Binding of piroxicam to synovial fluid and plasma proteins in patients with rheumatoid arthritis

Summary The protein binding of piroxicam in synovial fluid and plasma from patients with rheumatoid arthritis was studied in vitro by equilibrium dialysis. The binding parameters were calculated from the experimental data with the Scatchard model, assuming binding to two classes of sites. Each plasma sample was diluted to an albumin concentration equal to that of synovial fluid from the same patient. The association constants for primary and secondary binding sites in the concentration range of piroxicam 4.5–90·10^–5 mol/l were similar in synovial fluid and in plasma. For synovial fluid K₁=2.38·10⁵ l/mol and K₂=2.29·10³ l/mol; for plasma K₁=1.93·10⁵ l/mol and K₂=2.08·10³ l/mol. The number of binding sites was also the same in the two fluids. Although the concentration of piroxicam in synovial fluid was about half that in plasma, the binding of piroxicam to protein in synovial fluid was the same as in plasma.     

Protein binding of salicylate in cutaneous hepatic porphyria

Summary (1) Plasma protein binding of salicylate was studied in 14 patients with cutaneous hepatic porphyria (CHP) and 11 normal subjects using ultrafiltration with centrifugation (membrane cones) and continuous ultrafiltration. (2) Albumin and haemoglobin levels were significantly reduced in patients with CHP, and salicylate binding by ultrafiltration/centrifugation was 65% compared with 84% in normal subjects. (3) Plasma porphyrin levels were raised, but did not correlate with salicylate binding, and protoporphyrin or uroporphyrin added to plasma did not alter the amount of drug bound. (4) Palmitate added to plasma reduced salicylate binding by 9 to 20% but a crossover of patient and normal plasma proteins and ultrafiltrates confirmed that no other ultrafiltrable metabolites present in patient plasma appeared to cause decreased binding. (5) Scatchard plots obtained by continuous ultrafiltration for normal and patient plasma showed a reduction in the number of primary and secondary binding sites and an increase in the intrinsic association constants for both these sites. (6) It was concluded that the decreased salicylate binding in CHP was due to a reduced albumin concentration and altered salicylate albumin interaction.     

Plasma and synovial fluid meclofenamic acid concentrations in patients with rheumatoid arthritis of the knee

Summary We have measured plasma and synovial fluid concentrations of meclofenamic acid at 2, 4, 8, and 12 h during steady-state administration (100 mg three times daily for 4–7 days). Paired plasma and synovial samples were obtained pre-treatment and at one of the above times in twelve patients with a diagnosis of rheumatoid arthritis. In addition, the extent of protein binding of meclofenamic acid was assessed in vitro in the pre-treatment plasma and synovial fluid specimens.Peak total concentrations of 1.73 and 0.86 µg·ml^–1 were observed in plasma (at 2 h) and synovial fluid (at 4 h) respectively. The extent of protein binding was 99.7 and 99.6% (not significantly different) in plasma and synovial fluid respectively.The results of this study are compared to those from similar reported studies of other nonsteroidal anti-inflamatory compounds.     

Pharmacokinetics of lumiracoxib in plasma and synovial fluid

BACKGROUND: Lumiracoxib is a new cyclo-oxygenase-2 (COX-2) selective inhibitor in development for the treatment of rheumatoid arthritis, osteoarthritis and acute pain. OBJECTIVE: To investigate the pharmacokinetics of lumiracoxib in plasma and knee joint synovial fluid from patients with rheumatoid arthritis. DESIGN: Open-label multiple-dose study evaluating the steady-state pharmacokinetics of lumiracoxib in plasma and synovial fluid after 7 days of treatment with lumiracoxib 400 mg once daily. PATIENT POPULATION: Males and females aged 18-75 years with rheumatoid arthritis, having moderate to significant synovial fluid effusion of the knee. OUTCOME MEASURES: Following a 7-day washout period for previous nonsteroidal anti-inflammatory drugs, 22 patients (17 female, 5 male) received lumiracoxib 400 mg once daily for seven consecutive days. On day 7, following an overnight fast, a final dose of lumiracoxib was administered and serial blood and synovial fluid samples were collected for up to 28 hours. Lumiracoxib and its metabolites (4'-hydroxy-lumiracoxib and 5-carboxy-4'-hydroxy-lumiracoxib) were measured by validated high performance liquid chromatography-mass spectrometry methods. The steady-state pharmacokinetics of lumiracoxib were evaluated in plasma and synovial fluid by both a population pharmacokinetic model and noncompartmental analysis.RESULTS: Lumiracoxib was rapidly absorbed (peak plasma concentration at 2 hours) and the terminal elimination half-life in plasma was short (6 hours). Lumiracoxib concentrations were initially higher in plasma than in synovial fluid; however, from 5 hours after administration until the end of the 28-hour assessment period, concentrations of lumiracoxib were higher in synovial fluid than in plasma. Peak drug concentration in synovial fluid occurred 3-4 hours later than the peak plasma concentration. The mean steady-state trough concentration of lumiracoxib in synovial fluid (454 microg/L) was approximately three times higher than the mean value in plasma (155 microg/L), and the area under the concentration-time curve from 12 to 24 hours after administration was 2.6-fold higher for synovial fluid than for plasma. Median lumiracoxib protein binding was similar in plasma and synovial fluid (range 97.9-98.3%). Concentrations of 4'-hydroxy-lumiracoxib, the active COX-2 selective metabolite, remained low in comparison with parent drug in both plasma and synovial fluid. The concentration of lumiracoxib in synovial fluid at 24 hours after administration would be expected to result in substantial inhibition of prostaglandin E(2) formation. CONCLUSION: The kinetics of distribution of lumiracoxib in synovial fluid are likely to extend the therapeutic action of the drug beyond that expected from plasma pharmacokinetics. These data support the use of lumiracoxib in a once-daily regimen for the treatment of rheumatoid arthritis.     

Salicylate protein binding in serum from young and elderly subjects as measured by diafiltration

Summary The protein binding of salicylate was measured by continuous ultrafiltration (diafiltration) at 22°C in serum obtained from 5 healthy young (mean age: 27 years) and 5 healthy elderly (mean age: 73 years) male volunteers. Unbound salicylate increased disproportionately with increasing total salicylate concentration, up to 7000 µmol, in all sera. The fraction bound of salicylate was significantly lower in sera from elderly but this was not due to decreased albumin or total protein concentrations. The binding of salicylate to serum proteins was characterized by two classes of binding sites. The high affinity site had an association constant of either 94901/mol (young) or 75601/mol (elderly) and the number of binding sites was either 4.7 (young) or 3.7 (elderly). The total binding capacity of the low affinity site, 1121/mol, in sera from elderly was significantly less than the binding capacity, 631l/mol, in sera from young. Differences in binding capacity of the low affinity site partially accounted for a two to three-fold increase in the salicylate free fraction in elderly sera. These data suggest that age-related differences in serum protein binding may influence salicylate pharmacokinetics.     

Protein binding of non-steroidal anti-inflammatory drugs in plasma and synovial fluid of arthritic patients

1 The protein binding of seven non-steroidal anti-inflammatory drugs (indomethacin, tolmetin, salicylic acid, ibuprofen, flurbiprofen, naproxen and GP53,633) and warfarin was investigated by equilibrium dialysis in simultaneous samples of synovial fluid and plasma from 12 arthritic patients. 2 The protein binding of all drugs studied except warfarin and flurbiprofen was significantly lower in synovial fluid than in plasma. 3 The decreased protein binding of these drugs is likely to explain the lower total drug concentrations found in synovial fluid in comparison to plasma. 4 The lower albumin concentration plays an important role in determination of reduced drug binding in synovial fluid compared to plasma and the fatty acid concentration in synovial fluid may also influence the protein binding of some of these drugs.     

The disposition of biphenylacetic acid following topical application

Summary Plasma and synovial fluid concentrations of biphenylacetic acid were determined following application of 3 g of 3% biphenylacetic acid gel to one knee of patients suffering from rheumatoid arthritis.The mean peak plasma concentration was 34 ng/ml. Synovial fluid concentrations tended to follow plasma concentrations but at a somewhat lower level, the mean peak synovial fluid concentration was 21 ng/ml. The average ratio of synovial fluid AUC (0–24 h) to plasma AUC (0–24 h) was 0.58, r=0.97.Where patients had bilateral effusions, the concentration in the ipsilateral knee at each time point examined was not significantly different to that in the contralateral knee, suggesting that absorption was initially into the plasma and subsequently into the synovium.     

Ibuprofen kinetics in plasma and synovial fluid of arthritic patients

After administration of a single dose and at steady state, ibuprofen concentrations were measured simultaneously in plasma and synovial fluid obtained from eight patients with rheumatoid arthritis. By seven hours after a dose at steady state, the mean synovial fluid: plasma ibuprofen concentration ratios were constant, and the synovial fluid levels were, on average, greater than those in plasma. The extent to which ibuprofen was bound to protein was somewhat greater in plasma than in synovial fluid. As a result, the mean synovial fluid:plasma free concentration ratio for seven-hour and later specimens was greater than that based on total concentrations. The degree of accumulation of ibuprofen in each fluid was minimal, consistent with its short half-life.     

In SCID Mice with Transplanted Joint Tissues from Rheumatism Patients,a Model Mice of Human Rheumatoid Arthritis,Anti-human Fas Antibody (R-125224) Distributes Specifically to Human Synovium

Purpose We investigated the tissue distribution of a humanized anti-human Fas monoclonal antibody, R-125224, in SCID mice transplanted with synovial tissues from patients with rheumatoid arthritis (SCID-HuRAg mice). The binding kinetics of R-125224 was also determined, using isolated human synovial cells. Materials and Methods Tissue distribution was assessed at 1, 24 and 168 h after intravenous administration of ¹²⁵I-R-125224 to SCID-HuRAg mice (0.4 mg/kg). The in vitro binding of ¹²⁵I-R-125224 to isolated human synovial cells was investigated. Results After intravenous administration of ¹²⁵I-R-125224 to SCID-HuRAg mice, the radioactivity distributed to various tissues at 1 h. Thereafter, the radioactivity in the tissues gradually decreased except for the transplanted synovial tissues, in which the radioactivity increased in a time-dependent manner, and at 168 h, the tissue/plasma concentration ratio was about 1. The in vitro binding affinity of ¹²⁵I-R-125224 to human synovial cells was high with a dissociation constant of 1.32 ± 0.62 nM and the binding was inhibited by non-labeled R-125224 in a concentration-dependent manner. Conclusion R-125224, a candidate compound for treating rheumatoid arthritis, specifically distributed to the pharmacological target site, human synovium transplanted in SCID mice, with high affinity.     

Simultaneous pharmacokinetics of alclofenace in plasma and synovial fluid in patients with rheumatoid arthritis.

The simultaneous pharmacokinetics of alclofenac in the plasma and synovial fluid of 10 patients with rheumatoid arthritis were studied after a single 1 g. oral dose. A gas-liquid chromatographic method was used for assaying alclofenac in both plasma and synovial fluid. Alclofenac readily appears in the plasma and synovial fluid.     

A comparison of plasma and synovial fluid profiles of standard and controlled-release formulations of ketoprofen in patients with rheumatoid arthritis

The plasma and synovial fluid profiles of standard and controlled-release formulations of ketoprofen were compared in 8 patients with rheumatoid arthritis. During chronic dosing with both forms of ketoprofen, peak drug concentrations were lower and occurred later in the synovial fluid than in the plasma. These findings were more pronounced in the case of the controlled-release formulation. The apparent elimination half-life of standard ketoprofen in synovial fluid was prolonged compared to its half-life in plasma, a finding which has not been previously documented. This may explain the clinical observation that, despite a very short plasma elimination half-life, standard ketoprofen exerts a satisfactory therapeutic effect when given twice daily. There was no accumulation of ketoprofen from either formulation in synovial fluid after steady state had been achieved. It is suggested that future pharmacological studies with anti-inflammatory agents should include both synovial fluid and plasma concentration data.     

D-penicillamine and D-penicillamine-protein disulphide in plasma and synovial fluid of patients with rheumatoid arthritis.

1. The plasma pharmacokinetics of D-penicillamine (D-pen) and D-penicillamine-albumin disulphide (D-pen-alb) were examined over a dosage interval in six patients with rheumatoid arthritis. In two of these, 24 h synovial fluid profiles of D-pen and D-pen-alb were also obtained. 2. D-pen was undetectable in plasma at the beginning of the study. The peak concentration (5.4 +/- 1.2 microM) occurred at between 45 min and 2 h and the mean elimination half-life was 0.6 h. D-pen-alb, however, was present at a mean plasma concentration of 19.1 microM prior to dosage, peaked at 26.2 microM and was eliminated with a half-life of 40 h. 3. D-pen concentrations in synovial fluid rose more slowly and peaked lower than in plasma. D-pen-alb was present in synovial fluid of the patients at 50.1% and 83.6%, respectively, of the simultaneous plasma concentration prior to dosage. Concentrations varied during the study interval, corresponding to changes in plasma concentrations. 4. These results demonstrate that D-pen forms stable conjugates with protein in treated patients. The presence of D-pen-alb in relatively high concentrations throughout the dosage interval contrasts with the low concentrations and rapid elimination of D-pen. Both D-pen and D-pen-alb were also shown to be present at the putative site of drug action (the inflamed synovial joint) in concentrations lower than those in plasma.     

Theoretical analysis of the binding of salicylate by human serum albumin: The relationship between free and bound drug and therapeutic levels

Summary The binding of salicylate by human serum albumin was analyzed by use of a computer program using previously published association constants and binding capacities for the two sets of binding sites on the protein. The analysis consisted of computing free and bound salicylate for a range of therapeutic and toxic concentrations from 181 to 7246 µmole/L (25 to 1000 mg/L). At low and therapeutic levels the total amount of bound drug would exceed the amount of free drug. At higher levels, which included therapeutic and toxic ranges, the amount of free drug would equal or exceed the amount of bound salicylate. At low levels of drug in the plasma, up to 2000 µmole/L the high affinity sites (Site 1), would bind most of the drug, but as the concentration of drug increased this site would approach saturation and the low affinity Site 2 would bind increasing amounts of salicylate. At high salicylate levels the amount of drug bound by the low affinity sites would exceed the amount bound by the high affinity sites. Computation also showed that when the total amount of protein in the analysis was reduced, from 5,4,3 to 2 gm%, as in hypoalbuminemia, the total amount of drug bound by the protein would decrease and the quantity of free drug would increase. The amount of drug bound by each of the two sets of sites also fell as the concentration of protein decreased. Some of the possible clinical implications of these findings are discussed.     

In vitro protein binding of diclofenac sodium in plasma and synovial fluid

The in vitro protein binding behavior of diclofenac sodium (sodium[o-(2,6-dichloroanilino)phenyl]acetate) in plasma and synovial fluid was investigated by equilibrium dialysis. The drug was highly protein bound (approximately 99.5%) and the extent of binding remained constant for drug concentrations of 2-10 micrograms/mL. Comparable results were obtained with human serum albumin solution (45 g/L) indicating that albumin is probably the responsible protein. The extent of binding remained relatively constant for drug concentrations of 0.25-10 micrograms/mL when albumin concentrations were greater than 25 g/L. For albumin concentrations less than 10 g/L, the extent of binding tended to decrease with increased drug concentration. This concentration (10 g/L) is substantially lower than that usually observed in plasma or synovial fluid of arthritic patients. Curvature of the Scatchard plot indicated the existence of two classes of sites. Excellent results were obtained from fitting of the data according to two classes of sites (r2 greater than 0.999). Parameter estimates (SEM) of the number of binding sites, n1 and n2, and the corresponding association constants, k1 and k2, were 2.26 (0.55), 10.20 (0.69), and 1.32 (0.54) X 10(5) M-1, and 3.71 (1.11) X 10(3) M-1, respectively. Simultaneous samples obtained from arthritic patients indicate considerably higher total protein and albumin concentrations in plasma compared with synovial fluid, but the albumin:total protein ratios were essentially the same. There was very little difference in plasma binding in arthritic patients compared with normal subjects. The extent of binding in synovial fluid samples was consistently lower than that for plasma samples (mean +/- SD of 99.5 +/- 0.2% versus 99.7 +/- 0.1%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Transsynovial distribution and protein binding of pirazolac in patients with rheumatoid arthritis

Summary Following a washout period of 7 days, twenty-one patients suffering from rheumatoid arthritis and 3 from osteo-arthritis, who all required articular puncture were given a non-steroidal anti-inflammatory drug pirazolac 450 mg b.d. for 7 days. After discontinuation of the treatment the subjects were divided into 4 groups each of 6 patients.The non protein bound fraction of pirazolac in synovial fluid (0.86%) was significantly higher than that in plasma (0.53%). The average pirazolac concentration in plasma within the dosing interval fluctuated between 30.9 µg/ml and 59 µg/ml, and in synovial fluid between 16.6 µg/ml and 29.9 µg/ml. The half-life of pirazolac calculated from the measured and interpolated data from all patients was 30.9 h in plasma and 66.2 h in synovial fluid. The absolute free concentrations in plasma and synovial fluid (approx. 250 ng/ml) were in the range of the IC₅₀-values for inhibition of cyclooxygenase in mouse peritoneal macrophages.     

Integrated plasma and synovial fluid pharmacokinetics of tenoxicam in patients with rheumatoid arthritis and osteoarthritis: factors determining the synovial fluid/plasma distribution ratio

Single oral doses of 40 mg of the nonsteroidal antiinflammatory drug, tenoxicam, were given to four patients (three with rheumatoid arthritis, one with osteoarthritis). The concentrations of the drug in synovial fluid and plasma were measured by a specific high-performance liquid chromatography method. The unbound fractions of the drug in both fluids were determined at pH 7.4 and 37 degrees C by equilibrium dialysis. The possible influence of the pH on the protein binding was also assessed. The total concentration time curves in plasma and synovial fluid were fitted to linear oral 1 and 2 compartment body models with an additional synovial fluid compartment connected to the central compartment. The unbound fractions of drug in synovial fluid and plasma were on average 0.015 and 0.011, respectively: not significantly different from each other. The protein binding of tenoxicam was pH dependent with increased free fractions at pH values less than 7.4. The average peak concentrations of tenoxicam in plasma and synovial fluid were 4.3 and 1.4 micrograms/ml, respectively. The mean ratio of the areas under the total concentration time curves in synovial fluid and plasma was 0.42, which corresponded to the steady state of equilibrium ratio of the total drug concentrations in the two body fluids. Two hypotheses were tested: hypothesis I assuming that equilibration across the synovial tissue takes place between the unbound, unionized tenoxicam molecules; hypothesis II assuming that equilibration across the synovial tissue is established between the unbound (unionized + ionized) tenoxicam molecules. Based on the available evidence hypothesis II was rejected.     

Plasma protein binding of prednisolone in normal volunteers and arthritic patients

Summary The plasma binding of prednisolone was studied in twenty normal volunteers and twenty rheumatoid arthritis patients. An in vitro assessment of the binding following the addition of prednisolone, prednisone, and hydrocortisone to the plasmas obtained from the subjects showed significant differences in the percentage of prednisolone bound. However, the differences observed were regarded as clinically insignificant. The plasma protein binding was determined by an in vitro equilibrium dialysis of the individual plasma samples at 37° C. Prednisolone levels on both sides of the dialysis membrane were determined using radioactivity and HPLC analytical methodologies. The percentages of prednisolone bound calculated from the analytical results of either the radiochemical or HPLC method were not significantly different. The change in the percentage of prednisolone bound to plasma proteins was studied as a function of the total prednisolone plasma concentration in a normal volunteer and in a systemic lupus erythematosis patient. As a result of prednisolone binding to both transcortin and albumin, the binding of prednisolone changes as a function of prednisolone concentration. The binding data were fitted using nonlinear least squares regression, and the affinity constants for the binding of prednisolone to transcortin and albumin were estimated.     

Aspirin and sodium salicylate inhibit proliferation and induce apoptosis in rheumatoid synovial cells

Aspirin has been reported to induce apoptosis in a variety of cell lines. In this study, we examined whether aspirin and sodium salicylate inhibit cell growth and induce apoptosis in rheumatoid synovial cells. Synovial cells were obtained from patients with rheumatoid arthritis, and the cells were treated with aspirin or sodium salicylate (0.1-10 mM) for 24 h. Cell proliferation and viability were assessed by 5-bromo-2'-deoxyuridine incorporation and by 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) assay, respectively. The apoptosis of synovial cells was identified by DNA fragmentation assay and terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay. Aspirin and sodium salicylate suppressed the proliferation (IC50 (concentration causing 50% inhibition of cell proliferation): 2.1 and 1.2 mM, respectively) and reduced the viability (IC50: 2.0 and 1.4 mM, respectively) of synovial cells in a concentration-dependent manner at 0.3-10 mM. Furthermore, they induced DNA fragmentation and increased the number of TUNEL-positive synovial cells. These results suggest that aspirin and sodium salicylate can inhibit the proliferation of rheumatoid synovial cells through induction of apoptosis.     

Concentrations of ibuprofen and the protein and pH value of synovial fluid and plasma following oral administration of ibuprofen in patients with arthritis

Concentrations of Ibuprofen and Protein Concentration and pH-Value in Synovial Fluid and Plasma Following Oral Administration of Ibuprofen in Patients Suffering from Arthritis. In 16 patients suffering from arthritis of the knee the concentration of ibuprofen in the synovial fluid was examined in correlation with the synovial fluid volume, cell count, pH value and protein concentration. The mean ibuprofen concentration in plasma 4 h after oral administration of 400 mg ibuprofen amounted to 15.45 micrograms/ml, the concentration in the synovial fluid was 9.4 micrograms/ml. Due to the inflammatory nature of the effusions the protein concentration in the synovial fluid was evidently increased to an average of 4.46 g/dl and thus was about 65% of the mean plasma protein concentration of 6.88 g/dl. The ibuprofen in the synovial fluid showed a correlation to the protein concentration. On the other hand, there were no significant differences between the pH value in the plasma and in the synovial fluid. There was no tendency to an acid pH. Furthermore, there was no correlation between ibuprofen concentration and cell count. The tests showed that the "accumulation" of the nonsteroidal antiinflammatory drug in the synovial fluid is positively correlated with the high protein concentration but not with the pH value.     

Plasma and synovial fluid kinetics of flurbiprofen in rheumatoid arthritis.

Clinical assessment, plasma and synovial fluid kinetics were studied in 29 rheumatoid patients receiving 100 mg flurbiprofen twice daily. Clinical assessment and pharmacokinetic measurements varied widely within the group of patients. The average values for plasma clearance, volume of distribution and elimination halflife of flurbiprofen were 0.65 +/- 0.24 ml min-1 kg-1, 0.160 +/- 0.093 l kg-1 and 3.1 +/- 1.7 h, respectively. Synovial fluid drug concentrations peaked later and were lower than corresponding plasma concentrations: 5.2 h and 4.4 mg l-1 as against 1.49 h and 12.5 mg l-1, respectively. At 48 h after an oral dose of flurbiprofen, all the drug had been cleared from the synovial fluid. Synovial fluid drug concentrations were not related to synovial fluid albumin concentration or pH. There was a weak relationship between synovial fluid drug concentration and the thermographic measurements of disease activity. The fractions of flurbiprofen not bound to protein in synovial fluid and plasma were not significantly different. A simple model is proposed to account for the plasma and synovial fluid pharmacokinetics.