Evaluation and application of a high performance liquid chromatographic method for prilocaine analysis in human plasma.

BACKGROUND: Prilocaine, a local anesthetic of the amide type, is frequently applied in substantial doses during tumescent liposuction. Although it cannot be excluded that the subcutaneously infiltrated narcotic may enter the circulation and trigger adverse systemic reactions, prilocaine plasma levels have rarely been measured during routine tumescent surgery. We established and evaluated a high performance liquid chromatography (HPLC) method for analysis of this narcotic and used it to measure the drug in plasma samples drawn in the course of tumescent liposuction with prilocaine local anesthesia. METHODS: After approval by the local ethics committee and written informed consent, 283 heparin plasma samples were collected from 132 patients during and about 6, 12, and 24 hours after tumescent liposuction with prilocaine infused at doses of 19 +/- 5 mg/kg body weight. Calibrators and controls were prepared by spiking blank plasma with prilocaine. Following addition of internal standard and sodium hydroxide, plasma was extracted with diisopropyl ether. For HPLC analysis, dried extracts were dissolved in methanol - 4.35 mmol/L ammonium phosphate, pH7.0, (60:40 v/v) and applied to a Synergy 4 microm Fusion-RP column (250 x 4.6 mm) rinsed with the same buffer. Analytes were detected by absorption at 237 nm. For liquid chromatography mass spectrometry (LC-MS), extracts were dissolved in acetonitrile - 2 mmol/L ammonium acetate - formic acid (5:95:0.2 v/v/v), applied to a Synergy 4 microm Polar-RP column (75 x 2 mm), and eluted with a gradient of acetonitrile in 2 mmol/L ammonium acetate - formic acid. Analytes were detected by an ion trap mass spectrometer with electrospray ionization run in a MS/MS mode. RESULTS: In the HPLC assay established, prilocaine and the internal standard lidocaine eluted at about 14 and 25 minutes, respectively. The limit of detection of prilocaine was 0.002 mg/L, the measurable range extended to 30 mg/L. At prilocaine concentrations between 0.08 and 10.0 mg/L, inter-assay coefficients of variation of 6.2 to 9.9% were obtained. Analyses of plasma pools spiked with variable amounts of prilocaine showed recoveries of 91-101%. Results measured in 20 plasma samples by both HPLC and an independent LC-MS assay agreed acceptably (Y(HPLC) = 0.07 + 1.19x(LC-MS), R 0.98). Prilocaine plasma concentrations measured by HPLC in 132 plasma samples drawn in the late phase of liposuction ranged between 0.01 and 32.0 mg/L, roughly one third of all samples exhibiting levels above 5 mg/L. About 6 hours later, prilocaine levels measured in 46 plasma samples were lower (0.13 - 1.56 mg/L) and decreased further in the evening of the operative day (n = 49, 0.10 - 0.62 mg/L) and on the morning of the first postoperative day (n = 55, 0.03 - 0.25 mg/L). CONCLUSIONS: An HPLC method for determination of prilocaine was established and successfully applied to analysis of this drug in human plasma. Our results clearly indicate that during tumescent liposuction a significant portion of the subcutaneously infiltrated prilocaine enters the circulation, resulting in potentially harmful blood levels in about one third of the patients studied. 6 hours after liposuction, however, all samples exhibited prilocaine plasma levels far below a critical concentration and these levels further decreased in the evening of the day of treatment and on the next morning.

Differences of propofol concentrations in mammalian whole blood and in corresponding plasma samples analyzed by high performance liquid chromatography.

BACKGROUND: In preparation for a study of the pharmacokinetics and elimination of propofol, a frequently used intravenous narcotic, we sought for a simple but accurate method for determining the drug in biological fluids from various mammalian species. MATERIALS AND METHODS: We established an isocratic high performance liquid chromatography (HPLC) assay with fluorimetric detection for quantification of propofol, studied the analytical characteristics of the method, and measured the narcotic in heparinized whole blood and corresponding plasma samples drawn from 5 subjects each of humans, pigs, sheep and goats prior to and after 10 minutes of constant infusion of propofol. RESULTS: Following protein precipitation with methanol, propofol was quantified in the alcoholic phase. With 30 microl extract, lower limits of detection and quantification of propofol were 2 and 10 microg I(-1), the measurable range extended to 8000 microg I(-1). Intra- and inter-assay CVs tested at propofol concentrations between 40 and 3000 microg I(-1) were < 3% and < 8%, respectively. Propofol levels ranged from 900 to 10,000 microg I(-1) after 10 minutes of drug infusion; among the animals treated with identical doses, pigs exhibited the highest and sheep the lowest circulating propofol concentrations. CONCLUSIONS: Analysis of propofol by the HPLC method described is highly practicable, sensitive and specific. Propofol concentrations measured in heparinized blood and corresponding plasma samples differ slightly; in addition to inter-individual variations, species-specific differences in the drug's disposition between plasma and blood cells were observed.