Loxoprofen sodium의 투여 경로에 따른 loxoprofen, trans- 및 cis-alcohol 대사체의 약물동태에 관한 연구

Abstract

Loxoprofen sodium ((sodium (±)-2-[4-(oxocyclopentylmethyl) phenyl] propionate dihydrate) is a non-steroidal antiinflammatory agent (NSAID) with analgesic and antipyretic activities and relatively weak gastrointestinal ulcerogenicity. Loxoprofen itself has only weak inhibitory activity against in vitro prostaglandin synthesis and its pharmacological effect is thought to be derived from (2S)-2-[4-(trans-(l′R, 2′S)-2′-hydroxycyclopentylmethyl)-phenyl] propionic acid, its trans-alcohol metabolite, by aromatic aldehyde-ketone reductase. Loxoprofen is typically administered by oral administration and, presently, no parenteral formulation is available commercially for loxoprofen. However, since parenteral administration of loxoprofen may be clinically relevant, the objective of this study is to compare pharmacokinetics of loxoprofen, trans- and cis-alcohol metabolites after three administration routes (i.e., intravenous, oral and intramuscular administrations) of loxoprofen sodium in rats. Saline containing loxoprofen sodium (l0mg dose as loxoprofen per ㎏ body weight) was administered by oral intubation, intravenous or intramuscular injection to Sprague-Dawley male rats. Concentrations of loxoprofen and its metabolites in plasma were assessed by an HPLC method. Moment analysis of concentration profiles for loxoprofen, trans- and cis-alcohol metabolites indicated that AUC ratios between loxoprofen and trans-alcohol metabolite for intramuscular administration was approximately 68% higher than that for intravenous administration (p<0.05, one-way ANOVA). Similarly, the ratio for intramuscular administration was 48% higher than that for oral administration. In contrast, cis-alcohol to loxoprofen AUC ratio for intramuscular administration was not found to be statistically different with other routes of administrations. To further study kinetic mechanism of enhanced AUC of trans-alcohol after intramuscular administration, distribution of loxoprofen, trans- and cis-alcohol metabolites were compared for the intramuscular and intravenous administrations. Therefore, loxoprofen sodium was injected to femoral vein and muscle in rats and six tissue samples (heart, kidney, liver, brain, lung and muscle) was collected for 6 hours. Tissue samples were homogenized and the cytosolic fraction was collected. The fraction was then deproteinated and an aliquot of the resulting supernatant was injected onto an HPLC assay for the three compounds. In brain, peaks of loxoprofen, trans- and cis-alcohol metabolites were not resolved because of large and broad peak of endogeneous peaks from the brain cytosol, and, thus, distribution study was not carried out in brain samples. In heart, lung and muscle, peaks of loxoprofen, trans- and cis-alcohol metabolites were not detectable, indicating that the three compounds were not distributed to these tissues to a significant extent. In contrast, the concentrations of the parent drug and trans- and cis-alcohol metabolites were readily detected in liver and kidney samples. The ratios of concentrations of loxoprofen, trans- and cis-alcohol in liver and kidney with respect to those in the plasma were found to be variable and less than the unity (i.e., tissue concentration smaller than the plasma concentration). Moreover, there is no appreciable difference in tissue distribution between intramuscular and intravenous administrations, Therefore, these observations strongly indicated that the muscular administration of loxoprofen sodium may lead to an enhanced level of active metabolite in the body and that the enhanced concentration does not appear to be associated with the alteration in distribution of the parent drug or the active metabolite. Taken together, a preferential formation of trans-alcohol metabolite in the muscle may occur for the intramuscular administration of loxoprofen sodium.;Loxoprofen sodium (sodium (±)-2-[4-(oxocyclopentylmethyl) phenyl] propionate dihydrate)은 비스테로이드성 소염진통제로서 체내에 투여되었을 때 aromatic aldehyde-ketone reductase에 의해 환원되어 생성된 활성대사체인 (2S)-2-[4-(trans-(1'R, 2'S)]-2-hydroxycyclomethyl)-phenyl] propionic acid, [2S-trans-(1'R, 2'S)]-alcohol (이하 trans-alcohol)에 의해 prostaglandin acid synthesis를 저해하는 작용을 갖는 prodrug이다. 현재 loxoprofen은 경구제제로만 임상에서 사용되고 있으며 근육주사제제는 개발된 바가 없다. 최근 비스테로이드성 소염진통제의 주사제형이 임상적 가치가 있다는 점이 인식되어 있으므로 본 연구에서는 loxoprofen이 근육주사 제제로 개발될 가능성이 크다고 보고 투여경로에 따른 loxoprofen과 그 alcohol 대사체들의 체내동태를 연구하고자 하였다. Sprague-Dawley male rat을 마취시킨 후 대퇴 정, 동맥을 cannulation하여 회복시켰다. Loxoprofen을 10 ㎎/㎏의 용량으로 경구, 정맥 및 근육투여를 하여 모약물(parent drug)인 loxoprofen의 area under the plasma concentration-time curve from time zero to time infinity (이하 AUC)에 대한 trans- 및 cis-alcohol 대사체의 AUC의 비를 비교한 결과, 근육투여에서 약리적 효과를 갖는 활성대사체인 trans-alcohol의 AUC의 비가 경구투여나 정맥투여에 비해 특징적으로 높았으며(p<0.05, one-way ANOVA) 비활성대사체인 cis-alcohol의 AUC의 비는 투여경로에 따른 차이가 없었다. 본 실험에서는 근육으로 투여된 loxoprofen의 경우 혈장 중 loxoprofen의 AUC에 대한 trans-alcohol 대사체의 AUC의 비가 증가한 것이 체내분포 차이에 기인하였기 때문인지를 연구하였다. 이를 위해 rat에 loxoprofen sodium을 대퇴 정맥과 대퇴 근육에 각각 투여하고 적절한 시간이 지난 후 심장, 신장, 간장, 뇌, 폐 및 근육의 6가지 조직을 취하여 각 조직 무게 2배의 생리식염수를 가하고 homogenize한 후 원심분리를 하여 상징액 100 ㎕를 취하였다. 여기에 zinc sulfate 20 ㎕와 내부표준물질 용액인 120 ㎕의 ketoprofen in acetonitrile을 가하여 제단백을 하고 원심분리를 한 뒤 상징액 100 ㎕를 HPLC에 주입하여 조직 중 loxoprofen, trans- 및 cis-alcohol 대사체의 농도를 정량하였다. 뇌에서는 큰 내인성 peak로 인하여 loxoprofen과 그 대사체들을 구별하기 어려웠고 심장, 폐 및 근육에서는 약물들이 검출되지 않았다. 간, 신장에서는 정맥투여와 근육투여의 경우 모두 모약물과 대사체의 농도가 시간에 따라 감소하는 경향을 보였으나 그 농도가 혈장에서의 약물의 농도에 비해 적고 variable하였으며 근육투여와 정맥투여시 체내분포의 차이가 보이지 않았다. 따라서 이 결과는 loxoprofen sodium이 근육투여된 뒤 trans-alcohol 대사체의 혈장 중 농도가 선택적으로 높은 결과가 나온 것은 투여 경로에 따른 체내분포의 차이점보다는 근육에서 환원효소에 의한 대사에 의한 것으로 사료되었다.