Interaction-induced spin polarization in quantum dots

The electronic states of lateral many-electron quantum dots in high magnetic fields are analyzed in terms of energy and spin. In a regime with two Landau levels in the dot, several Coulomb-blockade peaks are measured. A zigzag pattern is found as it is known from the Fock-Darwin spectrum. However, only data from Landau level 0 show the typical spin-induced bimodality, whereas features from Landau level 1 cannot be explained with the Fock-Darwin picture. Instead, by including the interaction effects within spin-density-functional theory a good agreement between experiment and theory is obtained. The absence of bimodality on Landau level 1 is found to be due to strong spin polarization.

Multiple transitions of the spin configuration in quantum dots

Single electron tunneling is studied in a many electron quantum dot in high magnetic fields. For such a system multiple transitions of the spin configuration are theoretically predicted. With a combination of spin blockade and Kondo effect we are able to detect five regions with different spin configurations. Transitions are induced with changing electron numbers.

Bioavailability and relative tissue distribution of [125I]-recombinant human thrombin following intravenous or subcutaneous administration to non-human primates

BACKGROUND

Recombinant human thrombin (rhThrombin) is being developed as a general adjunct to hemostasis. Endogenous thrombin is rapidly inactivated by complex formation with antithrombin III and other inhibitors. It follows that these inhibitors will also inactivate any rhThrombin that reaches the systemic circulation.

OBJECTIVES

Study goals were to determine the pharmacokinetic characteristics of [(125)I]-rhThrombin and [(125)I]-rhThrombin complexed to endogenous inhibitors, and the tissue distribution of rhThrombin-associated radioactivity in non-human primates. Hematology, serum chemistry and coagulation status were also monitored.

METHODS

[(125)I]-rhThrombin was administered intravenously (i.v.; 3.5 U kg(-1)) or subcutaneously (s.c.; 350 U kg(-1)) to male cynomolgus monkeys. Plasma was analyzed for rhThrombin-associated radioactivity and non-compartmental analysis was used to determine the corresponding pharmacokinetic parameters. A size exclusion-high pressure liquid chromatography (SE-HPLC) method was used to quantitate rhThrombin complexes, non-complexed rhThrombin, and free [(125)I]. Whole-body gamma scintigraphy was used to follow radioactivity localization up to 72 h postdose.

RESULTS

No adverse events were observed following [(125)I]-rhThrombin administration. The pharmacokinetic profile of rhThrombin-associated radioactivity following i.v. injection was multi-exponential with an initial half-life of approximately 10 min. Following both i.v. and s.c. dosing, the terminal half-life was approximately 15 h. SE-HPLC analysis revealed that rhThrombin was rapidly complexed to antithrombin III and other inhibitors in the systemic circulation following i.v. administration. Thus, rhThrombin-associated radioactivity in the blood was complexed and presumed inactive. [(125)I]-rhThrombin inhibitor complexes accumulated and were eliminated in the liver following both routes of administration.

CONCLUSIONS

These data suggest that rhThrombin rapidly binds to endogenous inhibitors following either i.v. or s.c. administration.

Probing a Kondo-correlated quantum dot with spin spectroscopy

We investigate the Kondo effect and spin blockade observed in a many-electron quantum dot and study the magnetic field dependence. At lower fields, a pronounced Kondo effect is found, which is replaced by the spin blockade at higher fields. In an intermediate regime, both effects are visible. We make use of this combined effect to gain information about the internal spin configuration of our quantum dot. We find that the data cannot be explained assuming regular filling of electronic orbitals. Instead, spin polarized filling seems to be probable.

Absence of a pharmacokinetic interaction between digoxin and levofloxacin

BACKGROUND

Levofloxacin, a broad-spectrum fluoroquinolone, may enhance digoxin bioavailability by eliminating intestinal flora that metabolize digoxin. Moreover, levofloxacin, which is eliminated primarily by glomerular filtration and active tubular secretion, may alter the elimination rate of digoxin. Because of the narrow therapeutic index of digoxin, it is important to evaluate the potential for interaction with levofloxacin when administered concomitantly.

METHODS

This was a placebo-controlled, randomized, double-blind, two-phase crossover study. Twelve healthy subjects (six males and six females) received 500 mg twice/day oral doses of levofloxacin or placebo for 6 days and a single oral dose of 0.4 mg digoxin on the morning of study day 5 along with levofloxacin or placebo.

RESULTS

There was no significant effect of levofloxacin on the pharmacokinetics (Cmax, AUC, and other disposition parameters) of oral digoxin. Steady-state levofloxacin absorption and disposition kinetics were also similar in the presence or absence of digoxin.

CONCLUSIONS

Results of this study suggest that an important pharmacokinetic interaction between levofloxacin and digoxin is unlikely to occur when administered concomitantly.

Pharmacokinetics/dynamics of 5c8, a monoclonal antibody to CD154 (CD40 ligand) suppression of an immune response in monkeys

The pharmacokinetics and pharmacodynamics (PK/PD) of chimeric (Ch5c8) and humanized (Hu5c8) 5c8, a monoclonal antibody that binds CD154 (CD40 ligand), thus blocking the interaction between CD40 and CD154, were investigated in cynomolgus monkeys. Single-dose groups (n = 3 animals per dose) received saline, 0.2, 1, 5 or 20 mg/kg i.v. doses of Hu5c8. The repeat-dose groups (n = 4 animals) received 0 or 5 mg/kg i.v. doses of Ch5c8 or Hu5c8 on days 1, 2, 3, 5, 7 and 9. The single-dose PK parameters showed dose proportionality, with a terminal half-life of 300 h, a volume of distribution at steady state of 73 ml/kg and clearance of 0.2 ml.h-1.kg-1. The repeat-dose regimen produced a longer terminal half-life (500 h) and lower clearance (0.13 ml.h-1.kg-1) than in the single-dose groups. The antibody titer to tetanus toxoid (ATT) challenge served as the immunodynamic marker. The primary ATT response consisted of a latent phase of approximately 10 days, during which the immune system was processing antigen but not yet producing antibody, a rise to an antibody maximum titer at approximately 18 days and a decline toward baseline by approximately 40 days in controls. The 5c8 produced a log(dose)-proportional reduction in the area under the curve of ATT. An indirect PK/PD model based on the kinetics of tetanus toxoid exposure and inhibition of ATT production in relation to 5c8 concentrations was developed. A median inhibitory concentration of 0.84 microg/ml and a efficacy of 0.84 reflected marked inhibition of ATT response by 5c8. The model provides quantitation of reduced ATT responses after 5c8 and was applicable to primary and secondary immune responses and to both single-dose and multiple-dose treatments. The monoclonal antibody 5c8 blocks the CD40 and CD154 interaction, producing consistent and substantive reduction in antibody formation after administration of tetanus toxoid, which can be characterized with PK/PD modeling. It is anticipated that 5c8 may have utility in the treatment of antibody-mediated autoimmune disease.

Impaired bioavailability of interferon beta-1a when administered intramuscularly by needle-free injection

Intramuscular (IM) or subcutaneous (SC) drug administration of small molecules and protein has been demonstrated by use of needle-free jet injection methods. One device that achieves needle-free parenteral administration, BIOJECTOR, is commercially available and was evaluated for IM delivery of interferon beta-1a. Recombinant human interferon beta-1a (IFN beta-1a) is a glycosylated protein containing 166 amino acids and has a molecular weight of 22.5 kDa. Needle-free jet injection of IFN beta-1a with the BIOJECTOR was assessed in a human Phase I trial. The study was a randomized, open-label crossover in which 12 healthy subjects each received 60 microg of IFN beta-1a as an IM injection by standard needle administration and by needle-free jet injection. Blood samples for pharmacokinetic (serum activity, PK) and pharmacodynamic (serum neopterin, PD) determinations were collected through 144 hours post-dose. Mean serum antiviral activity AUC values for needle-free and standard needle injection were 218 and 531 U x h/ml, respectively; corresponding C(max) values were 19.7 and 29.0 U/ml. Median T(max) following both treatments was 12 hours. The relative bioavailability of IFN beta-1a, needle-free to standard needle injection, was 41.1% with 90% confidence limits of 24.4% to 69.3%. Mean serum neopterin E(AUC) values for needle-free and standard needle injection were 114 and 325 ng x h/mL, respectively; corresponding E(max) values were 2.3 and 5.6 ng/mL. The ratio of serum neopterin E(AUC), needle-free to standard needle, was 34.9% with 90% confidence limits of 23.4% to 52.1%. Injection site reactions were substantially more frequent following needle-free injection; however, systemic side effects were less frequent. Intramuscular needle-free jet injection and needle-based injection of a 22.5-kDa glycoprotein do not produce equivalent systemic PK or PD responses.

Pharmacokinetic profile of levofloxacin following once-daily 500-milligram oral or intravenous doses

The pharmacokinetics of once-daily oral levofloxacin (study A) or intravenous levofloxacin (study B) in 40 healthy male volunteers were investigated in two separate randomized, double-blind, parallel-design, placebo-controlled studies. Levofloxacin at 500 mg or placebo was administered orally or intravenously as a single dose on day 1; daily oral or intravenous dosing resumed on days 4 to 10. In a third study (study C), the comparability of the bioavailabilities of two oral and one intravenous levofloxacin formulations were investigated with 24 healthy male subjects in an open-label, randomized, three-way crossover study. Levofloxacin at 500 mg as a single tablet or an intravenous infusion was administered on day 1; following a 1-week washout period, subjects received the second regimen (i.e., the other oral formulation or the intravenous infusion); the third and final regimen was administered following a 1-week washout period. The concentrations of drug in plasma and urine were measured by validated high-pressure liquid chromatography methods. Pharmacokinetic parameters were estimated by noncompartmental methods. In both study A (oral levofloxacin) and study B (intravenous levofloxacin), steady state was attained within 48 h after the start of the multiple dosing on day 4. Levofloxacin pharmacokinetics were linear and predictable for the single and multiple 500-mg, once-daily oral and intravenous dosing regimens, and the values of the pharmacokinetic parameters for the oral and intravenous administrations were similar. Study C indicated that levofloxacin was rapidly and completely absorbed from the oral tablets, with mean times to the maximum concentration of drug in serum of approximately 1.5 h and mean absolute bioavailability of > or =99%. These results support the interchangeability of the oral and intravenous routes of levofloxacin administration.

Pharmacokinetics and safety of oral levofloxacin in human immunodeficiency virus-infected individuals receiving concomitant zidovudine

This phase I, double-blind, randomized, placebo-controlled, parallel-design study was conducted to evaluate the safety and pharmacokinetics of levofloxacin in human immunodeficiency virus (HIV)-infected subjects concomitantly receiving a stable regimen of zidovudine (AZT). Sixteen HIV-infected males with CD4-cell counts ranging from 100 to 550 and not experiencing significant AZT intolerance were enrolled. Subjects received levofloxacin (350 mg of levofloxacin hemihydrate) or a placebo (eight subjects per treatment group) as a single oral dose on day 1, multiple doses every 8 h from days 3 to 9, and a single dose on day 10. On days 1 and 10, an AZT dose (100 mg) was administered concurrently with the study drug. In between these doses, AZT was administered according to the regimen used by the subject prior to entering the study up to a maximum of 500 mg/day. Plasma levofloxacin concentrations were monitored for 36 h after levofloxacin dosing on day 1, immediately prior to the morning doses on days 3 to 9, and for 72 h after dosing on day 10. Plasma AZT concentrations were monitored on day 0 for baseline (for 6 h after the AZT dose) and for 4 h after the AZT doses on days 1 and 10. Levofloxacin was rapidly absorbed (time to maximum plasma concentration, approximately 1.0 h) and extensively distributed in the body with an apparent volume of distribution of approximately 104 liters (approximately 1.34 liters/kg). Steady-state conditions on day 10 were confirmed. Pharmacokinetic profiles of levofloxacin from single doses and multiple (three-times-daily) doses were similar, with a moderate accumulation (observed day 10-to-day 1 ratio of the maximum plasma concentration, approximately 185% versus expected 169%; for the corresponding ratio of the area under the concentration-time curve from 0 to 8 h [AUC(0-8)], the values were observed 217% versus expected 169%) at steady state. Mean average steady-state peak plasma concentration, plasma levofloxacin concentration at the end of the dosing interval, AUC(0-8), terminal half-life, and total body clearance were 7.06 microg/ml, 3.62 microg/ml, 37.4 microg x h/ml, 7.2 h, and 9.4 liters/h (0.12 liters/h/kg), respectively. Pharmacokinetic profiles of levofloxacin in HIV-infected patients did not appear to be affected by the concomitant administration of AZT; nor were AZT pharmacokinetics altered by levofloxacin. Oral administration of 350 mg of levofloxacin hemihydrate every 8 h appeared to be well tolerated by the subjects. There were no apparent differences in adverse events between the two treatment groups. There were no clinically significant changes from baseline in any laboratory parameter or vital sign following treatments observed in this study. The study results suggest that there is no need for levofloxacin dosage adjustment in HIV-seropositive subjects who concomitantly receive AZT.

Absence of age and gender effects on the pharmacokinetics of a single 500-milligram oral dose of levofloxacin in healthy subjects

The influence of age and gender on the pharmacokinetics of levofloxacin in healthy subjects receiving a single oral 500-mg dose of levofloxacin was investigated in this parallel design study. Six young males (aged 18 to 40 years), six elderly males (aged > or = 65 years), six young females (aged 18 to 40 years), and six elderly females (aged > or = 65 years) were enrolled and completed the study. The study reveals that the bioavailability (rate and extent) of levofloxacin was not affected by either age or gender. In both age (young and elderly) and gender (male and female) groups of subjects, peak concentrations in plasma were reached at approximately 1.5 h after dosing; renal clearance of levofloxacin accounted for approximately 77% of total body clearance, and approximately 76% of the administered dose was recovered unchanged in urine over the 36 h of collection. The apparent differences in the calculated pharmacokinetic parameters for levofloxacin between the age groups (young versus elderly) and between the gender groups (males versus females) could be explained by differences in renal function among the subjects. A single dose of 500 mg of levofloxacin administered orally to both young and old, male and female healthy subjects was found to be safe and well tolerated. As the differences in levofloxacin kinetics between the young and the elderly or the males and the females are limited and are mainly related to the renal function of the subjects, dose adjustment based on age or gender alone is not necessary.

Pharmacokinetics and distribution in tissue of FK-037, a new parenteral cephalosporin

A single 1-g or 2-g intravenous dose of the cephalosporin FK-037 was given over 30 min in a cross-over-designed study, to each of six healthy male volunteers, and the concentrations of the drug were measured in plasma and cantharides-induced blister fluid over the subsequent 12 h. Urine was collected over 24 h. After a washout period of 6 weeks, during which the blisters healed, the study was repeated at the other dose level. Following the 1-g dose, the mean peak concentration in plasma was 83.8 micrograms/ml, and after the 2-g dose it was 142.6 micrograms/ml. The mean peak concentrations in the inflammatory fluid were 37.9 and 63.3 micrograms/ml, respectively. The mean elimination half-lives from plasma and inflammatory fluid were 2.0 and 2.5 h, respectively, after 1 g and 2.0 h and 3.7 h, respectively, after 2 g. The amounts of penetration into inflammatory fluid (as assessed by ratios of areas under the concentration-time curves) were 109.9 and 110.5% following doses of 1 and 2 g, respectively. The proportions of the administered drug recovered in the urine by 24 h were 87.6 and 85.7%, respectively. Our results indicate that FK-037 should prove to be efficacious in the treatment of a wide range of systemic infections.

Activity of levofloxacin in a murine model of tuberculosis

The activity of levofloxacin (LEV) was evaluated in a murine model of tuberculosis. Approximately 10(7) viable Mycobacterium tuberculosis ATCC 35801 were given intravenously to 4-week-old female outbred mice. In a dose-response study, treatment with LEV at 100, 200, and 400 mg/kg of body weight was started 1 day after infection and was given daily for 28 days. Viable cell counts were determined from homogenates of spleens and lungs. A dose-related reduction in organism cell counts in organs was noted for LEV. The activities of LEV at 100, 200, and 300 mg/kg were compared with those of first-line antituberculosis agents. Both isoniazid and rifampin were more active than LEV. There was no difference in activity between LEV and either ethambutol or pyrazinamide against splenic organisms. The activities of ethambutol and LEV at the two higher doses were comparable against lung organisms. LEV at 300 mg/kg was more active than pyrazinamide against lung organisms. The activity of LEV was compared with those of two other quinolones, ofloxacin and sparfloxacin. LEV at 200 mg/kg had more than twofold greater activity than ofloxacin at the same dose. Sparfloxacin at 100 mg/kg was more active than LEV at 200 mg/kg; however, the activities of sparfloxacin at 50 mg/kg and LEV at 200 mg/kg were comparable. The promising activity of LEV in M. tuberculosis-infected mice suggests that it is a good candidate for clinical development as a new antituberculosis agent.

Absorption of danazol after administration to different sites of the gastrointestinal tract and the relationship to single- and double-peak phenomena in the plasma profiles

The absorption of danazol (100 mg) after oral or intraintestinal administration to the proximal jejunum or proximal ileum has been studied in healthy female subjects. The extent of danazol absorption after administration as a solubilized glycerol mono-oleate emulsion formulation was approximately twofold and fourfold greater after oral dosing when compared with jejunal or ileal administration, respectively. Although not statistically significant in this study, the extent of absorption after jejunal administration was generally greater than after ileal administration. After oral dosing, qualitative assessment identified the presence of double peaks or major shouldering characteristics in 14 of the 16 individual danazol plasma concentration-time profiles, whereas only single peaks were present after intraintestinal administration. These data are consistent with the double peaking phenomena after oral administration of the emulsion formulation being stomach-related. The double peaking effect may be explained in terms of a probable combination of gastric emptying regulated absorption (due to the presence of the lipid in the emulsion formulation) and the dependence of danazol solubility on bile salt solubilization within the upper small intestine.

Bioequivalence of oral and intravenous ofloxacin after multiple-dose administration to healthy male volunteers

The bioequivalence of oral and intravenous ofloxacin was investigated after the administration of multiple doses of 400 mg every 12 h to 20 healthy male volunteers in a randomized, crossover, open-label study. Ofloxacin concentrations in plasma were evaluated after 4 days of oral or intravenous (1-h infusion) dosing with a 3-day wash-out period between regimens. As expected, delivery to the systemic circulation took slightly longer after the oral dosing (time to maximum concentration of drug in serum of 1.7 h) relative to the 1-h intravenous infusion, but the systemic availabilities of ofloxacin by the two routes of administration were equivalent (area under the concentration-time curve from 0 to 12 h ratio of 95%). Since previous studies have not demonstrated any change in the bioavailability of ofloxacin in infectious disease patients, this study supports the interchangeability of these dosing regimens.

Effect of food and a monoglyceride emulsion formulation on danazol bioavailability

The bioavailability of a single 100-mg dose of danazol delivered from the commercial formulation (hard gelatin capsule) and from an experimental lipid emulsion formulation of danazol was studied in 11 healthy female volunteers in both fed and fasted states. The emulsion formulation (fasted) increased bioavailability fourfold compared with the capsule (P = .0001); the difference, however, was not significant in the fed state. Food increased the bioavailability of the capsule formulation more than threefold over fasted administration (P = .0001). In a separate study of 12 female volunteers, single doses of the emulsion formulation of danazol administered with food demonstrated essentially dose-proportional pharmacokinetics over the dose range studied (50-200 mg). The authors conclude that factors that increase the extent of solubilization lead to significant enhancement in the bioavailability of danazol.

Pharmacokinetic profiles of ciprofloxacin after single intravenous and oral doses

Ciprofloxacin was administered to 12 healthy male volunteers at doses of 300 and 400 mg intravenously (i.v.) and 500 and 750 mg orally in a randomized, double-blind, single-dose, four-period crossover study. On each treatment day, each subject received both oral and i.v. formulations, one of which was a placebo. Blood and urine samples were obtained through 24 h postdose. By each dosing route, the pharmacokinetic profiles were dose proportional. The 400-mg i.v. dose was equivalent to the 500-mg oral dose with respect to the area under the concentration-time curve and was equivalent to the 750-mg oral dose with respect to the maximum concentration of ciprofloxacin in serum. The oral bioavailability was 78.0%. The steady-state volume of distribution averaged 178 liters, and the terminal half-life in serum after i.v. dosing was approximately 4.3 h. Renal clearance accounted for approximately 60% of total body clearance. No significant adverse events were associated with either route of administration.

Self-emulsifying drug delivery systems: formulation and biopharmaceutic evaluation of an investigational lipophilic compound

Self-emulsifying drug delivery systems (SEDDSs) represent a possible alternative to traditional oral formulations of lipophilic compounds. In the present study, a lipophilic compound, WIN 54954, was formulated in a medium chain triglyceride oil/nonionic surfactant mixture which exhibited self-emulsification under conditions of gentle agitation in an aqueous medium. The efficiency of emulsification was studied using a laser diffraction sizer to determine particle size distributions of the resultant emulsions. An optimized formulation which consisted of 25% (w/w) surfactant, 40% (w/w) oil, and 35% (w/w) WIN 54954 emulsified rapidly with gentle agitation in 0.1 N HCl (37 degrees C), producing dispersions with mean droplet diameters of less than 3 microns. The self-emulsifying preparation was compared to a polyethylene glycol 600 (PEG 600) solution formulation by administering each as prefilled soft gelatin capsules to fasted beagle dogs in a parallel crossover study. Pharmacokinetic parameters were determined and the absolute bioavailability of the drug was calculated by comparison to an i.v. injection. The SEDDS improved the reproducibility of the plasma profile in terms of the maximum plasma concentration (Cmax) and the time to reach the maximum concentration (tmax). There was no significant difference in the absolute bioavailability of WIN 54954 from either the SEDDS or the PEG formulations.

In vitro and in vivo activities of WIN 54954, a new broad-spectrum antipicornavirus drug

WIN 54954 (5-[5-[2,6-dichloro-4-(4,5-dihydro-2-oxazolyl)phenoxy]pentyl]-3- methylisoxazole) is a new member of the class of broad-spectrum antipicornavirus compounds known to bind in a hydrophobic pocket within virion capsid protein VP1. In plaque reduction assays, WIN 54954 reduced plaque formation of 50 of 52 rhinovirus serotypes (MICs ranged from 0.007 to 2.2 micrograms/ml). A concentration of 0.28 microgram/ml was effective in inhibiting 80% of the 52 serotypes tested (EC80). WIN 54954 was also effective in inhibiting 15 commonly isolated enteroviruses, with an EC80 of 0.06 microgram/ml. Furthermore, WIN 54954 was effective in reducing the yield of two selected enteroviruses in cell culture by 90% at concentrations approximately equal to their MICs. The therapeutic efficacy of intragastrically administered WIN 54954 was assessed in suckling mice infected with coxsackievirus A-9 or echovirus type 9 (Barty) 2.5 days prior to initiation of therapy. Single daily doses of 2 and 100 mg/kg protected 50% of the mice from developing paralysis (PD50) following infection with coxsackievirus A-9 and echovirus-9, respectively. At the PD50 doses for these two viruses, levels of WIN 54954 in serum were maintained above the in vitro MICs for a significant portion of the dosing interval. The dose-dependent reduction in viral titers observed in coxsackievirus A-9-infected mice correlated well with the therapeutic dose response. The potency and spectrum of WIN 54954 make it a potentially useful compound for the treatment of human enterovirus and rhinovirus infections.

The theophylline-enoxacin interaction: II. Changes in the disposition of theophylline and its metabolites during intermittent administration of enoxacin

The pharmacokinetics of theophylline and its three major metabolites, 3-methylxanthine, 1-methylurate, and 1,3-dimethylurate, were studied during intermittent administration of enoxacin. The addition of enoxacin (400 mg, twice daily) to a theophylline dosing regimen (150 mg, twice daily) resulted in an immediate fall in plasma theophylline metabolite concentrations. Mean steady-state theophylline concentration in plasma during the dosing interval increased from 3.17 to 8.23 micrograms/ml. The mean 12-hour recovery of total theophylline metabolite decrease from 76.3 to 38.6 mg. After the discontinuation of enoxacin, but not theophylline, the plasma theophylline metabolite levels immediately increased to near or above the concentrations observed before enoxacin coadministration. Concurrently, theophylline concentrations decreased to levels equivalent to those observed before enoxacin coadministration. In general, the changes in plasma theophylline concentrations observed after the addition of discontinuation of enoxacin were complete within 3 days.

The theophylline-enoxacin interaction: I. Effect of enoxacin dose size on theophylline disposition

Theophylline interacts pharmacokinetically with a variety of other drugs. Recently enoxacin was found to change theophylline's disposition. In a four-subject, four-way crossover study enoxacin was administered every 12 hours at four levels (0, 25, 100, and 400 mg) for 14 doses. With the ninth dose of enoxacin, 200 mg theophylline was coadministered. Blood and urine samples were assayed by sensitive and specific assays for the parent drugs and their metabolites. Significant reduction in the formation of theophylline's three major metabolites occurred on coadministration of enoxacin. At the 400 mg dose level, enoxacin caused a threefold decrease in theophylline's plasma clearance, a fourfold decrease in the urinary recovery of 3-methylxanthine and 1,3-dimethylurate, and a threefold decrease in the recovery of 1-methylurate.

Single dose and steady-state pharmacokinetics of adinazolam after oral administration to man

An aqueous solution containing 1 mg of adinazolam mesylate per ml was administered orally as a single dose (40 mg) and with loading doses followed by hourly doses such that final dose rates of 1, 2, and 3 mg h-1 were administered to steady-state. Four subjects exhibited linear steady-state kinetics, while the other four exhibited Michaelis-Menten kinetics, based on measurement by HPLC of both unchanged drug and the major N-demethyl metabolite. The drug is very rapidly absorbed and has an intrinsic clearance of total (bound + free) drug which averaged 2.14 l min-1 based on the steady-state data and 1.17 l min-1 based on the single dose data, but these means do not differ significantly. The apparent metabolite clearance, CLmc/fm (where fm = fraction of adinazolam converted to the N-demethyl metabolite), averaged 0.170 l min-1 based on steady-state data and 0.179 l min-1 based on single dose data and these means do not differ significantly. Pharmacokinetic parameters, such as these clearances, had large intersubject variations. Three types of bioavailabilities were estimated from the data.

A pharmacokinetic comparison of cephalexin and cefadroxil using HPLC assay procedures

The pharmacokinetics of cephalexin and cefadroxil were compared following single 500 mg oral doses to 12 healthy male volunteers. Doses were administered after an overnight fast according to a crossover design. Plasma and urinary levels of both compounds were determined by HPLC procedures. Cephalexin was absorbed rapidly, achieving a mean peak plasma level of 17.5 micrograms ml-1 at 1 h, compared to 16 micrograms ml-1 at 1.8 h for cefadroxil. Elimination half-lives of cephalexin and cefadroxil were 0.7 and 1.1 h, respectively. The area under the cefadroxil plasma curve was significantly larger than that for cephalexin. However, after allowing for differences in elimination rate constants and assuming equal distribution volumes, plasma data indicated the compounds were equally well absorbed. Only 70 per cent of cefadroxil was recovered in urine compared to 87 per cent of cephalexin during the 12 h following drug administration. The therapeutic significance of the different pharmacokinetic characteristics of cephalexin and cefadroxil, if any, may be a function also of their pharmacologic activity and/or the sensitivity of the target organism.

Vancomycin disposition during continuous ambulatory peritoneal dialysis: a pharmacokinetic analysis of peritoneal drug transport

Expressions are presented to describe the absorption and also clearance of drugs administered into the peritoneal cavity of patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Application of the expressions to vancomycin kinetics in five male CAPD patients showed that therapeutic levels of vancomycin can readily be achieved and maintained in the systemic circulation by administering the appropriate loading and maintenance doses. The intrinsic peritoneal clearance of vancomycin reported here is higher than the apparent clearances reported previously, averaging 300 to 500 ml/min under the conditions used in this study. The low apparent clearances previously reported are useful clinically although they do not represent the true efficiency of vancomycin removal by CAPD. The degree to which apparent clearance underestimates the true intrinsic clearance is exponentially related to the dwell time of dialysate in the peritoneum. Intraperitoneal administration is a practical alternative to other routes for CAPD patients needing antibiotic or other therapy.

Bioavailability of hydrocortisone from commercial 20-mg tablets

The relative bioavailability of hydrocortisone was determined from four different 20-mg tablet formulations and one suspension in 15 healthy male volunteers; results were compared with in vitro dissolution rates. Plasma levels of hydrocortisone were determined by a liquid chromatography method developed in this laboratory. Dissolution of the tablet formulations, using the official USP test, varied from 7.8 to 93.8% in 30 min. Similar plasma profiles were obtained from all tablet products, and there were no differences among tablets in the cumulative percentage of drug absorbed. There were no clear trends in any pharmacokinetic parameter values among the tablet dosages, and the four products were considered bioequivalent. The suspension dosage yielded significantly higher plasma levels compared with some of the tablet formulations during the initial 30-min postdose, significantly higher cumulative absorption at 0.5 and 1.0 h compared with one tablet formulation, and significantly higher ka and Cmax, and shorter tmax values, compared with some of the tablets.

Bioavailability of hydrochlorothiazide from tablets and suspensions

The bioavailability of hydrochlorothiazide was determined following single oral 25-, 50-, 100-, and 200-mg tablet and suspension doses in 12 healthy male volunteers. Plasma and urine levels of hydrochlorothiazide were determined by HPLC. Plasma levels of hydrochlorothiazide were satisfactorily described by a triexponential function. Mean peak plasma levels, Cmax (127-135, 270-280, and 437-490 ng/mL from the 25-, 50-, and 100-mg doses, respectively) were dose proportional, as were areas under plasma profiles, AUC0----36. Mean percentage recovery of unchanged hydrochlorothiazide in 48-h urine samples accounted for 50-59, 54-55, 60-63, and 54-57% of the 25-, 50-, 100-, and 200-mg doses, respectively. There were no significant differences among these values. Correlation coefficients between 48-h urinary recovery of hydrochlorothiazide and the plasma values (Cmax and AUC0----36) for the 25-, 50-, and 100-mg doses were 0.73 and 0.84. There were no differences in the net increases in electrolyte excretion among the treatments during the 0-12-h postdose period. The systematic availability of hydrochlorothiazide, unlike that of chlorothiazide, is dose proportional in the therapeutic range.