What is an intravenous (IV) muscle relaxer?

From the Guidelines

Intravenous (IV) muscle relaxers are medications administered directly into the bloodstream to cause temporary muscle paralysis or relaxation, with common examples including vecuronium, rocuronium, and succinylcholine, which are primarily used during surgical procedures to facilitate intubation and improve operating conditions, as supported by the most recent guidelines 1.

Key Characteristics of IV Muscle Relaxers

• These medications work by blocking neuromuscular transmission at the junction between nerves and muscles, preventing muscle contraction.
• Dosing varies by medication; for example, succinylcholine is typically given at 1-2 mg/kg IV push for rapid sequence intubation, while rocuronium is administered at 0.6-1.2 mg/kg, with specific dosing recommendations for children, such as succinylcholine at 1.8 mg/kg for those under 1 month, 2 mg/kg for those 1 month to 1 year, 1.2 mg/kg for those 1 to 10 years, and 1 mg/kg for those over 10 years 1.
• The choice between succinylcholine and rocuronium should be based on the desired duration of muscle relaxation, the risk of difficult intubation, and the presence or risk of a neuromuscular disease, with rocuronium being a good alternative to succinylcholine, especially when sugammadex is available for reversal 1.

Administration and Monitoring

• These medications should only be administered by trained healthcare professionals in settings with proper airway management capabilities, as they can cause respiratory depression or complete paralysis.
• Patients receiving these medications require ventilatory support and continuous monitoring of vital signs and neuromuscular function, with a focus on preventing complications such as prolonged paralysis, histamine release causing hypotension, and malignant hyperthermia.
• The use of muscle relaxants can improve conditions for mask ventilation and intubation, especially in cases of difficult intubation, and should be guided by quantitative assessment of neuromuscular blockade using a monitor 1.

Safety Considerations

• The administration of a muscle relaxant during anaesthesia in patients with upper airway obstruction is considered a standard in adults, including in situations where a rescue tracheotomy is decided, with succinylcholine and rocuronium being commonly used options 1.
• The risk of anaphylaxis with muscle relaxants, including succinylcholine and rocuronium, should be considered, with some studies suggesting a higher risk with succinylcholine, while others indicate a similar risk between the two medications 1.
• Sugammadex can be used to reverse the effects of rocuronium, providing a faster and more reliable recovery time compared to succinylcholine, but its use should be guided by the availability of the medication and the patient's individual needs 1.

From the FDA Drug Label

Atracurium besylate is an intermediate-duration, nondepolarizing, skeletal muscle relaxant for intravenous administration. Cisatracurium Besylate Injection, USP is a non-depolarizing skeletal muscle relaxant for intravenous administration. Succinylcholine is used to produce neuromuscular blockade and to facilitate tracheal intubation.

An intravenous (IV) muscle relaxer is a type of medication that is administered through a vein to cause muscle relaxation. Examples of IV muscle relaxers include:

• Succinylcholine: a depolarizing muscle relaxant
• Cisatracurium: a non-depolarizing muscle relaxant
• Atracurium: a non-depolarizing muscle relaxant These medications are used to facilitate tracheal intubation and to provide muscle relaxation during surgical procedures 2, 3, 4.

From the Research

Definition and Characteristics of IV Muscle Relaxers

• IV muscle relaxers, also known as neuromuscular blocking agents (NMBAs), are drugs that relax muscles by blocking the transmission of nerve impulses to muscles 5, 6, 7.
• They are commonly used in anesthesia to facilitate tracheal intubation, surgery, and other medical procedures.
• Examples of IV muscle relaxers include rocuronium, vecuronium, atracurium, and rapacuronium 5, 6, 7, 8.

Types of IV Muscle Relaxers

• Non-depolarizing muscle relaxants, such as rocuronium and vecuronium, work by competing with acetylcholine for receptors at the neuromuscular junction, thereby blocking the transmission of nerve impulses to muscles 5, 7.
• Depolarizing muscle relaxants, such as succinylcholine, work by activating the acetylcholine receptors, causing a brief period of muscle contraction followed by relaxation 9.

Properties and Effects of IV Muscle Relaxers

• Rocuronium has a rapid onset of action, with good to excellent intubating conditions achieved within 60-90 seconds 5, 6, 7.
• Vecuronium has a slower onset of action compared to rocuronium, but has a similar duration of action 7.
• Atracurium has a slower onset of action compared to rocuronium, but has a longer duration of action 6, 8.
• Rapacuronium has a rapid onset of action, but has a shorter duration of action and may cause more adverse effects 6.