▁EC 5 0 ▁value ▁of ▁only ▁ 7 , 7 6 5 ▁ ± ▁ 6 1 0 ▁n M . ▁ ▁After ▁an ▁or al ▁do se , ▁about ▁ 7 0 % ▁of ▁the ▁drug ▁is ▁ex cret ed ▁from ▁the ▁body ▁within ▁ 2 4 ▁hours . ▁About ▁ 1 9 % ▁of ▁that ▁is ▁ex cret ed ▁as ▁the ▁un met abol ised ▁drug ▁and ▁the ▁rest ▁as ▁various ▁met abol ites . ▁ ▁In ▁tri als ▁performed ▁on ▁r ats , ▁it ▁has ▁been ▁found ▁that ▁after ▁sub cut aneous ▁administration ▁of ▁phen met raz ine , ▁both ▁optical ▁is om ers ▁are ▁equally ▁effective ▁in ▁reducing ▁food ▁int ake , ▁but ▁in ▁or al ▁administration ▁the ▁le vo ▁is omer ▁is ▁more ▁effective . ▁In ▁terms ▁of ▁central ▁stim ulation ▁however , ▁the ▁de xt ro ▁is omer ▁is ▁about ▁ 4 ▁times ▁as ▁effective ▁in ▁both ▁methods ▁of ▁administration . ▁ ▁The ▁salt ▁which ▁has ▁been ▁used ▁for ▁immediate - release ▁form ulations ▁is ▁phen met raz ine ▁hydro ch lor ide ▁( P rel ud in ). ▁S ust ained - release ▁form ulations ▁were ▁available ▁as ▁res in - bound , ▁rather ▁than ▁sol ub le , ▁sal ts . ▁Both ▁of ▁these ▁dos age ▁forms ▁share ▁a ▁similar ▁bio av ail ability ▁as ▁well ▁as ▁time ▁to ▁peak ▁on set , ▁however , ▁sust ained - release ▁form ulations ▁offer ▁improved ▁ph arm ac ok inet ics ▁with ▁a ▁steady ▁release ▁of ▁active