Bioavailability of fluticasone propionate and mometasone furoate aqueous nasal sprays.

OBJECTIVES: To compare the systemic exposure for intranasal mometasone furoate (MF) and fluticasone propionate (FP) aqueous nasal sprays (ANS) in terms of serum and urinary cortisol parameters and plasma pharmacokinetics. METHODS: Twelve healthy subjects completed this three-way, cross-over study. They received FPANS (50 microg/spray), MFANS (50 microg/spray) or placebo ANS, eight sprays per nostril every 8 h for 4 days. Cortisol measurements were made at baseline and day 4. FP and MF plasma concentrations were also measured on day 4. RESULTS: MFANS produced similar mean plasma AUC (123 pmol/l h) to FPANS (112 pmol/l h). Despite the use of high doses, necessary to generate adequate pharmacokinetic data, only minor reductions in cortisol parameters were found, with no difference between FPANS and MFANS. CONCLUSIONS: FP and MF have similar and very low systemic bioavailability when administered intranasally using a high-dose regimen. It is therefore unlikely that therapeutic doses of intranasal FP or MF will produce dissimilar or significant degrees of systemic exposure or systemic effects.

Pharmacokinetics, toxicokinetics, distribution, metabolism and excretion of linezolid in mouse, rat and dog.

1. Linezolid (ZYVOX), the first of a new class of antibiotics, the oxazolidinones, is approved for treatment of Gram-positive bacterial infections. 2. The aim was to determine the absorption, distribution, metabolism and excretion (ADME) of linezolid in mouse, rat and dog in support of preclinical safety studies and clinical development. 3. Conventional replicate study designs were employed in animal experiments, and biofluids were assayed by HPLC or HPLC-MS. 4. Linezolid was rapidly absorbed after p.o. dosing with an p.o. bioavailability of > 95% in rat and dog, and > 70% in mouse. Twenty-eight-day i.v./p.o. toxicokinetic studies in rat (20-200mg kg(-1) day(-1)) and dog (10-80 mg kg(-1) day(-1)) revealed neither a meaningful increase in clearance nor accumulation upon multiple dosing. 5. Linezolid had limited protein binding (<35%) and was very well distributed to most extravascular sites, with a volume of distribution at steady-state (V(ss)) approximately equal to total body water. 6. Linezolid circulated mainly as parent drug and was excreted mainly as parent drug and two inactive carboxylic acids, PNU-142586 and PNU-142300. Minor secondary metabolites were also characterized. In all species, the clearance rate was determined by metabolism. 7. Radioactivity recovery was essentially complete within 24-48 h. Renal excretion of parent drug and metabolites was a major elimination route. Parent drug underwent renal tubular reabsorption, significantly slowing parent drug excretion and allowing a slow metabolic process to become rate-limiting in overall clearance. 8. It is concluded that ADME data were relatively consistent across species and supported the rat and dog as the principal non-clinical safety species.

A review of the pharmacology and pharmacokinetics of inhaled fluticasone propionate and mometasone furoate.

BACKGROUND: Fluticasone propionate is an established corticosteroid administered intranasally for the treatment of rhinitis or by oral inhalation for the treatment of asthma. Mometasone furoate, a closely related corticosteroid currently available in an intranasal formulation, is being investigated in an oral inhalation formulation for the treatment of asthma. OBJECTIVE: This article reviews available data on the comparative structure-activity relationships, chemistry, pharmacology, pharmacokinetics, and systemic bioavailability of fluticasone propionate and mometasone furoate to assess whether claims of differences in the absolute systemic bioavailability of the 2 compounds are supported by the published literature. METHODS: Information for this review was identified through a MEDLINE search of the literature from 1966 to the present that contained the term mometasone or fluticasone. The resulting list was narrowed by excluding articles dealing with dermatologic applications. A systematic review was conducted of the identified literature pertaining to the molecular structure, topical potency, lipophilicity, pharmacokinetics, and bioavailability of the 2 agents. Additionally, the pharmacology of the 2 moieties was assessed by a review of the available literature on receptor binding affinity, transactivation and transrepression potency, and inhibition of inflammatory-cell cytokine expression. RESULTS: Based on the available data, fluticasone propionate and mometasone furoate have similar physicochemical properties and structure-activity relationships. When administered intranasally, mometasone furoate is reported to have comparable relative systemic bioavailability to that of fluticasone propionate (mean plasma area under the curve, 123 pmol x h/L vs 112 pmol x h/L, respectively). When administered as a single dose by dry powder inhaler, orally inhaled fluticasone propionate is reported to have a total systemic bioavailability of approximately 17%, whereas that of mometasone furoate is reported to be < 1%. However, the mometasone furoate bioavailability study that reported the latter value used lower drug doses and a less sensitive assay than the fluticasone propionate bioavailability study. When multiple-dose data were used, mometasone furoate had an estimated 11% systemic bioavailability, similar to that of fluticasone propionate. CONCLUSIONS: Inhaled fluticasone propionate and mometasone furoate appear to have comparable potential systemic absorption and, based on the total systemic bioavailabilities of the parent compounds, have a low potential for systemic side effects at the recommended clinical doses. However, in the case of mometasone furoate, the contribution of the active metabolites to systemic effects has not been adequately assessed.

Beclomethasone dipropionate: absolute bioavailability, pharmacokinetics and metabolism following intravenous, oral, intranasal and inhaled administration in man.

AIMS: To assess the absolute bioavailability, pharmacokinetics and metabolism of beclomethasone dipropionate (BDP) in man following intravenous, oral, intranasal and inhaled administration. METHODS: Twelve healthy subjects participated in this seven-way cross-over study where BDP was administered via the following routes: intravenous infusion (1000 microg), oral (4000 microg, aqueous suspension), intranasal (1344 microg, aqueous nasal spray) and inhaled (1000 microg ex-valve, metered dose inhaler). The contribution of the lung, nose and gut to the systemic exposure was assessed by repeating the inhaled, intranasal and oral dosing arms together with activated charcoal, to block oral absorption. Blood samples were collected for 24 h postdose for the measurement of BDP, beclomethasone-17-monopropionate (B-17-MP) and beclomethasone (BOH) in plasma by liquid chromatography tandem mass spectrometry. RESULTS: Intravenous administration of BDP (mean CL 150 l h-1, Vss 20 l, t(1/2) 0.5 h) was associated with rapid conversion to B-17-MP which was eliminated more slowly (t1/2 2.7 h). In estimating the parameters for B-17-MP (mean CL 120 l h-1, Vss 424 l) complete conversion of BDP to B-17-MP was assumed. The resultant plasma concentrations of BOH were low and transient. BDP was not detected in plasma following oral or intranasal dosing. The mean absolute bioavailability (%F, 90% CI; nominal doses) of inhaled BDP was 2% (1-4%) and not reduced by coadministration of charcoal. The mean percentage F of the active metabolite B-17-MP was 41% (31-54%), 44% (34-58%) and 62% (47-82%) for oral, intranasal and inhaled dosing without charcoal, respectively. The corresponding estimates of nasal and lung absorption, based on the coadministration of charcoal, were < 1% and 36% (27-47%), respectively. CONCLUSIONS: Unchanged BDP has negligible oral and intranasal bioavailability with limited absorption following inhaled dosing due to extensive (95%) presystemic conversion of BDP to B-17-MP in the lung. The oral and intranasal bioavailabilities of the active metabolite B-17-MP were high and similar, but direct absorption in the nose was insignificant. The total inhaled bioavailability of B-17-MP (lung + oral) was also high (62%) and approximately 36% of this was due to pulmonary absorption. Estimates of oral bioavailability and pulmonary deposition based on total BOH were approximately half those found for B-17-MP.

Systemic bioavailability of fluticasone propionate administered as nasal drops and aqueous nasal spray formulations.

AIMS: To measure and compare the systemic bioavailability of fluticasone propionate aqueous nasal spray and a new nasal drop formulation, using a sensitive analytical method and high dose regimen. METHODS: Volunteers received four 800 microg doses of fluticasone propionate as a nasal spray or drops over 2 days, separated by an 8 h dose interval. On day 2, blood samples were collected for assay of fluticasone propionate plasma concentrations. RESULTS: The mean systemic exposure, for both formulations was 8.5 pg x ml(-1) x h (drops) and 67.5 pg x ml(-1) x h (spray). Mean absolute bioavailabilities were estimated to be 0.06% (drops) and 0.51% (spray), by reference to historical intravenous data. CONCLUSIONS: Both formulations exhibited low systemic bioavailability, even at 12 times the normal daily dose. The bioavailability from the nasal drops was approximately eight times lower than from the nasal spray.

Single-dose and steady-state pharmacokinetic and pharmacodynamic evaluation of therapeutically clinically equivalent doses of inhaled fluticasone propionate and budesonide, given as Diskus or Turbohaler dry-powder inhalers to healthy subjects.

Direct comparisons of the pharmacokinetic (PK) and systemic pharmacodynamic (PD) properties of inhaled corticosteroids after single and multiple dosing in the same subjects are scarce. The objective of this study was to compare thePK/PDproperties of clinically equivalent, single, and multiple doses of dry-powder formulations of inhaled fluticasone propionate (FP 200 and 500 microg via Diskus) and budesonide (BUD, 400 and 1,000 microg via Turbohaler). Fourteen healthy subjects completed a double-blind, double-dummy, randomized, placebo-controlled, five-way crossover study consisting of a single dose administered at 8 a.m. on day 1 followed by 4 days of twice-daily dosing at 8 a.m. and 8 p.m. on days 2 to 5. Serum concentrations of FP and BUD were measured using validated liquid chromatography/ mass spectrometry assays. The 24-hour cumulative cortisol suppression (CCS) in serum was monitored as the pharmacodynamic surrogate marker. Peak serum concentrations following single and multiple dosing were observed 10 to 30 minutes after inhalation for BUD and 30 to 90 minutes afterinhalation of FP with no influence of dose ordosingregimen. After a single dose of 1000 microg BUD and 500 microg FP the median estimates of terminal half-life and mean residence time were 3.5 and 3.9 hours for BUD and 10.1 and 12.0 hours for FP, respectively. Using previously reported intravenous data, the mean absorption times (MAT) were calculated to be around 2 hours and 7 hours for BUD and FP respectively. On average, the area under the curve (A UC) at steady state (day 5) was up to 30% higher for BUD compared to that over a 12-hour period following the first dose on day 1, whereas A UC estimates were 50% to 80% higherforFP at steady state, indicating accumulation. However, the steady-state Cmax values were seven to eight times and AUC values three to four times higher for BUD than for FP. Comparison of active treatment data with placebo showed that CCS after a single dose was not pronounced for any of the doses/drugs studied. On day 5, both doses of BUD caused statistically significant suppression (CCS of 19% for the 400 microg dose and 36% for the 1,000 microg dose). For FP only the high dose had a statistically significant effect on serum cortisol (CCS of 14% for the 200 microg dose and 27% for the 500 microg dose). Compared to BUD, FP has slower pulmonary absorption and slower elimination kinetics. However, following inhalation of therapeutically equipotent, multiple twice-daily doses in healthy subjects, the systemic effects of FP delivered via Diskus on AUC24 serum cortisol were relatively low and similar to those of BUD delivered via Turbohaler.

From hydrofluoroalkane pressurized metered dose inhalers (pMDIs) and comparability with chlorofluorocarbon pMDIs.

Fluticasone propionate pressurized metered dose inhalers (pMDIs) containing the hydrofluoroalkane (HFA) propellant, HFA 134a, are being developed to replace existing chlorofluorocarbon (CFC) pMDIs. This is part of the ongoing worldwide project to limit the damage to the earth's ozone layer. The in vivo performance and dose proportionality of fluticasone propionate HFA 134a pMDIs was examined for fluticasone propionate doses of 400, 1000 and 2000 microg using the 50, 125 and 250 microg strength pMDIs, respectively. The 125 and 250 microg strength HFA 134a pMDIs were compared with corresponding fluticasone propionate CFC pMDIs. Twenty-three healthy subjects participated in this single dose, randomized, five-way, cross-over study. Serial blood samples were collected 24 h post-dose to measure fluticasone propionate plasma concentrations. Twenty-four hour urinary-free cortisol was also measured before and after dosing. A dose-proportional increase in plasma fluticasone propionate concentrations was observed with increasing dose for the HFA 134a pMDIs. This was associated with a dose-related decrease in urinary cortisol excretion. Similar or lower fluticasone propionate systemic exposure was observed with the HFA 134a pMDIs compared to the corresponding CFC inhalers. The differences in systemic exposure observed for the HFA 134a and CFC pMDIs were too small to produce a differential effect on urinary cortisol excretion. Since fluticasone propionate has negligible oral bioavailability, the systemic exposure, which arises only from pulmonary absorption, is a measure of lung deposition. There was a good correlation between the in vitro fine particle mass produced by the different strengths and types of pMDI and the systemic exposure to fluticasone propionate. Therefore, the fluticasone propionate HFA 134a pMDI is an acceptable pharmaceutical alternative to the current CFC pMDI, producing similar lung deposition and no increase in systemic exposure at microgram equivalent doses.

Comparison of pharmacokinetics and systemic effects of inhaled fluticasone propionate in patients with asthma and healthy volunteers: a randomised crossover study.

BACKGROUND: Inhaled corticosteroids are currently the cornerstone of asthma treatment. Some studies of high-dose fluticasone propionate in patients with no or mild asthma have, however, suggested substantial systemic absorption. We investigated the pharmacokinetics of fluticasone propionate in patients with asthma receiving appropriate doses for severity. METHODS: We did a double-blind, randomised, crossover study in 11 patients with asthma and 13 matched healthy controls (age 20-65 years; asthma patients forced expiratory volume in 1 s <75% and stable on high-dose inhaled corticosteroids). Patients received one 1000 microg intravenous dose or 1000 microg daily for 7 days inhaled (via spacer device) fluticasone propionate. In the 12 h after dosing, we monitored plasma fluticasone propionate and cortisol concentrations by mass spectrometry and competitive immunoassay with use of direct chemiluminescence. Analysis was by intention to treat. FINDINGS: After inhalation, geometric mean values were significantly lower in the asthma group than in controls for fluticasone propionate plasma area under curve (1082 [95% CI 850-1451] vs 2815 pg mL(-1) h(-1) [2262-3949], -62% difference [45-72]; p<0.001), maximum concentrations (117 [91-159] vs 383 pg/mL [302-546], -68% [-50 to -81]; p<0.001), and systemic bioavailability (10.1 [7.9-14.0] vs 21.4% [15.4-32.2], -54% [-27 to -70]; p=0.001). Intravenous-dose clearance, volume of distribution at steady state, plasma half-life, and mean residence time, were similar in the two groups. Less suppression of plasma cortisol concentrations was seen in the asthma group than in controls 4-12 h after inhaled fluticasone propionate. INTERPRETATION: Systemic availability of fluticasone propionate is substantially less in patients with moderate to severe asthma than in healthy controls. Inhaled corticosteroids that are absorbed through the lungs need to be assessed in patients who are receiving doses appropriate for disease severity, and not in normal volunteers.

Pharmacokinetics of fluticasone propionate inhaled via the Diskhaler and Diskus powder devices in healthy volunteers.

OBJECTIVE: The aim of these studies was to determine the absolute bioavailability in healthy volunteers of inhaled fluticasone propionate (FP) administered as a single dose via the Diskhaler and Diskus powder devices, and the pharmacokinetics of inhaled FP after repeated administration via the Diskhaler device. METHODS: In 2 of the studies, single inhaled doses of FP were administered via the Diskhaler and the Diskus powder devices, and, in the third study, repeated doses of FP were administered via the Diskhaler. In the single dose studies, 12 healthy volunteers were randomised to receive FP 1000 microg by inhalation and FP 250 microg intravenously, using a double-blind crossover design. In the repeated dose study, 24 healthy volunteers received FP 1000 microg twice daily for 7.5 days. RESULTS: Systemic exposure to FP after administration of a single 1000 microg inhaled dose of FP via the 2 powder devices was similar; the area under the plasma FP concentration-time curve (AUC) to infinite time (AUCinfinity) was 2.08 microg/L x h [95% confidence intervals (CI): 1.63-2.64] for Diskhaler and 2.49 microg/L x h (95% CI: 2.09-2.96) for Diskus. Maximum plasma FP concentration (Cmax) was 0.34 microg/L for both devices. Mean bioavailability values via the Diskhaler and Diskus were 11.9% (95% CI: 9.0-15.7%) and 16.6% (95% CI: 13.6-20.3%), respectively. No clinically significant reductions in urinary cortisol excretion were recorded in these 2 studies. After repeated administration with the Diskhaler, steady state was achieved by dose 3 (i.e. day 2) onwards. After dose 15, the AUC up to 12 hours (AUC12h) was 2.25 microg/L x h and Cmax was 0.38 microg/L. The mean steady-state to single dose accumulation ratio after twice-daily administration was 1.49 (95% CI: 1.36-1.62). CONCLUSION: The pharmacokinetics of FP administered by the 2 powder devices are similar in healthy volunteers, although systemic bioavailability was greater with the Diskus.

Systemic exposure to fluticasone propionate administered via metered-dose inhaler containing chlorofluorocarbon or hydrofluoroalkane propellant.

OBJECTIVE: The pharmacokinetic profile of a single dose of inhaled fluticasone propionate (FP) administered via a metered-dose inhaler (MDI), containing either a chlorofluorocarbon (CFC) or hydrofluoroalkane (HFA) propellant was investigated in healthy volunteers. METHODS: Two randomised, double-blind, crossover studies were conducted, each in 12 male volunteers. Both studies compared pharmacokinetic data after a single inhaled dose of FP 1000 microg from a MDI containing either CFC (CFC MDI) or HFA (HFA MDI) with a single intravenous dose of FP 250 microg. RESULTS: The maximum plasma FP concentrations after inhalation via the 2 types of MDI were almost identical (0.56 and 0.54 microg/L for CFC MDI and HFA MDI, respectively); bioavailability values of inhaled FP from the 2 MDIs were also similar (geometric mean values: 26.4% via the CFC MDI and 28.6% via the HFA MDI). Inhalation of FP via both MDI formulations produced similar reductions in urinary cortisol excretion over 12 and 24 hours postdose. CONCLUSION: The bioavailability values of FP after inhalation via a CFC MDI and an HFA MDI are similar. The 2 formulations deliver comparable amounts of FP, and systemic exposures to FP from the 2 devices, measured by urinary cortisol excretion, are not significantly different.

Pharmacokinetics of fluticasone propionate inhaled via the Diskhaler and Diskus powder devices in patients with mild-to-moderate asthma.

OBJECTIVE: The aim of these studies was to compare the pharmacokinetics of inhaled fluticasone propionate (FP) after repeated administration via the Diskus or Diskhaler dry powder inhalers (DPIs) to patients with mild-to-moderate asthma. METHODS: Both studies evaluated the pharmacokinetics of inhaled administration of FP via a DPI to patients with mild-to-moderate asthma, according to a randomised, double-blind, placebo-controlled design. In the first study, FP 100 microg or 500 microg was administered twice daily via the Diskhaler for 6 weeks and, in the second, FP 500 microg was administered via the Diskus or Diskhaler for 12 weeks. RESULTS: In the first study, plasma FP concentrations could be detected consistently only with the higher dose; the lower dose produced concentrations close to or below the 0.025 microg/L quantification limit of the radioimmunoassay used. From detailed analysis of a subgroup of patients receiving the 500 microg dosage, steady-state plasma FP concentrations were attained within one week of commencing treatment. After 4 weeks, the maximum plasma FP concentration (Cmax) in this subgroup was 0.096 microg/L [95% confidence interval (CI) 0.066-0.141] and the area under the plasma FP concentration-time curve up to the last quantifiable concentration (AUClast) was 0.491 microg/L x h (95% CI: 0.256-0.940). The steady-state to single dose accumulation ratio for FP after twice-daily administration varied between patients: a ratio of approximately 1.7 was recorded after comparison of Cmax at week 4 and day 1. In the second study, the point estimate of the Diskus to Diskhaler ratio for Cmax in all patients was 0.91 (90% CI: 0.76-1.10) after 4 weeks' treatment. From a detailed analysis of a subgroup of patients, the corresponding ratio for AUClast at the same time point was 1.15 (90% CI: 0.69-1.94), indicating no significant difference in systemic exposure to FP between the 2 devices. Steady-state kinetics were achieved by week 1: the point estimate ratios of Cmax and AUClast at week 4 compared with week 1 were 0.88 (90% CI: 0.66-1.16) and 0.95 (90% CI: 0.66-1.36), respectively. Administration of FP via either DPI had no effect on plasma cortisol levels over the 12-hour postdose period. CONCLUSION: In patients with asthma receiving repeated inhaled doses of FP, the systemic exposure (AUC) after inhalation from the Diskus was similar to that from the Diskhaler, with no difference between the DPIs in the effects on cortisol suppression. The 2 DPIs therefore have very similar pharmacokinetic profiles.

Comparison of the systemic availability of fluticasone propionate in healthy volunteers and patients with asthma.

OBJECTIVES: The aim of this analysis was to compare the systemic exposure to inhaled fluticasone propionate (FP) after administration of either single or repeated dose regimens via dry powder and metered-dose inhalers in patients with asthma and healthy volunteers. BACKGROUND: The pharmacokinetics of FP, a topically active glucocorticoid administered by inhalation for the treatment of asthma and rhinitis, are well characterised in healthy volunteers. As asthma is characterised by pathophysiological changes in the lung, it may be inappropriate to use data from studies in healthy volunteers to predict the deposition and absorption of FP in patients with asthma. METHODS AND RESULTS: Pooled data from 13 pharmacokinetic studies showed that the systemic availability of FP (measured as area under the plasma FP concentration-time curve) after single or multiple administration by inhalation was 2 to 3 times lower in patients with asthma than in healthy volunteers. This observation correlated well with the systemic effects of FP in the 2 groups. Reduction in 24-hour urinary cortisol excretion after inhalation of FP (determined in 9 of the studies) was greater in healthy volunteers than in patients with asthma. The hypothalamic-pituitary-adrenal axis suppression caused by systemic exposure to FP in adults with asthma is therefore substantially less than that in healthy volunteers. CONCLUSION: Differences in the deposition of FP in the lungs of patients with asthma, probably caused by obstructed inspiratory airflow, may explain this observation.

Bioavailability of orally administered micronised fluticasone propionate.

OBJECTIVE: The aim of this study was to determine the absolute oral bioavailability of fluticasone propionate (FP) in healthy volunteers. METHODS: A 3-period incomplete block crossover design was used. On separate occasions, 21 male volunteers received a single 250 microg intravenous dose of FP (n = 21) and twice daily oral doses of either micronised FP 0.1 mg (n = 9), 1 mg (n = 12), 10 mg (n = 11) or placebo (n = 9) for 4 days. RESULTS: FP was not measurable in the plasma after twice daily oral administration of a 0.1 mg dose. FP concentrations just above the limit of quantification could be measured in only 5 volunteers, and only at some time points, after administration of FP 1 mg twice daily. At a dose of 10 mg twice daily the absolute oral bioavailability of the drug was <1% when a liquid chromatography-mass spectrometry assay was used to assess plasma concentrations. Only oral doses of FP 10 mg twice daily, 10 times greater than the recommended maximum inhaled dose, produced any detectable change in urinary cortisol excretion. CONCLUSION: The results of this study confirm that oral absorption of FP into the systemic circulation is negligible. The swallowed portion of an inhaled dose of FP is unlikely to increase the systemic exposure to the drug, thus decreasing the likelihood of adverse systemic effects.

Serum inhibitory titers and serum bactericidal titers for human subjects receiving multiple doses of the antibacterial oxazolidinones eperezolid and linezolid.

In Phase I trials subjects received multiple doses of eperezolid (PNU-100592; formerly U-100592) and linezolid (PNU-100766; formerly U-100766), and steady-state samples were drawn at the projected peak and trough timepoints. Serum inhibitory titer and serum bactericidal titer values were determined using single strains of Staphylococcus aureus, Enterococcus faecalis, and Streptococcus pneumoniae. Serum inhibitory titer values generally correlated with drug concentration in serum and inherent organism susceptibility. Against S. aureus and E. faecalis sera from patients dosed with either drug were generally inhibitory at the peak timepoint, but at trough only linezolid exhibited a persistent effect. No bactericidal activity was seen for either drug against S. aureus or E. faecalis. The sera from patients dosed with either drug exhibited inhibition of S. pneumoniae at peak and trough. Bactericidal activity was seen against S. pneumoniae for both drugs at peak time and at trough for many of the sera for patients on the higher dose regimens. The results demonstrated that the sera from most human subjects dosed with eperezolid or linezolid were inhibitory to S. aureus and E. faecalis and S. pneumoniae and that many of the samples exhibited bactericidal activity for S. pneumoniae.

A comparative population pharmacokinetic analysis for methylprednisolone following multiple dosing of two prodrugs in patients with acute asthma.

AIMS: To conduct a randomized, parallel group comparison of the population pharmacokinetics of the two methylprednisolone (MP) prodrugs Promedrol (MP suleptanate) and Solu-Medrol (MP succinate) in patients hospitalized with acute asthma. METHODS: Ninety volunteers were included in the pharmacokinetic analysis. Each volunteer received a dosage regimen of 40 mg (MP equivalents) i.v. 6 hourly for 48 h. The bio-conversion and disposition of a 40 mg (MP equivalent) i.v. dose of either MP suleptanate or MP succinate to MP was modelled as a first order input, and a mono-exponential elimination phase. RESULTS: Population modelling indicated that the only difference in MP pharmacokinetics between MP suleptanate and MP succinate was in the input rate constant (66.0 h-1 vs 5.5 h-1 respectively). Based on individual Bayesian estimates, the exposure of patients to MP was marginally lower for MP suleptanate although the parameter estimates were not significantly different for half-life (2.7 h vs 3.0 h), steady-state AUC (2007.0 ng ml-1 h vs 2321.0 ng ml-1 h) and steady-state Cmax (698.4 ng ml-1 vs 647.8 ng ml-1) for MP suleptanate and MP succinate respectively. CONCLUSIONS: It was concluded that for the multiple dosage regimen used in patients with acute asthma the systemic exposure to MP following dosing with MP suleptanate is similar to that arising from MP succinate. In addition the differences in the pharmacokinetics for the prodrugs resulted in only a small difference in the relative bioavailability of MP for MP suleptanate (0.94) compared with MP succinate.

Pharmacokinetic and pharmacodynamic assessment of bioavailability for two prodrugs of methylprednisolone.

AIMS: The aim of this study was to establish whether pharmacokinetic differences between two pro-drugs of methylprednisolone (MP) are likely to be of clinical significance. METHODS: This study was a single-blind, randomized, crossover design comparing the bioequivalence of MP released from the pro-drugs Promedrol (MP suleptanate) and Solu-Medrol (MP succinate) after a single 250 mg (MP equivalent) intramuscular injection to 20 healthy male volunteers. Bioequivalence was assessed by conventional pharmacokinetic analysis, by measuring pharmacodynamic responses plus a novel approach using pharmacokinetic/pharmacodynamic modeling. The main measure of pharmacodynamic response was whole blood histamine (WBH), a measure of basophil numbers. RESULTS: The MP Cmax was less for MP suleptanate due to a longer absorption halflife of the prodrug from the intramuscular injection site. The bioavailability of MP was equivalent when based on AUC with a MP suleptanate median 108% of the MP succinate value (90% CI: 102-114%). For Cmax the MP suleptanate median was 81% of the MP succinate value (90% CI: 75-88%). The tmax for MP from MP suleptanate was delayed relative to MP succinate. The median difference was 200% (90% non-parametric CI: 141-283%). The area under the WBH effect-time curve (AUEC) and the maximum response (Emax) were found to be equivalent (90% CI: 98-113% and 93-109% respectively). The maximum changes in other white blood cell counts, blood glucose concentration and the parameters of the pharmacodynamic sigmoid Emax model (EC50, Emax and gamma) were also not significantly different between prodrugs. CONCLUSIONS: MP suleptanate is an acceptable pharmaceutical alternative to MP succinate. The use of both pharmacokinetic and pharmacodynamic response data together gives greater confidence in the conclusions compared with those based only on conventional pharmacokinetic bioequivalence analysis.

Pharmacokinetics and tissue distribution of cisplatin and conjugates of cisplatin with carboxymethyldextran and A5B7 monoclonal antibody in CD1 mice.

The plasma disposition kinetics and tissue distribution of platinum was evaluated following intravenous bolus administration to CD1 immune-competent mice of cisplatin, cisplatin conjugated to anti-CEA monoclonal antibody A5B7 via a carboxymethyl dextran (CMdextran) carrier molecule, and cisplatin coupled to the CMdextran in the absence of antibody. In addition, the in vivo characteristics of 125I-labeled A5B7 were compared with and without conjugation to CMdextran. Conjugation of cisplatin [clearance (CL = 0.62 mL/min/g, volume of distribution at steady-state (Vdss) = 16 mL/g] to CMdextran restricted its tissue distribution (Vdss = 0.43 mL/g) and reduced its systemic clearance (CL = 0.055 mL/min/g). Subsequent conjugation of the complex to A5B7 further reduced both its distribution (Vdss = 0.20 mL/g) and clearance (CL = 0.016 mL/min/g). Clearance of A5B7 (CL = 0.002 mL/min/g) was increased by conjugation to CMdextran (CL = 0.014 mL/min/g); tissue distribution was unchanged. A5B7-CMdextran-cisplatin was relatively stable in plasma and other tissues, except the liver. The extent of distribution of platinum into tissues (lung, liver, muscle, kidney) was markedly influenced by conjugation, with the influence being greatest for unmodified cisplatin and least for the A5B7-CMdextran conjugate. However, the time courses of tissue distribution, expressed in mean residence time scales, were similar, implying a common mechanism controlling tissue uptake.

Altered clearance of N-1 methylnicotinamide associated with the use of low doses of cyclosporine.

To improve the monitoring of patients on low doses of cyclosporine there is a need for new tests of tubular function. N-1 methylnicotinamide (NMM) is an endogenous organic cation that is secreted by the proximal tubule and its clearance can be measured. In 27 patients with psoriasis, serial measurements of NMN clearance, plasma aldosterone, plasma chloride, bicarbonate, and magnesium were compared with changes in the radionuclide measurement of glomerular filtration rate and renal blood flow before, during, and after a 3-month course of low-dose cyclosporine (< 5 mg/kg/d). N-1 methylnicotinamide clearance decreased significantly with cyclosporine only (2.5 mg/kg/d, n = 10, P < 0.01). Recovery of NMN clearance lagged behind that of glomerular filtration rate and renal blood flow. Serum magnesium decreased significantly on cyclosporine (2.5 mg/kg, n = 10, P < 0.01; 5 mg/kg, n = 9, P < 0.0001). In the whole group, plasma potassium increased significantly (n = 27, P < 0.02) and plasma aldosterone was inappropriately low. Low doses of cyclosporine in psoriasis cause a reduced clearance of NMN, hypomagnesemia, and a variable hyperchloremic acidosis. Nifedipine may alter these biochemical variables without necessarily improving renal hemodynamics. The delayed recovery of NMN clearance in comparison with renal haemodynamic measurements following cyclosporine therapy suggests that this noninvasive test of tubular function may be a marker of persisting cyclosporine nephrotoxicity and that it should be evaluated further.