA currents, while presence of the β2 subunit conferred highest efficacy for allosteric modulation of the GABA response. With regard to α subunits, carisoprodol was most efficacious at enhancing the actions of GABA in receptors incorporating the α1 subunit. The ability to directly gate the receptor was generally comparable regardless of the α subunit isoform, although receptors incorporating the α3 subunit showed significantly reduced direct gating efficacy and affinity. In extrasynaptic (α1β3δ and α4β3δ) receptors, carisoprodol had greater efficacy than GABA as a direct gating agonist. In addition, carisoprodol allosterically potentiated both EC20 and saturating GABA concentrations in these receptors. In assessing voltage-dependence, we found direct gating and inhibitory effects were insensitive to membrane voltage, whereas allosteric modulatory effects were affected by membrane voltage. Our findings demonstrate direct and allosteric effects of carisoprodol at synaptic and extrasynpatic GABAARs and that subunit isoform influences these effects.

Carisoprodol withdrawal induced delirium: A case study

A 43-year-old woman with chronic back pain found relief by taking carisoprodol, a centrally acting skeletal muscle relaxant. She had acquired large amounts of the prescription medication through the Internet and was taking approximately three hundred 350 mg tablets each week, at times up to fifty tablets per day. She then abruptly stopped the medication and presented to the emergency room one week later with waxing and waning attention, confusion, disorientation and visual hallucinations. Oral lorazepam was dosed according to a protocol employing the Clinical Institute Withdrawal Assessment of Alcohol Scale (CIWA). Her symptoms of delirium resolved rapidly and she was discharged home on day three. A review of the literature did not show any other reports of carisoprodol withdrawal induced delirium. Such withdrawal symptoms could be expected as the mechanism of action of carisoprodol is similar to that of hypnotic sedatives. Its availability and ease with which it can be acquired through the Internet puts it at great risk for a drug of abuse.

A case report of carisoprodol dependence

Carisoprodol is a centrally acting skeletal muscle relaxant whose active metabolite is meprobamate. There have been few reports of carisoprodol abuse from India. This is a report of a case with carisoprodol dependence. The patient also had poly substance abuse of alcohol, nicotine, benzodiazepine and dextropropoxyphene. Although no specific withdrawal syndrome could be identified, the patient had symptoms of anxiety, insomnia, restlessness and craving. Clinicians must be aware of the dependence potential of carisoprodol and need to be cautious in its prescription, especially in view of its free availability in the Indian market.