In vivo pharmacokinetic, pharmacodynamic and brain concentration comparison of fentanyl and para-fluorofentanyl in rats.

In 2022, para-fluorofentanyl (pFF) rose to the 6th most reported drug and the most reported fentanyl analog in the United States according to the Drug Enforcement Administration (DEA). pFF differs from fentanyl by the addition of a single fluorine group. To date, pFF has not been extensively evaluated in vivo and is frequently seen in combination with fentanyl. In the present study, the pharmacodynamic (PD) and pharmacokinetic (PK) properties and brain region-specific concentrations of pFF were evaluated in male Sprague-Dawley rats and compared to fentanyl. A 300 µg/kg subcutaneous dose of fentanyl or pFF was administered to assess PD and PK parameters as well as brain region concentrations. PD parameters were evaluated via a tail flick test to evaluate analgesia and core body temperature to measure hypothermia, a surrogate marker of overall opioid toxicity. Fentanyl and pFF were found to be equally active at the tested dose in terms of tail flick response with both compounds producing an analgesic response that lasted up to 240 min post-drug treatment. pFF induced a significantly greater hypothermic effect compared to fentanyl with a maximum temperature decrease of -5.6 ℃. Plasma PK parameters (T1/2, AUC, etc.) did not differ between fentanyl and pFF. However, pFF concentrations in the medulla, hippocampus, frontal cortex and striatum were more than two times the fentanyl concentrations. The increase in brain concentrations and greater hypothermic effect suggests that pFF is potentially more dangerous than fentanyl.

The relations between impulsivity, opioid use, and nonmedical prescription opioid use motives: An examination within three large urban emergency departments.

Impulsivity is a transdiagnostic risk factor for multiple disorders, including opioid use disorders (OUDs). However, scant work has examined if impulsivity facets distinguish individuals reporting nonmedical opioid use from those who use opioids as prescribed, particularly in important settings such as emergency departments (EDs). Further, no studies, to our knowledge, have examined the relations between impulsivity facets and motives for nonmedical prescription opioid use (NMPOU). Using data from EDs, this study examined if impulsivity facets (assessed via the [negative] urgency, premeditation, perseverance, sensation seeking, and positive urgency) related to nonmedical opioid use and if these facets related to OUD severity among individuals reporting past-year opioid use. Among patients reporting past 3-month NMPOU, the relation between motives for use and impulsivity was examined. Results indicated all facets (except lack of perseverance) distinguished patients reporting nonmedical opioid use from individuals abstaining from opioid use and those who used opioids as prescribed, with particularly large effect sizes for positive and negative urgency. Similarly, among patients reporting past 12-month opioid use, all facets (except lack of perseverance) significantly distinguished individuals who were OUD negative from those with severe OUD, with positive and negative urgency showing the strongest relations. Multiple motives were associated with certain UPPS-P facets, particularly positive urgency, negative urgency, and sensation-seeking. Results suggest that the relation between impulsivity and opioid use characteristics varies across facets of impulsivity, with emotion-based impulsivity being the most relevant. Implications for screening and interventions are discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Association of genetic variants in CYP3A5, DRD2 and NK1R with opioid overdose.

In 2023, 3651 Ohioans died because of an opioid overdose. Of those opioid overdoses, 3579 (98%) of which were attributed to fentanyl. We evaluated the association between 180 candidate single nucleotide polymorphisms (SNPs) and self-reported, nonfatal opioid overdose history from a prospective sample of 1301 adult patients (≥18 years of age) seen in three urban emergency departments in Ohio. Candidate SNPs included 120 related to the dopamine reward pathway and 60 related to pharmacokinetics. Of the 821 patients who reported having been exposed to opioids in their lifetime, 95 (11.6%) also reported having experienced an opioid-related overdose. Logistic regression, adjusting for age and biologic sex, was used to characterize the association between each SNP and opioid overdose, correcting for multiple comparisons. Three SNPs, located in three different genes were associated with opioid overdose: increased odds with CYP3A5 (rs776746) and DRD2 (rs4436578), and decreased odds with NKIR (rs6715729). Homozygotic CYP3A5 (rs776746) had the highest adjusted odds ratio (OR) of 6.96 (95% CI [2.45, 29.23]) and homozygotic NK1R (rs6715729) had the lowest OR of 0.28 (95% CI [0.14, 0.54). Given that CYP3A5 (rs776746) has been associated with increased plasma concentrations of fentanyl, rs776746 could potentially be utilized as a prognostic risk indicator for the potential of an opioid overdose. NK1R regulates the expression of the neurokinin-1 receptor, a regulator of respiration and NK1R (rs6715729) represents a novel genetic marker for a decreased risk of opioid overdose risk.

State program enables the identification of factors associated with naloxone awareness, self-efficacy, and use for overdose reversal: A cross-sectional, observational study in an urban emergency department population.

INTRODUCTION: To assist the state of Ohio in addressing the opioid epidemic, the Ohio Attorney General appointed experts in a variety of academic disciplines to the Scientific Committee on Opioid Prevention and Education (SCOPE). The focus of SCOPE is the application of scientific principles to the development of prevention and educational strategies for reducing substance use disorder and related harms (e.g., promoting naloxone awareness). Naloxone awareness is a step in the naloxone cascade, which is a useful model for understanding the sequential steps laypeople must take to prepare themselves to intervene using naloxone; other steps include training and previous administration experience. Prior work has explored correlates of these steps among individuals with risky substance use, but fewer studies have focused on broader populations containing potential bystanders (e.g., family and community members). METHODS: This study was a secondary data analysis of patients from three urban emergency departments. Subsamples differed across five models (n = 479-1208) and included opioid-exposed and -naïve participants. Logistic regression characterized clinically useful sociodemographic predictors (e.g., race, ethnicity, education, employment, housing status) of naloxone awareness, self-efficacy (which relates to training), and previous-overdose administration. Two additional logistic regressions tested associations between risk factors for witnessing an opioid overdose and two cascade steps (awareness and self-efficacy). RESULTS: Non-White race, Hispanic ethnicity, and lower education predicted not being aware of naloxone; non-White race also predicted lower naloxone self-efficacy, and older age predicted lack of previous-overdose administration. Having family members with risky opioid use was heavily associated with awareness, while personal substance-use behaviors and previous overdose witnessing were associated with both awareness and higher naloxone self-efficacy. CONCLUSIONS: Characteristics associated with lower likelihood of completing each cascade step highlight opportunities for targeted interventions. Specifically, findings indicated the importance of expanding naloxone education and training programs to more diverse populations and to family members of individuals with risky opioid use. Further, these findings demonstrate how a state-funded program such as SCOPE can have a positive impact on identifying strategies that may assist in reducing mortality associated with opioid overdose.

Opioid use disorder risk alleles in self-reported assigned African American/Afro-Caribbean and European biogeographical genetic ancestry groups and in males and females.

The influence of genetic variants related to opioid use disorder (OUD) was evaluated using multiple logistic regression analysis in self-reported assigned African American/Afro-Caribbean and European biogeographical ancestry groups (BGAGs) and by sex. From a sample size of 1301 adult patients (>18 years of age) seen in emergency departments of three medical centers in Ohio, six variants were found to be associated with OUD. Two of the variants, rs2740574 (CYP3A4) and rs324029 (DRD3), were included in the analysis having met criteria of at least five subjects for each BGAG, variant carrier status, and OUD status combinations. Variant carriers in the African/Afro-Caribbean BGAG had slightly lower predicted probabilities of OUD. Variant carriers in the European BGAG had slightly higher predicted probabilities of OUD. Relative to sex, all the six variants met evaluation criteria (five subjects for all sex, variant, and OUD status combinations). No statistically significant interactions were found between a given variant, BGAGs and sex. Findings suggest variant testing relative to OUD risk can be applied across BGAGs and sex, however, studies in larger populations are needed.

Bile acids and the gut microbiome are involved in the hyperthermia mediated by 3,4-methylenedioxymethamphetamine (MDMA).

Hyperthermia induced by phenethylamines, such as 3,4-methylenedioxymethamphetamine (MDMA), can lead to life-threatening complications and death. Activation of the sympathetic nervous system and subsequent release of norepinephrine and activation of uncoupling proteins have been demonstrated to be the key mediators of phenethylamine-induced hyperthermia (PIH). Recently, the gut microbiome was shown to also play a contributing role in PIH. Here, the hypothesis that bile acids (BAs) produced by the gut microbiome are essential to PIH was tested. Changes in the serum concentrations of unconjugated primary BAs cholic acid (CA) and chenodeoxycholic acid (CDCA) and secondary BA deoxycholic acid (DCA) were measured following MDMA (20 mg/kg, sc) treatment in antibiotic treated and control rats. MDMA-induced a significant hyperthermic response and reduced the serum concentrations of three BAs 60 min post-treatment. Pretreatment with antibiotics (vancomycin, bacitracin and neomycin) in the drinking water for five days resulted in the depletion of BAs and a hypothermic response to MDMA. Gut bacterial communities in the antibiotic-treated group were distinct from the MDMA or saline treatment groups, with decreased microbiome diversity and alteration in taxa. Metagenomic functions inferred using the bioinformatic tool PICRUSt2 on 16S rRNA gene sequences indicated that bacterial genes associated to BA metabolism are less abundant in the antibiotic-MDMA treated group. Overall, these findings suggest that gut bacterial produced BAs might play an important role in MDMA-induced hyperthermia.

Xylazine does not enhance fentanyl reinforcement in rats: A behavioral economic analysis.

The adulteration of illicit fentanyl with the alpha-2 agonist xylazine has been designated an emerging public health threat. The clinical rationale for combining fentanyl with xylazine is currently unclear, and the inability to study fentanyl/xylazine interactions in humans warrants the need for preclinical research. We studied fentanyl and xylazine pharmacodynamic and pharmacokinetic interactions in male and female rats using drug self-administration behavioral economic methods. Fentanyl, but not xylazine, functioned as a reinforcer under both fixed-ratio and progressive-ratio drug self-administration procedures. Xylazine combined with fentanyl at three fixed dose-proportion mixtures did not significantly alter fentanyl reinforcement as measured using behavioral economic analyses. Xylazine produced a proportion-dependent decrease in the behavioral economic Q0 endpoint compared to fentanyl alone. However, xylazine did not significantly alter fentanyl self-administration at FR1. Fentanyl and xylazine co-administration did not result in changes to pharmacokinetic endpoints. The present results demonstrate that xylazine does not enhance the addictive effects of fentanyl or alter fentanyl plasma concentrations. The premise for why illicitly manufacture fentanyl has been adulterated with xylazine remains to be determined.

Dopamine Concentration Changes Associated with the Retrodialysis of Methylone and 3,4-Methylenedioxypyrovalerone (MDPV) into the Caudate Putamen.

Structural modifications to synthetic psychoactive cathinones (SPCs), a class of drugs that contain a ß-keto modification of the phenethylamine pharmacophore of amphetamine, induce differences in dopamine transporter (DAT) activity. Here, in vivo retrodialysis was utilized to deliver the SPCs 3,4-methylenedioxypyrovalerone (MDPV, a DAT inhibitor) or methylone (a DAT substrate) into the caudate putamen of male Sprague-Dawley rats. Dialysate samples were collected prior to and post drug administration, and temporal changes in dopamine concentration were quantified using HPLC-EC methods. Methylone elicited a 200% increase and MDPV a 470% increase in dopamine levels at the 10 min time point. The findings demonstrate that in vivo retrodialysis can be used to evaluate the effects of SPCs on neurotransmission in the brain.

Effects of the designer drug 4-methylamphetamine on core temperature and serotonin levels in the striatum and hippocampus of rats.

New psychoactive substances (NPS) are typically synthesized in clandestine laboratories in an attempt to chemically modify already federally regulated drugs in an effort to circumvent the law. Drugs derived from a phenethylamine pharmacophore, such as 4-chloroamphetamine and 3,4-methylenedioxymethamphetamine (MDMA), reliably induce thermogenesis and serotonergic deficits in the striatum and hippocampus of rodents. 4-methylamphetamine (4-MA), a relative newcomer to the NPS scene, was originally investigated in the mid-1900 s as a potential anorexigenic agent. With its phenethylamine pharmacophore, 4-MA was hypothesized to produce similar toxicological alterations as its chemical analogs. In the present study, three doses (1.0, 2.5, and 5.0 mg/kg, ip.) of 4-MA were administered to rats twice daily for two days. Core temperature data were calculated and analyzed as temperature area under the curve (TAUC). On the second day of dosing, a hypothermic response to 4-MA (2.5 and 5.0 mg/kg) was noted between 0.5 and 2.0 h post-treatment. Only the highest dose of 4-MA decreased body weight on the second day of treatment and maintained this reduction in weight for seven days after treatment ceased. None of the doses of 4-MA evaluated significantly altered serotonin levels in the hippocampus or striatum seven days after final treatment. The present findings demonstrate that the 4-methyl substitution to amphetamine generates a pharmacological and toxicological profile that differs from other similar phenethylamine analogs.

The dopamine 3 receptor as a candidate biomarker and therapeutic for opioid use disorder.

Here, we present recent studies suggesting that specific DRD3 single nucleotide polymorphisms (SNPs, e.g. rs324029 and rs2654754) might serve as prognostic biomarkers for opioid use disorder (OUD). Additionally, preclinical studies with novel dopamine 3 receptor (D3R) partial agonists and antagonists have been evaluated as candidate OUD therapeutics and have shown a reduced risk of cardiovascular toxicity compared with the original D3R antagonist. From these findings, we argue that DRD3 SNPs could serve as a diagnostic tool for assessing OUD risk and that more research is warranted examining the D3R as a safe and effective therapeutic target for treating OUD.

Screening for problematic opioid use in the emergency department: Comparison of two screening measures.

Study objective: Earlier intervention for opioid use disorder (OUD) may reduce long-term health implications. Emergency departments (EDs) in the United States treat millions with OUD annually who may not seek care elsewhere. Our objectives were (1) to compare two screening measures for OUD characterization in the ED and (2) to determine the proportion of ED patients screening positive for OUD and those who endorse other substance use to guide future screening programs. Methods: A cross-sectional study of randomly selected adult patients presenting to three Midwestern US EDs were enrolled, with duplicate patients excluded. Surveys were administered via research assistant and documented on tablet devices. Demographics were self-reported, and OUD positivity was assessed by the DSM 5 checklist and the WHO ASSIST 3.1. The primary outcome was the concordance between two screening measures for OUD. Our secondary outcome was the proportion of ED patients meeting OUD criteria and endorsed co-occurring substance use disorder (SUD) criteria. Results: We enrolled 1305 participants; median age of participants was 46 years (range 18-84), with 639 (49.0%) Non-Hispanic, White, and 693 (53.1%) female. Current OUD positivity was identified in 17% (222 out of 1305) of the participants via either DSM-5 (two or more criteria) or ASSIST (score of 4 or greater). We found moderate agreement between the measures (kappa = 0.56; Phi coefficient = 0.57). Of individuals screening positive for OUD, 182 (82%) endorsed criteria for co-occurring SUD. Conclusions: OUD is remarkably prevalent in ED populations, with one in six ED patients screening positive. We found a high prevalence of persons identified with OUD and co-occurring SUD, with moderate agreement between measures. Developing and implementing clinically feasible OUD screening in the ED is essential to enable intervention.

Influence of carbon side chain length on the in vivo pharmacokinetic and pharmacodynamic characteristics of illicitly manufactured fentanyls.

Since 2016, illicitly manufactured fentanyls and fentanyl analogs (referred to as IMFs) have contributed to an increase in drug overdoses. Although fentanyl has been characterized and evaluated extensively in animals and humans, many of the clandestinely synthesized analogs of fentanyl have not and users may unknowingly ingest these IMFs leading to overdose and potentially death. The pharmacodynamic (PD) and pharmacokinetic (PK) properties of four IMFs and fentanyl were evaluated in Sprague-Dawley rats. A 300-µg/kg subcutaneous dose of each compound (fentanyl, acetylfentanyl, cyclopropylfentanyl, butyrylfentanyl, and valerylfentanyl) was given. PD parameters were measured using a tail flick meter and core body temperature. Blood was drawn to evaluate PK parameters utilizing liquid chromatography tandem mass spectrometry (LC-MS/MS). Fentanyl displayed the greatest and longest lasting analgesia with a tail flick response of 10 s (the maximum cutoff). Additionally, fentanyl produced an average -4.9°C in core body temperature resulting in the greatest decrease in core body temperature. Acetylfentanyl, with the shortest carbon side chain, displayed the shortest T½, and lowest AUC and Cmax and resulted in an increase in body temperature. There were no other PK differences among the IMFs assessed. As IMFs are commonly seen on the streets and can pose significant risks to users (although these risks do depend on other factors such as dose and route of administration), there is a benefit to having the pharmacological properties of these compounds characterized to better understand the potential harm to humans.

Better together: utilizing an interprofessional course and escape room to educate healthcare students about opioid use disorder.

BACKGROUND: The aim of the present study was to determine the impact of an innovative interprofessional educational activity on healthcare professional students' learning. The educational activity targeted student knowledge of opioid use disorder (OUD) and perceptions of working with an interprofessional team while caring for patients with OUD. METHODS: Students from nursing, pharmacy, physician assistant, dentistry, social work, and medicine programs were recruited to participate in the interprofessional educational activity. The educational experience included seven asynchronous modules and a virtual synchronous escape room. Prior to the educational programming, participants completed a pre-survey that assessed their knowledge and attitudes towards working on an interprofessional team and perceptions of patients with OUD. The asynchronous modules were required in order to participate in the escape room and each module contained its own pre/post quiz to assess student knowledge. RESULTS: A total of 402 students participated in the course. Prior to participating in the course, students disagreed that they had extensive educational experience with SUD (2.45 ± 0.79). The students displayed significant improvement in the knowledge based areas after completing the seven asynchronous modules. The largest significant area of knowledge-based improvement was seen in treatment of OUD where on the pre-quiz 65.54 ± 20.21% were answered correctly compared to 95.97 ± 9.61% on the post-quiz. Participation in the escape room significantly changed the students' perceptions of working in interprofessional teams while managing patients with OUD. Of the eleven perception variables assessed, seven showed a significant increase in the post-survey. Following the escape room, participants also strongly agreed that they now would refer patients to colleagues in other disciplines. CONCLUSIONS: An interprofessional educational experience including both an asynchronous course and virtual synchronous escape room can increase participant knowledge around OUD and may improve student perceptions of working with an interprofessional team and caring for patients with OUD.

Designer benzodiazepine rat pharmacokinetics: A comparison of alprazolam, flualprazolam and flubromazolam.

Designer benzodiazepines, including flualprazolam and flubromazolam, are clandestinely produced to circumvent federal regulations. Although flualprazolam and flubromazolam are structurally similar to alprazolam, they do not have an approved medical indication. Flualprazolam differs from alprazolam by the addition of a single fluorine atom. Whereas, flubromazolam differs by the addition of a single fluorine atom and substitution of a bromine for a chlorine atom. The pharmacokinetics of these designer compounds have not been extensively evaluated. In the present study, we evaluated flualprazolam and flubromazolam in a rat model and compared the pharmacokinetics of both compounds to alprazolam. Twelve male, Sprague-Dawley rats were given a 2 mg/kg subcutaneous dose of alprazolam, flualprazolam and flubromazolam and plasma pharmacokinetic parameters were evaluated. Both compounds displayed significant two-fold increases in volume of distribution and clearance. Additionally, flualprazolam displayed a significant increase in half-life leading to a nearly double half-life when compared to alprazolam. The findings of this study demonstrate that fluorination of the alprazolam pharmacophore increases pharmacokinetic parameters including half-life and volume of distribution. The increase in these parameters for flualprazolam and flubromazolam leads to an overall increased exposure in the body and a potential for greater toxicity than alprazolam.

Influence of adrenalectomy on the gut microbiome and MDMA-induced hyperthermia.

The increased use of the stimulant drug, 3,4-methylenedioxymethamphetamine (MDMA), more commonly known as Ecstasy, Molly or X, has been linked to the development of life-threatening hyperthermia in human and animal models. The current study aimed to investigate the role of the gut-adrenal axis in MDMA-induced hyperthermia by assessing the influence of the acute exogenous supplementation with norepinephrine (NE) or corticosterone (CORT) to adrenalectomized (ADX) rats following MDMA administration. MDMA (10 mg/kg, sc) resulted in significant increase of body temperature in SHAM animals compared to ADX animals at 30-, 60- and 90-min timepoints post-MDMA treatment. The attenuated MDMA-mediated hyperthermic response seen in ADX animals was partially restored by the exogenous administration of NE (3 mg/kg, ip) or CORT (3 mg/kg, ip) 30 min after MDMA treatment. Additionally, 16 S rRNA analysis revealed distinct changes in the gut microbiome composition and diversity notable by the higher abundance of minor phyla Actinobacteria, Verrucomicrobia and Proteobacteria in ADX rats compared to control and SHAM rats. Furthermore, MDMA administration resulted in marked changes in the dominant phyla Firmicutes and Bacteroidetes and minor phyla Actinobacteria, Verrucomicrobia and Proteobacteria in ADX animals. The most notable changes in the gut microbiome upon CORT treatment were reported with increase in Bacteroidetes and decrease in Firmicutes phyla whereas NE treatment resulted in increase in Firmicutes and decrease in Bacteroidetes and Proteobacteria post treatment. These results suggest a correlation between the sympathoadrenal axis, gut microbiome structure and diversity and MDMA-mediated hyperthermia.

Genetic Variants Associated With Opioid Use Disorder.

Genetics are presumed to contribute 30-40% to opioid use disorder (OUD), allowing for the possibility that genetic markers could be used to identify personal risk for developing OUD. We aimed to test the potential association among 180 candidate single nucleotide polymorphisms (SNPs), 120 of which were related to the dopamine reward pathway and 60 related to pharmacokinetics. Participants were randomly recruited in 2020-2021 in a cross-sectional genetic association study. Self-reported health history including Diagnostic and Statistical Manual of Mental Disorders (DSM-5) OUD criteria and buccal swabs were collected. A total of 1,301 participants were included in the analyses for this study. Of included participants, 250 met the DSM-5 criteria for ever having OUD. Logistic regression, adjusting for age and biologic sex, was used to characterize the association between each SNP and DSM-5 criteria consistent with OUD. Six SNPs found in four genes were associated with OUD: increased odds with CYP3A5 (rs15524 and rs776746) and DRD3 (rs324029 and rs2654754), and decreased odds with CYP3A4 (rs2740574) and CYP1A2 (rs2069514). Homozygotic CYP3A5 (rs15524 and rs776746) had the highest adjusted odds ratio of 2.812 (95% confidence interval (CI) 1.737, 4.798) and 2.495 (95% CI 1.670, 3.835), respectively. Variants within the dopamine reward and opioid metabolism pathways have significant positive (DRD3 and CYP3A5) and negative (CYP3A4 and CYP1A2) associations with OUD. Identification of these variants provides promising possibilities for genetic prognostic and therapeutic targets for future investigation.

Influence of fecal microbial transplant (FMT) between male and female rats on methamphetamine-induced hyperthermia.

OBJECTIVE: To investigate the effect of bidirectional fecal microbial transplant (FMT) between male and female rats on methamphetamine (MA)-induced hyperthermia. METHODS: FMT was performed between male and female rats prior to MA (10 mg/kg, sc) treatment. Core body temperature, plasma drug and norepinephrine (NE) levels were measured and compared between treatment groups. 16S rRNA gene sequencing of bacterial communities between male and female rats was performed. RESULTS: MA treatment resulted in significantly higher core body temperatures in male groups (control and FMT-treated) compared to MA-treated female groups (control and FMT-treated). Plasma concentrations of MA and amphetamine were higher in females than males. Whereas, plasma norepinephrine (NE) levels were not different between male and female rats 90 minutes after MA treatment. At the phyla level, the microbiome of male and female control rats were dominated by Firmicutes and Bacteroidetes. Males had a higher relative abundance of Firmicutes and lower relative abundances of Bacteroidetes than females. The FMT procedure changed the recipient group towards their donor with males getting closer to their donors than females. In the control groups following MA treatment, Firmicutes increased and Bacteroides decreased in females and males. Conversely, in the FMT treatment groups following MA treatment, Firmicutes decreased while Bacteroidetes increased in females and males. CONCLUSIONS: Although definite differences in the structure and diversity of the gut microbiome were observed using 16S rRNA gene sequencing of bacterial communities between male and female rats, these differences do not seem to contribute to the sex-based differences in MA-induced hyperthermia.

Reversal of temperature responses to methylone mediated through bi-directional fecal microbiota transplantation between hyperthermic tolerant and naïve rats.

The synthetic cathinone ("bath salt") methylone induces a hyperthermia response and with chronic administration tolerance to this hyperthermia has been reported. The microbiome-gut-brain axis has been implicated in multiple bodily systems and pathologies, and intentional manipulation of the gut-microbiome has yielded clinically significant results. Here, we examined the effects of bi-directional Fecal Microbiota Transplantation (FMT) between methylone-induced hyperthermic tolerant (MHT) and methylone-naïve (MN) rats. Rats treated with methylone once per week developed tolerance to methylone-induced hyperthermia by the fourth week. Once tolerant, daily bi-directional FMT between the two groups were performed for seven days prior to the next methylone treatment. The FMT abated the developed tolerance in the MHT group. When treated with methylone for the first time following FMT, recipient MN rats displayed significant tolerance to hyperthermia despite it being their initial drug treatment. Post-FMT, MHT rats displayed elevations in norepinephrine and expression of UCP1, UCP3 and TGR5 in brown adipose tissue, with reductions in expression of TGR5 and UCP3 in skeletal muscle. The pre- and post-FMT methylone tolerance phenotypes of transplant recipients are concurrent with changes in the relative abundance of several classes of Proteobacteria, most evident for Gammaproteobacteria and Alphaproteobacteria. MHT recipients demonstrated a marked increase in the relative proportion of the Firmicutes class Erysipelotrichia. These findings suggest that transplantation of gut-microbiomes can confer phenotypic responses to a drug and that the microbiome may be playing a major role in sympathomimetic-mediated hyperthermia. Abbreviations: 3,4-methylenedioxymethamphetamine (MDMA); methylone-induced hyperthermic tolerant (MHT); methylone-naïve (MN); fecal microbiota transplantation (FMT); uncoupling protein (UCP); subcutaneous (sc); intraperitoneal (ip); brown adipose tissue (BAT); skeletal muscle (SKM); sympathetic nervous system (SNS); norepinephrine (NE); quantitative PCR (qRT-PCR); quantification cycle (Cq); High Performance Liquid Chromatography-Electrochemical Detection (HPLC-EC); amplicon sequence variants (ASVs); principal coordinates analysis (PCoA); permutational multivariate analysis (PERMANOVA).