Multiple human serum binding of two thienopyridinic derivatives, ticlopidine and PCR 2362, and their distribution between HSA, alpha1-acid glycoprotein and lipoproteins

The Binding of Two Dihydropyridines to Isolated and Native Plasma Lipoproteins

The objectives of this study were to investigate the mechanisms involved in the interaction of two calcium antagonists, isradipine and amlodipine, with isolated lipoprotein fractions in-vitro and to determine the distribution of isradipine among individual plasma lipoproteins ex-vivo in healthy volunteers (n = 8) and in hypercholesterolaemic patients (n = 12).

The total binding affinity of isradipine to isolated low density lipoprotein (LDL) was markedly higher compared with amlodipine; total binding affinity (nKa) of isradipine vs amlodipine was 1·60 ± 0·08 times 107 vs 4·14 ± 0·33 times 106  m-1, respectively. Binding to high density lipoprotein (HDL) was also higher with isradipine, nKa = 1·04 ± 0·04 times 105  m−1, compared with that of amlodipine, nKa = 3·82 ± 0·18 times 104  m−1. The distribution study ex-vivo demonstrated the different relative affinity of isradipine for the plasma lipoproteins: HDL > LDL > very-low density lipoprotein (VLDL). Isradipine binding correlated linearly with the cholesterol levels in LDL and VLDL; however, binding to HDL did not correlate with the cholesterol level in this fraction. There was no significant competitive binding effect of cyclosporin A (1–5 μgmL−1) on isradipine binding to individual lipoprotein fractions.

It is likely that, in addition to the structure of surface apoproteins, the factors determining the interaction of calcium antagonists with plasma lipoproteins also include the plasma level of each lipoprotein fraction as well as the lipophilicity of the drug.

Human alpha-1-glycoprotein and its interactions with drugs

For about half a century, the binding of drugs to plasma albumin, the "silent receptor," has been recognized as one of the major determinants of drug action, distribution, and disposition. In the last decade, the binding of drugs, especially but not exclusively basic entities, to another plasma protein, alpha 1-acid glycoprotein (AAG), has increasingly become important in this regard. The present review points out that hundreds of drugs with diverse structures bind to this glycoprotein. Although plasma concentration of AAG is much lower than that of albumin, AAG can become the major drug binding macromolecule in plasma with significant clinical implications. Also, briefly reviewed are the physiological, pathological, and genetic factors that influence binding, the role of AAG in drug-drug interactions, especially the displacement of drugs and endogenous substances from AAG binding sites, and pharmacokinetic and clinical consequences of such interactions. It can be predicted that in the future, rapid automatic methods to measure binding to albumin and/or AAG will routinely be used in drug development and in clinical practice to predict and/or guide therapy.

Pharmacokinetics of ticlopidine in the rabbit

There is no information about the pharmacokinetics of ticlopidine in rabbits. Such information is valuable in designing appropriate dosing regimens for experimental studies of the drug with ultimate applications in man. The disposition kinetics of ticlopidine at three dose levels were evaluated in three groups of six rabbits which received 10, 50 or 100 mgkg(-1) drug once daily via the oral-gastric route. Blood samples were collected at predetermined times after the third dose. Plasma concentrations of the unchanged drug were determined by a validated liquid chromatography-mass spectrometry method with a limit of detection of 5 microg L(-1). There was a disproportionate increase in the mean maximum plasma concentration (Cmax) and the area under the plasma drug-concentration-time curve (AUC) for the 10 and 50 mgkg(-1) doses. The apparent terminal half-life (t1/2beta), apparent volume of distribution (Vdbeta/F), and total plasma clearance (CLp/F) of the drug were all dose-dependent. For example, t1/1beta for the 10, 50 and 100 mgkg(-1) doses were 1.04+/-0.10, 4+/-24+/-1.92 and 12.80+/-6.35 h, respectively, whereas the Vdbeta/F values for the corresponding doses were 214 31, 475 221 and 998+/-420 Lkg(-1), respectively. These results show that the 100-mgkg(-1) dose produces plasma ticlopidine concentrations similar to those found in man after administration of 250 mg of the drug. It is suggested that 100 mg kg(-1) might be the appropriate dose of ticlopidine for use in rabbit experimental studies with ultimate application to man.

Differences in the lipoprotein binding profile of halofantrine in fed and fasted human or beagle plasma are dictated by the respective masses of core apolar lipoprotein lipid

Halofantrine hydrochloride (Hf) is an orally active, highly lipophilic antimalarial indicated for the treatment of multi-drug resistant Plasmodium falciparum. In this study, we have examined the binding profile of Hf to the various classes of human and beagle plasma lipoproteins as such interactions have been implicated in a post-prandial plasma lipoprotein-induced decrease in the total clearance and volume of distribution of Hf. The distribution of Hf within plasma was dominated by interaction with the various classes of plasma lipoproteins, and the characteristics and extent of binding were markedly different between species and between pre- and post-prandial plasma. In an attempt to understand the basis for the differential binding of Hf to the various lipoprotein fractions, the relationship between the proportion of Hf associated with each lipoprotein fraction (as a function of the respective mass of protein, triglyceride, cholesterol, and phospholipid) was investigated. The data indicated that the distribution of Hf between plasma lipoproteins was highly correlated with the apolar lipid load of individual plasma lipoprotein fractions suggesting that the mechanism of association was primarily via solubilization in the lipoprotein apolar lipid core. These data suggest that acute changes in plasma lipoprotein profiles, such as encountered post-prandially or in disease states such as malaria, will likely have an impact on the plasma lipoprotein binding of Hf.

Antioxidant properties of ticlopidine on human low density lipoprotein oxidation

We found that ticlopidine, at therapeutically relevant concentrations (2.5-10 microM), but not aspirin nor salicylate, significantly counteracted copper-driven human LDL oxidation. Ticlopidine, at 5 and 10 microM, was also antioxidant on peroxyl radical-induced LDL oxidation; yet it was ineffectual on thiol and ascorbate oxidation mediated by peroxyl radicals themselves, suggesting that drug antioxidant capacity is somehow related to the lipoprotein nature of the oxidizable substrate, but not to radical scavenging. The drug could not indeed react with the stable free radical 1,1-diphenyl-2-pycrylhydrazyl, nor had apparent metal complexing-inactivating activity. Thus, ticlopidine has antioxidant effects on LDL oxidation, which, together with its anti-platelet activity, could confer peculiar antiatherogenic properties to the drug in vivo.

Pharmacokinetics of KRM-1648, a new benzoxazinorifamycin, in rats and dogs

The pharmacokinetics of 3'-hydroxy-5'-(4-isobutyl-1-piperazinyl) benzoxazinorifamycin (KRM-1648) in rats and dogs given a single oral dose of 3, 30, or 100 mg/kg of body weight were studied. In the rats, the concentrations of KRM-1648 in plasma, whole blood, and tissues peaked between 2.0 and 24.0 h, with elimination half-lives ranging from 6.2 to 19.5 h. The peak concentrations and the areas under the concentration-versus-time curves (AUC) for whole blood and tissues were 2 to 277 times higher than those for plasma. The high levels of KRM-1648 in tissues were consistent with its large volume of distribution (in excess of 10 liters/kg). A nonlinear increase in peak concentrations and AUCs for plasma, whole blood, and tissues occurred as the dose was increased and was consistent with the dose-dependent decrease in bioavailability. In the dogs, KRM-1648 levels in plasma and whole blood also exhibited a late time to the peak concentration (ranging from 4.0 to 11.2 h), a long elimination half-life (ranging from 15.2 to 24.0 h), and nonlinear kinetics. KRM-1648 exhibited high levels of plasma protein binding (more than 99%) and a high degree of affinity for lipoproteins in the plasma of both animals. After administration of KRM-1648, measurable levels of its metabolites, 25-deacetyl KRM-1648 in rats and 25-deacetyl KRM-1648 and 30-hydroxy KRM-1648 in dogs, were found in the biological samples tested. Thus, KRM-1648 is characterized by a high tissue affinity, a long elimination half-life, and nonlinear pharmacokinetics.

Stereoselective binding of tertatolol and of 4-hydroxytertatolol to human plasma proteins

The binding of racemic tertatolol and 4-hydroxytertatolol and of their enantiomers was compared in alpha 1-acid glycoprotein and albumin solutions. The binding rate of S(-)tertatolol to alpha 1-acid glycoprotein was much greater than that of R(+)tertatolol, the binding of the racemate being intermediate. It was the reverse for the binding to albumin, although the differences were slight. The binding of 4-hydroxytertatolol racemate and enantiomers was very low as compared to the binding of tertatolol, and there were no statistically significant differences in the binding of the 4-hydroxytertatolol enantiomers to either alpha 1-acid glycoprotein or albumin.

The blood binding of cefotiam and cyclohexanol, metabolites of the prodrug cefotiam hexetil, in-vitro

The binding of cefotiam and cyclohexanol to human serum, isolated proteins and erythrocytes has been studied in-vitro by equilibrium dialysis. The two molecules are 50% bound to serum proteins and the free fraction for both compounds remained constant within the therapeutic concentration range. Human serum albumin (HSA) was exclusively responsible for the cefotiam binding (48%) with a saturable process characterized by one binding site (n = 1.00 +/- 0.14) with a very weak affinity (Ka = 1457 +/- 352 M-1). Like other cephalosporins, cefotiam showed no binding to alpha 1-acid glycoprotein, lipoproteins or gamma-globulins. Cyclohexanol is mainly bound to HSA with a weak affinity (Ka approximately 1,800 M-1) but lipoproteins and alpha 1-acid glycoprotein bind about 30% of bound cyclohexanol in serum. Interactions with free fatty acids (FFA) or bilirubin were studied at physiopathological concentrations. HSA-bound cefotiam was displaced by FFA (1260 microM) and bilirubin (330 microM), whereas the cyclohexanol binding was inhibited only by FFA. The cefotiam binding site seems to be close to the warfarin site (site I) whereas cyclohexanol probably shares the diazepam site (site II) on HSA. There is no mutual inhibition of binding between cefotiam and cyclohexanol at therapeutic levels. The binding of both compounds to erythrocytes is low and restricted when measured in the presence of plasma.

Use of 1-anilino-8-naphthalene sulfonate as a fluorescent probe in the investigation of drug interactions with human alpha-1-acid glycoprotein and serum albumin

We report a rapid method for the characterization of the human serum albumin (HSA) and alpha-1-acid glycoprotein (AAG) interactions with drugs. The binding of 1-anilino-8-naphthalene sulfonate (ANS) to AAG and HSA was measured by fluorescence spectroscopy. Fluorescence data indicated that ANS was bound tightly to at least one site on AAG, with an affinity constant of 1.35 x 10(6) M-1. The fluorescence of an ANS:AAG complex was quenched by the binding of various drugs. Fluorescence quenching of the HSA:ANS complex showed a single site with an affinity constant of 0.72 x 10(6) M-1. The interaction of AAG and HSA with ANS or other drugs was also studied by comparative equilibrium dialysis. [14C]Pipequaline was used as an AAG and HSA site marker. [14C]Pipequaline seems to share sites I (azapropazone) and II (diazepam and ibuprofen) of HSA. However, high concentrations of warfarin were unable to displace [14C]pipequaline. On the other hand, it was shown that palmitic acid decreased, whereas bilirubin increased the pipequaline binding.

Tianeptine binding to human plasma proteins and plasma from patients with hepatic cirrhosis or renal failure

1. The binding of tianeptine to human plasma, isolated plasma proteins, red blood cells and to plasma from patients with cirrhosis or renal failure was studied in vitro by equilibrium dialysis. 2. Tianeptine is highly bound to plasma (95%) at therapeutic concentrations (0.3-1 microM). No saturation of the binding sites was seen. 3. Human serum albumin (HSA) was shown to be mainly responsible for this binding (94%) with a saturable process characterized by one binding site with a moderate affinity (Ka = 4.2 x 10(4) M-1) and a non-saturable process with a low total affinity (nKa = 1.2 x 10(4) M-1). 4. Like many basic and amphoteric drugs, tianeptine showed a saturable binding to alpha 1-acid glycoprotein (AAG) with one site and a moderate affinity (Ka = 3.7 x 10(4) M-1). Its binding to lipoproteins and red blood cells (RBC) was weak and non-saturable. Over the range of therapeutic drug concentrations (0.3-1 microM), the unbound fraction in blood remains constant (4.5%). 5. Interactions were studied using non-esterified fatty acids (NEFA) at pathological concentrations; they altered tianeptine binding to plasma and to isolated HSA. Tianeptine seems to bind to a HSA site different from sites I (warfarin) and II (diazepam), but close to site II. It also shares the only basic-site on AAG. However, at therapeutic drug concentrations (0.3-1 microM), not all of these interactions occur. 6. The binding of tianeptine varied according to HSA, AAG and NEFA concentrations both in patients and healthy subjects. In patients with chronic renal failure having high NEFA concentrations the unbound fraction of tianeptine (fu) increased from 0.045 to 0.153 compared with normal (P less than 0.001). In cirrhotic patients, with relatively low HSA concentrations, the fu of tianeptine increased from 0.045 to 0.088 compared with normal (P less than 0.01). 7. Multiple regression analysis of all of the data indicated that the fu of tianeptine was related significantly to HSA, NEFA and AAG concentrations, with a particularly strong correlation with NEFA concentrations. Therefore, variation of HSA and NEFA concentrations in patients on maintenance therapy may cause an increase of tianeptine fu.

Pipequaline transport from blood to brain and liver: role of plasma protein-bound drug

Brain uptake of pipequaline (45319 RP) has been studied in-vivo after a single capillary transit by intracarotid injection to rats. Pipequaline is extensively bound to plasma proteins: i.e. human serum albumin (HSA), alpha-1-acid glycoprotein (AAG), lipoproteins and blood cells, mainly erythrocytes. The dialysable drug fraction as measured in-vitro by equilibrium dialysis at 37 degrees C, was inversely related to the concentration of binding component. Similarly, the brain uptake of pipequaline was inversely related to the protein concentration of the injected solution. However, the measured brain uptake of pipequaline was higher than those predicted by in-vitro measurements of dialysable drug for all proteins and erythrocytes, except HSA. These results show that a fraction of bound pipequaline as measured in-vitro is available for transport through the blood brain barrier. HSA-bound pipequaline is an exception as it is restricted to the vascular space. Pipequaline was totally cleared by the liver through a single passage.

Blood distribution of tenoxicam in humans: a particular HSA drug interaction

Blood binding of tenoxicam was studied in vitro by equilibrium dialysis. Isolated human plasma proteins and blood cells were checked, and the distribution of the bound form was then calculated. The results showed that tenoxicam is mainly bound to HSA and that binding percentages are not different when measured in plasma (98.4%) and in an HSA solution at physiological concentration (704 microM, 98.15%). In these conditions, within the range of 1-150 microM, the tenoxicam binding percentage remained constant, evidence of a nonsaturable process. When a lower HSA concentration (10 microM) was used, the binding parameters of the tenoxicam interaction were calculated by using the same equilibrium dialysis data, by 3 methods of analysis- a stoichiometric method and site-oriented methods, fixing or not the number of HSA binding sites (n) as integer values. The best fit was observed with the first method, suggesting that two main interactions occurred. The site-oriented method gave lesser fits, the better being observed when n was not fixed. Its value, 1.77, suggest the possibility of two binding sites, one of them not preformed. The effects of known markers of site I, warfarin and apazone, of site II, diazepam and ibuprofen and of palmitic acid showed that tenoxicam is bound simultaneously to both sites I and II. The binding capacity of site I for tenoxicam is enhanced by diazepam: as this compound alone is bound to site II, this result suggests that the two HSA binding sites are not independent.

Effects of the binding of imipramine to erythrocytes and plasma proteins on its transport through the rat blood-brain barrier

Brain extraction of a tricyclic antidepressant, imipramine, was investigated using the carotid injection technique in the rat. The extent to which drug binding to plasma proteins and erythrocytes could inhibit the brain extraction was measured. Equilibrium dialysis showed that imipramine is highly bound to human serum albumin (HSA), alpha 1-acid glycoprotein (AAG), lipoproteins, and erythrocytes. The free dialyzable drug fraction was inversely related to the protein concentration. Despite this degree of binding, no significant reduction in the brain extraction of the drug was observed in the presence of HSA, lipoprotein, or erythrocytes. Only AAG reduced the brain transport of this drug in a ratio related to the protein concentration. However, the rat brain extraction was higher than expected from the in vitro measurement of the dialyzable fraction. These data indicate that the amount of circulating imipramine available for penetration in brain exceeds widely the dialyzable fraction of the drug as measured in vitro.

Binding of indapamide to serum proteins and erythrocytes

The binding of indapamide to isolated serum proteins and erythrocytes was studied in order to understand its blood distribution. In serum, indapamide was mainly bound to alpha 1-acid glycoprotein with a high affinity (K = 73.4/mM), and to albumin and lipoproteins. Indapamide was bound to erythrocytes via a saturable process with a high affinity (K = 385/mM and N = 57 microM for an hematocrit value of 0.48), and erythrocytes were the main binding component in blood (more than 80% of indapamide was associated to erythrocytes in blood). The binding to serum proteins affected indapamide distribution in blood, and alpha 1-acid glycoprotein was shown to be the more effective protein in decreasing the amount of indapamide associated to erythrocytes.

Cicletanine binding to human plasma proteins and erythrocytes, a particular HSA-drug interaction

The binding of cicletanine to human serum, isolated proteins and red blood cells was studied in vitro by equilibrium dialysis. Our results show this drug is highly bound to serum (97.3%) at therapeutic levels. No saturation to the binding sites was seen. Human serum albumin was shown to mainly responsible for this binding (93.5%) with a saturable process characterized by one binding site with a moderate affinity (K = 75800 M-1) and a non saturable process with a low total affinity (nK = 6400 M-1). Like many basic lipophilic drugs, cicletanine showed a saturable binding to alpha-1-acid glycoprotein with one site and a moderate affinity (K = 38,800 M-1). Its binding to lipoproteins and red blood cells was weak and non saturable. Over the range of therapeutic concentrations, the unbound fraction in blood remains constant (3.6%). Moreover, interactions were studied using bilirubin and non esterified fatty acids at pathological concentrations and these endogenous compounds did not alter cicletanine binding human serum or to human serum albumin likewise cicletanine shared the diazepam-site on HSA but no inhibition could take place between cicletanine and the drugs sharing the same binding site in serum at therapeutic levels.

Binding in vitro of pipequaline (45319 RP) onto plasma proteins and blood cells in man

Serum binding of pipequaline, a new anxiolytic drug, was studied in vitro by equilibrium dialysis. The percent binding in serum is high, 96.3%, and remains constant within the range of therapeutic concentrations. Investigations performed on isolated proteins with a wide range of concentrations showed one site with a high affinity constant (Ka = 450,000 M-1) for alpha 1-acid glycoprotein and two sites with a lower affinity constant (Ka = 58,000 M-1) for human serum albumin. Binding to lipoproteins was saturable, with an affinity constant of 22,000 less than or equal to Ka less than or equal to 35,000 M-1. Over the range of therapeutic concentrations, the ratio of pipequaline concentrations in serum and red blood cells remained constant (14.4%) and was shown to be dependent on the free fraction of pipequaline in serum.

Effect of erythrocytes and plasma protein binding on the transport of progabide and SL 75102 through the rat blood-brain barrier

Brain extraction of two antiepileptic compounds, progabide and its acid metabolite, SL 75102, was investigated using the carotid injection technique in the rat. The extent to which drug binding to plasma proteins could inhibit the brain extraction was measured. Equilibrium dialysis at 4 degrees showed that both drugs were highly bound to human serum proteins, mainly to serum albumin. Progabide is also bound to red blood cells and to lipoproteins. The free dialyzable drug fraction was inversely related to the protein concentration. Similarly, the brain extraction of the drugs in the presence of either albumin, or red blood cells for progabide was inversely related to their respective concentrations. However, the rat brain extraction of both drugs was higher than expected from the in vitro measurement of dialyzable fraction. Furthermore, despite a significant degree of progabide binding to lipoproteins, no significant reduction in the brain extraction of the drug was observed. These data indicate that the amount of circulating progabide or SL 75102 available for penetration in a peripheral tissue such as brain exceeds the dialyzable fraction of drug. However, the in vivo exchangeable drug fraction still parallels the dialyzable fraction, except if the drug is lipoprotein-bound.

Binding of 8-methoxypsoralen to human serum proteins and red blood cells

Serum binding of 8-methoxypsoralen (8-MOP) was studied by equilibrium dialysis. In therapeutic concentrations, 8-MOP binding in serum was high, 91.4%, and constant, indicating concentration-independent kinetics. This binding involved the two main proteins, human serum albumin and alpha 1-acid glycoprotein, in a saturable process with one class of binding sites (n) and affinity constants (Ka) of 1.295 X 10(4) mol/l and 2.115 X 10(4) mol/l, respectively. Binding to lipoproteins and gamma globulins was negligible and non-saturable in therapeutic concentrations, with nKa values of 0.35, 0.024, 0.013 and 0.0004 mumol/l for VLDL, LDL, HDL and gamma globulins, respectively. Inhibition of 8-MOP serum binding was observed with salicylic acid and indomethacin, but not with diazepam, warfarin or erythromycin. Over a range of therapeutic concentrations, the ration of 8-MOP concentration in red blood cells (RBCs) and in serum was constant at 20.3% and three times higher than would be expected if a simple diffusion of the 8-MOP plasma free fraction (fu) occurred. According to the measured and calculated parameters, simulations of 8-MOP blood binding in pathological states (hypoalbuminaemia with or without inflammation) showed variations of fu which were partially 'buffered' by RBCs. Simulation of 8-MOP protein binding at cutaneous interstitial fluid level showed that fu is approximately 30% and permitted prediction of a decrease of fu available to the epidermis in case of local or systemic inflammation. This may imply an increase in the minimum phototoxic dose relevant for PUVA and explain some cases of 'poor' responsiveness of psoriatic patients to PUVA therapy.

Binedaline binding to plasma proteins and red blood cells in humans

Serum binding of binedaline, a new antidepressant drug, was studied in vitro by equilibrium dialysis. The percent of binding in serum is high, 99.2%, and remains constant within the range of therapeutic concentrations; no saturation to the binding sites was seen. Investigations performed on isolated proteins with a wide range of concentrations showed one site with a high affinity constant (Ka = 2 X 10(6) M-1) for alpha 1-acid glycoprotein and two sites with a low affinity constant (Ka = 3 X 10(4) M-1) for human serum albumin. Binding to lipoproteins was nonsaturable, with a total affinity constant of 1.25 X 10(5) less than nKa less than 2.79 X 10(6) M-1. Over the range of therapeutic concentrations, the ratio of binedaline concentrations in serum and red blood cells remained constant (1%) and was shown to be dependent on the free fraction of binedaline in serum.

Diclofenac binding to albumin and lipoproteins in human serum

The binding of diclofenac to human serum albumin (HSA) and to lipoproteins was studied in vitro by equilibrium dialysis. Binding to HSA is characterized by two classes of sites with one site each (K1 = 5 X 10(5) M-1 and K2 = 0.6 X 10(5) M-1). The binding to lipoproteins was shown to be saturable with a larger number of binding sites and low association constants. The evidence of two specific binding sites on HSA was confirmed by circular dichroism data. In addition, an identification of those sites was performed by displacement of fluorescent probes. The data show that the high affinity site (K1 = 5 X 10(5) M-1) is likely to be shared by benzodiazepines while the second one (K2 = 0.6 X 10(5) M-1) is common with the warfarin site.

Binding of clometacin to human serum albumin. Interactions with clofibrate, indomethacin, salicylic acid and warfarin

The binding of clometacin to human serum albumin (HSA) was studied in vitro by equilibrium dialysis. Our results show that binding to HSA is 99% at therapeutic levels. Binding is characterized by several numbers of binding sites (n = 8) with a moderate association constant (K = 2.7 X 10(4) M-1) and by another non-saturable phenomenon (nK = 4200 M-1). Moreover, interactions were studied with many drugs. Clometacin binding was altered by indomethacin, warfarin, chlorophenoxyisobutyrate (CPIB) and salicylic acid (SA). Conversely, clometacin inhibited the binding of these drugs. Finally, all these results were compared with those previously obtained with indomethacin, a positional isomer of clometacin.

Plasma protein binding of the reversible type A MAO inhibitor cimoxatone (MD 780515)

Binding of a new selective reversible type A MAO inhibitor cimoxatone (MD 780515) to plasma proteins was studied in vitro by equilibrium dialysis. Binding to 580 microM human serum albumin (HSA) and to total plasma proteins was 93-96% and independent of cimoxatone concentration (0.15-207 microM). The drug was mainly bound to HSA with two binding sites and a moderate association constant (K = 2.9 X 10(4) M-1). Free fatty acids did not modify cimoxatone binding to HSA. Cimoxatone was also moderately bound to isolated lipoprotein fractions; alpha 1-acid glycoprotein and gamma-globulins did not play an important role in the binding of cimoxatone. MD 770222, the O-demethyl metabolite, appeared to be bound to HSA at the same binding sites as cimoxatone. However, no interaction occurred between the two compounds for 580 microM HSA. L-Tryptophan, bilirubin, the benzodiazepines flunitrazepam and oxazepam, imipramine and aspirin, did not displace cimoxatone from its binding sites. On the other hand, warfarin and phenylbutazone decreased cimoxatone binding to 29 microM HSA but no interaction occurred with 580 microM HSA.