Reversion of the SCID phenotype by human T cell grafts. Development of cross-species immunocompetence

Due to defective recombinase function, mice with severe combined immunodeficiency (SCID) lack functional lymphocytes and can accept human lymphoid xenografts. Xenografted animals (SCIDhum) are thought to provide a neutral environment for in vivo studies of normal, malignant or HIV-infected human cells. SCIDhum often develop endogenous, EBV+ lymphomas in the graft and in the our study two-thirds of 142 SCIDhum mice did so. Surprisingly, one-third of animals developed reversion of the SCID phenotype rapidly after human T cell engraftment. 90% of tumors occurred in nonrevertant and only 10% in revertant mice. These revertant animals showed immunologic tolerance for normal human B lymphocytes, maintained stable levels of mouse and human IgM and IgG. In addition, they generated competent mouse T cells able to kill transformed (EBV+) but not fresh B cells from the same donor nor unrelated human B cell lines. The tolerance for human lymphoid cells and the cross-species antitumor competence of host T lymphocytes imply unexpected recognition and selection events. Rather than a neutral "bioreactor," these observations mark the SCID host as potentially active participant in a composite immune system generated by xenografting.

Reversion of the SCID phenotype by human T cell grafts. Development of cross-species immunocompetence

Due to defective recombinase function, mice with severe combined immunodeficiency (SCID) lack functional lymphocytes and can accept human lymphoid xenografts. Xenografted animals (SCIDhum) are thought to provide a neutral environment for in vivo studies of normal, malignant or HIV-infected human cells. SCIDhum often develop endogenous, EBV+ lymphomas in the graft and in the our study two-thirds of 142 SCIDhum mice did so. Surprisingly, one-third of animals developed reversion of the SCID phenotype rapidly after human T cell engraftment. 90% of tumors occurred in nonrevertant and only 10% in revertant mice. These revertant animals showed immunologic tolerance for normal human B lymphocytes, maintained stable levels of mouse and human IgM and IgG. In addition, they generated competent mouse T cells able to kill transformed (EBV+) but not fresh B cells from the same donor nor unrelated human B cell lines. The tolerance for human lymphoid cells and the cross-species antitumor competence of host T lymphocytes imply unexpected recognition and selection events. Rather than a neutral "bioreactor," these observations mark the SCID host as potentially active participant in a composite immune system generated by xenografting.

A comparative study of the toxicity of chemically reactive xenobiotics towards adherent cell cultures: selective attenuation of menadione toxicity by buthionine sulphoximine pretreatment

Metabolic activation to reactive intermediates is a prerequisite for many forms of chemically-induced toxicity. Hepa 1c1c-9 cells were exposed to varying concentrations of several reactive metabolites implicated in adverse drug reactions and the toxicity of the compounds assessed using applied fluorescence technology. Cytotoxicity was assessed using the fluorescence of 2', 7'-bis-(2-carboxyethyl)-5-(6)-carboxy-fluorescein as an index of cell viability. The role of glutathione in cellular defence against these chemicals was investigated by pretreating the target cells overnight with buthionine sulphoximine, a specific inhibitor of glutathione synthesis. Depletion of intracellular glutathione augmented the toxicity of N-acetyl-p-benzoquinone imine (1.5-3-fold at 100 and 10 microM). Toxicity produced by the hydroxylamine of sulphamethoxazole (500 microM) was dependent entirely on pretreatment of the cells with buthionine sulphoximine (% cell death = 33 +/- 16 compared with 0 +/- 4 in untreated cells, P < 0.05). By contrast, the lethal effects of the model quinone, menadione, were attenuated markedly following glutathione depletion. The data obtained suggest that this assay, previously used with suspension cultures, may be useful in the rapid in-vitro screening of putative reactive intermediates. Moreover, the application of such methodology should prove beneficial for the elucidation of cellular mechanisms of defence and detoxification.

Human anti-endoplasmic reticulum autoantibodies produced in aromatic anticonvulsant hypersensitivity reactions recognise rodent CYP3A proteins and a similarly regulated human P450 enzyme(s)

Hypersensitivity reactions to aromatic anticonvulsants are associated with anti-liver microsomal antibodies which recognise rodent proteins. The reactivity of these antibodies, the regulation of the rodent antigens and the identity of the human autoantigen have been investigated. Dexamethasone elevated markedly the levels of an immunoreactive mouse protein(s) which exhibited a Mr (53 kDa) and inducibility consistent with the major Cyp3a product. Immunoblots conducted with hepatic microsomes from control and induced rats and purified rat P450s confirmed that these antibodies also recognised constitutive (3A2) and inducible (3A1) rat CYP3A products. Negligible reactivity was observed with microsomes from human B-lymphoblastoid cell lines expressing CYP1A1, 1A2, 2A6, 2D6, 2E1, 3A4 or epoxide hydrolase. Analysis of a phenotyped human liver bank revealed that the antibodies recognised a 52.5 kDa microsomal protein which exhibited marked heterogeneity in its expression and appeared to be regulated co-ordinately with human CYP2C8 and 3A3/4. The inter-individual variation in the expression of this protein(s) and its potential induction by anticonvulsant therapy together with an inherited deficiency in drug detoxification capacity may explain predisposition to these immunoallergic reactions.

Human anti-cytochrome P450 antibodies in aromatic anticonvulsant-induced hypersensitivity reactions

Aromatic anticonvulsants such as phenytoin, phenobarbital and carbamazepine are associated with a hypersensitivity syndrome (fever, rash lymphadenopathy, hepatitis) suggestive of an immune component. We have identified immunoglobulin G antibodies in the sera of nine affected patients which recognize a 53-kD protein which is constitutively expressed and PB inducible in rat liver microsomes. No such reactivity was observed in sera from healthy controls, patients on chronic phenytoin therapy without toxicity or patients with hepatic failure not receiving anticonvulsants. Using highly purified rat hepatic cytochrome P450, P450 3A1 was identified as the major antigenic species, whereas less intense reactivity was noted with P450 2C11. P450 2C6 and 3A2 were minor antigens in some patients. In all patients, the apparent constitutive and phenobarbital-inducible expression of the antigen was a composite effect of antibodies reacting with at least two isozymes, one of which was constitutively expressed and the other PB inducible. In human liver, a 53-kD antigen was expressed to a greater extent in microsomes from a patient with a fatal hepatotoxic reaction to phenytoin compared to microsomes from normal liver or from a sulfonamide hepatitis patient. Western blotting with microsomes prepared from lymphoblastoid cell lines transfected with different human hepatic cytochromes P450 failed to identify P450s 1A1, 1A2, 2A3, 2B6, 2C9, 2D6, 2E1, 3A4 or epoxide hydrolase as the target antigen. Identification of the antigen will be important in understanding the relationship between drug metabolism and the subsequent immune response in the pathogenesis of these rare but severe forms of drug toxicity.

Reactions of the nitroso and hydroxylamine metabolites of sulfamethoxazole with reduced glutathione. Implications for idiosyncratic toxicity

N4-oxidation of sulfonamides has been implicated in the pathogenesis of idiosyncratic reactions to these antimicrobials. In vitro toxicity assays employing mononuclear leukocytes as target cells have shown that the toxicity of sulfamethoxazole hydroxylamine (SMX-HA) is inhibited by exogenous glutathione, suggesting that conjugation with glutathione is an important detoxification pathway. However, in these experiments, significant depletion of cellular glutathione only occurred at concentrations of SMX-HA greater than or equal to 300 microM. At concentrations of SMX-HA which produce 50% toxicity in mononuclear leukocytes (approximately 100 microM), there was not a significant loss of glutathione. SMX-HA also caused a small but significant increase in oxidized glutathione concentrations. In cell-free experiments, reduced glutathione (GSH) prevented the autooxidation of SMX-HA to nitrososulfamethoxazole (nitroso-SMX). During this process, oxidized glutathione was formed. GSH rapidly reacted with nitroso-SMX to form a labile semimercaptal conjugate. Physiologically relevant concentrations of GSH (i.e. 1 mM) favored thiolytic cleavage of the semimercaptal to form SMX-HA. Isomerization of the semimercaptal to the more stable sulfinamide occurred at low GSH concentrations. Purified glutathione transferases had no effect on the reaction of SMX-HA with GSH. Therefore, glutathione is important in protecting cells from the toxicity of SMX-HA largely by preventing its further oxidation to nitroso-SMX. Stable glutathione conjugates are likely to be formed only in small quantities under physiological conditions. Conjugation with glutathione would not be expected to be a major pathway for clearance of the hydroxylamine and nitroso metabolites of sulfonamides.

Exogenous but not endogenous EBV induces lymphomas in beige/nude/xid mice carrying human lymphoid xenografts

Epstein--Barr virus (EBV) is a latent human herpes virus that growth-transforms EBV receptor/CD21+ B cells and is associated with several high-frequency malignancies. Reactivation of latent EBV occurs in approximately 1/3 of organ graft recipients and a majority of AIDS patients; EBV-positive B lymphoproliferative lesions represent often fatal complications in organ transplantation and late-stage AIDS. Although such lymphomas can arise from endogenous virus, the high tumor risk in EBV-seronegative transplant recipients implies de novo infection, in particular virus transmission with intra-graft B lymphocytes. Since SCID mice engrafted with human lymphocytes (SCIDhum) typically develop endogenous EBV+ (human) tumors in their graft it is difficult to study exogenous virus transmission in this model. We here demonstrate that beige/nude/xid mice engrafted with human lymphoid cells (BNXhum) selectively accept human B but not T cell grafts. Unexpectedly these mice fail to develop endogenous lymphomas observed in SCIDhum mice engrafted in parallel. However, injection of as few as less than 500 EBV particles produces rapidly fatal, polyclonal lymphomas in BNXhum animals. This virus sensitivity of BNXhum approaches conditions for EBV transmission with organ grafts.

The transport of digoxin across the perfused human placental lobule

The cardiac glycoside, digoxin, is clinically used to treat fetal tachyarrhythmias and congestive heart failure. The time course of digoxin transfer across the human placenta was studied by dually perfusing an isolated lobule of the human placenta in vitro. Viability of the placental preparation was validated by measuring the rates of glucose and oxygen consumption, lactate production and synthesis of the protein hormone, chorionic gonadotropin. Following administration of 5 ng/ml digoxin to the maternal circulation, digoxin appeared in the fetal circulation within 5 min. The disappearance of digoxin from the maternal circulation was biexponential and best fit a two-compartment pharmacokinetic model. Mean calculated volume of the central compartment (257 +/- 6.3 ml) was consistent with the actual volume of the in vitro maternal circulation (246 +/- 7.4 ml). The half-life of the distribution phase was 9.7 +/- 3.3 min, and half-life of the terminal elimination phase was 362 +/- 83 min. After 30 min of perfusion, the amount of digoxin leaving the maternal circulation and appearing in the fetal circulation was constant at a fetomaternal mass ratio of 0.36 +/- 0.04. This ratio was maintained through to the end of the 3-hr experiment. All of the digoxin leaving the maternal circulation could be accounted for either in the fetal circulation or bound to placental tissue. The time to achieve equal concentrations on both sides of the placenta was estimated to be 268 +/- 34 min. These data are consistent with in vivo data obtained in humans, and support the relevance of using the in vitro placental perfusion model to obtain information regarding placental drug transfer in humans.

Cellular toxicity of sulfamethoxazole reactive metabolites--II. Inhibition of natural killer activity in human peripheral blood mononuclear cells

Based on the identification of intracellular esterase activity as one early target of sulfamethoxazole hydroxylamine (SMX-HA), we wished to determine if the metabolite affected immune functions which involve esterases. The natural killer (NK) activity of human peripheral blood mononuclear cells (PBMC) was assessed with a cell concentration fluorescence technique following exposure to SMX-HA. When K562 target cells were incubated (4 hr/37 degrees) with various ratios of untreated PBMC effector to K562 target cells (E:T), NK activity increased from 17.8 +/- 3.1% (mean +/- SEM; N = 12) at an E:T ratio of 5:1 to 46.2 +/- 2.0% at an E:T ratio of 40:1. Pretreatment of fresh PBMC with 0.1 to 1.0 mM SMX-HA produced a concentration-dependent inhibition of NK activity (E:T ratio 40:1) reaching approximately 80% at 1 mM SMX-HA. Maximum suppression of NK activity was completed within a 60-min pretreatment period with measurable inhibition detected within 30 min. The viability of effector cells was not affected by the metabolite during the pretreatment period. Therefore, the SMX-HA effects could not be directly attributed to decreased viability of the effector cells; they were irreversible and could be prevented by the inclusion of exogenous reduced glutathione (GSH) in a concentration-dependent manner. Given the important roles of NK cells in immune responsiveness and host resistance, our findings of rapid functional inactivation of the cytolytic effector function provide a possible link between idiosyncratic drug toxicity and drug effects directly on components of the immune system.

Cellular toxicity of sulfamethoxazole reactive metabolites--I. Inhibition of intracellular esterase activity prior to cell death

Reactive metabolites produced by oxidative metabolism of the parent compound are considered responsible for the toxicity of a number of drugs, including idiosyncratic reactions to sulfonamide antibiotics. Using sulfamethoxazole hydroxylamine (SMX-HA) as a model compound, we report the use of a pH-sensitive fluorescent probe, 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF), to identify early subcellular targets of chemically synthesized, toxic drug metabolites in peripheral blood mononuclear cells. When toxicity was assessed with this probe immediately after a 2-hr drug challenge, SMX-HA produced a concentration-dependent decrease in cellular fluorescence which was not accompanied by the development of compromised cell membrane integrity until 18 hr later. Dissipation of pH gradients across the cell membrane with nigericin and monensin demonstrated that decreased intracellular pH was only a small component of SMX-HA-induced toxicity. Loading cells with BCECF 30 min prior to SMX-HA challenge produced only a 3% decrease in cellular fluorescence at an SMX-HA concentration of 1 mM, whereas addition of BCECF after drug challenge resulted in a 71% decrease in fluorescence, consistent with a direct drug effect on cellular esterase activity. This was confirmed by monitoring BCECF cleavage in cell lysates in the presence and absence of SMX-HA. These studies demonstrate that inhibition of cellular esterase activity accounted for the observed loss of cellular fluorescence after drug exposure. Since changes in cellular fluorescence at 2 hr correlated well with cell death at 18 hr, we conclude that SMX-HA inhibition of intracellular esterase activity is an early event in the process that terminates in metabolite-induced cell death.

Interactions between N-acetyl-p-benzoquinone imine and fluorescent calcium probes: implications for mechanistic toxicology

Intracellular free calcium ([Ca2+]i) homeostasis has been implicated as an early target in both cellular necrosis and apoptosis. In this study, we have used peripheral blood mononuclear cells (PBMC) as target cells to investigate the effects of several reactive metabolites associated with drug toxicity on [Ca2+]i in order to delineate further early events in cytotoxicity. Compounds implicated in both drug-induced necrosis (N-acetyl-p-benzoquinone imine; NAPQI) and drug hypersensitivity (sulfamethoxazole hydroxylamine; SMX-HA) were examined and their effects on [Ca2+]i compared with those of the T cell mitogen phytohemagglutinin (PHA; 1.5 micrograms/ml) and the calcium ionophore ionomycin (2.5 microM). PHA and ionomycin produced characteristic elevations in [Ca2+]i as monitored by an increase in the fluorescence of fluo-3-loaded cells. SMX-HA did not significantly affect [Ca2+]i at concentrations previously shown to be cytotoxic to PBMC (100 and 500 microM), suggesting that Ca2+ homeostasis is not an early target for SMX-HA toxicity. Addition of NAPQI (250 microM) to fluo-3-loaded cells produced a marked decrease in fluorescence which was not reversed by ionomycin. Conversely, addition of NAPQI to cells loaded with indo-1 resulted in a rapid increase in fluorescence. This effect, however, was found to be attributable to NAPQI addition per se rather than to an increase in [Ca2+]i. HPLC and fluorescence analysis of samples generated from the decomposition of NAPQI revealed the presence of several products which fluoresced intensely at the excitation/emission wavelength pairs of a number of fluorescent probes commonly used to monitor [Ca2+]i.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a microplate reader in an assay of glutathione reductase using 5,5'-dithiobis(2-nitrobenzoic acid)

The use of 96-well microtiter plates and a programmable microplate reader to measure glutathione reductase in an assay based on reduction of 5,5'-dithiobis(2-nitrobenzoic acid) by GSH generated from an excess of GSSG is described. Samples are prepared in 96-well plates and absorbance at 415 nm with a reference wavelength of 595 is determined every 30 s for 3 min. The rate of increase in absorbance is directly proportional to the amount of glutathione reductase in the sample. Activity in an unknown sample is determined from a standard curve. The assay is rapid and allows many small samples to be analyzed in replicates of two or more at the same time.

Fluorescence-based viability assay for studies of reactive drug intermediates

Studies of drug toxicity, toxicologic structure-function relationships, screening of idiosyncratic drug reactions, and a variety of cytotoxic events and cellular functions in immunology and cell biology require the sensitive and rapid processing of often large numbers of cell samples. This report describes the development of a high-sensitivity, high-throughput viability assay based on (a) the carboxyfluorescein derivative 2'-7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) as a vital dye, (b) instrumentation capable of processing multiple small (less than 100 cells) samples, and (c) a 96-well unidirectional vacuum filtration plate. Double staining of cultured peripheral blood mononuclear cells with BCECF and propidium iodide (PI) showed no overlap between PI+ (nonviable) and BCECF+ (viable) cells by flow cytometric analysis. Optimal conditions were developed for dye loading and minimizing physical cell damage and fluorescence quench during the assay procedure. The ratio of BCECF fluorescence to internal standard fluorescent particles was linear from 40 to greater than 20,000 cells with a signal:noise ratio of approximately 3 at 40 cells/well. Sulfamethoxazole hydroxylamine (SMX-HA) was used as a model toxic drug metabolite to explore the validity of the BCECF procedure. SMX-HA, but not its parent compound sulfamethoxazole, resulted in a dose dependent loss of cellular fluorescence and the parallel accumulation of PI+ nonviable cells. When compared to the currently used tetrazolium dye reduction viability assay, the BCECF method was 3-fold more sensitive, greater than 10-fold faster, and required 1/10-1/100 the cell numbers.

A method for meta-analysis of epidemiological studies

This article presents a stepwise approach for conducting a meta-analysis of epidemiological studies based on proposed guidelines. This systematic method is recommended for practitioners evaluating epidemiological studies in the literature to arrive at an overall quantitative estimate of the impact of a treatment. Bendectin is used as an illustrative example. Meta-analysts should establish a priori the purpose of the analysis and a complete protocol. This protocol should be adhered to, and all steps performed should be recorded in detail. To aid in developing such a protocol, we present methods the researcher can use to perform each of 22 steps in six major areas. The illustrative meta-analysis confirmed previous traditional narrative literature reviews that Bendectin is not related to teratogenic outcomes in humans. The overall summary odds ratio was 1.01 (chi 2 = 0.05, p = 0.815) with a 95 percent confidence interval of 0.66-1.55. When the studies were separated according to study type, the summary odds ratio for cohort studies was 0.95 with a 95 percent confidence interval of 0.62-1.45. For case-control studies, the summary odds ratio was 1.27 with a 95 percent confidence interval of 0.83-1.94. The corresponding chi-square values were not statistically significant at the p = 0.05 level.

Drug metabolite toxicity assessed in human lymphocytes with a purified, reconstituted cytochrome P-450 system

Evaluation of idiosyncratic drug reactions in predisposed individuals is limited by ethical concerns arising from rechallenge with the suspected offending agent. A previously developed in vitro method using human lymphocytes and a murine microsomal drug metabolizing system has been used to examine toxicity due to acetaminophen (APAP), sulfonamide antibiotics and aromatic anticonvulsants. An improved method is described in which toxic APAP metabolites are generated by a purified and reconstituted cytochrome P-450 system, minimizing the amount of exogenous detoxification enzymes in the assay. Toxicity is assessed by an objective, automated method based on the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide to an insoluble purple formazan by the mitochondria of viable cells and correlates with that based on trypan blue exclusion. Toxicity required cytochrome P-450 and NADPH, and was inhibited by SKF 525A. Exogenous glutathione also decreased toxicity in a concentration-dependent manner. Lymphocytes from a glutathione synthetase-deficient patient exhibited markedly enhanced toxicity to APAP exceeding the 95% CL of 10 control subjects over a concentration range of 10 to 1000 micrograms/ml. The data are consistent with the generation of cytochrome P-450-dependent reactive metabolites which subsequently can be detoxified by glutathione. This method allows one to address specifically individual differences in detoxification pathways. The use of an automated assessment of cell viability may prove useful in preclinical screening of new compounds for their propensity to cause "idiosyncratic" drug reactions in a predisposed population.

Comparative bioavailability study of three sustained release quinidine formulations

The absorption characteristics of 3 sustained release quinidine formulations were assessed in 12 healthy male volunteers in a randomised 3-way crossover trial. Each formulation ('Quinidex' 300mg, 'Biquin Durules' 250mg and 'Quinaglute Dura-Tabs' 324mg) was administered as a single tablet every 12 hours for 5 days. Peak quinidine serum concentrations of 2.7 +/- 0.8 mg/L occurred 2.5 +/- 1.1 hour after 'Quinaglute' administration, significantly higher (p less than 0.01) than concentrations of 1.6 +/- 0.4 mg/L achieved 4.2 +/- 1.1 hours following 'Biquin' dosing and 1.7 +/- 0.6 mg/L attained 3.9 +/- 2.7 hours after 'Quinidex' ingestion. The extent of absorption based on AUC infinity and normalised for the anhydrous quinidine content was similar for the 3 products. Following multiple dosing, the mean steady-state trough concentration of quinidine was 2.06 +/- 0.56 mg/L for 'Quinidex', significantly greater (p less than 0.05) than that of 'Biquin' (1.18 +/- 0.67 mg/L) or 'Quinaglute' (1.58 +/- 0.58 mg/L). The rate of absorption was found to be much slower for 'Quinidex' than for the other 2 sustained release quinidine formulations. Comparison of the residual sums of squares from simple linear regression of Wagner-Nelson plots did not demonstrate a preference for a zero- or first-order absorption model. Nevertheless, the absorption of 'Quinidex' was twice as prolonged as that of 'Biquin' and 'Quinaglute' regardless of model; first-order absorption half-lives were 2.83 +/- 1.02 hours, 1.25 +/- 0.6 hours and 1.43 +/- 0.88 hours, respectively. The data also suggest that 'Quinidex' absorption may continue beyond 12 hours in some subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of serum theophylline concentrations following administration of sustained-release beads in applesauce to asthmatic preschool children

A sustained-release theophylline preparation (Theo-Dur Sprinkle) was evaluated in young asthmatic patients aged 1 to 6 years and receiving a daily dose of 23.4 +/- 2.0 mg/kg (mean +/- SD) to determine, on the basis of serial serum concentrations obtained over a 12-hour dosing interval at steady state, the suitability of such a product in patients likely to metabolize the drug very rapidly. Peak theophylline concentrations of 15.1 +/- 4.1 mg/L were achieved 5.5 +/- 1.5 hours after dosing. The mean maximum to minimum concentration difference was 6.9 +/- 2.2 mg/L for the dosing interval studied. Fluctuations in theophylline concentration less than 100% were achieved in nine of the 12 study patients. Use of the "sprinkle-technique" with Theo-Dur Sprinkle appears to be a simple and effective method of maintaining acceptable fluctuations in serum theophylline concentrations in preschool asthmatic children.

Ceftazidime disposition in acute and stable cystic fibrosis

Ceftazidime disposition after an intravenous dose of 50 mg/kg infused over 20 min was followed in 10 subjects with cystic fibrosis (CF) hospitalized with acute pulmonary exacerbations and in 10 healthy subjects. Serum ceftazidime elimination t 1/2 decreased from 105.3 +/- 12.4 min (mean +/- SD) in controls to 90.0 +/- 11.1 min in subjects with CF. Calculated distribution volumes were both larger in subjects with CF. When normalized for body surface area, total body clearance (Cl) was 41.9% greater in the CF group (142.4 +/- 16.9 and 100.5 +/- 10.3 ml/min/1.73 m2). Normalization for body weight revealed 64.8% greater Cl in subjects with CF. Fraction of dose recovered in urine was of the same order for each group, while renal clearance (ClR) was 40.9% greater in the subjects with CF (130.1 +/- 11.4 and 92.7 +/- 11.6 ml/min/1.73 m2). Five subjects with CF were restudied while infection-free 119 to 219 days after the original study day. With the exception of a 10% increase in the volume of distribution at steady state while infection-free, kinetic parameters were much the same. No changes in Cl or ClR were evident from one study day to the next. Acute pulmonary infection does not appear to alter ceftazidime clearance in CF. The mechanism underlying increased ceftazidime Cl and ClR in CF is not apparent from the present data.

Glucagon therapy for beta-blocker overdose

Two cases of severe beta-blocker overdose are presented that were treated successfully with glucagon therapy. The effects of glucagon in reversing the cardiovascular depression of profound beta-blockade, including its mechanism of action, onset and duration of action, dosage and administration, cost and availability, and side effects are reviewed. Medical complications of beta-blocker overdose include hypotension, bradycardia, heart failure, impaired atrioventricular conduction, bronchospasm and, occasionally, seizures. Atropine and isoproterenol have been inconsistent in reversing the bradycardia and hypotension of beta-blocker overdose. Glucagon increases heart rate and myocardial contractility, and improves atrioventricular conduction. These effects are unchanged by the presence of beta-receptor blocking drugs. This suggests that glucagon's mechanism of action may bypass the beta-adrenergic receptor site. Because it may bypass the beta-receptor site, glucagon can be considered as an alternative therapy for profound beta-blocker intoxications. The doses of glucagon required to reverse severe beta-blockade are 50 micrograms/kg iv loading dose, followed by a continuous infusion of 1-15 mg/h, titrated to patient response. Glucagon-treated patients should be monitored for side effects of nausea, vomiting, hypokalemia, and hyperglycemia. The high cost and limited availability of glucagon may be the only factors precluding its future clinical acceptance.

High-pressure liquid chromatographic analysis of ceftazidime in serum and urine

A rapid and sensitive high-pressure liquid chromatographic procedure was developed for quantitative analysis of a new semisynthetic cephalosporin, ceftazidime, in serum and urine. A good linear relationship was established between peak height and the amount of ceftazidime injected over a concentration range of 1.9 to 30 micrograms/ml. Recovery was approximately 90% at concentrations of 3, 15, and 30 micrograms/ml. The method is specific for ceftazidime, with no interference noted from 11 other beta-lactam antibiotics tested. The assay is accurate, reproducible, and useful for pharmacokinetic studies in humans as demonstrated in two subjects.