Pharmacokinetics of [18F]fleroxacin in patients with acute exacerbations of chronic bronchitis and complicated urinary tract infection studied by positron emission tomography.

The pharmacokinetics of fleroxacin, a new broad-spectrum fluoroquinolone, were measured by positron emission tomography (PET) with [18F]fleroxacin in five patients with acute bacterial exacerbations of chronic bronchitis and in five patients with symptomatic, complicated urinary tract infection. Two studies were performed with each patient, one within 24 h of the initiation and one within 24 h of the completion of a 7-day course of fleroxacin, 400 mg/day. For each study, the patient received an infusion of that day's therapeutic dose of fleroxacin (400 mg) supplemented with approximately 740 MBq of [18F]fleroxacin, and serial PET images and blood samples were collected for 6 to 8 h starting at the initiation of the infusion. Between studies, the drug was administered orally. In all infected tissues, there was rapid accumulation of radiolabeled drug, with stable levels achieved within 1 h after completion of the infusion. In kidneys, accumulation was greater in the presence of active infection (P < 0.01), while in lungs, accumulation was lower (P < 0.02). Infection of the lung or urinary tract had no effect on drug delivery to uninvolved tissues. Also, there was no difference between the results obtained at the beginning and the end of therapy. Overall, peak concentrations of drug many times the MIC at which 90% of the infecting organisms are inhibited (MIC90) were achieved in the kidneys (> 30 micrograms/g), prostate glands (> 11 micrograms/g), and lungs (> 14 micrograms/g). Plateau concentrations (2 to 8 h; given as mean micrograms per gram +/- standard error of the mean) of drug in kidneys (15.11 +/- 0.55), prostate glands (5.08 +/- 0.19), and lungs (5.75 +/- 0.22) were also well above the MIC90 for most relevant pathogens. All patients had a good therapeutic response to fleroxacin.     

Pharmacokinetics of [18F]Trovafloxacin in Healthy Human Subjects Studied with Positron Emission Tomography

Tissue pharmacokinetics of trovafloxacin, a new broad-spectrum fluoroquinolone antimicrobial agent, were measured by positron emission tomography (PET) with [¹⁸F]trovafloxacin in 16 healthy volunteers (12 men and 4 women). Each subject received a single oral dose of trovafloxacin (200 mg) daily beginning 5 to 8 days before the PET measurements. Approximately 2 h after the final oral dose, the subject was positioned in the gantry of the PET camera, and 1 h later 10 to 20 mCi of [¹⁸F]trovafloxacin was infused intravenously over 1 to 2 min. Serial PET images and blood samples were collected for 6 to 8 h, starting at the initiation of the infusion. Drug concentrations were expressed as the percentage of injected dose per gram, and absolute concentrations were estimated by assuming complete absorption of the final oral dose. In most tissues, there was rapid accumulation of the radiolabeled drug, with high levels achieved within 10 min after tracer infusion. Peak concentrations of more than five times the MIC at which 90% of the isolates are inhibited (MIC₉₀) for most members of Enterobacteriaceae and anaerobes (>10-fold for most organisms) were achieved in virtually all tissues, and the concentrations remained above this level for more than 6 to 8 h. Particularly high peak concentrations (micrograms per gram; mean ± standard error of the mean [SEM]) were achieved in the liver (35.06 ± 5.89), pancreas (32.36 ± 20.18), kidney (27.20 ± 10.68), lung (22.51 ± 7.11), and spleen (21.77 ± 11.33). Plateau concentrations (measured at 2 to 8 h; micrograms per gram; mean ± SEM) were 3.25 ± 0.43 in the myocardium, 7.23 ± 0.95 in the lung, 11.29 ± 0.75 in the liver, 9.50 ± 2.72 in the pancreas, 4.74 ± 0.54 in the spleen, 1.32 ± 0.09 in the bowel, 4.42 ± 0.32 in the kidney, 1.51 ± 0.15 in the bone, 2.46 ± 0.17 in the muscle, 4.94 ± 1.17 in the prostate, and 3.27 ± 0.49 in the uterus. In the brain, the concentrations (peak, ~2.63 ± 1.49 μg/g; plateau, ~0.91 ± 0.15 μg/g) exceeded the MIC₉₀s for such common causes of central nervous system infections as Streptococcus pneumoniae (MIC₉₀, <0.2 μg/ml), Neisseria meningitidis (MIC₉₀, <0.008 μg/ml), and Haemophilus influenzae (MIC₉₀, <0.03 μg/ml). These PET results suggest that trovafloxacin will be useful in the treatment of a broad range of infections at diverse anatomic sites.     

Pharmacokinetics of 18F-labeled fluconazole in healthy human subjects by positron emission tomography.

The distribution of fluconazole in tissue of human volunteers was determined by positron emission tomographic scanning over a 2-h period following the infusion of a tracer dose of 18F-fluconazole (5 to 7 mCi) plus 400 mg of unlabeled drug (the standard daily dose of fluconazole). Previous studies have validated this approach for animals. From serial positron emission tomographic imaging and blood sampling, pharmacokinetics of fluconazole in tissue were determined. There was significant distribution of the radiolabeled drug in all organs studied, with nearly constant levels achieved by 1 h. Plateau concentrations of fluconazole in key organs (micrograms per gram) included the following: whole brain, 4.92 +/- 0.17; heart, 6.98 +/- 0.20; lung, 7.81 +/- 0.46; liver, 12.94 +/- 0.24; spleen, 22.96 +/- 2.5; kidney, 11.23 +/- 0.61; prostate, 8.24 +/- 0.58; and blood, 3.76 +/- 0.30. Since levels of fluconazole of > 6 micrograms/g are needed to treat infection with most strains of Candida and levels of > 10 micrograms/g are needed for Cryptococcus neoformans, Coccidioides immitis, and Histoplasma capsulatum, the following predictions can be made. The current standard dose of 400 mg/day should be more than adequate in the treatment of urinary tract and hepatosplenic candidiasis but problematic in the treatment of candidal osteomyelitis, even with the higher levels that develop after multiple doses. Similarly, higher doses should be considered, particularly in immunocompromised patients, with infection with C. neoformans, H. capsulatum, and C. immitis that involves the central nervous and musculoskeletal systems.     

Pharmacokinetics of 18F-labeled fleroxacin in rabbits with Escherichia coli infections, studied with positron emission tomography.

18F-labeled fleroxacin was used to measure the pharmacokinetics of fleroxacin in healthy and infected animals by positron emission tomography (PET) and tissue radioactivity measurements. In all experiments, a pharmacological dose of unlabeled drug (10 mg/kg) was coinjected with the tracer. The pharmacokinetics of [18F]fleroxacin was measured in groups of healthy mice (n = six per group) at 10, 30, 60, and 120 min after injection and in groups of rats with Escherichia coli thigh infections (n = six per group) at 60 and 120 min after injection by radioactivity measurements in excised tissues. In healthy rabbits (n = 4) and in rabbits with E. coli thigh infections (n = 4), tissue concentrations of drug were determined by serial PET imaging over 2 h; after the final image was acquired, animals were sacrificed and concentrations measured by PET were compared with the results of tissue radioactivity measurements. In all three species, there was rapid equilibration of [18F]fleroxacin to significant concentrations in most peripheral organs; low concentrations of drug were detected in the brain. Accumulations of radiolabeled drug in infected and healthy thigh muscles were similar. Peak concentrations of drug of more than three times the MIC for 90% of members of the family Enterobacteriaceae (greater than 100-fold for most organisms) were achieved in all tissues except brain and remained above this level for more than 2 h. Especially high peak concentrations were achieved in the kidney (greater than 75 micrograms/g), liver (greater than 50 micrograms/g), blood (greater than 25 micrograms/g), and bone and lung (greater than 10 micrograms/g).Since the MICs for 90% of all Enterobacteriaceae are <2 micrograms/ml, fleroxacin should be particularly useful in treating gram-negative infections affecting these tissues. In contrast, the low concentration of drug delivered to the brain should limit the toxicity of the drug for the central nervous system.     

Activity of fleroxacin alone and in combination with clindamycin or metronidazole in experimental intra-abdominal abscesses.

To assess the potential efficacy of fleroxacin in combination with clindamycin or metronidazole in mixed aerobic and anaerobic infections, we used a rat model of intra-abdominal abscesses in which the inoculum consisted of pooled rat feces mixed with BaSO4. Two hours after bacterial challenge, antimicrobial therapy was begun intravenously with regimens designed to stimulate human pharmacokinetics. A combination of clindamycin and gentamicin was included as an established treatment regimen. After 8.5 days of therapy, final bacterial counts in abscesses showed that fleroxacin alone or combined with metronidazole or clindamycin effectively eradicated Escherichia coli, with bacterial densities of < or = 2.84 +/- 0.1, < or = 2.9 +/- 0.1, and < or = 2.9 +/- 0.1 (mean +/- standard error of the mean) log10 CFU/g, respectively. The addition of either clindamycin or metronidazole to fleroxacin substantially enhanced the effectiveness of the regimens against Bacteroides fragilis, with bacterial counts of < or = 3.0 +/- 0.1 or < or = 2.9 +/- 0.1 log10 CFU/g, respectively, versus 9.2 +/- 0.2 log10 CFU/g for fleroxacin alone. The combination of metronidazole and fleroxacin also resulted in a significantly greater reduction of peptostreptococci and Bacteroides thetaiotaomicron than fleroxacin alone (< or = 2.9 +/- 0.1 versus 6.1 +/- 0.9 log10 CFU/g and 3.3 +/- 0.4 versus 8.3 +/- 0.1 log10 CFU/g, respectively). Except for those of B. fragilis, counts of other anaerobes were reduced to a greater extent by metronidazole plus fleroxacin than by clindamycin plus fleroxacin, although differences were not always significant. Metronidazole plus fleroxacin was at least as active a clindamycin plus gentamicin against all species and was significantly more active against Clostridium spp. No regimen effectively eradicated enterococci from the abscesses. These results suggest that the addition of either metronidazole or clindamycin would effectively enhance the spectrum of fleroxacin for treatment of mixed aerobic and anaerobic infections.     

Influence of rifampin on fleroxacin pharmacokinetics.

Staphylococcus aureus infections have been successfully treated in animal models with the combination of fleroxacin and rifampin. We studied the influence of rifampin, a potent cytochrome P-450 inducer, on the pharmacokinetics and biotransformation of fleroxacin in 14 healthy young male volunteers. Subjects were given 400 mg of fleroxacin orally once a day for 3 days to reach steady state. After a wash-out period of 2 days, the same subjects received 600 mg of rifampin orally once daily for 7 days. On days 5 to 7 of rifampin treatment, 400 mg of fleroxacin was again administered once daily. Concentrations of fleroxacin as well as its two major urinary metabolites, N-demethyl- and N-oxide-fleroxacin, in plasma and urine were determined by reverse-phase high-performance liquid chromatography. The extent of hepatic enzyme induction by rifampin was confirmed by a significant increase of 6-beta-hydroxycortisol urinary output from 160.8 +/- 41.4 to 544.8 +/- 120.7 micrograms/4 h. There were no significant changes in the peak fleroxacin concentration in plasma (6.3 +/- 1.2 versus 6.2 +/- 1.9 mg/liter), time to maximum concentration of fleroxacin in plasma (1.1 +/- 0.9 versus 1.3 +/- 1.1 h), or renal clearance (58.3 +/- 16.4 versus 61.9 +/- 19.2 ml/min). The area under the curve AUC (71.4 +/- 15.8 versus 62.2 +/- 13.7 mg.h/liter) and the terminal half-life of fleroxacin (11.4 +/- 2.2 versus 9.2 +/- 1.1 h) decreased (P < 0.05), while the total plasma clearance increased from 97.7 +/- 21.6 to 112.3 +/- 25.8 ml/min (P < 0.01). Despite being statistically significant, this 15% increase in total plasma clearance does not appear to be clinically relevant. Metabolic clearance by N demethylation was increased ( 6.9 +/- 2.4 versus 12.5 +/- 3.2 ml/min; P < 0.01), whereas clearance by N oxidation did not change (5.8 +/- 1.1 versus 5.8 +/- 1.5 ml/min). Fleroxacin elimination was slightly increased (about 15%) through induction of metabolic clearance to N-demethyl-fleroxacin. Since fleroxacin levels remained above the MIC for 90% of the tested isolates of methicillin-susceptible S. aureus for at least 24 h, dose adjustment does not appear necessary, at least for short-term treatments.     

Role of the glucosamine pathway in fat-induced insulin resistance.

To examine whether the hexosamine biosynthetic pathway might play a role in fat-induced insulin resistance, we monitored the effects of prolonged elevations in FFA availability both on skeletal muscle levels of UDP-N-acetyl-hexosamines and on peripheral glucose disposal during 7-h euglycemic-hyperinsulinemic (approximately 500 microU/ml) clamp studies. When the insulin-induced decrease in the plasma FFA levels (to approximately 0.3 mM) was prevented by infusion of a lipid emulsion in 15 conscious rats (plasma FFA approximately 1.4 mM), glucose uptake (5-7 h = 32.5+/-1.7 vs 0-2 h = 45.2+/-2.8 mg/kg per min; P < 0.01) and glycogen synthesis (P < 0.01) were markedly decreased. During lipid infusion, muscle UDP-N-acetyl-glucosamine (UDP-GlcNAc) increased by twofold (to 53.4+/-1.1 at 3 h and to 55.5+/-1.1 nmol/gram at 7 h vs 20.4+/-1.7 at 0 h, P < 0.01) while glucose-6-phosphate (Glc-6-P) levels were increased at 3 h (475+/-49 nmol/gram) and decreased at 7 h (133+/-7 vs 337+/-28 nmol/gram at 0 h, P < 0.01). To discern whether such an increase in the skeletal muscle UDP-GlcNAc concentration could account for the development of insulin resistance, we generated similar increases in muscle UDP-GlcNAc using three alternate experimental approaches. Euglycemic clamps were performed after prolonged hyperglycemia (18 mM, n = 10), or increased availability of either glucosamine (3 micromol/kg per min; n = 10) or uridine (30 micromol/kg per min; n = 4). These conditions all resulted in very similar increases in the skeletal muscle UDP-GlcNAc (to approximately 55 nmol/gram) and markedly impaired glucose uptake and glycogen synthesis. Thus, fat-induced insulin resistance is associated with: (a) decreased skeletal muscle Glc-6-P levels indicating defective transport/phosphorylation of glucose; (b) marked accumulation of the endproducts of the hexosamine biosynthetic pathway preceding the onset of insulin resistance. Most important, the same degree of insulin resistance can be reproduced in the absence of increased FFA availability by a similar increase in skeletal muscle UDP-N-acetyl-hexosamines. In conclusion, our results support the hypothesis that increased FFA availability induces skeletal muscle insulin resistance by increasing the flux of fructose-6-phosphate into the hexosamine pathway.     

Serum bactericidal activity of ceftazidime: continuous infusion versus intermittent injections.

Since beta-lactam antibiotics have concentration-independent killing, bacterial eradication is a function of the time the serum drug concentration remains above the drug's MIC (T > MIC). We compared the serum bactericidal titers (SBTs) of ceftazidime given by continuous infusion (CI) or by intermittent bolus dosing (BD) against two clinical isolates each of Pseudomonas aeruginosa and Escherichia coli to determine if CI would allow lower daily dosing while still providing equal bactericidal activity compared with BD. This was an open-labeled, randomized, steady-state, four-way crossover study with 12 healthy volunteers. The ceftazidime regimens were 1 g every 8 h (q8h) BD, 1 g q12h BD, 3 g over 24 h CI, and 2 g over 24 h CI. The areas under the bactericidal curves were calculated by the trapezoidal rule using the reciprocal of the SBT. For all organisms the areas under the bactericidal curves for intermittent versus the CI regimens were the same for equal doses (P > 0.05). For both strains of E. coli all four regimens provided SBTs of > or = 1:2 over the dosing interval and 100% T > MIC. The 1-g q8h BD and q12h BD regimens provided T > MIC of 82 and 52%, respectively, for both P. aeruginosa isolates (MICs, 4 micrograms/ml). In comparison, the 2- and 3-g CI regimens always maintained SBTs of > or = 1:2 and T > MIC over the 24-h period as serum drug concentrations were 12.8 +/- 3.0 and 18.2 +/- 4.5 micrograms/ml, respectively. CI optimizes the pharmacodynamic and pharmacoeconomic profile of ceftazidime by providing adequate antibacterial activity over the 24-h dosing period with a reduction in the total daily dose of the antimicrobial agent.     

Transplacental pharmacokinetics of dideoxyinosine in pigtailed macaques.

To determine whether dideoxyinosine is actively transported across the placenta, four pregnant macques (Macaca nemestrina) near term and their fetuses were infused intravenously in random order with simultaneous doses of dideoxyinosine (42.5 micrograms/min/kg of body weight) and antipyrine (41.7 micrograms/min/kg) for 30 h. The infusions took place after the dams had been chronically catheterized at 128 +/- 0.8 days of gestation. In a third infusion, the dams alone received a higher dosage of dideoxyinosine (425 micrograms/min/kg) and the same dosage of antipyrine (41.7 micrograms/min/kg). Samples of maternal and fetal blood and amniotic fluid were collected at intervals for up to 30 h. The concentrations of dideoxyinosine and antipyrine were determined by high-performance liquid chromatography. The transplacental maternal-fetal drug clearances were compared by the paired Student's t test. The ratio (mean +/- standard deviation) of the steady-state plasma dideoxyinosine concentration in the fetus to that in the dam was 0.49 +/- 0.10 at the low dideoxyinosine infusion rate and 0.51 +/- 0.00 at the high dideoxyinosine infusion rate. The clearance associated with maternal-fetal transfer of the drug, CLdf (0.38 +/- 0.21 ml/min/kg), was not significantly different (P > 0.05) from the clearance associated with fetal-maternal transfer of the drug, CLfd (0.56 +/- 0.27 ml/min/kg). Also, CLdf was not significantly different (P > 0.05) from CLfd when normalized with respect to the corresponding transplacental clearance of antipyrine (0.07 +/- 0.04 CLdf versus 0.09 +/- 0.04 CLfd). ur data indicate that passage of dideoxyinosine across the placenta in pregnant M. nemestrina near term is passive and constant over the dosage range studied.     

Metabolic effects of the nocturnal rise in cortisol on carbohydrate metabolism in normal humans.

Glucocorticoid concentrations vary throughout the day. To determine whether an increase in cortisol similar to that present during sleep is of physiologic significance in humans, we studied the disposition of a mixed meal when the nocturnal rise in cortisol was mimicked or prevented using metyrapone plus either a variable or constant hydrocortisone infusion. When glucose concentrations were matched with a glucose infusion, hepatic glucose release (2.6 +/- 0.2 vs. 1.5 +/- 0.4 nmol/kg per 6 h) was higher (P < 0.05) while glucose disappearance (5.9 +/- 0.3 vs. 7.3 +/- 0.9 mmol/kg per 6 h) and forearm arteriovenous glucose difference (64 +/- 24 vs. 231 +/- 62 mmol/dl per 6 h) were lower (P < 0.05) during the variable than basal infusion. The greater hepatic response during the variable cortisol infusion was mediated (at least in part) by inhibition of insulin and stimulation of glucagon secretion as reflected by lower (P < 0.05) C-peptide (0.29 +/- 0.01 vs. 0.38 +/- 0.04 mmol/liter per 6 h) and higher (P < 0.05) glucagon (42.7 +/- 2.0 vs. 39.3 +/- 1.8 ng/ml per 6 h) concentrations. In contrast, the decreased rates of glucose uptake appeared to result from a state of "physiologic" insulin resistance. The variable cortisol infusion also increased (P < 0.05) postprandial palmitate appearance as well as palmitate, beta-hydroxybutyrate, and alanine concentrations, suggesting stimulation of lipolysis, ketogenesis, and proteolysis. We conclude that the circadian variation in cortisol concentration is of physiologic significance in normal humans.     

Compartmentalization of angiotensin II generation in the dog heart. Evidence for independent mechanisms in intravascular and interstitial spaces.

Angiotensin-converting enzyme inhibitors have beneficial effects that are presumably mediated by decreased angiotensin II (ANG II) production. In this study, we measure for the first time ANG I and ANG II levels in the interstitial fluid (ISF) space of the heart. ISF and aortic plasma ANG I and II levels were obtained at baseline, during intravenous infusion of ANG I (5 microM, 0.1 ml/min, 60 min), and during ANG I + the angiotensin-converting enzyme inhibitor captopril (cap) (2.5 mM, 0.1 ml/min, 60 min) in six anesthetized open-chested dogs. ISF samples were obtained using microdialysis probes inserted into the left ventricular myocardium (3-4 probes/dog). ANG I increased mean arterial pressure from 102+/-3 (SEM) to 124+/-3 mmHg (P < 0.01); addition of cap decreased MAP to 95+/-3 mmHg (P < 0.01). ANG I infusion increased aortic plasma ANG I and ANG II (pg/ml) (ANG I = 101+/-129 to 370+/-158 pg/ml, P < 0.01; and ANG II = 22+/-40 to 466+/-49, P < 0.01); addition of cap further increased ANG I (1,790+/-158, P < 0.01) and decreased ANG II (33+/-49, P < 0.01). ISF ANG I and ANG II levels (pg/ml) were > 100-fold higher than plasma levels, and did not change from baseline (8,122+/-528 and 6,333+/-677), during ANG I (8,269+/-502 and 6, 139+/-695) or ANG I + cap (8,753+/-502 and 5,884+/-695). The finding of very high ANG I and ANG II levels in the ISF vs. intravascular space that are not affected by IV ANG I or cap suggests that ANG II production and/or degradation in the heart is compartmentalized and mediated by different enzymatic mechanisms in the interstitial and intravascular spaces.     

Ciprofloxacin absorption is impaired in patients given enteral feedings orally and via gastrostomy and jejunostomy tubes.

Twenty-six hospitalized patients participated in a randomized crossover study to evaluate the effect of enteral feedings on ciprofloxacin absorption when given orally or via gastrostomy or jejunostomy tubes. Patients in the oral group received an intact 500-mg ciprofloxacin tablet alone or ciprofloxacin plus three oral doses of Sustacal (240 ml given 8 h before, with, and 4 h after ciprofloxacin administration). Patients with gastrostomy or jejunostomy tubes received 500 mg of crushed ciprofloxacin in 60 ml water via the feeding tube. After a washout period, the patients received ciprofloxacin with a continuous enteral formula (Jevity) given at 60 to 90 ml/h beginning 6 h before drug administration and continuing for 10 h. Serial blood samples were analyzed for ciprofloxacin concentration by high-performance liquid chromatography. The maximum ciprofloxacin concentrations in serum for ciprofloxacin given and for ciprofloxacin plus enteral feeding for the oral, gastrostomy, and jejunostomy groups were (mean +/- standard deviation) 2.59 +/- 1.24 versus 1.43 +/- 0.61 micrograms/ml (P < 0.05), 3.68 +/- 1.36 versus 2.27 +/- 0.67 micrograms/ml (P < 0.05), and 3.78 +/- 1.87 versus 1.45 +/- 0.48 micrograms/ml (P < 0.05), respectively. Corresponding values for area under the concentration-time curve were 13.4 +/- 8.32 versus 9.44 +/- 4.74 micrograms/h/ml (P < 0.05) 15.9 +/- 6.62 versus 7.44 +/- 3.16 (micrograms/h/ml (P < 0.05), and 18.1 +/- 9.37 versus 5.82 +/- 2.63 micrograms.h/ml (P < 0.05). We conclude that enteral feedings given orally or via gastrostomy or jejunostomy tubes resulted in a 27 to 67% reduction in the mean bioavailability of ciprofloxacin in hospitalized patients. The decreased absorption may be clinically important, especially when the enteral feeding is coadministered with ciprofloxacin by the oral and jejunostomy tube routes. Reductions in maximum levels of ciprofloxacin in serum as a result of feedings given via a gastrostomy tube are similar to those following oral administration on an empty stomach, making a clinically important interaction by this route less likely.     

In vivo maternal-fetal pharmacokinetics of stavudine (2',3'-didehydro-3'-deoxythymidine) in pigtailed macaques (Macaca nemestrina).

To determine whether stavudine (2',3'-didehydro-3'-deoxythymidine) is actively transported in vivo across the placenta and to determine the extent of its transfer, stavudine was administered as an intravenous bolus to four near-term macaques (Macaca nemestrina) (5 mg/kg of body weight via the femoral vein) or to their fetuses (10 mg/kg via the carorid artery) at gestational age 134 +/- 5 days, with the administrations about 1 week apart. Antipyrine (a passive diffusion marker) was always coadministered (20 mg/kg) with stavudine. Samples of maternal and fetal plasma and amniotic fluid were collected at frequent intervals up to 240 min after the dose. In a separate experiment, three animals received stavudine for 30 h at a low rate of infusion (22 micrograms/min/kg via the femoral vein) to the dam or at a 10-fold-higher rate of infusion (220 micrograms/min/kg), separated by at least one week, in order to determine if the transplacental transfer of stavudine is saturable. Antipyrine (41.7 micrograms/min/kg) was coinfused with stavudine. Samples of maternal and fetal plasma and amniotic fluid were collected at regular intervals for up to 30 h. The concentrations of stavudine and antipyrine were determined by high-performance liquid chromatography. The transplacental maternal-fetal drug clearances were compared by the paired Student t test. The clearance associated with maternal-fetal transfer of the drug (CLdf) (0.54 +/- 0.08 ml/min/kg) was not significantly different (P > 0.05) from the clearance associated with fetal-maternal transfer of the drug, CLfd (0.66 +/- 0.11 ml/min/kg). Also, CLdf was not significantly different (P > 0.05) from CLfd when normalized with respect to the corresponding transplacental clearance of antipyrine (0.23 +/- 0.04 versus 0.36 +/- 0.25). The ratios of the steady-state plasma stavudine concentration in the fetus to that in the dam were 0.77 +/- 0.06 at the low stavudine infusion rate and 0.81 +/- 0.09 at the high stavudine infusion rate. The obtained data indicate that transfer of stavudine across the placenta is passive and constant over the dose range studied.     

Interleukin-1 beta modulates the growth and phenotype of neonatal rat cardiac myocytes.

Mononuclear cell infiltration and local cytokine elaboration are hallmarks of inflammatory and immunologic heart diseases. To test the hypothesis that cytokines can modulate cardiac myocyte growth and phenotype, myocytes cultured from neonatal rat hearts were exposed to IL-1 beta, an inflammatory cytokine prevalent in myocardial inflammation. IL-1 beta (2 ng/ml, 24 h) increased [3H]leucine incorporation by 30 +/- 4% (P < 0.001, n = 29) and net cellular protein content by 20 +/- 4% (P < 0.001, n = 27), but had no effect on DNA synthesis. Northern hybridization showed that IL-1 beta increased prepro-atrial natriuretic factor (ANF) mRNA (5.8 +/- 1.5-fold, P < 0.01, n = 13) and beta-myosin heavy chain (beta-MHC) mRNA (> 10-fold, n = 4), and decreased mRNA levels for sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2) (-46 +/- 7%; P < 0.001; n = 11), calcium release channel (CRC) (-65 +/- 11%, P < 0.001, n = 8) and voltage-dependent calcium channel (VDCC) (-53 +/- 7%, P < 0.001, n = 8). NG-monomethyl-L-arginine (1 mM), an inhibitor of nitric oxide (NO) synthesis, did not inhibit the IL-1 beta-induced protein synthesis or changes in mRNA levels. In ventricular myocardium obtained from adult rats treated with lipopolysaccharide (4 mg/kg intraperitoneally 18 h) to stimulate systemic cytokine production, there were changes in the mRNA levels for beta-MHC (6 +/- 1-fold, P < 0.01, n = 4), SERCA2 (-65 +/- 4%, P < 0.0001, n = 4), CRC (-67 +/- 5%, P < 0.001, n = 4), and VDCC (-58 +/- 5%, P < 0.001; n = 4) that were qualitatively similar to those observed in cultured myocytes. Thus, IL-1 beta, acting via an NO-independent mechanism, caused myocyte hypertrophy associated with induction of fetal genes (ANF and beta-MHC) and downregulation of three important calcium regulatory genes (SERCA2, CRC, and VDCC). IL-1 beta may contribute to the abnormal structural and functional alterations of cardiac myocytes in conditions marked by mononuclear cell infiltration.     

Impact of dosing schedule upon suppression of a retrovirus in a murine model of AIDS encephalopathy.

We studied the impact of zidovudine (AZT) in Cas-Br-M murine leukemia virus-infected NFS-N mice after administration by once-daily bolus or continuous infusion. While higher peak concentrations of AZT were achieved by once-daily dosing, continuous AZT infusion at 25 micrograms/h maintained levels > 1 microM in plasma and > 0.2 microM in the brain. Continuous infusion provided significantly better viral inhibition, even though total doses were only one-third that of the once-daily therapy group.     

Mechanism of free fatty acid-induced insulin resistance in humans.

To examine the mechanism by which lipids cause insulin resistance in humans, skeletal muscle glycogen and glucose-6-phosphate concentrations were measured every 15 min by simultaneous 13C and 31P nuclear magnetic resonance spectroscopy in nine healthy subjects in the presence of low (0.18 +/- 0.02 mM [mean +/- SEM]; control) or high (1.93 +/- 0.04 mM; lipid infusion) plasma free fatty acid levels under euglycemic (approximately 5.2 mM) hyperinsulinemic (approximately 400 pM) clamp conditions for 6 h. During the initial 3.5 h of the clamp the rate of whole-body glucose uptake was not affected by lipid infusion, but it then decreased continuously to be approximately 46% of control values after 6 h (P < 0.00001). Augmented lipid oxidation was accompanied by a approximately 40% reduction of oxidative glucose metabolism starting during the third hour of lipid infusion (P < 0.05). Rates of muscle glycogen synthesis were similar during the first 3 h of lipid and control infusion, but thereafter decreased to approximately 50% of control values (4.0 +/- 1.0 vs. 9.3 +/- 1.6 mumol/[kg.min], P < 0.05). Reduction of muscle glycogen synthesis by elevated plasma free fatty acids was preceded by a fall of muscle glucose-6-phosphate concentrations starting at approximately 1.5 h (195 +/- 25 vs. control: 237 +/- 26 mM; P < 0.01). Therefore in contrast to the originally postulated mechanism in which free fatty acids were thought to inhibit insulin-stimulated glucose uptake in muscle through initial inhibition of pyruvate dehydrogenase these results demonstrate that free fatty acids induce insulin resistance in humans by initial inhibition of glucose transport/phosphorylation which is then followed by an approximately 50% reduction in both the rate of muscle glycogen synthesis and glucose oxidation.     

Sustained pulmonary hypertension and right ventricular hypertrophy after chronic hypoxia in mice with congenital deficiency of nitric oxide synthase 3.

Chronic hypoxia induces pulmonary hypertension and right ventricular (RV) hypertrophy. Nitric oxide (NO) has been proposed to modulate the pulmonary vascular response to hypoxia. We investigated the effects of congenital deficiency of endothelial NO synthase (NOS3) on the pulmonary vascular responses to breathing 11% oxygen for 3-6 wk. After 3 wk of hypoxia, RV systolic pressure was greater in NOS3-deficient than in wild-type mice (35+/-2 vs 28+/-1 mmHg, x+/-SE, P < 0.001). Pulmonary artery pressure (PPA) and incremental total pulmonary vascular resistance (RPI) were greater in NOS3-deficient than in wild-type mice (PPA 22+/-1 vs 19+/-1 mmHg, P < 0.05 and RPI 92+/-11 vs 55+/-5 mmHg.min.gram.ml-1, P < 0.05). Morphometry revealed that the proportion of muscularized small pulmonary vessels was almost fourfold greater in NOS3-deficient mice than in wild-type mice. After 6 wk of hypoxia, the increase of RV free wall thickness, measured by transesophageal echocardiography, and of RV weight/body weight ratio were more marked in NOS3-deficient mice than in wild-type mice (RV wall thickness 0.67+/-0.05 vs 0.48+/-0.02 mm, P < 0.01 and RV weight/body weight ratio 2.1+/-0.2 vs 1.6+/-0.1 mg. gram-1, P < 0.05). RV hypertrophy produced by chronic hypoxia was prevented by breathing 20 parts per million NO in both genotypes of mice. These results suggest that congenital NOS3 deficiency enhances hypoxic pulmonary vascular remodeling and hypertension, and RV hypertrophy, and that NO production by NOS3 is vital to counterbalance pulmonary vasoconstriction caused by chronic hypoxic stress.     

In vivo activity and pharmacodynamics of cefotaxime or ceftriaxone in combination with fosfomycin in fibrin clots infected with highly penicillin-resistant Streptococcus pneumoniae.

Using a clinical pneumococcal strain for which MICs were 2, 0.5, 0.5, and 16 mg/liter for penicillin, cefotaxime, ceftriaxone, and fosfomycin, respectively, we studied the efficacies of these antibiotics alone and in combination in one or two doses or in continuous infusion over 6 h in the treatment of the prolonged (48-h) experimental fibrin clot infections in rabbits. Doses were chosen to obtain low antibiotic concentrations. We observed the highest bacterial reductions (change in log10 CFU per gram) with the following five regimens: combination of cefotaxime plus fosfomycin given in two divided doses 6 h apart (each at 50 mg/kg of body weight given intravenously (4.2 +/- 0.7 CFU/g), ceftriaxone (8 mg/kg given once intravenously) along with one or two doses of fosfomycin (3.79 +/- 0.6 and 3.95 +/- 0.5 CFU/g), cefotaxime alone administered in two divided doses (3.6 +/- 0.4 CFU/g), and a 6-h continuous infusion of cefotaxime (100 mg/kg) with fosfomycin (100 mg/kg) (3.5 +/- 0.4 CFU/g). The bacterial reductions obtained with these five regimens were all higher than those obtained with the other regimens tested (P < 0.05). The time of bacterial regrowth was significantly delayed with the two doses of the cefotaxime-fosfomycin regimens (23.2 +/- 11 h) compared with those with the other combinations (P < 0.05). The rate of bacterial regrowth with this regimen was even lower than that observed with cefotaxime alone given in two doses (P < 0.05). By a multivariate analysis, the most important independent parameters for efficacy were the maximal concentrations of beta-lactam antibiotics and the residual concentration of fosfomycin and, for the combinations, the log of the area under the concentration-time curve/MIC ratio for beta-lactam antibiotics. From these findings, the combinations cefotaxime or ceftriaxone plus fosfomycin could be proposed for the treatment of infections caused by highly penicillin-resistant pneumococci.     

Glutamine: a major gluconeogenic precursor and vehicle for interorgan carbon transport in man.

To compare glutamine and alanine as gluconeogenic precursors, we simultaneously measured their systemic turnovers, clearances, and incorporation into plasma glucose, their skeletal muscle uptake and release, and the proportion of their appearance in plasma directly due to their release from protein in postabsorptive normal volunteers. We infused the volunteers with [U-14C] glutamine, [3-13C] alanine, [2H5] phenylalanine, and [6-3H] glucose to isotopic steady state and used the forearm balance technique. We found that glutamine appearance in plasma exceeded that of alanine (5.76 +/- 0.26 vs. 4.40 +/- 0.33 mumol.kg-1.min-1, P < 0.001), while alanine clearance exceeded glutamine clearance (14.7 +/- 1.3 vs. 9.3 +/- 0.8 ml.kg-1.min-1, P < 0.001). Glutamine appearance in plasma directly due to its release from protein was more than double that of alanine (2.45 +/- 0.25 vs. 1.16 +/- 0.12 mumol.kg-1.min-1, P < 0.001). Although overall carbon transfer to glucose from glutamine and alanine was comparable (3.53 +/- 0.24 vs 3.47 +/- 0.32 atoms.kg-1.min-1), nearly twice as much glucose carbon came from protein derived glutamine than alanine (1.48 +/- 0.15 vs 0.88 +/- 0.09 atoms.kg-1.min-1, P < 0.01). Finally, forearm muscle released more glutamine than alanine (0.88 +/- 0.05 vs 0.48 +/- 0.05 mumol.100 ml-1.min-1, P < 0.01). We conclude that in postabsorptive humans glutamine is quantitatively more important than alanine for transporting protein-derived carbon through plasma and adding these carbons to the glucose pool.     

Killing activity of cefpirome against penicillin-resistant Streptococcus pneumoniae isolates from patients with meningitis in a pharmacodynamic model simulating the cerebrospinal fluid concentration profile.

An in vitro pharmacodynamic model was used to determine the killing kinetics of cefpirome against 20 Streptococcus pneumoniae strains (penicillin G MICs, > 0.125 to 2 micrograms/ml) isolated from patients with meningitis. The concentration of cefpirome was adjusted dynamically to simulate the median concentration profile obtained in the cerebrospinal fluid of adults after the infusion of a single dose of 2 g. The cefpirome MIC at which 90% of isolates are inhibited was 0.5 microgram/ml. Bactericidal activity was observed at 6 h, with mean killing of 3.51 +/- 0.34 log10 CFU/ml for all strains for which the cefpirome MIC was < 0.5 microgram/ml. In contrast, for strains for which the cefpirome MIC was > or = 0.5 microgram/ml, killing was significantly less (P < 0.05), with a mean reduction of only 2.86 +/- 0.57 log10 CFU/ml.