| AIM: Develop a rapid and sensitive method for the determination of octreotide in beagle dog's plasma by liquid chromatography-mass spectrometry (LC-MS/MS). For the pharmacokinetics study, the method were used to quantify the octreotide concentrations in plasma after an intravenous injection of sandostatin and intramuscular injections of sandostatin LAR and Jinsai octreotide LAR.STUDY METHOD: Octreotide and the internal standard, triptorelin, were precipitated from the matrix by acetonitrile, then washed with dichloromethane and separated on a Zorbax-extend C18 column employing a 1% formic acid/methanol gradient system. Detection was carried out by multiple reaction monitoring (MRM) on an API 4000 LC-MS/MS system with an ESI interface in the positive ion mode. MRM was performed at low resolution using the mass transition ion-pairs m/z 510.5→m/z 120.1 and m/z 656.5→m/z 175.8 for octreotide and triptorelin, respectively. The linearity, specificity, precision, accuracy, recovery and stability were estimated for the validations of the assay.The concentrations of octreotide in health beagle dogs'plasma were measured after intravenous injection of sandostatin at 0.022 mg/kg and intramuscular injections of sandostatin LAR and Jinsai octreotide LAR (1.4 mg/kg). After the plasma concentration–time profile was shown, the area under the curve (AUC0-t) was determined by the linear trapezoidal rule. The two one-sided tests procedure carried out at a significance level of 0.05, and the mean Jinsai octreotide LAR/sandostatin LAR ratios of AUC0?t (after log-transformed) were computed.RESULTS: A highly selective, sensitive, rapid and reproducibility method for the determination of octreotide in beagle dogs'plasma by using LC-MS/MS has been developed and validated in this study. The standard curve of octreotide was linear over a working range of 0.050-50 ng/ml with the lower limit of quantitation (LLOQ) of 0.050 ng/ml and the limit of detection (LOD) of 0.020 ng/ ml. The accuracy was in the range 90.1-109% and the intra- and inter-day precision was <8.37%. It showed relative high and stable recovery for the sample preparing procedure. The samples were stable in three freeze-thaw cycles test, in the autosampler at room temperature for 12 h and in storage at ?20°C for 60 days. The methods, which kept the conformance to the relevant standards of Pharmacopoeia of People's Republic of China, were ideally suited for the study of pharmacokinetics of octreotide.The results of pharmacokinetics study of octreotide showed that: Compared to sandostatin, the LAR octreotide, which required only one monthly intramuscular injection depending on its sustained release, avoided the repeated daily hypodermic injections or prolonged intravenous infusions and exhibited wider application in the clinical treatment of disease of digestive tract, endocrine tumors and acromegaly. Furthermore, both sandostatin LAR and Jinsai octreotide LAR had no cumulative effect after repeated intramuscular injections.The results of bioequivalence evaluation of octreotide LAR showed that: The mean AUC0-t (0-1200 h) of sandostatin LAR after intramuscular injected at dose of 1.4 mg/kg was 578.9±83.04 ng·h/ml, while that of Jinsai octreotide LAR with the same administration dose was 568.0±256.1 ng·h/ml. The relative bioavailability of Jinsai octreotide LAR (sandostatin LAR as reference) was 98.12%. The two one-sided tests illustrated that there was no significant difference in bioavailability of the two LAR microsphere formulations. |
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