Pharmacokinetics and bioequivalence of oxybutynin sustained-release capsule and conventional tablet in healthy volunteers

AIM To study the pharmacokinetics and bioequivalence of oxybutynin sustained-release capsule and conventional tablet in healthy volunteers.METHODS Twenty healthy male volunteers were given oxybutynin in single and multiple doses in this experiment.A HPLC-MS method was applied to determine the serum concentration of oxybu- tynin,the pharmacokinetic parameters and bioequivalence were evaluated by program 3P97.RESULTS Theρ_(max),t_(max), t(?),AUC_(?)and AUC_(?)of oxybutynin sustained-release capsule and conventional tablet from the single-dose study were as follows:(8.27±7.28)μg·L~(-1)and(17.16±12.17)μg·L~(-1),(2.55±0.85)h and(0.82±0.35)h,(6.23±2.78)h and(5.54±2.18)h,(51.94±40.27)μg·h·L~(-1)and(49.84±34.33)μg·h·L~(-1),(57.25±40.78)μg·h·L~(-1)and(54.68±36.44)μg·h·L~(-1).The maximum serum concentration of sustained-release capsule was decreased, the relative bioavailability of single oral sustained-release capsule to conventional tablet F_(?)was(104.15±15.47)%. The pharmacokinetic parameters of oxybutynin sustained-release capsule and conventional tablet after multiple dose were as follows:ρ_(max)~(ss)were(24.00±10.41)μg·L~(-1)and(15.37±8.00)μg·L~(-1)respectively;ρ_(min)~(ss)were(1.59±0.80)μg·L~(-1)and(1.33±0.80)μg·L~(-1)respectively;ρ_(av)~(ss)were(5.01±2.22)μg·L~(-1)and(2.49±1.17)μg·L~(-1)respectively; AUC~(ss)were(120.19±53.24)μg·h·L~(-1)and(59.85±28.01)μg·h·L~(-1)respectively;DF were(446.23±135.27)% and(579.75±148.10)% respectively.The mean DF of multiple dose sustained-release capsule was lower than that of conventional tablet.CONCLUSION The sustained-release capsules are extendedly released.The test and reference preparations are bioequivalent for AUC_(?),but not bioequivalent forρ_(max).