Pharmacokinetic Study of Ketoprofen Isopropyl Ester-Loaded Lipid Microspheres in Rat Blood Using Microdialysis

Determination of entrapment efficiency and drug phase distribution of submicron emulsions loaded silybin

This paper compared the performance of ultrafiltration (UF), ultracentrifugation (UC) and microdialysis (MD) for determining the entrapment efficiency (EE) of submicron emulsions (SE) loaded with a model drug, silybin (SB). Also, a novel way was created to evaluate the drug phase distribution of SE. The EE of SEI, SEII and SEIII with a range of particle sizes (109.8, 171.7 and 213.2 nm) and the drug phase distribution of SEII and SEIII were separately determined by the three methods. The EEs of SEI were 99.8%, 91.1%, 84.4% determined by MD, UF, UC, respectively, and the EEs of SEII and SEIII were 99.5%, 86.4%, 72.1% and 99.4%, 84.3%, 66.3%, separately. The accuracy of MD to determine EE of SE is much less than that of UF. Although UC is the fastest and most simple to use, its results are the least reliable. The sequence of the amount of drug in SE is as follows: O/W interface, aqueous phase and oil phase. Over 80% of SB was in the O/W interface of SEII and SEIII individually. The method created is reliable for quantifying the phase distribution of drug in submicron emulsions.

Nano-LC-MS/MS for the monitoring of angiotensin IV in rat brain microdialysates: Limitations and possibilities

To broaden our knowledge about the central role of the angiotensin IV (Ang IV) peptide, we aimed to monitor its extracellular concentration in the brain using in vivo microdialysis. Ang IV was measured in the dialysates using a previously developed nano-LC-MS/MS assay with an LOD of 50 pM. Using this assay, baseline levels of Ang IV in dialysates from different brain structures were undetectable. However, immediately after microdialysis probe insertion, Ang IV could be detected in a concentration that varied between 120 and 187 pM. Using the zero-net-flux method, the extracellular levels of Ang IV in the striatum were estimated at 46 pM. These data may indicate that Ang IV is mainly present intracellularly. In addition, Ang IV was clearly measurable after striatal perfusion of Ang II. On the other hand, our nano-LC-MS/MS method was successful for the detection of Met-enkephalin and neurotensin in dialysates from the rat. In conclusion, the nano-LC-MS/MS method coupled with microdialysis is well suited to monitor the biologically significant conversion between Ang II and Ang IV in vivo, but physiological extracellular levels of Ang IV appear too low to be detected.

Rapid online-SPE-MS/MS method for ketoprofen determination in dermal interstitial fluid samples from rats obtained by microdialysis or open-flow microperfusion

Pharmacokinetic studies of topical ketoprofen formulations using continuous sampling techniques such as microdialysis (MD) or open-flow microperfusion (OFM) require sensitive assays due to small sample volumes. A simple and easy online-SPE-MS/MS method for ketoprofen analysis was developed for both MD and OFM samples obtained from rat dermal tissue. The quantification range is 25-5000 ng/ml with a limit of detection of 3 ng/ml using only 10 microl sample volume. The method is characterized by a simple setup using a short polymeric SPE column (OASIS HLB) for desalting with 1.5 min run times in combination with a sensitive MS detection in negative ESI MRM mode. An easy sample workup procedure was used which enables high throughput analysis of a large number of samples for pharmacokinetic studies. In addition, a commercial available (fenoprofen) as well as an isotopically labelled (deuterated ketoprofen) standard were investigated as potential internal standards. The method was validated according to FDA guidelines for bioanalytical validation in terms of accuracy, intra-batch and inter-batch precision, linearity, matrix effect, recovery and stability for both internal standards. Accuracies were 98-113% (fenoprofen) and 95-108% (deuterated ketoprofen), intra-batch precision was 2-3% R.S.D. (fenoprofen) and 2-6% R.S.D. (deuterated ketoprofen), and inter-batch precision was 2-6% R.S.D. (fenoprofen) and 3-6% R.S.D. (deuterated ketoprofen) over the entire quantification range. The presented method was applied to dermal interstitial fluid samples obtained in a topical administration study of ketoprofen in rats.