Diphenidol 在家兔體內代謝之研究 Metabolism study of diphenidol
中文摘要
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diphenidol 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-aminovaleric 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。
英文摘要
Diphenidol is a synthetic antivertigo and antiemetic agent. It apparently exerts a specific effect in the therapy of vertigo, nausea and vomiting. It is used wildly in clinical application for more than thirty years. The pharmacokinetics of diphenidol in rabbits has been studied in our laboratory by normal phase HPLC analysis. There is
no diphenidol detectable in the plasma after oral administration in rabbits. Only when the dose was up to 150 mg/kg, a giant peak appeared just about 0.7 minute ahead the retention 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 biological samples. The limit of qualification of diphenidol in this HPLC analytical method is 100 ng/ml. The calibration curves express good linearity within the concentration range of 100 to 4000 ng/ml (r>0.99).
The coefficients of variation of the intraday 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 concentration-time profiles of diphenidol could be described by a bi-exponential equation. In addition, two tablets of diphenidol
(CephadolO) were orally given to one healthy male volunteer. Due to the limit of qualification, no detectable diphenidol can be found 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 metabolite 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 results suggested that the hydroxylation and open piperidine ring following glucuronidation metabolism of diphenidol were principal 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- diphenyl-4-hydroxybutyl)-d-aminovaleric acid was the major metabolite in human.
We can conclude that species different metabolism exists in diphenidol's biotransformation. Hydroxylated glucuronidation in phenyl ring of diphenidol in rabbits would replace by piperidine ring opening oxidation of diphenidol in human.
Due to lack of authentic compounds, it's a pity that we can't determine the absolute structure of diphenidol's metabolites, and also make difficult to further study on the formation pharmacokinetics of diphenidol metabolism.
