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Modafinil

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Modafinil chemical structure
Modafinil

2-((diphenylmethyl)sulfinyl)-acetamide
CAS number
68693-11-8 		ATC code
N06BA07
Chemical formula C15H15NO2S
Molecular weight 273.351
Bioavailability ?
Metabolism Hepatic, including CYP3A4 and other pathways
Elimination half-life 12–15 h
Excretion Urine (as metabolites)
Pregnancy category C
Legal status Schedule IV (USA)
Routes of administration Oral

Modafinil (commercial trade names Provigil, Modiodal (UK, France), Vigil (Germany), Sparlon (US), Alertec (Canada), and possibly Vigicer) is an eugeroic drug generally prescribed to treat narcolepsy, made by the pharmaceutical company Cephalon Inc.. It is not a typical stimulant and is often described as a "wakefulness promoting agent." It is currently under study as a treatment for depression, and it is being prescribed off-label for ADD/ADHD. In mass-media advertisments and websites, Cephalon markets the drug for improving 'alertness' and reducing 'excessive daytime sleepiness.' Cephalon has also developed and tested Nuvigil, a non-racemic version of modafinil with a longer duration of action.

Indications

Modafinil is available to treat narcolepsy, as well as obstructive sleep apnea/hypopnea syndrome (OSAHS), and shift work sleep disorder (SWSD). Modafinil has been shown to allow some people who suffer from excessive daytime sleepiness to remain awake without impairment of performance. In some cases modafinil produces side-effects such as headache (13% of users), nervousness (8%), nausea (5%), rashes, and intestinal problems.

The usual prescription is for a single dose to be taken shortly after waking; its effects last for most of the day without preventing normal sleep at night. The biological halflife in the human body is about 15 hours. However many patients develop a slight tolerance and report that a single dose only works well for 8 to 12 hours, and that they need to take modafinil twice a day or more. Cephalon hopes to soon release the longer-lasting Nuvigil (r-modafinil) as a "truly once-a-day" wakefulness medication. In 2006, the FDA sent Cephalon an "approvable letter" for Nuvigil, pending agreement on the final product labeling.

Modafinil is not indicated for complaints of lack of energy or fatigue; but it appears to be very helpful for some patients. It has also been used in the treatment of hypersomnia, a disorder in which patients lack the capacity for meaningful sleep and may require ten or more hours per day.

In January of 2005, researchers at the University of Pennsylvania published the results of a small study, which found that modafinil may help recovering cocaine addicts fight their addiction. Similar published case reports suggest that modafinil might also be useful in the treatment of amphetamine addiction.

Clinical trials have suggested that modafinil may be effective for treatment of Attention-deficit hyperactivity disorder (ADHD). In December of 2004, Cephalon submitted a supplemental new drug application (sNDA) to market Sparlon (TM), a brand name of tablets containing higher doses of modafinil (85, 170, 255, 340, and 425 mg) for the treatment of ADHD in children and adolescents ages 6 through 17. Data from three successful clinical trials were submitted by the company to the FDA for evaluation as part of the approval process. On October 20, 2005, the FDA issued an "approvable letter" in response. However, in March of 2006, the FDA advisory committee voted 12-to-1 against approval without more data, citing concerns that a single reported case of a skin rash reaction in a 1,000 patient trial could be Stevens-Johnson syndrome.[1]. The FDA recomended an additional study of 3,000 children to investigate if the reaction was a fluke, and has pushed back the final deadline for its decision on Sparlon (modafinil for the treatment of adolescent ADHD) until August 22, 2006.

Pharmacology

The exact mechanism of action is unclear, although in vitro studies have shown it to inhibit the reuptake of dopamine. While co-administration of a dopamine antagonist decreases the stimulant effect of amphetamine, it does not negate the wakefulness-promoting actions of modafinil. Modafinil activates glutaminergic circuits while inhibiting GABA. Modafinil is thought to have less potential for abuse than other stimulants due to the absence of any significant euphoric or pleasurable effects.

The central stimulating effect of modafinil shows dose and time-related features. The effect tends to be enhanced by chlorination but reduced by methylation. Modafinil blocks the reuptake of norepinephrine by the noradrenergic terminals on sleep-promoting neurons from the ventrolateral preoptic nucleus (VLPO). Such a mechanism could be at least partially responsible for the wake-promoting effect of modafinil.

Modafinil has a binding affinity (Ki) of about 4,000 nmol/L for the dopamine reuptake transporter, and no significant binding to the norepinephrine reuptake transporter.

A newly proposed mechanism of action involves brain peptides called orexins, also known as hypocretins. Orexin neurons are found in the hypothalamus but project to many different parts of the brain, including several areas that regulate wakefulness. Activation of these neurons increases dopamine and norepinephrine in these areas. There are two receptors for hypocretins, namely hcrt1 and hcrt2. Animal studies have shown that animals with defective orexin systems show signs and symptoms similar to narcolepsy. Modafinil seems to activate these orexin neurons thus promoting wakefulness. However, a study of genetically modified dogs lacking orexin receptors showed that modafinil still promoted wakefulness in these animals, suggesting that orexin activation is not required for the effects of modafinil.

It is possible that modafinil acts by a synergistic combination of mechanisms including direct inhibition of dopamine reuptake, indirect inhibition of norepinephrine reuptake in the VLPO and orexin activation.

It has been shown in rats that modafinil increases histamine release in the brain, and this may be a possible mechanism of action in humans.[2]

History

Modafinil originated with the late 1970s invention of a series of benzhydryl sulfinyl compounds, also including adrafinil, by scientists working with the French pharmaceutical company Lafon. Adrafinil was first offered as an experimental treatment for narcolepsy in France in 1986. Modafinil is the primary metabolite of adrafinil and has similar activity but is much more widely used. It has been prescribed in France since 1994 under the name Modiodal, and in the US since 1998 as Provigil. It was approved for use in the UK in December 2002. Modafinil is marketed in the US by Cephalon Inc., who leased the rights from Lafon. Cephalon eventually purchased Lafon in 2001. In 2005, a petition by a private individual was filed with the FDA requesting over-the-counter sale of modafinil.[3]

Formulation patent

A U.S. patent (No. 4,927,855) was granted to Lafon for modafinil in 1990. The FDA granted modafinil orphan drug status in 1993. The formulation patent expired on the 30th of March, 2006

Particle size patent

Cephalon filed for U.S. Patent 5,618,845, covering pharmaceutical compositions of modafinil, in 1994. That patent, granted in 1997, was reissued in 2002 as RE37,516, which provides Cephalon with patent protection for certain preparations of the drug in the United States until 2014, which is now apparently extended to April 6, 2015 after Cephalon received a six-month patent extension from the FDA.[4] However, a settlement in which Cephalon apparently paid out $200 million to four generic drug manufacturers[5] may mean that generic forms of the drug become available in April 2012 (October 2011 prior to the six month extension).

Some competing pharmaceutical manufacturers have applied to the FDA to market a generic form of modafinil in 2006. At least one withdrew their application after early opposition by Cephalon based on their new patent on particle sizes. There is some question as to whether a particle size patent is sufficient protection against the manufacture of generics. Pertinent questions include whether modafinil may be modified or manufactured to avoid the granularities specified in the new Cephalon patent, and whether patenting particle size is invalid because particles of appropriate sizes are likely to be obvious to practitioners skilled in the art.

Military

The French government indicated that the Foreign Legion used modafinil during certain covert operations. Modafinil has reportedly been investigated by the United States military for use by its soldiers. One study on helicopter pilots suggested that 600 mg of modafinil given in three doses can be used to keep pilots alert with only 8 hours of sleep in an 88 hour period. Another study on fighter pilots showed that 300 mg modafinil given in three divided 100-mg doses sustained the flight control accuracy of sleep-deprived F-117 pilots to within about 27 percent of baseline levels.

Currently, modafinil is causing controversy throughout the sporting world, with many high profile cases attracting major press coverage as prominent United States athletes have tested positive for these doping substances. Some athletes that were found to have used modafinil protested as the drug was not on the prohibited list at the time of their offence; however, the World Anti-Doping Agency (WADA) maintains it is a substance related to those already banned, so the decisions stand. The agency added modafinil to the list of prohibited substances on August 3, 2004, ten days before the start of the 2004 Summer Olympics.

Modafinil is currently classified as a Schedule IV controlled substance under United States federal law.

It is not a controlled substance under the Misuse of Drugs Act in the United Kingdom and is available on prescription without legal restrictions.

See also

References

  1. ^ Briefing document (2006) (PDF)
  2. ^ T. Ishizuka (2003) Neurosci. Lett. 339(2), 143-6.
  3. ^ FDA
  4. ^ "bizjournals.com"
  5. ^ E. Pringle (2006)
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