Esmodafinil

Esmodafinil (also known as (S)-modafinil or (+)-Modafinil) is the enantiopure isolation of the (S) enantiomer of modafinil. Unlike armodafinil, esmodafinil has never been marketed on its own.

Esmodafinil is suspected to be less clinically useful for treating conditions that modafinil and armodafinil are marketed for, such as narcolepsy, sleep-shift work disorder, and obstructive sleep apnea.

Pharmacokinetics
Esmodafinil possesses a substantially shorter half life (3–5 hours) compared to armodafinil (10–13 hours).

Pharmacodynamics
Esmodafinil has a 3 times lower affinity for the dopamine transporter compared to armodafinil. Both enantiomers of modafinil preferentially bind to the dopamine transporter in an inward facing conformation.

Preclinical research
Esmodafinil has been researched for the treatment of cocaine addiction. Like armodafinil, esmodafinil attenuates the effects of cocaine by occupying the dopamine transporter. While doing so, esmodafinil increases dopamine in the nucleus accumbens to a lesser extent than cocaine. However, the short half-life of esmodafinil has been cited as reason to investigate armodafinil as a cocaine addiction treatment instead.

Analysis in biological samples
Modafinil is considered a stimulant doping agent and as such is prohibited by World Anti-Doping Agency in sports competitions. The validated methods are researched to separately quantify modafinil enantiomers in the real samples.