Assess the Effect of Metaxalone 640 mg (M640) Compared to Tizanidine 8 mg on Truck Driving Ability and Cognition

Every participant will receive active study drug and one (1) comparator in two (2) stages, one after the other. Each drug will be taken one (1) time after a high fat meal. Vital signs and discussion of medications, illness or injury are considered safety assessments and will be discussed at every visit.

The Screening Visit will be followed by the Baseline (Visit 1) 1-14 days later. At the Baseline Visit participants will be given written tests to measure thinking process. You will also be asked to take a computer driving simulation test.

Visits 2 and 3 approximately one (1) week apart will be the dosing days after eating a high fat meal within 30 minutes. The testing from the Baseline Visit will be repeated at four (4) hours and 1.5 hours after dosing with comparator drug.

The End of Study safety visit will take place two (2) weeks later. Participants will be given discharge instructions.

Inclusion criteria

• equal to or greater than 18 years old
• equal to or less than 65 years old
• weight at least 120 pounds
• medically healthy
• able to eat a high fat meal

Exclusion criteria

• medications known to affect sleep-wake cycle
• current use of cimetidine
• current use of certain anti-depressants
• current use of certain antibiotics
• positive urine drug test for mind altering medications