Pharmacokinetics of Oral and Inhaled Terbutaline after Exercise in Trained Men

Beyond bronchodilation: Illuminating the performance benefits of inhaled beta2 -agonists in sports

Given the prevalent use of inhaled beta2 -agonists in sports, there is an ongoing debate as to whether they enhance athletic performance. Over the last decades, inhaled beta2 -agonists have been claimed not to enhance performance with little consideration of dose or exercise modality. In contrast, orally administered beta2 -agonists are perceived as being performance enhancing, predominantly on muscle strength and sprint ability, but can also induce muscle hypertrophy and slow-to-fast fiber phenotypic switching. But because inhaled beta2 -agonists are more efficient to achieve high systemic concentrations than oral delivery relative to dose, it follows that the inhaled route has the potential to enhance performance too. The question is at which inhaled doses such effects occur. While supratherapeutic doses of inhaled beta2 -agonists enhance muscle strength and short intense exercise performance, effects at low therapeutic doses are less apparent. However, even high therapeutic inhaled doses of commonly used beta2 -agonists have been shown to induce muscle hypertrophy and to enhance sprint performance. This is concerning from an anti-doping perspective. In this paper, we raise awareness of the circumstances under which inhaled beta2 -agonists can constitute a performance-enhancing benefit.

Inhaled salbutamol induces leanness in well-trained healthy females but not males during a period of endurance training: a randomised controlled trial

Introduction

Many athletes use short-acting inhaled β2-agonists multiple times weekly during training sessions to prevent exercise-induced bronchoconstriction, but it is unclear if treatment impairs training outcomes. Herein, we investigated performance adaptations in well-trained females and males training with prior inhalation of salbutamol.

Methods

19 females and 21 males with maximal oxygen uptake (V'O2max) of 50.5±3.3 and 57.9±4.9 mL·min-1·kg-1, respectively, participated in this double-blinded, placebo-controlled, parallel-group study. We randomised participants to placebo or salbutamol inhalation (800-1600 µg·training day-1) for 6 weeks of combined endurance (1× per week) and high-intensity interval training (2× per week). We assessed participants' body composition, V'O2max and muscle contractile function, and collected vastus lateralis muscle biopsies.

Results

Salbutamol induced a sex-specific loss of whole-body fat mass (sex×treatment: p=0.048) where only salbutamol-treated females had a fat mass reduction compared to placebo (-0.8 kg at 6 weeks; 95% CI: -0.5 to -1.6; p=0.039). Furthermore, salbutamol-treated females exhibited a repartitioning effect, lowering fat mass while gaining lean mass (p=0.011), which was not apparent for males (p=0.303). Salbutamol negatively impacted V'O2max in both sexes (treatment main effect: p=0.014) due to a blunted increase in V'O2max during the initial 4 weeks of the intervention. Quadriceps contractile strength was impaired in salbutamol-treated females (-39 N·m; 95% CI: -61 to -17; p=0.002) compared to placebo at 6 weeks. Muscle electron transport chain complex I-V abundance increased with salbutamol (treatment main effect: p=0.035), while content of SERCAI, β2-adrenoceptor and desmin remained unchanged.

Conclusion

Inhaled salbutamol appears to be an effective repartitioning agent in females but may impair aerobic and strength-related training outcomes.

Clinical pharmacokinetics of terbutaline in humans: a systematic review

Terbutaline is used for the management of bronchospasm associated with asthma, bronchitis, emphysema, and chronic obstructive pulmonary disease. A systematic review would be beneficial to assess the impact of routes of administration, stereoisomerism, disease states, smoking, age, exercise, and chronobiology on pharmacokinetics (PK) of terbutaline in humans. PubMed and Google Scholar databases were searched to screen all the relevant articles consisting of at least one of the PK parameters after administration of oral, inhaled, and intravenous (IV) terbutaline in humans. Oral studies of terbutaline depicted a linear relationship between plasma concentration (C_p) and the administered dose. The IV studies demonstrated multi-exponential behavior for disposition and renal clearance. Higher systemic availability was observed with inhaled as compared to oral route, and chrono-pharmacokinetic behavior was notable. Time to reach maximum plasma concentration (T_max) was prolonged, and maximum plasma concentration (C_max) was lowered after exercise. The primary route of excretion in chronic kidney disease (CKD) patients is reported to be nonrenal. In pregnant women, the C_p of terbutaline is lowered and clearance is increased. The addition of theophylline to terbutaline did not affect the PK of terbutaline; hence, both can be used without dose adjustment. This review summarizes all the available PK parameters of terbutaline, and it may be helpful for researchers in the development and evaluation of PK models as well as in designing optimal dosage regimens in different clinical conditions.

Muscle hypertrophic effect of inhaled beta2 -agonist is associated with augmented insulin-stimulated whole-body glucose disposal in young men

Abstract

Rodent studies highlight enhancement of glucose tolerance and insulin sensitivity as potential clinically relevant effects of chronic beta₂‐agonist treatment. However, the doses administered to rodents are not comparable with the therapeutic doses used for humans. Thus, we investigated the physiological effects of prolonged beta₂‐agonist treatment at inhaled doses resembling those used in respiratory diseases on insulin‐stimulated whole‐body glucose disposal and putative mechanisms in skeletal muscle and adipose tissue of healthy men. Utilizing a randomized placebo‐controlled parallel‐group design, we assigned 21 healthy men to 4 weeks daily inhalation of terbutaline (TER; 4 mg × day⁻¹, n = 13) or placebo (PLA, n = 8). Before and after treatments, we assessed subjects’ whole‐body insulin‐stimulated glucose disposal and body composition, and collected vastus lateralis muscle and abdominal adipose tissue biopsies. Glucose infusion rate increased by 27% (95% CI: 80 to 238 mg × min⁻¹, P = 0.001) in TER, whereas no significant changes occurred in PLA (95% CI: −37 to 195 mg × min⁻¹, P = 0.154). GLUT4 content in muscle or adipose tissue did not change, nor did hexokinase II content or markers of mitochondrial volume in muscle. Change in lean mass was associated with change in glucose infusion rate in TER (r = 0.59, P = 0.03). Beta₂‐agonist treatment in close‐to‐therapeutic doses may augment whole‐body insulin‐stimulated glucose disposal in healthy young men and part of the change is likely to be explained by muscle hypertrophy. These findings highlight the therapeutic potential of beta₂‐agonists for improving insulin sensitivity.

Key points

While studies in rodents have highlighted beta₂‐agonists as a means to augment insulin sensitivity, these studies utilized beta₂‐agonists at doses inapplicable to humans.

Herein we show that a 4‐week treatment period with daily therapeutic inhalation of beta₂‐agonist increases insulin‐stimulated whole‐body glucose disposal in young healthy lean men.

This effect was associated with an increase of lean mass but not with changes in GLUT4 and hexokinase II or basal glycogen content in skeletal muscle nor GLUT4 content in abdominal adipose tissue.

These findings suggest that the enhanced insulin‐stimulated whole‐body glucose disposal induced by a period of beta₂‐agonist treatment in humans, at least in part, is attributed to muscle hypertrophy.

Our observations extend findings in rodents and highlight the therapeutic potential of beta₂‐agonists to enhance the capacity for glucose disposal and whole‐body insulin sensitivity, providing important knowledge with potential application in insulin resistance.

The beta2 -adrenergic receptor - a re-emerging target to combat obesity and induce leanness?

Treatment of obesity with repurposed or novel drugs is an expanding research field. One approach is to target beta₂ -adrenergic receptors because they regulate the metabolism and phenotype of adipose and skeletal muscle tissue. Several observations support a role for the beta₂ -adrenergic receptor in obesity. Specific human beta₂ -adrenergic receptor polymorphisms are associated with body composition and obesity, for which the Gln27Glu polymorphism is associated with obesity, while the Arg16Gly polymorphism is associated with lean mass in men and the development of obesity in specific populations. Individuals with obesity also have lower abundance of beta₂ -adrenergic receptors in adipose tissue and are less sensitive to catecholamines. In addition, studies in livestock and rodents demonstrate that selective beta₂ -agonists induce a so-called 'repartitioning effect' characterized by muscle accretion and reduced fat deposition. In humans, beta₂ -agonists dose-dependently increase resting metabolic rate by 10-50%. And like that observed in other mammals, only a few weeks of treatment with beta₂ -agonists increases muscle mass and reduces fat mass in young healthy individuals. Beta₂ -agonists also exert beneficial effects on body composition when used concomitantly with training and act additively to increase muscle strength and mass during periods with resistance training. Thus, the beta₂ -adrenergic receptor seems like an attractive target in the development of anti-obesity drugs. However, future studies need to verify the long-term efficacy and safety of beta₂ -agonists in individuals with obesity, particularly in those with comorbidities.

An Abductive Inference Approach to Assess the Performance-Enhancing Effects of Drugs Included on the World Anti-Doping Agency Prohibited List

Some have questioned the evidence for performance-enhancing effects of several substances included on the World Anti-Doping Agency's Prohibited List due to the divergent or inconclusive findings in randomized controlled trials (RCTs). However, inductive statistical inference based on RCTs-only may result in biased conclusions because of the scarcity of studies, inter-study heterogeneity, too few outcome events, or insufficient power. An abductive inference approach, where the body of evidence is evaluated beyond considerations of statistical significance, may serve as a tool to assess the plausibility of performance-enhancing effects of substances by also considering observations and facts not solely obtained from RCTs. Herein, we explored the applicability of an abductive inference approach as a tool to assess the performance-enhancing effects of substances included on the Prohibited List. We applied an abductive inference approach to make inferences on debated issues pertaining to the ergogenic effects of recombinant human erythropoietin (rHuEPO), beta₂-agonists and anabolic androgenic steroids (AAS), and extended the approach to more controversial drug classes where RCTs are limited. We report that an abductive inference approach is a useful tool to assess the ergogenic effect of substances included on the Prohibited List-particularly for substances where inductive inference is inconclusive. Specifically, a systematic abductive inference approach can aid researchers in assessing the effects of doping substances, either by leading to suggestions of causal relationships or identifying the need for additional research.

Pharmacokinetics of salmeterol and its main metabolite α-hydroxysalmeterol after acute and chronic dry powder inhalation in exercising endurance-trained men: Implications for doping control

As of 2020, use of beta₂ -agonist salmeterol is restricted by the World Anti-Doping Agency (WADA) and is only permitted by inhalation at therapeutic doses not exceeding 200 μg in 24 h. In contrast to beta₂ -agonists salbutamol and formoterol, WADA has not established a urine threshold for salmeterol despite its muscle hypertrophic actions observed in animals. Herein, we investigated plasma (0-4 h) and urine (0-24 h) concentrations (by ultra-high-performance liquid chromatography-tandem mass spectrometry [UHPLC-MS/MS]) of salmeterol and α-hydroxysalmeterol after dry powder inhalation at supratherapeutic (400 μg) and high therapeutic (200 μg) doses, and after seven consecutive days of therapeutic inhalation (200 μg × day^-1 ) in 11 healthy endurance-trained men. During each trial, participants inhaled salmeterol before 1½ h moderate-intensity cycling. Mean ± SD maximum urine concentrations of salmeterol unadjusted for specific gravity reached 4.0 ± 1.6, 2.1 ± 1.5, and 2.2 ± 1.1 ng × ml^-1 for 400 μg, 200 μg, and seven consecutive days of 200 μg, respectively, with corresponding maximum urine concentrations of α-hydroxysalmeterol being 11.6 ± 6.1, 5.7 ± 4.6, and 6.5 ± 2.6 ng × ml^-1 . Within the relevant window for doping control (first 6 h post-inhalation), the present data (119 samples), along with 64 biobank urine samples, showed that a combined salmeterol and α-hydroxysalmeterol urine threshold with equal cut-offs of 3.3 ng × ml^-1 was superior to a salmeterol-only threshold to discriminate therapeutic (200 μg) from supratherapeutic use (400 μg) with a sensitivity of 24% with 0% false positives when applying the WADA technical document (TD2019DL.v2) method of specific gravity adjustment. Thus, a combination of urine salmeterol and α-hydroxysalmeterol concentrations may be suitable for discriminating between therapeutic and supratherapeutic prohibited inhalation of salmeterol.

The Effects of Inhaled Terbutaline on 3-km Running Time-Trial Performance

Terbutaline is a prohibited drug except for athletes with a therapeutic use exemption certificate; terbutaline's effects on endurance performance are relatively unknown. Purpose: To investigate the effects of 2 therapeutic (2 and 4 mg) inhaled doses of terbutaline on 3-km running time-trial performance. Methods: A total of 8 men (age 24.3 [2.4] y; weight 77.6 [8] kg; and height 179.5 [4.3] cm) and 8 women (age 22.4 [3] y; weight 58.6 [6] kg; and height 163 [9.2] cm) free from respiratory disease and illness provided written informed consent. Participants completed 3-km running time trials on a nonmotorized treadmill on 3 separate occasions following placebo and 2- and 4-mg inhaled terbutaline in a single-blind, repeated-measures design. Urine samples (15 min postexercise) were analyzed for terbutaline concentration. Data were analyzed using 1-way repeated-measures analysis of variance, and significance was set at P < .05 for all analyses. Results: No differences were observed for completion times (1103 [201] s, 1106 [195] s, 1098 [165] s; P = .913) for the placebo or 2- and 4-mg inhaled trials, respectively. Lactate values were higher (P = .02) after 4 mg terbutaline (10.7 [2.3] mmol·L^-1) vs placebo (8.9 [1.8] mmol·L^-1). Values of forced expiratory volume in the first second of expiration (FEV₁) were greater after inhalation of 2 mg (5.08 [0.2]; P = .01) and 4 mg terbutaline (5.07 [0.2]; P = .02) compared with placebo (4.83 [0.5] L) postinhalation. Urinary terbutaline concentrations were mean 306 (288) ng·mL^-1 and 435 (410) ng·mL^-1 (P = .2) and peak 956 ng·mL^-1 and 1244 ng·mL^-1 after 2 and 4 mg inhaled terbutaline, respectively. No differences were observed between the male and female participants. Conclusions: Therapeutic dosing of terbutaline does not lead to an improvement in 3-km running performance despite significantly increased FEV₁. The findings suggest that athletes using inhaled terbutaline at high therapeutic doses to treat asthma will not gain an ergogenic advantage during 3-km running performance.

Advancing the analysis of terbutaline in urine samples using novel enzyme hydrolysis

Aim: To investigate the efficiency of two new fast-acting enzymes, recombinant arylsulfatase (IMCS-PSF) and mutant β-glucuronidase from Escherichia coli (IMCSzyme), in hydrolyzing specific terbutaline metabolites. Materials & methods: Two purified novel enzymes are used to precisely determine the amount of each metabolite in urine at different time points after oral administration. After systematically evaluating the hydrolysis efficiency of the novel enzymes compared with commercially available enzymes, these recently developed enzymes were applied to establish the separate urine concentration profiles of terbutaline and each metabolite. Results & discussion: The results highlight the highly efficient arylsulfatase enzyme expressed from E. coli for urine analysis of terbutaline while suggesting sulfoconjugates as the main terbutaline metabolites. Conclusion: This study demonstrated the high efficiency of the IMCS-PSF enzyme in hydrolyzing terbutaline conjugates in comparison with other enzyme reagents typically used for the analysis of terbutaline and sulfoconjugates are the main terbutaline metabolites in urine.

Hypertrophic effect of inhaled beta2 -agonist with and without concurrent exercise training: A randomized controlled trial

Due to a high prevalence of asthma and exercise-induced bronchoconstriction in elite athletes, there is a high use of beta₂ -adrenoceptor agonists (beta₂ -agonists) in the athletic population. While anabolic in rodents, no study has been able to detect hypertrophy in humans after chronic beta₂ -agonist inhalation. We investigated whether inhaled beta₂ -agonist, terbutaline, alters body composition and metabolic rate with and without concurrent exercise training in healthy young men. Sixty-seven participants completed a 4-week intervention of daily terbutaline (8 × 0.5 mg) or placebo treatment without concurrent training (habitual; n = 23), with resistance (n = 23) or endurance (n = 21) training 3 times weekly. Before and after the interventions, participant's body composition was determined by dual-energy X-ray absorptiometry and resting metabolic rate and substrate oxidation by indirect calorimetry. Terbutaline increased lean body mass by 1.03 kg (95% CI 0.29-1.76; P < .05) and 1.04 kg (95% CI 0.16-1.93; P < .05) compared to placebo in the habitual and resistance training group, respectively, but had no effect compared to placebo in the endurance training group [-0.56 kg (95% CI -1.74-0.62; P > .05)]. Fat mass, bone mineral content, and resting metabolic rate did not change differently between treatments with the intervention. Daily inhalation of terbutaline in near-therapeutic doses induces skeletal muscle growth. This observation should be a concern for antidoping authorities.

Preparation of a Sustained-Release Nebulized Aerosol of R-terbutaline Hydrochloride Liposome and Evaluation of Its Anti-asthmatic Effects via Pulmonary Delivery in Guinea Pigs

An aerosolized liposome formulation for the pulmonary delivery of an anti-asthmatic medication was developed. Asthma treatment usually requires frequent administration of medication for a sustained bronchodilator response. Liposomes are known for their sustained drug release capability and thus would be a suitable delivery system for prolonging the therapeutic effect of anti-asthmatic medication. Liposomes prepared by thin film hydration were loaded with a model drug, R-terbutaline hydrochloride(R-TBH), using an ammonium sulfate-induced transmembrane electrochemical gradient. This technique provided an encapsulation efficiency of up to 71.35% and yielded R-TBH liposomes with a particle size of approximately 145 ± 20 nm. According to stability studies, these R-TBH liposomes should be stored at 4°C before usage. Compared to R-TBH solution, which showed 90.84% release within 8 h, liposomal R-TBH had a cumulative release of 73.53% at 37°C over 192 h. A next generation impactor (NGI) was used to analyze the particle size distribution in the lungs of R-TBH liposome aerosol in vitro at 5°C. The therapeutic efficacy of the nebulized aerosol of the R-TBH liposomes was assessed via pulmonary delivery in guinea pigs. The results showed that, compared to the R-TBH solution group, the R-TBH liposome group had a prolonged anti-asthma effect.

Chronic β2 -adrenoceptor agonist treatment alters muscle proteome and functional adaptations induced by high intensity training in young men

KEY POINTS

While several studies have investigated the effects of exercise training in human skeletal muscle and the chronic effect of β₂ -agonist treatment in rodent muscle, their effects on muscle proteome signature with related functional measures in humans are still incompletely understood. Herein we show that daily β₂ -agonist treatment attenuates training-induced enhancements in exercise performance and maximal oxygen consumption, and alters muscle proteome signature and phenotype in trained young men. Daily β₂ -agonist treatment abolished several of the training-induced enhancements in muscle oxidative capacity and caused a repression of muscle metabolic pathways; furthermore, β₂ -agonist treatment induced a slow-to-fast twitch muscle phenotype transition. The present study indicates that chronic β₂ -agonist treatment confounds the positive effect of high intensity training on exercise performance and oxidative capacity, which is of interest for the large proportion of persons using inhaled β₂ -agonists on a daily basis, including athletes.

ABSTRACT

Although the effects of training have been studied for decades, data on muscle proteome signature remodelling induced by high intensity training in relation to functional changes in humans remains incomplete. Likewise, β₂ -agonists are frequently used to counteract exercise-induced bronchoconstriction, but the effects β₂ -agonist treatment on muscle remodelling and adaptations to training are unknown. In a placebo-controlled parallel study, we randomly assigned 21 trained men to 4 weeks of high intensity training with (HIT+β₂ A) or without (HIT) daily inhalation of β₂ -agonist (terbutaline, 4 mg dose^-1 ). Of 486 proteins identified by mass-spectrometry proteomics of muscle biopsies sampled before and after the intervention, 32 and 85 were changing (false discovery rate (FDR) ≤5%) with the intervention in HIT and HIT+β₂ A, respectively. Proteome signature changes were different in HIT and HIT+β₂ A (P = 0.005), wherein β₂ -agonist caused a repression of 25 proteins in HIT+β₂ A compared to HIT, and an upregulation of 7 proteins compared to HIT. β₂ -Agonist repressed or even downregulated training-induced enrichment of pathways related to oxidative phosphorylation and glycogen metabolism, but upregulated pathways related to histone trimethylation and the nucleosome. Muscle contractile phenotype changed differently in HIT and HIT+β₂ A (P ≤ 0.001), with a fast-to-slow twitch transition in HIT and a slow-to-fast twitch transition in HIT+β₂ A. β₂ -Agonist attenuated training-induced enhancements in maximal oxygen consumption (P ≤ 0.01) and exercise performance (6.1 vs. 11.6%, P ≤ 0.05) in HIT+β₂ A compared to HIT. These findings indicate that daily β₂ -agonist treatment attenuates the beneficial effects of high intensity training on exercise performance and oxidative capacity, and causes remodelling of muscle proteome signature towards a fast-twitch phenotype.

Beta2-adrenergic stimulation increases energy expenditure at rest, but not during submaximal exercise in active overweight men

PURPOSE

β₂-Agonists have been proposed as weight-loss treatment, because they elevate energy expenditure. However, it is unknown what effect β₂-agonists have on energy expenditure in overweight individuals. Furthermore, the influence of β₂-agonist R- and S-enantiomer ratio for the increased energy expenditure is insufficiently explored.

METHODS

Nineteen males were included in the study of which 14 completed. Subjects were 31.6 (±3.5) years [mean (±95% CI)] and had a fat percentage of 22.7 (±2.1)%. On separate days, subjects received either placebo or inhaled racemic (rac-) formoterol (2 × 27 µg). After an overnight fast, energy expenditure and substrate oxidation were estimated by indirect calorimetry at rest and during submaximal exercise. Plasma (R,R)- and (S,S)-formoterol enantiomer levels were measured by ultra-performance liquid chromatograph-mass spectrometry.

RESULTS

At rest, energy expenditure and fat oxidation were 12% (P ≤ 0.001) and 38% (P = 0.006) higher for rac-formoterol than placebo. Systemic (R,R):(S,S) formoterol ratio was correlated with change in energy expenditure at rest in response to rac-formoterol (r = 0.63, P = 0.028), whereas no association was observed between fat percentage and rac-formoterol-induced change in energy expenditure. During exercise, energy expenditure was not different between treatments, although carbohydrate oxidation was 15% higher (P = 0.021) for rac-formoterol than placebo. Rac-formoterol-induced shift in substrate choice from rest to exercise was related to plasma ln-rac-formoterol concentrations (r = 0.75, P = 0.005).

CONCLUSION

Selective β₂-adrenoceptor agonism effectively increases metabolic rate and fat oxidation in overweight individuals. The potential for weight loss induced by β₂-agonists may be greater for R-enantiopure formulations.