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.

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.

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.

Cisplatin metabolites in plasma, a study of their pharmacokinetics and importance in the nephrotoxic and antitumour activity of cisplatin.

For rats dosed with cisplatin the rate of appearance in plasma of ultrafilterable metabolites containing platinum has been investigated using HPLC. At least seven species containing platinum in addition to cisplatin are present 15 min following injection i.p. of 15 mg kg-1. Unchanged cisplatin has been almost completely eliminated from the plasma within 3 hr of dosing; however, metabolite species are still present. The same metabolite species form when cisplatin is incubated in vitro with plasma although in different proportions. After incubation for 24 hr at 37 degrees a mixture of metabolites is produced which contains less than 4% cisplatin. This mixture, when injected i.p. into rats, is nephrotoxic at doses of platinum at which cisplatin is not. The mixture of metabolites has considerably less antitumour activity than cisplatin when tested against the mouse L1210 leukemia assay. Although no metabolite species has been unequivocally identified we present evidence which suggests that amongst the principle metabolite species are an hydrolysis product and methionine substitution products of cisplatin. A mixture of cisplatin methionine substitution complexes showed neither antitumour nor nephrotoxic properties. However, an hydrolysis product was shown to be nephrotoxic at a dose of platinum at which cisplatin is not. The work reported here is the first direct experimental demonstration that cisplatin metabolites are more nephrotoxic but less effective antitumour agents than the parent compound.

The renal fractional clearance of platinum antitumour compounds in relation to nephrotoxicity.

The fractional renal clearance of platinum relative to inulin was measured in the conscious rat during the period 60-70 min after injection of the nephrotoxic drug, cisplatin, or its non-nephrotoxic analogues (trans-dichlorodiammine platinum II, carboplatin or iproplatin). The fractional clearance of platinum was between 3 and 4 for cisplatin and its analogues. Platinum from cisplatin and its trans isomer is essentially irreversibly bound whilst that from carboplatin and iproplatin is largely reversibly bound to blood proteins. Probenecid and triethanolamine both caused an increase whereas furosemide caused a decrease in the fractional clearance of total platinum from cisplatin. Choline chloride had no nett effect on the fractional clearance of total platinum. Both furosemide and triethanolamine made no significant difference to the severity of cisplatin induced nephrotoxicity. However, probenecid enhanced cisplatin induced nephrotoxicity and choline chloride was capable of blocking cisplatin induced nephrotoxicity. We conclude that the renal tubular transport of platinum is not per se responsible for the nephrotoxicity of platinum compounds. However, in the case of cisplatin, or one of its metabolites, renal tubular transport may be a prerequisite for nephrotoxicity.

A study of the protective effect of chloride salts on cisplatin nephrotoxicity.

In rats NaCl and NH4Cl (25 mmoles/kg, p.o.) were found to be equally effective at preventing nephrotoxicity when administered to rats 90 min before cisplatin (5 mg/kg i.p.) but (NH4)2SO4 did not protect. The severity of nephrotoxicity, taken as the maximum elevation in blood urea concentration, showed a high degree of correlation with urinary chloride concentration, but not with urinary pH or volume. Sodium chloride did not protect against nephrotoxicity when administered 3 or 24 hr after cisplatin. Sodium chloride showed protection against nephrotoxicity caused by cisplatin metabolites only at low doses of platinum. For animals pretreated with NaCl (25 mmoles/kg) or water p.o. the urinary excretion of total platinum, cisplatin and six of the seven metabolites separated by hplc was not significantly different between the two treatments during the 0-5-hr period post dosing. However, one metabolite, possibly a nephrotoxic hydrolysis product, was excreted in significantly smaller amounts in the urine of animals pretreated with NaCl (P less than 0.05). Furthermore, in all cisplatin treated animals the amount of this species excreted correlated with the severity of nephrotoxicity. Whilst this suggests that chloride ions may protect against the nephrotoxicity of cisplatin by inhibiting its rate of metabolism this metabolite accounts for only 2.5% of the platinum excreted. Furthermore, the data do not exclude the possibility that NaCl prevents cisplatin-induced nephrotoxicity by preventing renal ischaemia, which may normally follow cisplatin treatment, or that the renal uptake or transport of platinum may be inhibited by NaCl.

The mechanism of renal clearance of cisplatin (cis-dichlorodiammine platinum ii) and its modification by furosemide and probenecid.

When isolated rat kidneys are perfused with 30 microM cisplatin there is net tubular transport of platinum, resulting in excretion of platinum at a rate 125% of the rate attributable to glomerular filtration alone. Probenecid and furosemide are drugs which have been reported to protect against cisplatin nephrotoxicity, by unknown mechanisms. When probenecid 0.3 mM is included in the perfusate net transport of platinum is increased to 200% of that accounted for by glomerular filtration alone. Increasing the concentration of probenecid to 3.0 mM does not significantly further increase the rate of excretion of platinum. The inclusion of furosemide 0.3 mM in the perfusate has no effect on the net tubular transport of platinum. However, at 3.0 mM furosemide causes a decrease in the net platinum transport and only 93% of platinum filtered at the glomerulus appears in the urine. Thin-layer chromatography revealed the presence of at least three platinum compounds in the urine in addition to cisplatin. We conclude that the renal excretion of cisplatin and its transformation products, even in this model system, is a complex process involving glomerular filtration, tubular excretion and tubular reabsorption.

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.

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.

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.

Disposition and nephrotoxicity of 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (APD), in rats and mice.

The purpose of this study was to investigate the disposition and the nephrotoxicity of 3-amino-1-hydroxypropylidene-1, 1-bisphosphonate (APD-pamidronate) in order to elucidate the mechanism of the non-linearity of the renal elimination of this drug. The fate of APD labelled with [14C]APD was studied in mice and rats for a range of doses (0.5-40 mg/kg) and indicators of renal function were monitored. In both species, the percentage of dose excreted during the first 24-h after treatment fell dramatically as a function of the dose. However, the renal burden of APD rose linearly for doses of APD below 10 mg/kg and increased non-linearly over this threshold. In contrast the concentration of APD in both bone and liver, which together account for a large proportion of the dose, appeared to increase proportionally with dose. There was no evidence, therefore, that the non-linear renal elimination of APD was due to an increased uptake of APD by tissues. Conversely, the significant fall in the renal excretion of APD was paralleled by a striking loss in body weight, and for high doses, by a fall in the creatinine clearance. An increased enzymuria suggested the loss of brush border membranes and the release of lysosomal contents by proximal tubular cells. Morphological studies confirmed this and revealed a focal proximal tubular necrosis 6 days post dosing. We conclude that the nephrotoxicity of APD accounts for the non-linear renal elimination of this drug.

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.

The inhibition of renal ATPase by cisplatin and some biotransformation products.

The anti-tumour drug cisplatin is a potent nephrotoxic agent. Renal Na+/K+-activated and Mg2+-activated ATPases are shown to be equally sensitive to cisplatin inhibition in vitro. An aged solution of cisplatin, containing hydrolysis products, is a thousand times more inhibitory to ATPase (ID50 8.0 X 10(-7) M) than freshly made cisplatin solutions (ID50 6.5 X 10(-4) M). Chloride ion concentrations of 0-150 mM in the assay mixtures do not affect either the extent of inhibition of ATPase by cisplatin or the time required for inhibition to develop. We conclude that cisplatin reacts directly with ATPase rather than that a hydrolysis product is responsible for the inhibition. Various amino acid complexes with cisplatin were tested for their ability to inhibit ATPase. Cysteine/cisplatin in a mole ratio of 1 : 1 is completely ineffective. Mono-substituted methionine/cisplatin is more inhibitory than cisplatin alone but di-substituted methionine/cisplatin is less effective. The reason for these observations and their significance to nephrotoxicity are discussed.

Plasma protein binding of APD: role of calcium and transferrin.

The bisphosphonate drug APD (pamidronate, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate) has been shown to bind to human plasma proteins. This was an unexpected observation since this hydrophilic, anionic drug is not typical of molecules that exhibit this characteristic. At a concentration of 5 micrograms/ml the extent of binding of APD to fresh human plasma in vitro was variable between subjects 30.2% +/- 8.5% (mean +/- S.D., n = 10). Binding was not influenced by the time or concentration of APD over the range 0.05-10.0 micrograms/ml. At 20 and 50 micrograms/ml some precipitation of APD occurred. Both calcium and iron play a role in the binding of APD to plasma proteins, addition of calcium to plasma increased the degree of binding of APD, whereas the calcium chelators EDTA and EGTA reduced the binding of APD. Similarly, addition of iron to plasma increased the binding and the inclusion of the iron chelator desferrioxamine diminished the binding of the drug. The effects of iron and desferrioxamine were less pronounced than those of calcium and EDTA, indicating that the majority of the binding involves calcium ions and a smaller contribution is made by ferric ions. The equilibrium dissociation constants (Kd) for APD binding to calcium and iron binding sites on plasma proteins were estimated to be 852 microM and 29 microM, respectively. Calcium binding sites were of high capacity but low affinity and the iron binding sites were of lower capacity and higher affinity. Electrophoresis of plasma proteins following incubation with [14C]APD revealed binding to the transferrin and globulin fractions. However, there was some dissociation of protein bound APD during the electrophoresis. The consequences of hypercalcaemia on the pharmacokinetics of APD are discussed.

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.