Modafinil

Modafinil (CAS 68693-11-8; molecular formula C15H15NO2S; molecular weight 273.35) is a wakefulness-promoting agent first synthesized at Laboratoire Lafon in France in the 1970s as the active metabolite of adrafinil and approved by the FDA in 1998 for excessive daytime sleepiness associated with narcolepsy, shift work sleep disorder, and obstructive sleep apnea. The compound is a racemic mixture; the (R)-enantiomer (armodafinil) carries the majority of the wakefulness-promoting activity and is marketed separately. The principal mechanism is binding to the dopamine transporter (DAT) with weak inhibitor affinity (Ki approximately 4 microM), producing modest extracellular dopamine elevation in the striatum and prefrontal cortex without the steep release kinetics characteristic of amphetamines or methylphenidate. Downstream effects include activation of orexinergic neurons in the lateral hypothalamus, elevation of histamine in the tuberomammillary nucleus, and increased glutamatergic tone in the prefrontal cortex with concurrent attenuation of GABAergic inhibition. The plasma half-life is 12 to 15 hours; oral bioavailability is high (greater than 80 percent); metabolism is hepatic via CYP3A4 and to a lesser extent via amide hydrolysis. Clinical efficacy in narcolepsy and shift work indications is well established; off-label use for cognitive enhancement in healthy individuals is widespread but the magnitude of cognitive benefit in healthy subjects is small and inconsistent across trials. Schedule IV in the United States. Common adverse events include headache, nausea, anxiety, and insomnia; rare serious events include Stevens-Johnson syndrome and DRESS. The compound is not a controlled substance under international treaty but is regulated nationally in most jurisdictions.