研究背景：
Rilpivirine是一種非核苷逆轉錄酶抑制劑，可用於治療初期的愛滋病毒感染者。Rilpivirine在人體主要是經由CYP3A4代謝來排除，因而誘導或抑制CYP3A的藥物可能影響rilpivirine的清除。由於CYP3A的活性在不同個體間有相當大的差異，造成相關藥品調整劑量上之困難，因此使用體內探針性試藥來評估酵素在不同個體內之代謝活性差異具有相當重要意義。Mosapride為新一代胃腸蠕動劑主要也是經由CYP3A代謝，先前研究發現以大白鼠動物模式靜脈注射及口服給予mosapride後其清除率與肝臟及腸道中CYP3A酵素含量成高度相關性，反映出mosapride做為CYP3A體內探針性試藥的可行性。
研究目的：
本研究將開發定量小體積血漿檢品中rilpivirine的分析方法，用以探討rilpivirine在大鼠體內之藥動學與交互作用，以及性荷爾蒙調節CYP3A活性對其受質藥動學之影響；並進一步討論CYP3A探針性試藥mosapride與受質rilpivirine由體內清除之相關性，同時驗證先前開發之mosapride有限單點採樣法的可行性。
研究方法：
首先以靜脈注射方式投予1-8 mg/kg的rilpivirine至大白鼠以研究其線性藥物動力學。在探討應用mosapride預測rilpivirine動力學的實驗中，大白鼠控制組不加處置或事先以抑制劑ketoconazole或誘導劑dexamethasone進行CYP3A活性的調節後，再同時由靜脈投予mosapride和rilpivirine。兩個藥物的血液檢體採樣收集至480分鐘，以分室模式估算其藥動參數。另外，對成熟公鼠和母鼠分別進行手術去勢和投予testosterone進行CYP3A活性調節，並探討兩藥物之動力學變化。
研究結果：
已成功開發一個靈敏的高效液相層析分析方法，並應用在定量小體積大鼠血漿中的rilpivirine。Rilpivirine在給藥劑量下呈線性藥動學。當給予持續輸注CYP3A抑制劑ketoconazole後，mosapride在大鼠體內之清除率顯著減低，然而rilpivirine之清除率則與控制組並無顯著差異；給予CYP3A誘導劑dexamethasone後，不論是rilpivirine或mosapride在大鼠體內之清除率皆增加。在去勢後的公鼠體內mosapride血中濃度明顯上升而rilpivirine血中濃度並無顯著變化。母鼠投予testosterone後，不論是rilpivirine或mosapride血中濃度皆下降。本實驗也再次確認mosapride 90分鐘單點血中濃度可以對其本身AUC有良好預測。Rilpivirine與mosapride兩者對於ketoconazole反應並不盡相同，可能是由於抑制類型與強度不同所導致；若僅分析控制組與誘導組可觀察到mosapride清除率與rilpivirine清除率有良好相關性(r=0.84, p<.0001)。另外，mosapride 90分鐘濃度點也可以對控制組與誘導組rilpivirine之清除率有良好預測。
研究結論：
以靜脈注射方式投予rilpivirine與mosapride後，兩者的清除率在控制組與誘導組呈現正相關。利用單點的血中濃度也可以對rilpivirine的控制組和誘導組清除率有相當程度的預測，因此對於mosapride作為大白鼠體內CYP3A活性探針性試藥的應用而言，提供了一個更方便並省時的評估方式。

Introduction:
Rilpivirine is a non-nucleoside reverse transcriptase inhibitor (NNRTI) of human immunodeficiency virus type-1 (HIV-1). It can be used in the treatment of naïve HIV-1 infected patients. The elimination of rilpivirine in man is mainly by metabolism. The major enzymes responsible for the metabolism of rilpivirine are CYP3A isozymes, thus drugs that induce or inhibit the CYP3A would change the clearance of rilpivirine. CYP3A is one of the most important CYP450 subfamilies expressed in the liver and small intestine with great variation. The use of CYP3A phenotyping probes in drug therapy is of great importance. Mosapride, a new prokinetic agent, is metabolized mainly by CYP3A enzymes. Previous studies showed that after intravenous and oral administration of mosapride, the hepatic and intestinal CYP3A contents correlate strongly with mosapride clearance in rats. And mosapride clearance can be used to assess hepatic CYP3A activity in rats.
Purpose:
The objectives of this study were to characterize the kinetics of a CYP3A substrate rilpivirine in rats after intravenous administration and to predict its exposure using a CYP3A probe mosapride. A new HPLC method for determination of rilpivirine in rat plasma was developed and applied to explore its kinetics.
Methods:
Rats received rilpivirine（1-8 mg/kg）intravenously in the dose-linearity groups. To investigate the applicability of mosapride as a CYP3A probe, rilpivirine and mosapride were administered simultaneously into the femoral vein of rats in the control groups. In the CYP3A modulation groups, rats received study drugs after pretreatment with ketoconazole（inhibition）or dexamethasone (induction). The plasma concentrations of rilpivirine and mosapride were followed for 480 min, and the kinetics parameters were estimated by compartmental analysis. In addition, surgical castration to the male adult rats and testosterone supplement to female adult rats were employed to further investigate the effect of sex hormone on the expression of CYP3A and rilpivirine pharmacokinetics.
Results:
A sensitive HPLC assay was developed and applied to quantify rilpivirine in small volume of rat plasma. Rilpivirine displayed linear kinetics in the dose range studied. In the presence of ketoconazole, clearance of mosapride decreased significantly, whereas that of rilpivirine remained unchanged. Induction with dexamethasone significantly altered the clearance of rilpivirine and mosapride. The plasma concentration of mosapride in male rats increased dramatically after surgical castration, however, the kinetics of rilpivirine remained unaltered. Testosterone supplement significantly decreased the systemic exposure of both drugs in female rats. Mosapride AUC can be well predicted by using a single point (90 min) of plasma concentration. The correlation between mosapride clearance and rilpivirine clearance were relatively good for all the study groups, and after pooling the constitutive control and induction groups together, the correlation coefficient was greater than 0.84 (p<.0001). With regards to limited sampling strategy, a relationship (R2 =0.71, p<.0001) was found between rilpivirine clearance and mosapride plasma concentration at 90 min.
Conclusion:
The pharmacokinetics of rilpivirine in rats following intravenous administration was linear. The strong correlation between the clearances of mosapride and rilpivirine supports the applicability of mosapride as an in vivo hepatic CYP3A probe. Mosapride concentration at 90 min after a single intravenous dose was useful to predict total body clearance of rilpivirine.

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