Open Veterinary Journal, (2026), Vol. 16(4): 2515-2520

Research Article

10.5455/OVJ.2026.v16.i4.51

Comparison of the neuromuscular effects, efficacy, and safety of rocuronium and atracurium in dogs with ambulatory anesthesia

Ayad Nouri Diaa Alhakim^*, Abd-Alhadi Jaithom Marzok and Dhurgham H. Al Haideri

Department of Veterinary Clinical Sciences, Faculty of Veterinary Medicine, University of Kufa, Kufa, Iraq

*Corresponding Author: Ayad Nouri Diaa Alhakim. Department of Veterinary Clinical Sciences, Faculty of Veterinary Medicine, University of Kufa, Kufa, Iraq. Email: ayadn.dheyaa [at] uokufa.edu.iq

Submitted: 23/11/2025 Revised: XX/XX/XX Accepted: 06/03/2026 Published: XX/XX/XX

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ABSTRACT

Background: Neuromuscular blocking agents are widely used in veterinary anesthesia to facilitate tracheal intubation and provide optimal surgical conditions. Quantitative neuromuscular monitoring enables accurate evaluation of neuromuscular effects while ensuring cardiovascular safety in anesthetized dogs.

Aim: This study aimed to quantify the neuromuscular effects, therapeutic effectiveness, and cardiovascular safety of rocuronium and atracurium during quantitative neuromuscular monitoring of dogs under ambulatory anesthesia.

Methods: A total of 18 healthy adult dogs were randomly divided into two groups. One group received 0.6 mg/kg IV of rocuronium, and the other received 0.5 mg/kg IV of atracurium after the induction of isoflurane anesthesia, with each group consisting of nine dogs. Neuromuscular transmission was quantified using calibrated train-of-four (TOF) acceleromyography. Onset time, duration of action, and recovery time to a TOF ratio ≥ 0.9 were measured concurrently with continuous monitoring of heart rate, mean arterial pressure, and oxygen saturation.

Results: The use of rocuronium resulted in a significantly faster onset of neuromuscular block compared with atracurium (p < 0.001), enabling rapid tracheal intubation. No significant differences were found between the two groups regarding the duration of action and recovery time. During the anesthesia period, cardiovascular parameters remained stable and comparable between the groups, and only one dog in the atracurium group experienced a minor, transient adverse effect.

Conclusion: The results suggest that both drugs are potent and do not harm dogs. In addition, rocuronium is a better option for quick procedures, whereas atracurium can be used in situations where it is not anticipated that the patient will be able to respond to reversal agents or has compromised organ function, due to its predictably less discomfort during the recovery phase.

Keywords: Ambulatory anesthesia, Atracurium, Dogs, Neuromuscular blockade, Rocuronium.

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Introduction

Neuromuscular blocking agents (NMBAs) play a fundamental role in modern veterinary anesthesia by facilitating tracheal intubation, providing optimal surgical conditions, and enabling controlled mechanical ventilation during general anesthesia (Clarke et al., 2014; Grimm et al., 2015). The clinical use of non-depolarizing NMBAs in small animal practice has increased substantially, particularly in ambulatory procedures where patient safety is a primary concern. Consequently, a rapid onset of action, predictable recovery profile, and minimal cardiovascular disturbance are considered essential characteristics for effective postoperative management (Ilkiw, 1999).

Rocuronium and atracurium are among the most commonly used non-depolarizing NMBAs in dogs; however, they differ markedly in their pharmacokinetic and pharmacodynamic properties (Sinclair, 2003). Rocuronium, an aminosteroid compound, is characterized by its rapid onset of neuromuscular blockade, making it especially suitable for rapid tracheal intubation and short surgical procedures requiring immediate muscle relaxation (Ko et al., 2000; Bertini et al., 2017). Nevertheless, rocuronium is primarily metabolized by the liver, and both its duration of action and recovery profile may vary considerably in animals with even mild hepatic impairment (Court and Greenblatt, 2000). As a result, further investigation into its clinical performance under different conditions remains warranted (Murrell and Johnson, 2006; Haskins, 2007; Tranquilli et al., 2007).

In contrast, atracurium belongs to the benzylisoquinolinium class of NMBAs and possesses the distinctive characteristic of organ-independent metabolism via Hofmann elimination and nonspecific ester hydrolysis (Murrell and Johnson, 2006; Tranquilli et al., 2007). This unique elimination pathway confers a predictable recovery profile and supports the use of atracurium in dogs with hepatic or renal dysfunction, as well as in clinical situations where neuromuscular reversal agents may not be readily available (Haskins, 2007).

Dogs undergoing ambulatory anesthesia require anesthetic protocols that provide adequate muscle relaxation while minimizing residual neuromuscular blockade and cardiovascular instability (Duke and Caulkett, 2015). Residual paralysis has been associated with postoperative respiratory complications, underscoring the importance of objective neuromuscular monitoring rather than reliance solely on clinical observation (Eger et al., 1965). Quantitative train-of-four (TOF) monitoring is therefore regarded as the gold standard for assessing neuromuscular transmission and determining adequate recovery, with a TOF ratio ≥ 0.9 considered indicative of safe neuromuscular function (Plaud and Bowman, 2020; Hellyer, 2022). Despite the widespread clinical use of rocuronium and atracurium, direct comparative studies evaluating their neuromuscular characteristics and cardiovascular safety under standardized conditions of ambulatory anesthesia in dogs remain limited (Cantalapiedra et al., 2012). Accordingly, the present study aimed to evaluate the onset, duration, and recovery of neuromuscular blockade induced by rocuronium and atracurium in healthy dogs using quantitative TOF monitoring, while simultaneously assessing hemodynamic stability during anesthesia (Sinclair; 2003; Yousef and Al-Saadi; 2018). It was hypothesized that rocuronium would provide a faster onset of neuromuscular blockade, whereas atracurium would offer a more predictable recovery profile, with both agents demonstrating acceptable cardiovascular safety.

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Materials and Methods

Animals and study design

This randomized controlled study involved 18 healthy adult mixed-breed dogs (body weight 20–25 kg; age 2–4 years) of both sexes. Health status was confirmed through thorough physical examination and routine clinical evaluation before inclusion. The dogs were randomly allocated into two equal groups (n=9 per group) as follows:

• Group R: Rocuronium administered intravenously at a dose of 0.6 mg/kg.

• Group A: Atracurium administered intravenously at a dose of 0.5 mg/kg.

All dogs were fasted for 8 hours before anesthesia, while free access to water was allowed. Premedication consisted of acepromazine administered intramuscularly at a dose of 0.02 mg/kg, 30 minutes before anesthetic induction (Ilkiw, 1999; Duke and Caulkett, 2015).

Anesthesia protocol

Anesthesia was induced using propofol at a dose of 4 mg/kg administered intravenously and titrated until the desired anesthetic depth was achieved. Anesthesia was subsequently maintained with isoflurane at an end-tidal concentration of 1.5%–2.0% in 100% oxygen delivered via a rebreathing system. Immediately after tracheal intubation, mechanical ventilation was initiated to maintain normocapnia, with end-tidal carbon dioxide values maintained between 35 and 40 mmHg (Haskins, 2007).

Neuromuscular monitoring

Neuromuscular transmission was monitored using a calibrated TOF-Watch SX® acceleromyograph. Following device calibration and stabilization of baseline twitch responses, supramaximal electrical stimulation was applied to the peroneal nerve, and the resulting response of the cranial tibial muscle was recorded. Limb temperature was maintained within physiological limits throughout the monitoring period to minimize variability in neuromuscular measurements (Murrell and Johnson, 2006; Reid et al., 2007; Beths et al., 2014).

Measured variables

The following neuromuscular variables were recorded:

• Onset time: Time interval from neuromuscular blocking agent administration to 95% depression of the first twitch (T1).

• Duration of action: Time from drug administration to recovery of T1 to 25%.

• Recovery time: Interval from 25% recovery of T1 to attainment of a TOF ratio ≥ 0.9.

Cardiovascular parameters, including heart rate (HR), mean arterial pressure (MAP), and peripheral oxygen saturation (SpO₂), were recorded at 5-minute intervals throughout the anesthetic period (Sinclair, 2003; Cantalapiedra et al., 2012).

Statistical analysis

Statistical analysis was performed using SPSS software version 28. Data normality was assessed using the Shapiro–Wilk test. Continuous variables were expressed as mean ± standard deviation (SD) and compared between groups using Student’s t-test. A p-value < 0.05 was considered statistically significant. Given the limited sample size, the study was considered exploratory, and the potential for type II error was acknowledged (Grimm et al., 2015).

Ethical approval

The study protocol was approved by the Institutional Animal Care and Use Committee (IACUC), University of Kufa (Protocol No. VET-2023-015, March 15, 2023). The experiment was conducted in accordance with institutional guidelines and internationally accepted standards for the care and use of animals in research (National Research Council, 2011).

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Results

The study was carried out on all dogs without any serious complications. Rocuronium and atracurium combined resulted in sufficient neuromuscular blockade and good anesthetic conditions in all the animals. Neuromuscular Blockade Characteristics Rocuronium achieved a significantly quicker onset of neuromuscular blockade than atracurium (p < 0.001). However, no statistically significant differences in the duration of action or recovery time were found among the groups (Table 1).

Table 1. Neuromuscular blockade parameters following rocuronium or atracurium administration in dogs (mean ± SD).

Table 1 shows that the three parameters—onset of action, duration, and recovery of the two neuromuscular blocking agents—are summarized. Rocuronium showed a quite rapid onset of blockade, whereas both groups had similar duration and recovery.

Figure 1 compares the neuromuscular profiles of rocuronium and atracurium, revealing a very short onset time linked with rocuronium and similar recovery features of both agents.

Fig. 1. Neuromuscular profiles of rocuronium and atracurium.

Hemodynamics

We observed lasting, unswerving, and similar cardiovascular variables among the groups right through anesthesia. No statistically significant difference was observed in HR, MAP, or SpO₂ between the dogs in the rocuronium and atracurium groups (Table 2).

Table 2. Hemodynamic parameters during anesthesia following administration of rocuronium or atracurium (mean ± SD).

Table 2 shows the hemodynamic parameters (HR, mean arterial pressure, and oxygen saturation values) obtained during anesthesia and shown in the table as per the treatment groups, with almost identical cardiovascular stability. One dog in the atracurium group had a brief episode of mild hypotension that resolved spontaneously and did not require any treatment. Besides that, no other significant adverse effects were noted.

Table 2 also shows the monitoring of HR, mean arterial pressure, and oxygen saturation during anesthesia, indicating that cardiovascular stability was comparable between both treatment groups. A dog treated with atracurium experienced a slight and temporary decrease in blood pressure, which, however, quickly normalized without any medical intervention. Moreover, no other clinically significant side effects were observed.

Figure 2 shows the hemodynamic and oxygenation parameters during anesthesia. Graphical representation of HR, mean arterial pressure, and peripheral oxygen saturation in dogs administered with rocuronium or atracurium, showing stable and comparable cardiovascular profiles throughout anesthesia.

Fig. 2. Hemodynamic and oxygenation parameters during anesthesia.

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Discussion

The present study evaluated and compared the neuromuscular blocking profiles and cardiovascular safety of rocuronium and atracurium in dogs using quantitative TOF monitoring during ambulatory anesthesia. The findings demonstrated that rocuronium produced a significantly faster onset of neuromuscular blockade, whereas both agents exhibited comparable duration of action and recovery characteristics, confirming their clinical applicability in veterinary anesthesia (Ko et al., 2000; Bertini et al., 2017).

The significantly shorter onset time observed with rocuronium can be attributed to its aminosteroid chemical structure and relatively low potency, which facilitates rapid diffusion to the neuromuscular junction and faster occupancy of acetylcholine receptors (Court and Greenblatt, 2000; Sinclair, 2003). Previous experimental and veterinary studies have also reported that inhalational anesthesia may accelerate the onset of rocuronium compared with benzylisoquinolinium neuromuscular blocking agents, further supporting its usefulness in procedures requiring rapid tracheal intubation (Ilkiw, 1999; Ko et al., 2000).

In contrast, atracurium exhibited a slower onset of action, which is consistent with its higher potency and distinct pharmacokinetic properties. Atracurium undergoes metabolism primarily through Hofmann elimination and nonspecific ester hydrolysis, resulting in a recovery process that is largely independent of hepatic and renal function (Court and Greenblatt, 2000; Bertini et al., 2017). These characteristics have been well documented in both human and veterinary anesthesia literature and support the preferential use of atracurium in patients with potential or established organ dysfunction (Clarke et al., 2014; Grimm et al., 2015). Neuromuscular function and anesthetic-related electrophysiological effects were interpreted in accordance with previously established studies evaluating volatile anesthetics and neuromuscular blocking agents in dogs (Kastrup et al., 2005; Sakata et al., 2019; Martin-Flores et al., 2023).

The duration of neuromuscular blockade and recovery time did not differ significantly between the two treatment groups. However, recovery following rocuronium administration showed slightly greater variability, which may be related to its partial dependence on hepatic uptake and biliary excretion (Court and Greenblatt, 2000; Sinclair, 2003). Similar variability has been reported in previous canine studies, emphasizing the importance of neuromuscular function monitoring when aminosteroid neuromuscular blocking agents are used (Ko et al., 2000).

Cardiovascular parameters remained stable in both groups throughout the anesthetic period, indicating that rocuronium and atracurium are hemodynamically safe when administered at recommended dosages. These observations are consistent with earlier studies reporting minimal or no clinically relevant effects of these agents on heart rate, arterial blood pressure, and oxygen saturation in anesthetized dogs (Haskins, 2007; Cantalapiedra et al., 2012). The absence of significant cardiovascular compromise supports their suitability for use in ambulatory surgical procedures.

A single transient hypotensive episode was observed in one dog receiving atracurium, which may have resulted from histamine release, a known adverse effect associated with benzylisoquinolinium neuromuscular blocking agents, particularly following rapid intravenous administration (Sinclair, 2003; Clarke et al., 2014). Although this event was mild and self-limiting, it underscores the importance of controlled injection rates and vigilant cardiovascular monitoring during atracurium administration (Grimm et al., 2015).

One of the principal strengths of this study is the use of objective quantitative TOF monitoring. Quantitative neuromuscular monitoring allows for precise detection of residual neuromuscular blockade, which cannot be reliably assessed based solely on clinical signs (Reid et al., 2007; Beths et al., 2014). Achieving a TOF ratio ≥ 0.9 is widely accepted as the benchmark for safe recovery of neuromuscular function, particularly with regard to airway protection and respiratory safety (Murrell and Johnson, 2006; Monteiro and Steagall, 2019).

Despite these strengths, certain limitations must be acknowledged. The relatively small sample size may limit the generalizability of the findings, and the study population consisted exclusively of healthy dogs. Consequently, further investigations involving larger cohorts and animals with concurrent systemic diseases are warranted to validate these results across diverse clinical settings (Yousef and Al-Saadi, 2018; Court and Greenblatt, 2000).

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Conclusion

Rocuronium and atracurium are both efficient and safe neuromuscular blocking agents for ambulatory anesthesia in dogs. The rapid onset of action of neuromuscular blockade by rocuronium makes it especially useful in situations where rapid tracheal intubation is needed. On the other hand, atracurium allows for reliable recovery and stable cardiovascular function; thus, it is appropriate for patients with possible organ dysfunction or when pharmacological reversal is not an option. The selection of an agent should depend on the urgency of the procedure, the health condition of the patient, and the availability of resources in the institution. Regular quantitative neuromuscular monitoring is advised to guarantee thorough recovery and maximize patient safety during ambulatory anesthesia.

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Acknowledgments

The author thanks the staff of the Department of Veterinary Clinical Sciences, University of Kufa, for their support during this study.

Conflict of interest

The author declares no conflict of interest.

Funding

This research received no external funding.

Authors' contributions

Ayad Nouri Diaa Alhakim: designed the study, conducted experiments, analyzed data, and prepared the manuscript. Abd-Alhadi Jaithom Marzok: monitoring the biological changes of the research animals (dogs), handling administrative matters, coordinating schedules, and making some corrections. Dhurgham H. Al Haideri: writing the research paper, compiling statistics, making some corrections, and conducting routine checkups for the dogs.

Data availability

Data supporting the findings of this study are available from the corresponding author upon reasonable request.

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