Impact of blood collection devices on clinical chemistry assays

Blood collection devices interact with blood to alter blood composition, serum, or plasma fractions and in some cases adversely affect laboratory tests. Vascular access devices may release coating substances and exert shear forces that lyse cells. Blood-dissolving tube additives can affect blood constituent stability and analytical systems. Blood tube stoppers, stopper lubricants, tube walls, surfactants, clot activators, and separator gels may add materials, adsorb blood components, or interact with protein and cellular components. Thus, collection devices can be a major source of preanalytical error in laboratory testing. Device manufacturers, laboratory test vendors, and clinical laboratory personnel must understand these interactions as potential sources of error during preanalytical laboratory testing. Although the effects of endogenous blood substances have received attention, the effects of exogenous substances on assay results have not been well described. This review will identify sources of exogenous substances in blood specimens and propose methods to minimize their impact on clinical chemistry assays.

Rubber stoppers as sources of contaminants in electrospray analysis of peptides and proteins

Using MS/MS, we have identified ions at m/z 399, 421, 609.4, and 819.9 as those of tris (2-butoxyethyl) phosphate, originating in the gray rubber stoppers commonly used as closures in commercial sources of peptides and proteins. The compound is readily extracted by contact with organic solvents such as alcohol or acetic acid and even by water alone. Zinc salts of proteins are also observed, presumably from zinc oxide fillers present in the stoppers.

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)

Clinical toxicity of cocaine adulterants

Adulterants are found in all street samples of cocaine. They add an unappreciated dimension to the clinical toxicity of cocaine abuse. Identification of these adulterants is necessary to separate their effects from those of cocaine. The comprehensive toxic screen, which provides multiple modalities of drug analysis, will be a key diagnostic tool in the further investigation of these inherently toxic agents and their impact on syndromes of cocaine intoxication.

The plasma protein binding of basic drugs

The plasma protein binding of basic drugs appears to vary more than was at first assumed and is related to the marked intra-and interindividual differences in one of the chief binding proteins, AAG. Changes in AAG concentrations will result in alterations in the distribution and metabolism of basic drugs which will complicate the interpretation of the relationship between total drug concentration and drug efficacy or toxicity. For some drugs, e.g. lignocaine, direct measurement of free concentrations may improve their clinical use but rapid and reliable techniques are as yet not readily available.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

Lidocaine disposition in obesity

Fourteen obese men (mean weight 124 +/- 8 kg (+/- standard error of the mean), percent ideal body weight (IBW) 169 +/- 10%), 11 obese women (96 +/- 6 kg; 174 +/- 11% IBW), 19 control men (69 +/- 1 kg; 93 +/- 2% IBW), and 12 control women (59 +/- 2 kg; 102 +/- 3% IBW), all of similar age and without clinical or laboratory evidence of cardiac or renal dysfunction, received a single 25-mg intravenous dose of lidocaine. Elimination half-life was markedly prolonged in obese compared with control men (2.69 +/- 0.2 vs 1.62 +/- 0.06 hour, p less than 0.001) and in obese compared with control women (2.95 +/- 0.1 vs 2.08 +/- 0.06 hour, p less than 0.01). This was not the result of a change in clearance (men, obese vs control: 1,427 +/- 117 vs 1,346 +/- 86 ml/min, difference not significant, [NS]; women: 1,089 +/- 83 vs 1,162 +/- 84 ml/min, NS), but rather of an increased absolute volume of distribution (Vd) in obese men (325 +/- 29 vs 186 +/- 12 liters, p less than 0.001) and obese women (264 +/- 20 vs 209 +/- 15 liters, p less than 0.025). Vd corrected for total body weight was unchanged in obesity for both men (2.67 +/- 0.22 vs 2.71 +/- 0.18 1/kg, NS) and women (2.88 +/- 0.31 vs 3.57 +/- 0.25, NS), suggesting that lidocaine Vd increases in parallel with body weight in both sexes. Because lidocaine clearance is determined mainly by hepatic blood flow, these findings suggest that extremes of body weight do not change hepatic blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Do evacuated blood collection tubes interfere with therapeutic drug monitoring?

The influence of various brands of evacuated blood collection systems (the old type, red stoppered Vacutainer; the new type, blue stoppered Vacutainer; Monoject and Venoject) on therapeutic drug monitoring was investigated. No interferences were found in the assay of ethosuximide, phenobarbital, phenytoin, valproic acid, digitoxin, digoxin, procainamide, gentamicin and theophylline. Using Monoject and old type Vacutainer tubes, lower levels were found in the disopyramide assay: 91.3 +/- 4.6% (p less than 0.05) and 91.7 +/- 7.0% (not significant) respectively, and in the quinidine assay: 82.8 +/- 6.7% (p less than 0.02) and 83.9 +/- 4.4% (p less than 0.001) respectively as compared with glass tubes. In the carbamazepine assay a decrease was found in the Monoject tubes only: 93.7 +/- 1.7% (p less than 0.01). The stoppers of Monoject tubes and the old type Vacutainer tubes contained the plasticizer tris-(2-butoxyethyl)phosphate (TBEP), which has been shown to be a potent inhibitor of the binding of several drugs to alpha 1-acid glycoprotein. Using the new type Vacutainer and the Venoject, no interferences were found.

Lidocaine clinical pharmacokinetics

A review of the clinical pharmacokinetics of lidocaine is presented. Available evidence suggests that antiarrhythmic effects are reasonably well correlated wih plasma concentration. Adverse effects also covary with plasma concentration, but available evidence suggests that the correlation is not strong. A simple, multiple-bolus loading schedule appears to be superior to techniques using loading infusions; most of the multiple-bolus protocols mandate that only enough drug be given to attain the desired pharmacologic effect. In contrast, the loading infusion protocols almost invariably require the administration of a fixed dose, regardless of what fraction of the dose has been given when arrhythmia suppression is achieved. Since multiple-bolus and constant-rate infusion techniques have been shown to reduce substantially the incidence of primary ventricular fibrillation, they should be considered appropriate prophylactic and treatment regimens for acute myocardial infarction patients.

On the role of alpha 1-acid glycoprotein in lignocaine accumulation following myocardial infarction

1 Blood plasma and free lignocaine concentrations have been measured 12 h after beginning a constant infusion of 2 mg/min and again at the end of the infusion (36-72 h) in five patients with myocardial infarction (MI) and compared with five control patients who did not develop objective evidence of MI. 2 In MI patients, total plasma concentration rose significantly between 12 h and the end of infusion. Because of an increase in alpha 1 acid glycoprotein (AAG) plasma binding increased, so that free drug concentration did not change. The rise in whole blood concentration was less than that in plasma as a result of drug redistribution out of red cells due to enhanced binding. 3 In control patients, neither blood nor plasma concentrations changed with time and plasma binding remained constant. Free drug concentrations, however, rose slightly. 4 The concentrations of GX and MEGX remained unchanged in all patients, but the ratio of lignocaine/MEGX concentrations fell in controls but rose in MI patients. 5 Pharmacokinetic modelling suggested that at least some of the rise in blood lignocaine concentration was due to reduced clearance resulting from enhanced plasma binding. 6 We conclude that the rise in AAG following MI is responsible for increased plasma binding and drug redistribution within blood. These changes, together with a reduction in lignocaine clearance, can explain much of the phenomenon of lignocaine accumulation in MI.

The influence of blood collection technique on serum and plasma protein binding of disopyramide

Serum and plasma disopyramide (D) protein binding was compared after blood was collected from four normal subjects in various Vacutainer tubes. The fraction of disopyramide bound to proteins in control serum and plasma was drug concentration dependent and correlated well with the capacity factor (N) associated with a high affinity protein binding site. D free fraction increased 60% at a postequilibrium concentration of 2 micrograms/ml in plasma following exposure of blood to green-top Vacutainer stoppers due to a 60% reduction in the affinity constant associated with the high affinity protein binding site. Heparin and EDTA had no effect on the plasma protein binding of D. These results suggest a competitive inhibition of disopyramide binding to alpha 1-acid-glycoprotein following contact of blood with rubber Vacutainer stoppers.

Clinical comparison of rapid infusion and multiple injection methods for lidocaine loading

A rapid infusion regimen for lidocaine loading (150 mg infusion over 18 minutes following a 75 mg priming injection) was evaluated in 12 patients. This was compared with multiple injection loading method in six patients involving three 50 mg injections over 18 minutes following the same priming dose. Both loading regimens were followed by a maintenance infusion of 2 mg/min. Predictably, the multiple injection method produced wide variations in lidocaine concentrations compared to the rapid infusion method. Some evidence of lidocaine toxicity (drowsiness, tinnitus) was seen in 13 of the 18 patients after the priming injection. During multiple injection loading, all six patients experienced side effects (drowsiness, tinnitus, dysarthria, or paresthesias.) Only 1 of 12 patients experienced a side effect (drowsiness) during rapid infusion loading. The difference in incidence of adverse reactions was significantly greater with the multiple injection regimen (p less than 0.01) but was associated with measurably greater drug levels.

Leaching of 2-(2-hydroxyethylmercapto) benzothiazole into contents of disposable syringes

A contaminant was found to leach into the contents of two brands of disposable syringes. It was identified as 2-(2-hydroxyethylmercapto) benzothiazole and is believed to be formed during manufacture of the syringes as a result of a reaction between 2-mercaptobenzothiazole, a rubber vulcanization accelerator, and ethylene oxide, used for sterilization. The contaminant was isolated form the rubber plunger-seal and identified using mass, NMR, and UV spectroscopic methods. The amount of contaminant appearing in the contents of syringes was measured; up to 140 micro g was found under clinically relevant conditions. This finding has important implications with respect to the use of these syringes for drug administration and for the collection of blood for drug analyses.

Determination of levamisole in plasma and animal tissues by gas chromatography with thermionic specific detection

A rapid and sensitive method has been developed for the determination of the anthelmintic levamisole in plasma and tissues from man and animals. The procedure involves the extraction of the drug and its internal standard from the biological material at alkaline pH, back-extraction into sulphuric acid and re-extraction into the organic phase (heptane-isoamyl alcohol). Several extraction steps can be omitted, however, whenever the gas chromatographic background permits and some operations can be simplified using Clin ElutTM extraction tubes. The analyses were carried out by gas chromatography using a nitrogen-selective thermionic specific detector. The detection limit was 5 ng, contained in 1 ml of plasma or in 1 g of the various tissues, and recoveries were sufficiently high (79-86%). The method was applied to human plasma samples in a comprehensive bioavailability study of levamisole in healthy volunteers, and to plasma and tissues in a residue trial in cattle. The effect of the blood collection technique on the plasma levels was also studied and pointed to decreased plasma concentrations when Vacutainer tubes were used.