The pharmacokinetic study was conducted in healthy human volunteers and compared the drug exposure profile of arbaclofen, under both fasted and fed conditions, following a single oral administration of a 5mg dose.
The data showed that there were no detectable S-isomer levels following arbaclofen administration and thus no evidence of any interconversion of arbaclofen (R-isomer) to S-isomer in vivo. Following arbaclofen administration, approximately 80% of the administered dose was recovered in the urine in unchanged form. The high recovery of unchanged R-isomer in the urine following arbaclofen administration indicates there is no significant effect of hepatic metabolism on the kinetics of arbaclofen.
There was comparable plasma exposure of R-isomer from 5mg of arbaclofen compared to 10mg of Lioresal, confirming that the exposure to the R-isomer is no greater following arbaclofen administration when compared with equivalent doses of an approved and marketed form of racemic baclofen.