Phenprobamate (3-phenylpropylcarbamate, Gamaquil, Isotonil) is a centrally acting muscle relaxant with mild sedative and anticonvulsant effects. Muscle relaxants can enhance and prolong the effect of narcotic drugs and enable to obtain same effect with a smaller amount of alcohol or illicit substance. Almost all of the centrally acting muscle relaxants have varying sedative effects on which their abuse potential mainly depends. Overdose is similar to barbiturates. Its mechanism of action is probably similar to meprobamate. Phenprobamate was previously used in humans as an anxiolytic, and is still sometimes used in general anesthesia and for treating muscle cramps and spasticity. Phenprobamate is still used in some European countries, but it has generally been replaced by newer drugs. Phenprobamate is metabolized by oxidative degradation of the carbamate group and ortho-hydroxylation of the benzene ring, and is eliminated in urine by the kidneys. Doses range from 400 to 800 mg, up to 3 times a day.

Atracurium is an intermediate-duration, nondepolarizing, skeletal muscle relaxant for intravenous administration. It is used, as an adjunct to general anesthesia, to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical ventilation. Most adverse reactions were suggestive of histamine release. Common side effects include flushing of the skin and low blood pressure. Drugs which may enhance the neuromuscular blocking action of atracurium include: enflurane; isoflurane; halothane; certain antibiotics, especially the aminoglycosides and polymyxins; lithium; magnesium salts; procainamide; and quinidine.

Mivacurium chloride (Mivacron) is a new benzylisoquinolinium choline-like diester neuromuscular blocking drug with an onset of action at equipotent doses that is comparable to atracurium and vecuronium but slower than succinylcholine. MIVACRON (a mixture of three stereoisomers) binds competitively to cholinergic receptors on the motor end-plate to antagonize the action of acetylcholine, resulting in a block of neuromuscular transmission. This action is antagonized by acetylcholinesterase inhibitors, such as neostigmine. MIVACRON is a short-acting neuromuscular blocking agent indicated for inpatients and outpatients, as an adjunct to general anesthesia, to facilitate tracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical ventilation.

Doxacurium chloride (formerly recognized as BW938U80 or BW A938U) is a neuromuscular-blocking drug or skeletal muscle relaxant in the category of non-depolarizing neuromuscular-blocking drugs, used adjunctively in anesthesia for endotracheal intubation or to facilitate mechanical ventilation. Unlike a number of other related skeletal muscle relaxants, it is rarely used adjunctively to facilitate endotracheal intubation. Doxacurium chloride is a mixture of three trans, trans stereoisomers, a dl pair [(1R,1'R ,2S,2'S ) and (1S,1'S ,2R,2'R )] and a meso form (1R,1'S,2S,2'R). NUROMAX binds competitively to cholinergic receptors on the motor end-plate to antagonize the action of acetylcholine, resulting in a block of neuromuscular transmission. This action is antagonized by acetylcholinesterase inhibitors, such as neostigmine.

Rocuronium (brand names Zemuron, Esmeron) is an aminosteroid non-depolarizing neuromuscular blocker or muscle relaxant used in modern anesthesia to facilitate endotracheal intubation by providing skeletal muscle relaxation, most commonly required for surgery or mechanical ventilation. Rocuronium bromide is a nondepolarizing neuromuscular blocking agent with a rapid to intermediate onset depending on dose and intermediate duration. It acts by competing for cholinergic receptors at the motor end-plate. This action is antagonized by acetylcholinesterase inhibitors, such as neostigmine and edrophonium. Most common adverse reactions are transient hypotension and hypertension.

Orphenadrine is an anticholinergic drug of the ethanolamine antihistamine class used to treat muscle pain and to help with motor control in Parkinson's disease but has largely been superseded by newer drugs. Orphenadrine binds and inhibits both histamine H1 receptors and NMDA receptors. It restores the motor disturbances induced by neuroleptics, in particular, the hyperkinesia. The dopamine deficiency in the striatum increases the stimulating effects of the cholinergic system. This stimulation is counteracted by the anticholinergic effect of orphenadrine. It may have a relaxing effect on skeletal muscle spasms and it has a mood elevating effect. Orphenadrine is indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute painful musculoskeletal conditions. Orphenadrine is an anticholinergic with a predominantly central effect and only a weak peripheral effect. In addition, it has mild antihistaminic and local anesthetic properties. Parkinson's syndrome is the consequence of a disturbed balance between cholinergic and dopaminergic neurotransmission in the basal ganglia caused by a decrease in dopamine. Orphenadrine restores the physiological equilibrium and has a favorable effect on the rigidity and tremor of Parkinson's disease and Parkinsonian syndromes. Adverse reactions of orphenadrine citrate are mainly due to the mild anticholinergic action of orphenadrine citrate and are usually associated with higher dosage. Dryness of the mouth is usually the first adverse effect to appear. When the daily dose is increased, possible adverse effects include tachycardia, palpitation, urinary hesitancy or retention, blurred vision, dilatation of pupils, increased ocular tension, weakness, nausea, vomiting, headache, dizziness, constipation, drowsiness, hypersensitivity reactions, pruritus, hallucinations, agitation, tremor, gastric irritation and rarely urticaria and other dermatoses

Pipecuronium is a piperazinyl androstane derivative, which is a non-depolarizing neuromuscular blocking agent, which was approved under brand name arduan for injection. It is a long-acting neuromuscular blocking agent, indicated as an adjunct to general anesthesia, to provide skeletal muscle relaxation during surgery. Arduan can also be used to provide skeletal muscle relaxation for endotracheal intubation. Pipecuronium undergoes very little metabolism and is excreted by the kidney and the liver. Owing to its relatively long duration of action and to the residual postoperative neuromuscular block (RPONB), the use of pipecuronium was discontinued in the United States and in several European countries. Because of its excellent safety profile, the use of pipecuronium has been maintained in several countries including China, Russia, Brazil, and Hungary, among others. Its safe use, however, is dependent on the availability of a reliable reversal drug. Although widely used, there are concerns with the use of neostigmine for reversal. Arduan is a powerful competitive antagonist of acetylcholine, since it can bind pre- and postsynaptic (N1) receptors of the transmitters.

Fazadinium (used as a bromide salt) is a muscle relaxant, which was applied in anesthesia under the name Fazadon. The current marketing status is unknown and the drug is supposed to be discontinued.

Mivacurium chloride (Mivacron) is a new benzylisoquinolinium choline-like diester neuromuscular blocking drug with an onset of action at equipotent doses that is comparable to atracurium and vecuronium but slower than succinylcholine. MIVACRON (a mixture of three stereoisomers) binds competitively to cholinergic receptors on the motor end-plate to antagonize the action of acetylcholine, resulting in a block of neuromuscular transmission. This action is antagonized by acetylcholinesterase inhibitors, such as neostigmine. MIVACRON is a short-acting neuromuscular blocking agent indicated for inpatients and outpatients, as an adjunct to general anesthesia, to facilitate tracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical ventilation.