DANTROLENE

Description

Dantrolene is a drug that causes spastic muscle contraction. Unlike other muscle relaxants, it has a direct effect on the contractile mechanism by interfering in the process of calcium ion release from the sarcoplasmic reticulum. This results in a lack of coordination in the mechanism of excitation––contraction of skeletal muscle, which has a greater effect on fast muscle fibers than on slow muscle fibers.

The Uses of DANTROLENE

Dantrolene is used for controlling the onset of clinical spasticity resulting from serious clinical cases such as wounds, paralysis, cerebral palsy, and disseminated sclerosis. Synonyms of this drug are dantrium and danlen.

The Uses of DANTROLENE

Relaxant (skeletal muscle).

Biological Functions

The site of action of dantrolene is believed to be at the sarcoplasmic reticulum in skeletal muscle cells. Dantrolene binds to a calcium channel protein (ryanodine receptor) on the sarcoplasmic reticulum to close the channel and inhibit the release of calcium; the alkaloid ryanodine activates the same receptor to open the channel.

Mechanism of action

Dantrolene is believed to act directly on the contractile mechanism of skeletal muscle to decrease the force of contraction in the absence of any demonstrated effects on neural pathways, on the neuromuscular junction, or on the excitable properties of the muscle fiber membranes. Cardiac muscle and smooth muscle are minimally affected by dantrolene, likely because calcium release from sarcoplasmic reticulum of these muscle cell types occurs via a mechanism that differs from skeletal muscle. The muscle relaxant effect of dantrolene on skeletal muscle, however, is not specific, and generalized muscle weakness occurs as a major adverse side effect. Like other hydantoins, dantrolene is a weak base (pKa = 7.5) that can cross the blood-brain barrier; thus, CNS depressant side effects (e.g., sedation) are common. Dantrolene sodium salt is slowly absorbed from the gastrointestinal tract. The mean half-life of the drug in adults is approximately 9 hours after a 100-mg dose. It is slowly metabolized by the liver to give the 5-hydroxy and acetamido (nitro reduction and acetylation) metabolites, as well as unchanged drug, excreted in the urine.

Clinical Use

Dantrolene is a hydantoin derivative that acts peripherally to reduce spasticity and is indicated for use in spinal cord injury, stroke, cerebral palsy, and multiple sclerosis.

Synthesis

Dantrolene, 1-[[[5-(4-nitrophenyl)-2-furanyl]methylene]amino]-2,4-imidazolidinedione (15.2.2), is synthesized by reacting 4-nitrophenyldiazonium chloride with furfurol, forming 5-(4-nitrophenyl)-2-furancarboxaldehyde (15.2.1), which is reacted further with 1-aminohydantoin, to give the corresponding hydrazone, dantrolene (15.2.2).