Free Drug Monitoring by Liquid Chromatography and Implications for Therapeutic Drug Monitoring

Propofol withdrawal syndrome in an adult patient with thermal injury

A 48-year-old man with a history of ethanol abuse and bipolar disease fell asleep while smoking in an intoxicated state. The patient received a 30% total body surface area burn involving his face and upper torso that resulted in an inhalation injury. Several attempts at weaning from mechanical ventilation failed due to his extreme agitation, which was unresponsive to benzodiazepines, opiates, and antipsychotic agents. Propofol therapy was begun in combination with valproic acid, fluoxetine, and risperidone to assist in the treatment of his severe agitation associated with the bipolar disease, inhibiting ventilatory weaning. Repeated attempts to discontinue propofol were associated with withdrawal symptoms such as severe agitation, tremors, tachycardia, tachypnea, and hyperpyrexia. His symptoms resolved only after each time the propofol infusion was restarted. The patient received propofol for 95 days for management of his agitation before dying from refractory septic shock and multiple organ failure.

Analysis of drugs and other toxic substances in biological samples for pharmacokinetic studies

The importance of the role of analysis of drugs and other toxic substances in biological samples (bioanalysis) in medicine, toxicology, pharmacology, forensic science, environmental research and other biomedical disciplines is self-evident. Among these disciplines, bioanalysis plays a special pivotal role in pharmacokinetics. The pharmacokinetic parameters, such as half-life, volume of distribution, clearance and bioavailability, of drugs and other compounds are derived from the concentrations of these analytes assayed in the biological samples collected at specified time points. The capability of analysts to develop sensitive and specific analytical methods for the assay of low concentrations of drugs and other toxic compounds in small amounts of biological samples has contributed significantly to the theoretical advances in pharmacokinetics and its applications in clinical pharmacology and the management of drug therapy in patients. The increased demands for pharmacokinetic applications in turn have stimulated the innovation and improvement in bioanalytical technologies. The reliability of the pharmacokinetic conclusions depends on the accuracy and precision of the analytical methods employed to assay the biological samples. Factors that affect the integrity of the bioanalytical data should therefore be controlled in analysis of biological samples for pharmacokinetics studies. The biological samples for drug concentration determination should be collected as specified in the study protocol with respect to the time and site of sampling. These samples should be processed to avoid extraneous interactions between the analytes and sampling devices or additives resulting in the redistribution of the analytes between components of the biological samples, such as displacement of drug binding and changes in the distribution of the analytes between plasma and red blood cells. The stability of the drugs and other analytes in the samples should also be evaluated to establish the conditions suitable for the transportation and storage of the samples to avoid chemical, photochemical and enzymatic degradation of the analytes. Various technologies have been utilized to assay biological samples for pharmacokinetic studies. The most frequently used are chromatography (high-performance liquid chromatography, gas chromatography and thin-layer chromatography), immunoassays and mass spectrometry.(ABSTRACT TRUNCATED AT 400 WORDS)

Direct determination of protein binding of phenytoin in serum by high-performance liquid chromatography

A reliable, routine method has been developed which speeds and simplifies the determination of free phenytoin levels in serum. The free fraction of the drug was determined by a single direct injection of serum (350 microL) into a high-performance liquid chromatography (HPLC) system. The mobile phase was a mixture of isopropanol (0.5%) and pH 7.4 phosphate buffer. An internal surface reversed-phase silica column, the Pinkerton column, was used with a flow rate of 1.0 mL/min at ambient temperature, and the wavelength was set at 254 nm. The resolution of free and bound phenytoin peaks was affected by the percentage of isopropanol, the serum volume injected, and the protein concentration in the sample. The concentrations of free and bound drug agreed well with those determined by the conventional ultrafiltration method (MPS-1). The determination of protein binding by HPLC appears to be a satisfactory method for routine therapeutic drug monitoring. The factors affecting the binding and chromatographic separation and the application of this method for clinical use are discussed.

A micromethod for the estimation of free levels of anticonvulsant drugs in serum

A micromethod for estimating free levels of phenobarbitone, phenytoin and carbamazepine in patients' sera is described. Serum samples are subjected to a process of ultrafiltration, the filtrates treated with acetonitrile and the drug concentration quantified using high performance liquid chromatography. The stability of free levels in specimens before and after storage is investigated. The method is reproducible and mean recovery exceeds 98.5% showing that there is no significant absorption of drug onto the filters used. There is no interference from other substances normally present in patients' sera and there is a good correlation between results obtained by this method and a fluorescence polarisation immunoassay with correlation coefficient between 0.975 and 0.999. Serum samples can be stored for a lengthy period before ultrafiltration without adverse effects. The relevance of the method to patient care is discussed.

Preanalytical considerations in drug assays in clinical pharmacokinetic studies

Many hospital pharmacy laboratories undertake drug analysis in biological fluids for the production of pharmacokinetic data. The success of such an undertaking very much depends on the selection of a suitable analytical method and a proper approach to sample collection and handling. This paper surveys the main types of biological specimens taken from the patients for pharmacokinetic drug analysis and discusses factors that affect them during or subsequent to their removal. Guidelines are provided in specimen handling and dealing with many problems which could arise prior to actual analysis. By its very nature this paper brings in many disciplines, the full details of which are well beyond its scope, however, some discussion on pharmacokinetic and bioavailability methods in relation to sampling procedures is included to put the matter into a proper perspective.

Vancomycin serum protein binding determination by ultrafiltration

Sixty-two serum concentrations were obtained from 12 infected patients enrolled in a vancomycin pharmacokinetic study. Both unbound and total serum vancomycin concentrations were measured using ultrafiltration and a commercial fluorescent polarization immunoassay. Ultrafiltrates were obtained by centrifugation at 1000 X g for ten minutes at room temperature and their assay indicated a range in protein binding from 7.9 to 71 percent. The mean protein binding (mean +/- SD) was 41.95 +/- 14.15 percent. No measurable adsorption of vancomycin onto the ultrafiltration membrane was noted. Orthogonal regression of unbound versus total vancomycin concentrations was described by the equation y = 0.597x-0.362 with a correlation coefficient of 0.948.