Myoflex Sr

Uses

Myoflex Sr is a semi-synthetic colchicine derivative used as an analgesic and anti-inflammatory.

Myoflex Sr is a skeletal muscle-relaxant drug used in the treatment of orthopedic, traumatic and rheumatologic disorders . It is indicated as an adjuvant drug in the treatment of painful muscle contractures and is indicated in acute spinal pathology, for adults and adolescents 16 years of age and older . Recent studies have examined its effect on muscle tone, stiffness, contractures, and soreness experienced by athletes during sporting competitions .

Myoflex Sr is also used to associated treatment for these conditions: Back Pain, Acute, Chronic Back Pain, Extra-Articular Rheumatism, Muscle Inflammation, Muscle Spasms, Musculoskeletal Pain, Nonspecific Pain Post Traumatic Injury, Osteoarthritis (OA), Pain, Post Surgical Pain, Post-traumatic pain, Postoperative pain, Rheumatoid Arthritis, Soreness, Muscle, Spasms, Spinal pain, Vertebral column pain, Inflammation localized, Localized pain, Mild to moderate pain, Musculoskeletal spasms

How Myoflex Sr works

Myoflex Sr, is a synthetic sulfur derivative of colchicoside, a naturally occurring glucoside contained in the Colchicum autumnale plant. Myoflex Sr has a selective and potent affinity for g-aminobutyric acid A (GABA-A) receptors and acts on muscular contractures by activating the GABA inhibitory pathways thereby behaving as a potent muscle relaxant . Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the human cortex . GABAergic neurons are involved in myorelaxation, anxiolytic treatment, sedation, and anesthetics. GABA can also modulate heart rate and blood pressure.

It also has an affinity for the inhibitory glycine receptors (i.e., have glycomimetic and GABA mimetic activity), therefore acts as a muscle relaxant. Glycine is an inhibitory neurotransmitter and acts as an allosteric regulator of NMDA (N-methyl-D-aspartate) receptors. It is involved in the processing of motor and sensory data, thereby regulating movement, vision, and audition. Inhibitory neurotransmitter in spinal cord, allosteric regulator of NMDA receptors .

In one study, thiocolchicoside inhibited the function of recombinant human strychnine-sensitive glycine receptors composed of the alpha1 subunit with a potency (median inhibitory concentration of 47 microM) lower than that apparent with recombinant GABA(A) receptors. The drug also inhibited the function of human nicotinic acetylcholine receptors made of the alpha4 and beta2 subunits, however, this effect was partial and moreover only apparent at high concentrations. Myoflex Sr demonstrated no effect on the function of 5-HT(3A) serotonin receptors .

Toxicity

Has been shown to cause chromosomal aneuploidy and male infertility. Should be avoided during all stages of pregnancy, lactation and puberty. Is a potential risk factor for cancer.

In 2013, The European Medical Association (EMA) mandated that the use of thiocolchicoside-containing medicines by mouth or injection should be restricted across the European Union (EU). These drugs are now recommended only as an add-on treatment for painful muscle contractures resulting from spinal conditions in adults and adolescents 16 years old and older. Additionally, the dose of thiocolchicoside by mouth or injection should be limited. This is due to experimental evidence suggesting that thiocolchicoside was metabolized into M2 or SL59.0955, that has the propensity to damage dividing cells, resulting in aneuploidy (an abnormal number or arrangement of chromosomes). As a result, the CHMP (committee for medicinal products for human use) examined the safety profile of this medicine and consider what regulatory action might be appropriate .

The CHMP reviewed the evidence, with consideration of opinions from experts in medicines safety, and concluded that aneuploidy may occur with M2 at levels not significantly greater than those measured after recommended doses of thiocolchicoside ingested orally. Aneuploidy is a strong risk factor for fetal harm, decreased fertility in men, and could theoretically increase the risk of developing cancer .

The maximum recommended oral dose is 8 mg every 12 hours; treatment length should not exceed 7 consecutive days. When given intramuscularly (IM), the maximum dose is 4 mg every 12 hours, for a maximum of 5 days .

In addition to the above toxicity, a study was done on the hepatotoxic potential of thiocolchicoside. It was observed that serum AST and ALT levels increased following of the administration oral thiocolchicoside at 8 mg/day. Two weeks after discontinuing thiocolchicoside therapy, liver enzymes had decreased to levels within the normal range. Although infrequent, thiocolchicoside should be considered a rare hepatotoxic agent in clinical practice .

Volume of Distribution

The apparent volume of distribution of thiocolchicoside is estimated to be approximately 42.7 L after an intramuscular injection of 8 mg .

Elimination Route

Oral bioavailability is ~25% After intramuscular administration, thiocolchicoside Cmax occur in 30 min and .reach values of 113 ng/mL after a 4 mg dose and 175 ng/mL after a 8 mg dose. The corresponding values of AUC are respectively 283 and 417 ng.h/mL. The pharmacologically active metabolite SL18.0740 is found at lower concentrations with a Cmax of 11.7 ng/mL occurring 5 h post administration and an AUC of 83 ng.h/mL .

After oral administration, no thiocolchicoside is detected in plasma. Only two metabolites are observed: The pharmacologically active metabolite SL18.0740 and an inactive metabolite SL59.0955. For both metabolites, maximum plasma concentrations occur 1hour after thiocolchicoside administration. After a single oral dose of 8 mg of thiocolchicoside the Cmax and AUC of SL18.0740 are about 60 ng/mL and 130 ng.h/mL respectively. For SL59.0955 these values are much lower: Cmax around 13 ng/mL and AUC ranging from 15.5 ng.h/mL (until 3h) to 39.7 ng.h/mL (until 24h) .

Half Life

Approximately 7.7h .

Clearance

Primarily extrarenal elimination (75% of the total body clearance) .

Elimination Route

Myoflex Sr is not eliminated unchanged, rather as one of three metabolites found in either feces (~79 %) or in urine 20%. 3- demethylcolchicine (M2) and 3-O-glucurono-demethylcolchicine (M1) are found in both urine and feces, where as di-demethylcolchicine is found only in feces .

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