Pharmacokinetics and variation in the clearance of oxycodone and hydrocotarnine in patients with cancer pain

Compound injections of oxycodone and hydrocotarnine are currently used as one of the treatment options for some cases with cancer pain. However, there have been no reports examining the factors that influence oxycodone and hydrocotarnine clearance, so detailed examination is necessary. As for hydrocotarnine, there have been no reports examining the pharmacokinetics. Therefore in this study, we determined the pharmacokinetics of oxycodone and hydrocotarnine in patients with cancer pain. The study was conducted on 19 patients, in whom pain control was attempted by using the compound injections of oxycodone and hydrocotarnine. We used HPLC-electrochemical detector (ECD) to determine oxycodone and hydrocotarnine serum concentrations, and used the nonlinear least-squares method (MULTI) for calculation of the pharmacokinetic parameters. Furthermore, we examined the factors that influence the clearance of oxycodone and hydrocotarnine by multiple regression analysis (step wise method). The pharmacokinetic parameters were as follows: Oxycodone; V _d=226.7±105.5 l (mean±S.D.), CL=37.9±25.1 l/h, t_1/2=4.1±1.9 h. Hydrocotarnine; V_d=276. 8±237.2 l, CL=95.1±64.3 l/h, t_1/2±2.0±0.7 h. The clearance of oxycodone represented by a regression formula was significantly correlated to the age, the presence or absence of within 7 d on the death or liver metastasis, or of the heart failure of the patients. The clearance of hydrocotarnine represented by a regression formula was significantly correlated to the presence or absence of within 7 d on the death or liver metastasis, or of the heart failure of the patients. The clearance also indicated that oxycodone concentration in the blood was likely to be higher in patients having these factors. Oxycodone/hydrocotarnine compound injections should be used with caution and dose reduction may be necessary in such populations.