Fission and uncoating of synaptic clathrin-coated vesicles are perturbed by disruption of interactions with the SH3 domain of endophilin

Coordination between sequential steps in synaptic vesicle endocytosis, including clathrin coat formation, fission, and uncoating, appears to involve proteinprotein interactions. Here, we show that compounds that disrupt interactions of the SH3 domain of endophilin with dynamin and synaptojanin impair synaptic vesicle endocytosis in a living synapse. Two distinct endocytic intermediates accumulated. Free clathrin-coated vesicles were induced by a peptide-blocking endophilin's SH3 domain and by antibodies to the proline-rich domain (PRD) of synaptojanin. Invaginated clathrin-coated pits were induced by the same peptide and by the SH3 domain of endophilin. We suggest that the SH3 domain of endophilin participates in both fission and uncoating and that it may be a key component of a molecular switch that couples the fission reaction to uncoating.

Pharmacokinetics and pharmacodynamics of levofloxacin against Streptococcus pneumoniae and Staphylococcus aureus in human skin blister fluid

The pharmacokinetics of levofloxacin in serum and in skin blister fluid (SBF) was determined for 20 volunteers after a single 500-mg oral dose of levofloxacin. In addition, ex vivo bactericidal activity of SBF against Streptococcus pneumoniae and Staphylococcus aureus was studied. SBF containing levofloxacin and granulocytes killed 5.2 log of Streptococcus pneumoniae bacteria and 2.0 log of Staphylococcus aureus bacteria during a 6-h incubation.

Inspired oxygen fraction after cardiopulmonary bypass: effects on pulmonary function with regard to endothelin-1 concentrations and venous admixture

Twenty consecutive patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) were allocated at random to group 1 (n = 10, high inspired oxygen fraction (FIO2) after CPB), or group 2 (n = 10, moderate FIO2 after CPB). The effects of each FIO2 on arterial and mixed venous concentrations of endothelin-1 (ET-1) and its precursor, Big ET-1, were measured. Venous admixture was calculated to assess the efficiency of pulmonary gas exchange. Patients whose lungs had been ventilated with a FIO2 of 1.0 (exposure time 70 min) after weaning from the CPB machine had significantly greater arterial and mixed venous Big ET-1 concentrations and venous admixture than patients whose lungs were ventilated with a FIO2 of 0.35. In contrast, ET-1 concentrations in the two groups were not significantly different. A reduction of FIO2 from 1.0 to 0.6 reduced venous admixture without lowering endothelial peptide concentrations. On the first postoperative day all peptide concentrations were similar in the two groups, whereas venous admixture remained non-significantly higher in group 1. A short period of high FIO2 immediately after CPB increases endothelin concentrations and pulmonary venous admixture.

Isoniazid plus sulphadoxine-pyrimethamine can reduce morbidity of HIV-positive patients treated for tuberculosis in Africa: a controlled clinical trial

An annual 20% excess mortality rate is observed in HIV-seropositive patients after treatment for tuberculosis. An affordable secondary prophylaxis against main opportunistic diseases is needed, i.e. against tuberculosis, toxoplasmosis, pneumocystosis and other infections occurring in this target population. This open prospective randomized study assessed morbidity and mortality in 2 cohorts of HIV-seropositive patients having recently recovered from pulmonary tuberculosis: 134 patients assigned to prophylactic treatment with isoniazid (INH, 300 mg once daily) plus sulphadoxine-pyrimethamine (S, 500 mg/P, 25 mg once weekly), and 129 were controls, comparable for sex, age, weight and HIV-serology. Patients were followed-up for up to 2 years: 192 person-years (PY) in the prophylaxis group and 142 PY in the control group. Four patients developed tuberculosis and 20 patients died in the prophylaxis group, compared to 10 and 23 controls, respectively. Sick days were reported by 22 patients in the prophylaxis group and by 77 patients in the control group. This prophylaxis was associated with a moderate decrease of mortality (log rank test: p = 0.1736), a significant decrease of tuberculosis incidence (log rank test: p = 0. 0234), a highly significant reduction of adverse events and sick days, and a prevention of wasting (p = 0.008) and anaemia (p = 0. 045). No death from toxoplasmosis occurred in the prophylaxis group as compared to 2 possible cases among controls; toxoplasmosis IgG levels declined in treated patients, but increased in controls (p = 0.01). There was no adverse drug reaction due to SP (10,006 doses) or to INH. Compliance with SP intake was good, but moderate as with INH intake. We conclude that a secondary prophylaxis with INH+SP represents a cost-effective measure to improve health conditions of HIV-infected adults in Côte d'Ivoire, following a full treatment course against tuberculosis.

Calorimetric analysis of the Ca(2+)-binding betagamma-crystallin homolog protein S from Myxococcus xanthus: intrinsic stability and mutual stabilization of domains

The betagamma-crystallin superfamily consists of a class of homologous two-domain proteins with Greek-key fold. Protein S, a Ca(2+)-binding spore-coat protein from the soil bacterium Myxococcus xanthus exhibits a high degree of sequential and structural homology with gammaB-crystallin from the vertebrate eye lens. In contrast to gammaB-crystallin, which undergoes irreversible aggregation upon thermal unfolding, protein S folds reversibly and may therefore serve as a model in the investigation of the thermodynamic stability of the eye-lens crystallins. The thermal denaturation of recombinant protein S (PS) and its isolated domains was studied by differential scanning calorimetry in the absence and in the presence of Ca(2+) at varying pH. Ca(2+)-binding leads to a stabilization of PS and its domains and increases the cooperativity of their equilibrium unfolding transitions. The isolated N-terminal and C-terminal domains (NPS and CPS) obey the two-state model, independent of the pH and Ca(2+)-binding; in the case of PS, under all conditions, an equilibrium intermediate is populated. The first transition of PS may be assigned to the denaturation of the C-terminal domain and the loss of domain interactions, whereas the second one coincides with the denaturation of the isolated N-terminal domain. At pH 7.0, in the presence of Ca(2+), where PS exhibits maximal stability, the domain interactions at 20 degrees C contribute 20 kJ/mol to the overall stability of the intact protein.

The domains of protein S from Myxococcus xanthus: structure, stability and interactions

Protein S from Myxococcus xanthus is a member of the beta gamma-crystallin superfamily. Its N and C-terminal domains (NPS and CPS, respectively) show a high degree of structural similarity and possess the capacity to bind two calcium ions per domain. For NPS, their positions were determined by X-ray diffraction at 1.8 A resolution, making use of molecular replacement with the NMR structure as search model. The overall topology of NPS is found to be practically the same as in complete protein S. In natural protein S, the domains fold independently, with a significant increase in stability and cooperativity of folding in the presence of Ca2+. The recombinant isolated domains are stable monomers which do not show any tendency to combine to "nicked" full-length protein S. In order to investigate the stability and folding of natural protein S and its isolated domains, spectroscopic techniques were applied, measuring the reversible urea and temperature-induced unfolding transitions at varying pH. The increment of Ca2+ to the free energy of stabilization amounts to -10 and -5 kJ/mol for NPS and CPS, respectively. For both NPS and CPS, in the absence and in the presence of 3 mM CaCl2, the two-state model is valid. Comparing DeltaGU-->N for CPS (-21 kJ/mol at pH 7, liganded with Ca2+) with its increment in the intact two-domain protein, the stability of the isolated domain turns out to be decreased in a pH-dependent manner. In contrast, the stability of Ca2+-loaded NPS (DeltaGU-->N=-31 kJ/mol, pH 7) is nearly unchanged down to pH 2 where Ca2+ is released (DeltaGU-->N=-26 kJ/mol, pH 2). In intact protein S, the N-terminal domain is destabilized relative to NPS. Evidently, apart from Ca2+ binding, well-defined domain interactions contribute significantly to the overall stability of intact protein S.

Xanthine oxidase inhibition by allopurinol affects the reliability of urinary caffeine metabolic ratios as markers for N-acetyltransferase 2 and CYP1A2 activities

OBJECTIVES

To evaluate the in vivo effect of xanthine oxidase (XO) inhibition by allopurinol on the determination of polymorphic N-acetyltransferase 2 (NAT2) and cytochrome P450 1A2 (CYP1A2) with urinary caffeine metabolic ratios.

METHODS

In an open, prospective study involving 21 healthy subjects (eight fast, 13 slow NAT2 acetylators) allopurinol (300 mg perday) was administered orally on trial days 1-8, followed by a wash-out period of 8 days. Urinary caffeine tests (200 mg caffeine p.o.) were performed repetitively. Urine was collected for 8 h and venous blood samples for the determination of allopurinol, oxypurinol and uric acid were drawn. The urinary caffeine metabolites 1-methyluric acid (1MU), 1-methylxanthine (1MX), 1,7-dimethyluric acid (17MU), 1,7-dimethylxanthine (17MX), 5-acetylamino-6-formylamino-3-methyluracil (AFMU), plasma allopurinol and oxypurinol were analysed using high-performance liquid chromatography (HPLC).

RESULTS

During XO inhibition by allopurinol, the formation of 1MU from 1MX and therefore the XO ratio 1MU/1MX decreased to 15.9 (1.2)% [mean with (SEM)] of baseline values (P < 0.005). The NAT2 ratio AFMU/1MX decreased likewise to 56.7 (6.3)% (P < 0.005). AFMU/(AFMU + 1MX + 1MU), an alternative NAT2 ratio, remained constant, but the CYP1A2 ratio (AFMU + 1MX + 1MU)/17MU, used to express CYP1A2 activity, transiently increased to 167 (13)% (P < 0.005). The NAT2 phenotype did not influence CYP1A2 and XO ratios or plasma oxypurinol pharmacokinetics.

CONCLUSIONS

Several caffeine metabolic ratios are commonly used to express the activities of NAT2, CYP1A2 and XO both in healthy volunteers and in polymedicated patients, although their reliability has not been evaluated thoroughly during concurrent drug administration. The findings of this study suggest that NAT2 phenotyping should be performed using the ratio AFMU/(AFMU + 1MX + 1MU) if an XO inhibitor may be present. It also shows that the determination of CYP1A2 activity with caffeine as a metabolic probe is considerably altered under these conditions. Thus, concomitant drug administration may impair the robustness of multiple pathways of the complex caffeine test. This points to the need for alternative probes, designed to assess only the activity of a single enzyme because, in contrast to healthy volunteers, in patients known or unknown drug interactions may often be present.

Acetaminophen is an inhibitor of hepatic N-acetyltransferase 2 in vitro and in vivo

Slow acetylators of the polymorphic N-acetyltransferase 2 (NAT2, EC 2.3.1.5) suffer more often from side-effects of NAT-substrates than fast acetylators. Since concomitant administration of drugs may inhibit NAT2, we studied the influence of acetaminophen on NAT2 in human hepatic cytosol in vitro and in healthy individuals. In-vitro acetylation was assessed in liver homogenate of one fast and one slow acetylator using sulfamethazine as a test substrate. Acetaminophen competitively inhibited sulfamethazine acetylation in fast and slow acetylator liver samples with Ki values of acetaminophen of 2144 micromol/l and 712 micromol/l, respectively. In additional experiments, exposure of human liver cytosol to p-aminophenol, a putative precursor of acetaminophen in this reaction, revealed production of substantial amounts of acetaminophen, which indirectly suggests that acetaminophen may bind to the active site of NAT2. In-vivo acetylation was quantified with a urinary caffeine assay in 20 healthy volunteers at baseline and after repetitive oral administration of 1000 mg acetaminophen every 6 h for 1 day. The ratio of the acetylated caffeine metabolite acetyl-amino-6-formylamino-3-methyluracil to 1-methylxanthine was reduced by 30.9% (range 11.0-50.1%) in fast acetylators (n = 10) and by 19.3% (range 0.2-36.5%) in slow acetylators (n = 10). Acetaminophen, a widely used over-the-counter drug, which shares structural similarities with acetylated products, inhibits NAT2 both in vitro and in vivo. These findings suggest that even compounds which are not metabolized by NAT2 may inhibit the enzyme and reduce its metabolic capacity.

Influence of intensive physical training on urinary nitrate elimination and plasma endothelin-1 levels in patients with congestive heart failure

BACKGROUND

Congestive heart failure (CHF) is associated with increased peripheral vascular resistance. Exercise-induced shear stress may release endothelial relaxing factors, such as nitric oxide (NO), and inhibit the production of vasoconstrictors such as endothelin-1 (ET-1) thereby modulating vascular tone. We examined the effect of intensive training on ET-1 plasma concentrations and NO-metabolite elimination in patients with CHF after acute myocardial infarction.

METHODS

Seventeen patients with CHF after a myocardial infarction were randomized to an exercise group (n = 9), who performed physical training for 8 weeks, or a control group (n = 8) who received usual care. A physical examination, pulmonary function test, and a maximum exercise test were performed, and 24-hour urinary nitrate elimination and ET-1 in plasma were determined before and at the end of the study period.

RESULTS

Maximal oxygen uptake remained unchanged in controls (17.9 +/- 1.4 to 18.1 +/- 1.5 mL/(kg min) but increased in the exercise group (from 20.4 +/- 0.75 to 26.7 +/- 1.4 mL/(kg min). After 8 weeks the urinary nitrate elimination in controls was significantly decreased (1.25 +/- 0.20 to 1.03 +/- 0.22 mmol/24 hours; P < 0.001), while it was unchanged in the exercise group (1.26 +/- 0.23 to 1.39 +/- 0.28; P = 0.71). Plasma ET-1 levels did not change after 8 weeks (7.87 +/- 0.62 versus 7.57 +/- 0.75 and 7.13 +/- 0.6 versus 7.35 +/- 0.7 pg/mL for control and exercise groups, respectively).

CONCLUSION

In patients with CHF after acute myocardial infarction nitrate elimination decreases over the subsequent 2 months. This trend was reversed by training. Because nitrate elimination mirrors endogenous NO production, these results suggest that training may positively influence endothelial vasodilator function.

Kinetic stabilisation of a modular protein by domain interactions

Protein S, a two-domain spore coat protein from Myxococcus xanthus, is structurally related to eye-lens Pr crystallins. No natural monomeric one-domain member of this protein superfamily is known. To determine the stability of the single domains and to explain the ubiquitous domain duplication, the isolated domains of protein S were constructed. The N-domain is thermodynamically more stable than the C-domain. In intact protein S, domain interactions lead to an apparent decrease in stability of the N-terminal domain, whereas the C-terminal domain is stabilised. In contrast, unfolding kinetics of both domains are decreased 100-fold due to interactions in the complete molecule.

Myxococcus xanthus spore coat protein S, a stress-induced member of the betagamma-crystallin superfamily, gains stability from binding of calcium ions

Protein S, a calcium-binding spore coat protein from the soil bacterium Myxococcus xanthus, belongs to a group of structurally related proteins, the betagamma-crystallin superfamily. Common features of this protein family are the Greek-key structural motif or crystallin fold, and the fact that all members are extremely stable long term. To investigate the correlation between the stability and Greek-key topology, protein S was cloned, expressed in Escherichia coli and purified to homogeneity. Ca2+ binding influences the native tertiary structure of protein S, whereas the secondary structure remains unaffected as shown by spectroscopic methods. Ca2+ ions enhance the conformational stability of protein S significantly. The midpoints of urea and guanidinium chloride-induced transitions show a difference of 1.4 M and 0.5 M denaturant, respectively, in the absence and in the presence of calcium. An equilibrium intermediate indicating independent domain folding can be detected at pH 2. In addition, thermal denaturation shows a clear deviation from the two-state model of folding, again with a strong stabilisation by Ca2+ ions. Temperature and denaturant-induced equilibrium transitions are fully reversible. Our data implicate a different strategy for achieving the high stability required for the biological function compared with the structurally related lens crystallins.

Rapid atrazine mineralisation in soil slurry and moist soil by inoculation of an atrazine-degrading Pseudomonas sp. strain

The evaluation of pesticide-mineralising microorganisms to clean-up contaminated soils was studied with the widely applied and easily detectable compound atrazine, which is rapidly mineralised by several microorganisms including the Pseudomonas sp. strain Yaya 6. The rate of atrazine removal was proportional to the water content of the soil and the amount of bacteria added to the soil. In soil slurry, 6 mg atrazine kg soil-1 was eliminated within 1 day after application of 0.3 g dry weight inoculant biomass kg soil-1 and within 5 days when 0.003 g kg soil-1 was used. In partially saturated soil (60% of the maximal water-holding capacity) 15 mg atrazine kg soil-1 was used. In unsaturated soil, about 60% [U-ring-14C] atrazine was converted to 14CO2 within 14 days. Atrazine was very efficiently removed by the inoculant biomass, not only in soil that was freshly contaminated but also in soil aged with atrazine for up to 260 days. The bacteria exposed to atrazine in unsaturated sterile soil were still active after starvation period of 240 days: 15 mg newly added atrazine kg soil-1 was eliminated within 5 days.

Safety and efficacy of a two-compartment Bayesian feedback program for therapeutic tobramycin monitoring in the daily clinical use and comparison with a non-Bayesian one-compartment model

The predictive value of a two-compartment Bayesian feedback program for tobramycin dose optimization was retrospectively evaluated in 199 hospitalized patients and compared with that of a simple non-Bayesian one-compartment model. Before dose adjustment, 64% of the patients were underdosed indicating that tobramycin monitoring is still necessary to avoid ineffective antibiotic therapy. When physicians adhered to the dose instructions calculated with the Bayesian method, 90% of the patients had optimal concentration-time profiles as opposed to only 53% of the 43 patients in whom dose recommendations were not followed. In young patients with normal renal function, precision and accuracy of the Bayesian feedback and the one-compartment method were well correlated, whereas in elderly patients (> 60 years) and patients with impaired renal function (estimated creatinine clearance < 60 ml/minute), the Bayesian method was significantly more precise. Multiple regression analysis revealed that renal function was the only independent variable predicting the performance of the Bayesian program. The results of this study indicate that the Bayesian feedback method is a reliable method for the therapeutic tobramycin monitoring under clinical conditions and in particular, elderly patients in whom renal impairment is frequent.

N-acetyltransferase 2 polymorphism in patients infected with human immunodeficiency virus

OBJECTIVES

To evaluate the prevalence of slow acetylation of hepatic N-acetyltransferase 2 (NAT2) in patients with different stages of human immunodeficiency virus (HIV) infection, to assess the relationship between acetylation capacity and the degree of immunosuppression, and to study the concordance between NAT2 phenotype and genotype.

METHODS

This prospective study in a consecutive sample of HIV-infected patients was performed in the outpatient department of a university hospital that provides primary and tertiary care. The NAT2 genotype was assessed by polymerase chain reaction and restriction fragment length polymorphism, the NAT2 phenotype was determined by caffeine test (urinary metabolic ratio of the caffeine metabolites 5-acetylamino-6-formylamino-3-methyluracil and 1-methylxanthine).

RESULTS

Fifty patients with Centers for Disease Control HIV infection stages A (10 patients), B (20 patients), and C (20 patients) were included in the study after each gave informed consent. According to genotyping and phenotyping, 32 (64%) patients were slow acetylators, with a concordance of the two methods of 96%. The overall distribution was similar to distributions reported in other white populations. The slow acetylator phenotype was found in seven, 16, and nine patients with stage A, B, and C, respectively. Eight of the 10 patients with previous adverse reactions to sulfonamides had slow acetylator phenotypes. Acetylation capacity was independent of CD4 cell counts.

CONCLUSIONS

This study revealed an excellent agreement between genotypes and phenotypes of NAT2 in patients with HIV infection. There was no increase in prevalence of slow acetylation in patients with advanced stages of the disease. This apparent discrepancy to an earlier study may be the result of differences in co-medication of the patients studied and may point to the relevance of drug interactions in the treatment of patients with HIV infection.

Endothelin-1 plasma levels in normal-tension glaucoma: abnormal response to postural changes

BACKGROUND

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide produced by vascular endothelial cells. ET-1 may have a role in the pathogenesis of various vascular diseases. There are reports in the literature that ET-1 plasma levels are raised in normal-tension glaucoma (NTG) patients.

METHODS

ET-1 concentration, plasma renin activity, and 24-h blood pressure were measured in 21 high-tension glaucoma (HTG) patients, 19 NTG patients, and 20 non-glaucomatous controls in supine and upright positions.

RESULTS

ET-1 plasma levels tended to be higher in NTG patients (3.2 +/- 2.2 pg/ml) than in HTG patients (2.2 +/- 0.6 pg/ml) and controls (2.6 +/- 0.7 pg/ml). The differences, however, were not statistically significant. The individual scatter was significantly greater in the NTG group, indicating that our NTG patients are a heterogeneous population. The physiological increase in ET-1 plasma level after changing from the supine to the upright position was absent in NTG patients. Plasma renin activities tended to be lower in NTG patients (1.2 +/- 1.2 ng/ml/h) than in HTG patients (1.3 +/- 0.8 ng/ml/h) and controls (2.0 +/- 1.7 ng/ml/h). This may explain why NTG patients had relatively low blood pressure despite high ET-1 levels.

CONCLUSIONS

Our data support the hypothesis that vascular dysfunction may be involved in the pathogenesis of optic nerve damage in normal-tension glaucoma.

Endothelin-1 in pulmonary hypertension associated with high-altitude exposure

BACKGROUND

Endothelin-1 is involved in chronic pulmonary hypertension. Its role in acute pulmonary hypertension due to hypoxia in humans is not clear. We therefore studied the influence of hypoxia caused by exposure to high altitude on plasma endothelin-1 levels, arterial blood gases, and pulmonary arterial pressure in subjects taking nifedipine or placebo.

METHODS AND RESULTS

Twenty-two healthy volunteers were investigated at low altitude (490 m) and high altitude (4559 m). Arterial blood gases were analyzed immediately, endothelin-1 was measured by radioimmunoassay, and pulmonary artery pressure was assessed by Doppler echocardiography. After baseline investigations, the mountaineers were allocated in a randomized double-blind fashion to receive either placebo or nifedipine (20 mg TID) during rapid ascent to high altitude within 22 hours. Tests were repeated at the high-altitude research laboratories located in the Capanna "Regina Margherita" (Italy, 4559 m). Plasma endothelin-1 was increased twofold at high altitude (5.9 +/- 2.2 pg/mL compared with 2.9 +/- 1.1 pg/mL, P < .05), was inversely related to arterial PO2 (r = -.46, P < .001), and correlated with pulmonary artery pressure (r = .52, P < .002). At high altitude, arterial endothelin-1 was lower (4.3 +/- 1.6 pg/mL) than venous endothelin-1 (5.9 +/= 2.2 pg/mL, P < .001), indicating either predominant production in the venous vasculature or pronounced clearance in the pulmonary circulation. The calcium antagonist nifedipine, which lowered pulmonary artery pressure at high altitude (32 +/- 5 versus 42 +/- 11 mm Hg, P < .05), had no influence on plasma endothelin-1 levels. The administration of 35% O2 at high altitude normalized arterial PO2, tended to decrease endothelin-1, and decreased pulmonary artery pressure accordingly.

CONCLUSIONS

We conclude that plasma endothelin-1 is increased at high altitude, but whether or not it represents an important pathogenetic factor for pulmonary hypertension remains to be investigated.

[Cyclosporin in autoimmune diseases]

At a symposium held in Zurich in November 1993, a series of presentations covered the optimal use of cyclosporin A (CsA) in autoimmune diseases. Besides its immunosuppressive effects in organ transplantation, CsA appears to be active in a variety of autoimmune disorders. Its most pronounced and beneficial clinical effects are seen in patients with severe rheumatoid arthritis. New clinical studies include the nephrotic syndrome in children and patients with systemic lupus erythematodes. The main concern remains CsA induced nephrotoxicity. For the treatment of autoimmune disorders CsA can be used at lower doses (< or = 5 mg/kg per day) than in transplantation medicine. Thus, monitoring of CsA blood concentrations is not usually necessary. The galenics of CsA has been optimized recently, an achievement which will further improve the clinical use of CsA. Due to increased knowledge of intracellular CsA binding proteins and of effects of CsA on T-lymphocytes and cytokine production, it can be expected that novel immunosuppressive compounds will be developed.

Netilmicin in the neonate: population pharmacokinetic analysis and dosing recommendations

Netilmicin pharmacokinetics were studied in neonates of 27 to 42 weeks' gestational age and 0.8 to 5.0 kg body weight in their first 2 weeks of life by the population pharmacokinetic approach. The data were best described by a two-compartment model. Clearance depends on body weight, gestational age, and postnatal age. Volume of distribution of the central and peripheral compartments was also related to body weight. Including these patient characteristics in the population pharmacokinetic regression model resulted in a marked reduction of the unexplained interindividual variability. This enabled us to derive dosage recommendations that result in peak and average concentrations within the desired range for 95% of the neonates with gestational age above 31 weeks, thus avoiding the need for individual drug-level monitoring in a well-defined large group of patients. Only for infants with gestational age less than 31 weeks who are less than 6 days old is individual dose adjustment based on serum concentration measurements required.

Population pharmacokinetics of tobramycin

1. Population pharmacokinetic parameters of tobramycin were determined in a heterogenous group of 97 patients using serum samples drawn for the routine monitoring of tobramycin concentrations, following multiple dosing regimens. 2. To describe the accumulation kinetics of tobramycin a two-compartment pharmacokinetic model was required. The best fit to the data was obtained when drug clearance (1 h-1) was related linearly to creatinine clearance (proportionality constant: 0.059 +/- 0.002 x CLcr (ml min-1)) and initial volume of distribution (1) was related linearly to body weight (proportionality constant: 0.327 +/- 0.014 x body weight (kg)). The intersubject variability in these two parameters was 32% and 3%, respectively, whilst the residual or intrasubject variability amounted to 21% of the tobramycin concentration. The terminal half-life of tobramycin, 26.6 +/- 9.4 h, was appreciably shorter than previously reported. 3. The population pharmacokinetic model was validated against data obtained from 34 independent patients and the predicted and observed concentrations were found to be in good agreement. The population pharmacokinetic model was used to design a priori dosing recommendations for tobramycin.

Pharmacokinetics of cyclosporine G in patients with renal failure

The pharmacokinetics of the cyclosporine A (CsA, Sandimmune) analogue Nva2-cyclosporine, or cyclosporine G (CsG) was investigated in 6 patients with terminal renal failure after a 4-hr intravenous infusion (3.5 mg/kg) and after oral administration (600 mg) of the drug. Blood samples were collected up to 38 hr and CsG concentrations were measured by radioimmunoassay and high-performance liquid chromatography. The resulting pharmacokinetic parameters of CsG were similar to those described for CsA in the same patient population. Based on HPLC determinations, a mean terminal elimination half-life of 18.9 hr was calculated. The total body clearance was 0.55 L/hr/kg, the volume of the central compartment was 0.32 L/kg, and the steady-state volume of distribution was 5.97 L/kg. After oral administration maximum CsG concentrations in blood were reached between 2.5 and 3 hr, and the bioavailability was in the range of 24-55% (mean 36%). The ratios between the polyvalent RIA and HPLC determinations were considerably larger after oral dosing than after i.v. infusion. The blood-to-plasma ratio was 1.23, which is smaller than that observed for CsA. These results suggest that in patients undergoing renal transplantation the same dosing strategies can be applied for CsG as have been established for CsA.