Diphenidol 在家兔體內代謝之研究
Diphenidol 是一個合成之抗暈眩劑及止吐劑，具有很好的特異性與療效，上市至今三十多年，已經 成為抗暈眩藥物中之首選藥，臨床應用上非常普遍；然而，在代謝的研究上仍少有相關的研究報告。
本研究室曾以正相高效液相層析法 (normal phase HPLC) 分析其在家兔體內的動態，發現口服投與 後，血液檢品中並無 diphenidol 存在，僅劑量高達 150 mg/kg 時，於 diphenidol 之滯留時間前 0.7 分 鐘出現一巨大峰線，與人體藥效相比較，顯示 diphenidol 之代謝途徑在不同種生物中有相當的差異。
本實驗採逆相高效液相層析法，探討 diphenidol 與其代謝物之分析方法，進而以 LC/MS/MS 分析其 代謝物之質譜，期能解得 diphenidol 於家兔及人體之代謝途徑。
本實驗之分析方法是利用逆相高效液相層析管柱，配合波長 220 nm 之紫外光檢測生物檢體中 diphe nidol 及其代謝物。 Diphenidol 之最低檢測濃度為 100 ng/ml ，在血漿濃度範圍每毫升 100-4000 ng 內，呈現良好的線性關係， r>0.99 。同日內與異日間分析之變異系數均小於 15 % 。顯示所開發之 分析方法，能準確的定量生物檢體中之 diphenidol 。
靜脈注射投與 6 mg/kg 之 diphenidol 於家兔，其藥物動力學呈現二室性模式特性，與先前利用正相 層析法所得結果相符合；另外將二顆 25 mg diphenidol 糖衣錠口服投與於一名健康男性志願者，採 取其生物檢體分析，唯因定量之最低濃度 (100 ng/ml) 尚不足以偵測到人體口服 diphenidol 之最高血 中濃度，因此無法求得人體之藥物動力學參數。
探討 diphenidol 之代謝途徑，另以 120 mg/kg 之 diphenidol 口服投與於家兔，利用所開發之 LC 分析 條件，配合 LC/MS/MS 檢測，並將血液及尿液檢品以 b-glucuronidase 水解，檢測共軛結合型之代謝 物。 Diphenidol 之代謝行 hydroxylation 、 glucuronidation 及開環形成羧基化合物之途徑。以口服投 與 diphenidol 於人體，則 diphenidol 之代謝以氧化開環形成 N-(4,4-diphenyl-4-hydroxybutyl)-d-amino valeric acid 為主。
結果顯示 diphenidol 在家兔與人主要的代謝途徑不同。唯並未能取得 diphenidol 代謝物之標準品更 正確的加以比對及定量，僅能由生物檢品中微量藥物的分析，藉由質譜結果初步的說明 diphenidol 在家兔與人體中代謝的可能途徑。
Metabolism study of diphenidol
Diphenidol is a synthetic antivertigo and antiemetic agent. It apparently exerts a specific effect in the therapy of vertigo, nause a and vomiting. It is used wildly in clinical application for more than thirty years. The pharmacokinetics of diphenidol in rabbi ts has been studied in our laboratory by normal phase HPLC analysis. There is no diphenidol detectable in the plasma after or al administration in rabbits. Only when the dose was up to 150 mg/kg, a giant peak appeared just about 0.7 minute ahead the r etention time of diphenidol. In this study, we developed a HPLC method to separate diphenidol and its major metabolite, and used LC/MS/MS for metabolites analysis.
Reverse phase column and UV detection at 220 nm are used to separate and detect diphenidol and its major metabolite in biol ogical samples. The limit of qualification of diphenidol in this HPLC analytical method is 100 ng/ml. The calibration curves e xpress good linearity within the concentration range of 100 to 4000 ng/ml (r>0.99). The coefficients of variation of the intrada y and interday validation are all within 15 %.
The pharmacokinetics of diphenidol was studied by intravenous administration of 6 mg/kg in three rabbits. The plasma conce ntration-time profiles of diphenidol could be described by a bi-exponential equation. In addition, two tablets of diphenidol (Ce phadolO) were orally given to one healthy male volunteer. Due to the limit of qualification, no detectable diphenidol can be fo und in human plasma. Therefore, we failed to complete the study of the pharmacokinetics of diphenidol in human.
The metabolism of diphenidol was studied in rabbits at high dose (120 mg/kg) administration. No diphenidol and its major me tabolite peak detected in rabbit's plasma and urine. In addition, there was also no metabolite peak detected in volunteer
's plasma. Treated samples with b-glucuronidase hydrolysis first was necessary. After analyzed by LC/MS/MS, the resu lts suggested that the hydroxylation and open piperidine ring following glucuronidation metabolism of diphenidol were princi pal biotransformation pathway in rabbits and human. Comparing the difference of diphenidol metabolite in rabbits and human : Hydroxylation in phenyl ring and following glucuronide conjugation was the major metabolite in rabbits, while N- (4,4-diph enyl-4-hydroxybutyl)-d-aminovaleric acid was the major metabolite in human.
