Adverse events of clenbuterol among athletes: a systematic review of case reports and case series.

Clenbuterol is a potent beta-2 agonist widely misused by professional athletes and bodybuilders. Information on clenbuterol associated adverse events is present in case reports and case series, though it may not be readily available. This systematic review aimed to critically evaluate the evidence of adverse events associated with clenbuterol among athletes. The search strategy was in accordance with PRISMA guidelines. Databases such as PubMed, Science Direct, Scopus, and Google Scholar were searched from 1990 to October 2021 to find out the relevant case reports and case series. There were 23 included studies. Using a suitable scale, the included studies' methodological quality analysis was evaluated. In total, 24 athletes experienced adverse events. Oral ingestion of clenbuterol was the most preferred route among them. The daily administered dose of clenbuterol was ranging from 20 µg to 30 mg. Major adverse events experienced by athletes were supraventricular tachycardia, atrial fibrillation, hypotension, chest pain, myocardial injury, myocarditis, myocardial ischemia, myocardial infarction, cardiomyopathy, hepatomegaly, hyperglycemia, and death. The cardiac-related complications were the most commonly occurring adverse events. Clenbuterol is notorious to produce life-threatening adverse events including death. Lack of evidence regarding the performance-enhancing effects of clenbuterol combined with its serious toxicities questions the usefulness of this drug in athletes.

Clenbuterol-induced myocarditis in a young man desiring to lose weight.

A young man in his late 20s was presented with acute chest pain, concave ST elevation in lateral and inferior leads on ECG and elevated cardiac troponin. A thorough clinical history was notable for clenbuterol abuse. Transthoracic echocardiography revealed a small area of hypokinesia in the inferior wall and cardiac magnetic resonance supported the diagnosis of acute myocarditis revealing signs of myocardial oedema and subepicardial delayed enhancement. The patient was managed conservatively and had an uneventful clinical course. Awareness of the possibility of clenbuterol myocardial toxicity in young men admitted due to chest pain is essential to prompt diagnosis and management of this condition.

Chomping at the Bit: A Descriptive Report on Pediatric Clenbuterol Ingestion.

INTRODUCTION: Clenbuterol hydrochloride is a selective beta-2 adrenergic agonist with uses in both humans and animals. Ingestions occurring within the United States are generally due to incidental ingestion of a veterinary product, use as a cutting agent for illicit substances, or illegal use for performance-enhancing purposes. CASE REPORT: A four-and-a-half year-old male presented approximately two-and-a-half hours after an accidental ingestion of an unknown quantity of clenbuterol. Initial laboratory results and electrocardiogram were remarkable for hyperglycemia, hypokalemia, and hypophosphatemia, with an electrocardiogram demonstrating sinus tachycardia. Heart rate ranged from 126 to 147 beats per minute while other vitals remained within normal limits. The patient was observed for 24 hours and discharged with normalized vital signs, laboratory results, and electrocardiogram. DISCUSSION: Clenbuterol hydrochloride is a beta-agonist with high potency, extended half-life, and bioavailability of 70% to 80%. Tachycardia occurs due to beta-1 receptor stimulation, as well as a homeostatic reflex to peripheral vasodilation. Hyperglycemia is not uncommon in exposures and intracellular shifting of potassium causes hypokalemia. Treatment is primarily supportive in nature, with hemodynamic management representing the primary focus of initial triage.

Exacerbation of ozone-induced pulmonary and systemic effects by ß2-adrenergic and/or glucocorticoid receptor agonist/s.

Agonists of ß2 adrenergic receptors (ß2AR) and glucocorticoid receptors (GR) are prescribed to treat pulmonary diseases. Since ozone effects are mediated through the activation of AR and GR, we hypothesized that the treatment of rats with relevant therapeutic doses of long acting ß2AR agonist (LABA; clenbuterol; CLEN) and/or GR agonist (dexamethasone; DEX) would exacerbate ozone-induced pulmonary and systemic changes. In the first study, male 12-week-old Wistar-Kyoto rats were injected intraperitoneally with vehicle (saline), CLEN (0.004 or 0.02 mg/kg), or DEX (0.02 or 0.1 mg/kg). Since dual therapy is commonly used, in the second study, rats received either saline or combined CLEN + DEX (each at 0.005 or 0.02 mg/kg) one day prior to and on both days of exposure (air or 0.8ppm ozone, 4 hr/day x 2-days). In air-exposed rats CLEN, DEX or CLEN + DEX did not induce lung injury or inflammation, however DEX and CLEN + DEX decreased circulating lymphocytes, spleen and thymus weights, increased free fatty acids (FFA) and produced hyperglycemia and glucose intolerance. Ozone exposure of vehicle-treated rats increased bronchoalveolar lavage fluid protein, albumin, neutrophils, IL-6 and TNF-α. Ozone decreased circulating lymphocytes, increased FFA, and induced hypeerglycemia  and glucose intolerance. Drug treatment did not reverse ozone-induced ventillatory changes, however, lung effects (protein and albumin leakage, inflammation, and IL-6 increase) were exacerbated by CLEN and CLEN + DEX pre-treatment in a dose-dependent manner (CLEN > CLEN + DEX). Systemic effects induced by DEX and CLEN + DEX but not CLEN in air-exposed rats were analogous to and more pronounced than those induced by ozone. These data suggest that adverse air pollution effects might be exacerbated in people receiving LABA or LABA plus glucocorticoids.

Death after misuse of anabolic substances (clenbuterol, stanozolol and metandienone).

A 34-year old male was found breathless and panting at home by his girlfriend three hours after a gym workout. Minutes later, he collapsed and died. Autopsy, histological and chemical analyses were conducted. The examination of the heart showed left ventricular hypertrophy, while the right coronary artery showed only a small vascular lumen (3 mm in diameter), due to its anatomical structure. In femoral blood concentrations of approx. 1 µg/L clenbuterol, approx. 56 µg/L stanozolol and approx. 8 µg/L metandienone, with trenbolone (

Complete Post-mortem Investigations in a Death Involving Clenbuterol After Long-term Abuse.

The body of a 61-year-old man was found at his home by his wife, lying on the floor, near the bathroom, around midnight. He was known to be training for bodybuilding, using anabolic steroids. Police investigations revealed the presence of two types of tablets at home, one supposed to contain clenbuterol (0.040 mg) and the other stanozolol (10 mg). Testing the tablets revealed different dosages from what was expected, i.e., 0.073 and 11.5 mg/tablet, for clenbuterol and stanozolol, respectively. External body examination and autopsy, which was performed the next day, revealed generalized organ congestion and lack of any traumatic injury (confirmed by radiology). Cardiomegaly, with a heart weighing 692 g, was obvious. Anatomic pathology tests did not reveal evidence of malformations, but atheromatous plaque was identified in the coronaries during complete histology investigations. Femoral blood, urine, bile, gastric contents and two strands of hair (6 cm) were collected for toxicology. These specimens were submitted to standard analyses, but also to a specific LC-MS-MS method for clenbuterol and stanozolol testing. Clenbuterol was identified in all the tissues, including femoral blood (1.1 ng/mL), urine (7.2 ng/mL), bile (2.4 ng/mL), gastric content (3.2 ng/mL) and hair (23 pg/mg). Stanozolol only tested positive in hair (11 pg/mg). All other analyses were negative, including blood alcohol and drugs of abuse. The pathologists concluded to cardiac insufficiency with support of cardiomegaly, in a context involving repetitive abuse of anabolic drugs. This case indicates that more attention should be paid to clenbuterol, a drug widely used as a stimulant by people who want to lose weight, athletes and bodybuilding practitioners.

Spontaneous hepatic rupture in a bodybuilder: a case report and review of the literatura

This article is the first description of a spontaneous hepatic rupture in a young bodybuilder with a history of clenbuterol and ephedrine alkaloid use. The patient presented with a sudden mid-epigastric pain and vomiting. Hemoglobin levels decreased a few hours later and a computed tomography scan was performed which revealed a rupture of the right liver capsule and hemoperitoneum. Two attempts at transarterial embolization did not control the bleeding and a right hemihepatectomy was performed. The pathological report identified a hepatic adenoma, a capsular tear and diffuse peliosis hepatis. The patient was discharged in a good condition after eleven days. Spontaneous hepatic ruptures are rare and life-threatening and are usually described in association with tumors, connective tissue diseases and gestosis. This article is a review of the available literature with regard to this condition, with a focus on its relation to peliosis hepatis and banned substance used by body image fanatics. The present case highlights the challenging diagnosis of this potentially fatal liver complication in a healthy appearing male, the risk associated with the online trade of performance enhancing drugs and its relation with peliosis hepatis

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Spontaneous hepatic rupture in a bodybuilder: a case report and review of the literature.

This article is the first description of a spontaneous hepatic rupture in a young bodybuilder with a history of clenbuterol and ephedrine alkaloid use. The patient presented with a sudden mid-epigastric pain and vomiting. Hemoglobin levels decreased a few hours later and a computed tomography scan was performed which revealed a rupture of the right liver capsule and hemoperitoneum. Two attempts at transarterial embolization did not control the bleeding and a right hemihepatectomy was performed. The pathological report identified a hepatic adenoma, a capsular tear and diffuse peliosis hepatis. The patient was discharged in a good condition after eleven days. Spontaneous hepatic ruptures are rare and life-threatening and are usually described in association with tumors, connective tissue diseases and gestosis. This article is a review of the available literature with regard to this condition, with a focus on its relation to peliosis hepatis and banned substance used by body image fanatics. The present case highlights the challenging diagnosis of this potentially fatal liver complication in a healthy appearing male, the risk associated with the online trade of performance enhancing drugs and its relation with peliosis hepatis.

Metabolic Effects of Clenbuterol and Salbutamol on Pork Meat Studied Using Internal Extractive Electrospray Ionization Mass Spectrometry.

Direct mass spectrometry analysis of metabolic effects of clenbuterol and salbutamol on pork quality at the molecular level is incredibly beneficial for food regulations, public health and the development of new anti-obesity drugs. With internal extractive electrospray ionization mass spectrometry (iEESI-MS), nutrients including creatine, amino acids, L-carnitine, vitamin B6, carnosine and phosphatidylcholines in pork tissue were identified, without sample pretreatment, using collision-induced dissociation (CID) experiments and by comparison with authentic compounds. Furthermore, normal pork samples were clearly differentiated from pork samples with clenbuterol and salbutamol via principal component analysis (PCA). Correlation analysis performed on the spectral data revealed that the above-mentioned nutrients strongly correlated with pork quality, and the absolute intensity of phosphatidylcholines in normal pork was much higher than pork contaminated by clenbuterol and salbutamol. Our findings suggested that clenbuterol and salbutamol may render effects on the activity of carnitine acyltransferase I, hence the process that L-carnitine transports long-chain fatty acids into mitochondria and the formation of phosphatidylcholines might be affected. However, the underlying metabolic mechanisms of clenbuterol and salbutamol on carnitine acyltransferase I requires more comprehensive studies in future work.

Collaborative Public Health Investigation of Clenbuterol-Adulterated Heroin Outbreak-Richmond, Virginia, March-April 2015.

CONTEXT: In March 2015, the Virginia Department of Health (VDH) was alerted by the Virginia Poison Center of a 6-patient cluster treated for severe clinical presentations after using heroin. Patients' symptoms were atypical for heroin use, and concern existed that patients were exposed to heroin that had been adulterated with or replaced by another substance. OBJECTIVE: To understand the extent and characterization of the outbreak and implement response measures to prevent further cases. The purpose of this report is to highlight the collaborative nature of a public health investigation among a diverse group of stakeholders. DESIGN: Active surveillance and retrospective case finding. SETTING: Richmond metro area community and hospitals. PARTICIPANTS: Regional poison centers, the Division of Consolidated Laboratory Services, the Department of Behavioral Health and Developmental Services, community partners, local law enforcement, and multiple VDH divisions. INTERVENTION: Outbreak investigation, communication to public health professionals, clinicians, and the community, and liaising with the local law enforcement. MAIN OUTCOME MEASURES: Outbreak control. RESULTS: Laboratory confirmation of clenbuterol in clinical specimens implicated it as the heroin adulterant. Thirteen patients met clinical and epidemiologic criteria for exposure to clenbuterol-adulterated heroin. All patients were associated with a localized area within Richmond, and patient interviews elucidated heroin supplier information. VDH collaborated with local law enforcement agents who investigated and arrested the supplier, leading to cessation of the outbreak. CONCLUSION: This outbreak highlights the value of policies and practices that support an integrated outbreak response among public health practitioners, poison center staff, laboratorians, clinicians, law enforcement agents, community groups, and other agencies. Collaboration enabled implementation of effective control measures-including those outside the purview of the health department-and should be standard practice in future outbreaks involving illicit substances.

Skeletal Muscle-specific G Protein-coupled Receptor Kinase 2 Ablation Alters Isolated Skeletal Muscle Mechanics and Enhances Clenbuterol-stimulated Hypertrophy.

GRK2, a G protein-coupled receptor kinase, plays a critical role in cardiac physiology. Adrenergic receptors are the primary target for GRK2 activity in the heart; phosphorylation by GRK2 leads to desensitization of these receptors. As such, levels of GRK2 activity in the heart directly correlate with cardiac contractile function. Furthermore, increased expression of GRK2 after cardiac insult exacerbates injury and speeds progression to heart failure. Despite the importance of this kinase in both the physiology and pathophysiology of the heart, relatively little is known about the role of GRK2 in skeletal muscle function and disease. In this study we generated a novel skeletal muscle-specific GRK2 knock-out (KO) mouse (MLC-Cre:GRK2fl/fl) to gain a better understanding of the role of GRK2 in skeletal muscle physiology. In isolated muscle mechanics testing, GRK2 ablation caused a significant decrease in the specific force of contraction of the fast-twitch extensor digitorum longus muscle yet had no effect on the slow-twitch soleus muscle. Despite these effects in isolated muscle, exercise capacity was not altered in MLC-Cre:GRK2fl/fl mice compared with wild-type controls. Skeletal muscle hypertrophy stimulated by clenbuterol, a ß2-adrenergic receptor (ß2AR) agonist, was significantly enhanced in MLC-Cre:GRK2fl/fl mice; mechanistically, this seems to be due to increased clenbuterol-stimulated pro-hypertrophic Akt signaling in the GRK2 KO skeletal muscle. In summary, our study provides the first insights into the role of GRK2 in skeletal muscle physiology and points to a role for GRK2 as a modulator of contractile properties in skeletal muscle as well as ß2AR-induced hypertrophy.

Clenbuterol activates the central IL-1 system via the ß2-adrenoceptor without provoking inflammatory response related behaviours in rats.

The long-acting, highly lipophilic, ß2-adrenoceptor agonist clenbuterol may represent a suitable therapeutic agent for the treatment of neuroinflammation as it drives an anti-inflammatory response within the CNS. However, clenbuterol is also known to increase the expression of IL-1ß in the brain, a potent neuromodulator that plays a role in provoking sickness related symptoms including anxiety and depression-related behaviours. Here we demonstrate that, compared to the immunological stimulus lipopolysaccharide (LPS, 250µg/kg), clenbuterol (0.5mg/kg) selectively up-regulates expression of the central IL-1 system resulting in a mild stress-like response which is accompanied by a reduction in locomotor activity and food consumption in rats. We provide further evidence that clenbuterol-induced activation of the central IL-1 system occurs in a controlled and selective manner in tandem with its negative regulators IL-1ra and IL-1RII. Furthermore, we demonstrate that peripheral ß2-adrenoceptors mediate the suppression of locomotor activity and food consumption induced by clenbuterol and that these effects are not linked to the central induction of IL-1ß. Moreover, despite increasing central IL-1ß expression, chronic administration of clenbuterol (0.03mg/kg; twice daily for 21days) fails to induce anxiety or depressive-like behaviour in rats in contrast to reports of the ability of exogenously administered IL-1 to induce these symptoms in rodents. Overall, our findings suggest that clenbuterol or other selective ß2-adrenoceptor agonists could have the potential to combat neuroinflammatory or neurodegenerative disorders without inducing unwanted symptoms of depression and anxiety.

Rhabdomyolysis Secondary to Clenbuterol Use and Exercise.

BACKGROUND: The literature regarding rhabdomyolysis secondary to illicit drug use is sparse. Clenbuterol is a bronchodilator approved for veterinary use, which in high doses can increase protein deposition and lipolysis similarly to anabolic steroids, and is thereby abused for bodybuilding and weight loss effects. Clenbuterol has previously been described in case reports to be cardiotoxic, with patient presentations similar to overdoses of sympathomimetic substances, but reports of rhabdomyolysis are limited to a single case series in horses. CASE REPORT: We report the first case of rhabdomyolysis secondary to clenbuterol in a human. Our patient used clenbuterol for muscle-building effects in addition to exercise for multiple days prior to presentation. The patient's chief complaint at Emergency Department (ED) presentation was discolored urine. Workup for rhabdomyolysis was initiated, and an initial creatine kinase was measured at 122,933 units/L. Our patient's rhabdomyolysis was successfully treated with supportive therapy, and the patient was eventually discharged to home with no identifiable disability. The patient's kidney function remained at baseline, and no acute kidney injury was experienced secondary to rhabdomyolysis. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Patients presenting to the ED may have been unintentionally exposed through cutting of illicit substances or through intentional use in bodybuilding. Clenbuterol has well-described cardiotoxic effects, and we report the additional toxicity of rhabdomyolysis with its use.

Pharmacokinetics of trantinterol and its metabolite in healthy elderly and young subjects.

OBJECTIVE: The aim of this study was to investigate and compare the pharmacokinetics of trantinterol and its active amphoteric carboxylic acid metabolite (1-carbonyl trantinterol) between the healthy elderly and young subjects. METHODS: This was a single-center, open-label, parallel-group study completed by 22 healthy subjects (≥65 years (the elderly group); 18-45 years (the young group); 9 males and 2 females per age group) receiving single oral dose of 50 µg trantinterol tablets. Blood samples were taken at intervals up to 48 hours post-dose. RESULTS: In both groups, maximum plasma concentration of trantinterol was researched at 0.9 hours, while the tmax of 1-carbonyl trantinterol differed slightly. Trantinterol Cmax and AUClast were higher in the elderly group than the young group, by 27% (90% CI, 0.95-1.69) and 77% (90% CI, 1.25-2.51), respectively. For 1-carbonyl trantinterol, Cmax, and AUClast were also higher, by 36% (90% CI, 1.04-1.78) and 71% (90% CI, 1.27-2.30), respectively, in the elderly group. The CL/F and V/F of trantinterol and 1-carbonyl trantinterol were significantly lower in the elderly group, while t1/2 of both did not show significant differences. CL/F of trantinterol and 1-carbonyl trantinterol were found to significantly correlate inversely with age, and positively with the baseline creatinine clearance. CONCLUSIONS: A single dose of 50 µg trantinterol was well tolerated. Significant changes in Cmax and AUC of trantinterol and 1-carbony trantinterol were seen in the elderly and may be clinically important.

Pilot trial of clenbuterol in spinal and bulbar muscular atrophy.

OBJECTIVE: To test the efficacy and tolerability of clenbuterol in patients with spinal and bulbar muscular atrophy (SBMA). METHODS: Twenty patients with a diagnosis of SBMA were given oral clenbuterol (0.04 mg/d) for 12 months. The primary efficacy end point was the change from baseline of the walking distance covered in 6 minutes at 12 months. Secondary end points included the change over time in muscle strength assessed with the Medical Research Council scale, the revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R), and forced vital capacity values. Safety was assessed by a series of laboratory and instrumental tests, as well as reporting of adverse events. RESULTS: Sixteen patients completed the study. There was a significant and sustained increase in walking distance covered in 6 minutes and forced vital capacity between the baseline and the 12-month assessments (p < 0.001). No differences were recorded in Medical Research Council or ALSFRS-R scores between baseline and follow-up assessments. Serious side effects, including those on heart function, were absent. A significant increase in serum creatine kinase levels was observed. CONCLUSIONS: Our findings suggest a positive effect of clenbuterol on SBMA disease progression. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that clenbuterol is effective in improving motor function in SBMA.

[Ingestion of anabolic steroids and ischaemic stroke. A clinical case report and review of the literature]. / Ingesta de esteroides anabolizantes e ictus isquemico. Presentacion de un caso clinico y revision de la bibliografia.

INTRODUCTION. Anabolic-androgenic steroids are synthetic substances derived from testosterone that are employed for their trophic effect on muscle tissue, among other uses. Their consumption can give trigger a series of adverse side effects on the body, including the suppression of the hypothalamus-pituitary-gonadal axis as well as liver, psychiatric and cardiovascular disorders. The most common effects are altered fat profiles and blood pressure values, cardiac remodelling, arrhythmias or myocardial infarcts. CASE REPORT. We report the case of a young male, with a background of anabolic-androgenic steroids abuse, who visited because of an acute neurological focus in the right hemisphere related with an ischaemic stroke. The aetiological study, including cardiac monitoring, echocardiograph and imaging studies (magnetic resonance and arteriography) and lab findings (thrombophilia, serology, autoimmunity, tumour markers) showed no alterations. CONCLUSIONS. The association between consumption of anabolic-androgenic steroids and cardiovascular pathologies is known, but its relation with cerebrovascular disease has not received so much attention from researchers.

Myocardial ischemia associated with clenbuterol abuse: report of two cases.

BACKGROUND: Clenbuterol is an orally administered long-acting beta-2 adrenergic agonist closely related to albuterol that, in recent years, has become a substance of abuse in the bodybuilding and athletic community. OBJECTIVES: We report two cases of acute myocardial ischemia associated with clenbuterol abuse in two healthy young male body builders. CASE REPORT: Two male bodybuilders, ages 18 and 22 years, presented to the Emergency Department with palpitations, nausea, vomiting, chest pain, diaphoresis, and tachycardia shortly after ingesting clenbuterol. Both patients experienced prolonged sinus tachycardia that, in one patient, was relatively resistant to both beta- and calcium channel blockade. Both patients were found to have elevated troponin levels, the first patient as high as 4.71 ng/mL (normal<0.04 ng/mL). Further investigation revealed normal coronary arteries at catheterization and normal cardiac magnetic resonance imaging in the first patient, and normal echocardiograms for both patients. The tachycardia gradually resolved and both patients recovered uneventfully. The etiology of cardiac ischemia in these patients is uncertain. CONCLUSIONS: Emergency physicians should be aware of the clinical presentation of clenbuterol abuse and overdose, and the possibility of related cardiac ischemia and rhythm disturbances. Suggested treatment includes intravenous fluids, oxygen, aspirin, beta-blockers, and benzodiazepines, although efficacy remains unproven.

[Dialysis for severe rhabdomyolysis 7 days after multiple trauma]. / Dialysepflichtige Rhabdomyolyse 7 Tage nach Polytrauma.

A case report of severe rhabdomyolysis in a 33-year-old motorcyclist after multiple trauma is described. The injuries included severe thoracic and abdominal trauma as well as injuries to the extremities and spinal column. During the first 3 days of treatment a forced volume therapy was performed because of increased levels of creatine kinase during which the patients condition stabilized both hemodynamically and respiratorily. On day 10 the patient developed a rise in temperature to 42°C with no evidence of a re-infection and the creatine kinase levels rose to 109,830 U/l. A continuous hemofiltration was started because of acute renal failure. The creatine kinase levels declined significantly and renal function also returned to normal with adequate diuresis up to day 20. After intensive questioning of the relatives a history of long-term use of anabolic steroids, clenbuterol as well as the intake of testosterone enanthate was conceded. Cocaine and amphetamines were also taken regularly by the patient.

Clenbuterol toxicosis in three Quarter Horse racehorses after administration of a compounded product.

CASE DESCRIPTION: 3 Quarter Horse racehorses were examined for suspected clenbuterol overdose 12 to 24 hours after administration by mouth of a compounded clenbuterol product. CLINICAL FINDINGS: All horses developed sinus tachycardia, muscle tremors, hyperhidrosis, and colic. Abnormalities on serum biochemical analysis included hyperglycemia, azotemia, and high creatine kinase activity. The presence of clenbuterol in the serum of all 3 horses and in the product administered was confirmed and quantified by use of liquid chromatography-electrospray tandem mass spectrometry. TREATMENT AND OUTCOME: Propranolol (0.01 mg/kg [0.005 mg/lb], IV) was administered to all 3 horses for antagonism of ß-adrenergic effects and caused a transient decrease in heart rate in all patients. All horses also received crystalloid fluids IV and other supportive treatment measures. Two horses were euthanatized (2 and 4 days after admission) because of complications. One horse recovered and was discharged 4 days after admission to the hospital. In the 2 nonsurviving horses, skeletal and cardiac muscle necrosis was evident at necropsy, and tissue clenbuterol concentrations were highest in the liver. CLINICAL RELEVANCE: Clenbuterol is a ß(2)-adrenergic receptor agonist licensed for veterinary use as a bronchodilator. At doses ≥ 10² µg/kg (4.5 µg/lb), in excess of those normally prescribed, ß-adrenergic stimulation by clenbuterol may cause sustained tachycardia, muscle tremors, hyperglycemia, and cardiac and skeletal muscle necrosis. Laminitis, acute renal failure, rhabdomyolysis, and cardiomyopathy were fatal complications associated with clenbuterol overdose in 2 horses in the present report. At the dose administered, propranolol was effective for short-term control of sinus tachycardia, but it did not alleviate all clinical signs in patients in the present report. These cases demonstrated the risks associated with the use of nonprescribed compounded medications for which the ingredients may be unknown.