Absorption of surfactants by membranes: erythrocytes versus synthetic vesicles

Three surfactants (chlorpromazine hydrochloride, thioridazine hydrochloride, and sodium deoxycholate) are found to absorb just as strongly into the protein-containing membranes of erythrocytes as into the phospholipid bilayers of synthetic vesicles. In the concentration region where hemolysis occurs and the Langmuir adsorption isotherm is no longer valid, one may use a phase partition model in which the erythrocyte membrane is one of the phases. The partition coefficients, expressed as the ratio of mole fraction surfactant in the membrane lipid phase to concentration of surfactant in the aqueous phase, have been calculated at the point of saturation in the erythrocyte membrane. These values are Ky = 430 M-1 (chlorpromazine, pH 5.9), 550 M-1 (deoxycholate, pH 7.6), and 640 M-1 (thioridazine, pH 5.9), in isotonic buffer at 27 degrees C. Corresponding values for synthetic vesicles made from dimyristoylphosphatidylcholine are Kx = 230 M-1 (chlorpromazine, 0.12 M buffer/KCl pH 5.9), 440 M-1 (deoxycholate, 0.20 M buffer/NaCl pH 8.0) and 510 M-1 (thioridazine, 0.12 M buffer/KCl pH 5.9), at 27 degrees C. It appears that the surfactants become an integral part of the bilayer in both vesicles and natural membranes and that the absorption is not of a peripheral nature. There is no evidence that the presence of proteins in the natural membrane inhibits the absorption of these surfactants in any way.

Interaction of chlorpromazine with myoglobin and hemoglobin. A comparative study

The mode and nature of the binding of chlorpromazine (CPZ), a psychotropic drug, with myoglobin, a monomeric muscle protein, were studied spectrofluorometrically and the results compared with those from the binding of CPZ to hemoglobin, a tetrameric allosteric protein from red blood cells (RBC). CPZ interacted with myoglobin in a non-cooperative mode, with a binding constant of 8.4 x 10(3) M-1 in 0.145 M NaCl, pH 6.8, whereas in the case of hemoglobin this interaction was found to be positively cooperative with a binding constant of 4.2 x 10(3) M-1. The interaction of CPZ with myoglobin was not influenced by the NaCl molarity of the solution, whereas CPZ interaction with hemoglobin significantly decreased with increasing NaCl molarity, indicating that CPZ-hemoglobin binding is mostly electrostatic in nature, whereas that of the CPZ-myoglobin complex is of a non-electrostatic type. Thermodynamic analysis revealed that binding of CPZ to hemoglobin was exothermic (delta H degrees = -2.65 kcal/mol), whereas binding to myoglobin was endothermic (delta H degrees = + 1.39 kcal/mol) with a high entropic contribution (delta S degrees = +23 cal/degree/mol), suggesting that CPZ binding to myoglobin is hydrophobic in nature. Such contrasting binding features of this drug have been discussed in the light of a typical subunit interaction property present and absent in hemoglobin and myoglobin, respectively.

Preparation of agglomerated crystals for direct tabletting and microencapsulation by the spherical crystallization technique with a continuous system

Adhesive and cohesive properties of chlorpromazine hydrochloride (CP) crystals were modified to improve their powder processing, e.g., direct tabletting and microencapsulation, by agglomeration. Moreover, sustained-released gelling microcapsules of CP were devised to prolong the pharmacological effect. The spherical crystallization technique was applied to prepare agglomerates for direct tabletting and microencapsulation to use them as core materials. The ethanolic solution dissolving CP was poured into a stirred cyclohexane, yielding spherically agglomerated crystals. The resultant agglomerates were free-flowing and easily packable spheres with average diameters of 200 to 1000 microns. The agglomerates reserved the high compressibility of the original powder having a small particle size (14 microns). The compression behavior represented by Heckel's equation suggested that the agglomerates were disintegrated to individual primary crystals at low compression pressures, and then they were closely repacked and plastically deformed at higher pressures. After agglomeration, microencapsulation was continuously performed in the same batch by a phase separation method. Coacervate droplets produced by pouring cyclohexane into a dichloromethane solution, dissolving polyvinyl acetate as a coating polymer, were added to the crystallization system under stirring, to prepare the microcapsules. By filling the microcapsules in gelatin hard capsules or tabletting them, their drug release rates became retarded compared with the physical mixture treated in the same way, having the same formulation as the microcapsules. This phenomenon was due to the gelation of polyvinyl acetate of the microcapsules in the dissolution medium, whose glass transition temperature is very low. This novel sustained-release dosage form is termed "gelled microcapsules."

23Na- and 1H-NMR studies of the action of chlorpromazine and imipramine on nigericin-mediated Na+ transport across phosphatidylcholine vesicular membranes

In order to elucidate the action of chlorpromazine (CPZ) and imipramine (IMP) on nigericin-mediated Na+ transport across phosphatidylcholine vesicular membranes, 23Na nuclear magnetic resonance was applied to the exchange system of Na+ ions present at the same concentration inside and outside unilamellar vesicles. CPZ and IMP added to the vesicles in micromolar concentrations produced an equal increase in the carrier-transport rate. The kinetic analysis, together with 1H-NMR observations of the reduction in membrane fluidity produced by the drugs and on the direct interaction between drugs and nigericin, allowed us to conclude that the drug-induced promotion of transport occurred not from the formation step of the Na(+)-nigericin complex nor from its diffusion step, but from its dissociation step. The formation of an adduct between drug and nigericin could be the cause of the drug effect and this proceeded much more efficiently at a membrane-water interface (stability constant Kb; 3 x 10(5) M-1) than in methanol (Kb; 5 x 10(2) M-1). The reason for the difference is also discussed.

ESR study of membrane perturbation and the lysis of liposomes induced by chlorpromazine

The mechanism of interaction between chlorpromazine (CPZ) and artificial lipid membranes, negatively or positively charged liposomes was studied by an electron spin resonance (ESR) technique. Analysis by a 5-doxyl stearic acid (DS) spin probe indicated that regardless of the electric charge of liposomes, CPZ disordered the hydrophobic region near the surface of lipid membranes at CPZ/lipid > 1. In the same CPZ/lipid range, the lysis of liposomes was observed, and it was considered that the formation of the CPZ/lipid mixed micelles as a consequence of this collapse of liposomes would probably lead to the disordering of the 5-DS reporting region. As to the middle portion of the fatty acyl chains reported by the 12-DS spin probe, the membrane disordering action of CPZ was only detected with the negatively charged liposomes at a ratio of CPZ/lipid < 1, but no membrane alteration was observed with the positively charged liposomes, regardless of the concentration range of CPZ used. In comparing these two opposite results, it is conceivable that the disordering at the 12-DS reporting region was probably induced by the cationized CPZ which would enter into the hydrocarbon-polar interface, leading to an expansion of the space between the hydrocarbon chains at this area. Also, a strong influence of CPZ on the innermost portion of the lipid bilayers was observed with both the negatively and positively charged liposomes, as reported by the 16-DS probe. This perturbing action presumably occurred when undissociated CPZ molecules penetrated into the center of the bilayers (lipid core), which could have resulted in a reduction of hydrophobic interactions of the lipid molecules.

Pharmacokinetics of chlorpromazine and key metabolites

A study was carried out in 11 healthy young men to investigate the pharmacokinetics of chlorpromazine (CPZ) after a bolus intravenous (i.v.) dose (10 mg) and three single oral doses (25, 50 and 100 mg), with a washout period of two weeks between doses. Plasma levels of CPZ, CPZ N-oxide (CPZNO), CPZ sulfoxide (CPZSO) and both free and conjugated 7-hydroxy-CPZ (7-HOCPZ) were measured by extraction radioimmunoassays. CPZ exhibited multicompartmental pharmacokinetics in most subjects. There was wide between-subject variability in half life (11.05 h), volume of distribution (1215 l), volume of distribution at steady state (642 l) and mean residence time (8.88 h), whereas systemic clearance was somewhat less variable (76.6 l.h-1). All metabolites were present in measurable concentrations in the plasma of 9 of 11 subjects after i.v. CPZ, whereas free 7-HOCPZ was not detected in the other 2 individuals. With the exception of CPZNO, the biological half lives of the primary metabolites were longer than the half life of CPZ. After oral administration, the percentage of CPZ reaching the systemic circulation intact (F%) was very low (4-38%) and dose dependent. Moreover, both within-subject and between-subject variances were very high. The maximum plasma concentration (Cmax) and area under the plasma concentration versus time curve extrapolated to infinite time (AUC) showed evidence of nonlinearity, whereas half life did not appear to be dose dependent. These data suggest that the high degree of variability in the pharmacokinetics of CPZ is a result of extensive first pass metabolism rather than variation in half life.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoassay reagents for psychoactive drugs. Part 3. Removal of phenothiazine interferences in the quantification of tricyclic antidepressants

Phenothiazines and their metabolites are known to interfere in the quantification of tricyclic antidepressants (TCAs). A method for selective chemical modification of phenothiazines by chloramine-T in the presence of TCAs is described. This method allows for accurate quantification of the TCA analyte in a serum sample without interference from the modified phenothiazine.

Immunoassay reagents for psychoactive drugs. I. The method for the development of antibodies specific to amitriptyline and nortriptyline

Amitriptyline and nortriptyline were structurally modified by the attachment of spacer arms to the aromatic ring which were subsequently attached to bovine serum albumin (BSA). Rabbits inoculated with these conjugates yielded polyclonal antisera with high selectivity and good titers. This approach required novel spacer arms and new conjugation methods. The antisera produced were characterized with respect to their cross-reactivity with amitriptyline, nortriptyline and their hydroxy metabolites as well as selected structurally related compounds.

Interactions between six psychotherapeutic drugs and plastic containers. Influence of plastic material and infusion solutions

The interactions of chlorpromazine, clomipramine, maprotiline and viloxazine hydrochlorides, and of clorazepate dipotassium salt and diazepam with polyvinyl chloride (PVC) and Stedim 6 infusion bags were studied. Stedim 6, is anew multilayer film whose inner layer is made of polyethylene. The drugs were in 5% dextrose and 0.9% sodium chloride isotonic solutions and the influence of these was also considered. The remaining concentrations of each drug were determined at regular time intervals in a 24-h period, by a spectrofluorometric method for chlorpromazine hydrochloride and by ultraviolet spectrophotometric methods for the other drugs. No binding was observed for viloxazine and maprotiline hydrochlorides whatever the infusion solution and the plastic container. A slight retention in PVC bags, but not in Stedim 6 ones, was noted for clomipramine hydrochloride and clorazepate dipotassium salt. This was more marked in the sodium chloride solution than in the dextrose one. Diazepam and chlorpromazine hydrochloride were bound both in PVC and Stedim 6 bags, but more in the former and more again in the sodium chloride solution than in the dextrose one. The results were explained in terms of the degree of crystallinity of the plastic material and the degree of lipophilicity of the drugs. Practical consequences are discussed.

Thiols as potential UV radiation protectors: an in vitro study

The following thiols were investigated with regard to their possible UV-radiation protective properties: captopril, cysteamine, ergothioneine, mesna, mercaptopropionylglycine, N-acetylcysteine, and penicillamine. As a measure for protection, the inhibition of in vitro irreversible photobinding of the labeled phototoxic drugs chlorpromazine (CPZ) and 8-methoxypsoralen (8-MOP) to protein and DNA was used. Besides photobinding to biomacromolecules, the photodegradation of CPZ and the formation of promazine (PZH) and hydroxypromazine (PZOH) were measured as well. Because of the H-atom and electron donating capacity of the thiols, the ratio [PZOH]/[PZH] was expected to be decreased and the photodegradation of CPZ was expected to be higher in the presence of thiols. Maximum inhibition of CPZ photobinding ranged for the different thiols between 21-100% (DNA) and 17-87% (human serum albumin). All thiols enhanced the photodegradation of CPZ (19-84%) and inhibited the ratio [PZOH]/[PZH] (90-97%). 8-MOP photobinding to human serum albumin was also clearly inhibited (75-96%), but remarkably less to DNA (2-41%). This study indicates that thiols are able to cope with a variety of reactive species. Scavenging of radicals, quenching of singlet molecular oxygen species and reaction with excited states seem to be essential mechanisms involved with this process.

Gel filtration chromatographic study on the self-association of surfactants and related compounds

After a brief survey of gel filtration chromatography (GFC) and the self-association equilibrium, it is shown that GFC is a unique tool for investigating the self-association of many substances, such as surfactants, chlorpromazine hydrochloride (CPZ), Methylene Blue (MB) and a sulfobetaine derivative (CHAPS) of cholic acid. The hydrodynamic radius of an aggregate can be estimated with the gel of large pore size, such as Sephadex G-200. This method is utilized for the study of the sphere-rod transition of surfactant micelles. A precise value of monomer concentration can be determined from the centroid elution volume of a frontal chromatogram on Sephadex G-10. This important parameter in self-associating systems allows us to determine the micellar aggregation number as a function of the total surfactant concentration. The derivative chromatogram can be used to detect slight changes in self-association. From these results, it is found that nonionic surfactants form premicelles including dimer and that multiple equilibrium model for micelle formation is more appropriate than mass-action model. The Tanford theory with some modifications appears to fit the concentration dependence of the aggregation properties of surfactants forming small globular micelles and allows us to estimate the stepwise aggregation constant and the micelle size distribution function. The pronounced cooperativity in the self-association of surfactants forms the basis of mass action model and the concept of the cmc, though they are actually approximations even for surfactants. They would be more inadequate, though often used, for the self-association of drugs and bile salts. The stepwise aggregation constant of MB is almost independent of aggregation numbers, which may be expected from the stacking mode of aggregation. The main aggregates of CPZ in 154 mM sodium chloride solution are dimer and 38-mer and its dimerization constant is smaller than that of MB and larger than those of surfactants. The stepwise aggregation constant of CHAPS has the maximum at hexamer and oscillates, depending on odd or even aggregation numbers. Thus, the aggregation pattern of a substance is closely related with the chemical structure of the hydrophobic group of its molecule. The definition of cmc is discussed together with its significance.

Structural changes by sulfoxidation of phenothiazine drugs

The side-chain conformations of psychoactive phenothiazine drugs in crystals are different from those of biologically inactive ring sulfoxide metabolites. This study examines the potential energies, molecular conformations and electrostatic potentials in chlorpromazine, levomepromazine (methotrimeprazine), their sulfoxide metabolites and methoxypromazine. The purpose of the study was to examine the significance of the different crystal conformations of active and inactive phenothiazine derivatives, and to determine why phenothiazine drugs lose most of their biological activity by sulfoxidation. Quantum mechanics and molecular mechanics calculations demonstrated that conformations with the side chain folded over the ring structure had lowest potential energy in vacuo, both in the drugs and in the sulfoxide metabolites. In the sulfoxides, side chain conformations corresponding to the crystal structure of chlorpromazine sulfoxide were characterized by stronger negative electrostatic potentials around the ring system than in the parent drugs. This may weaken the electrostatic interaction of sulfoxide metabolites with negatively charged domains in dopamine receptors, and cause the sulfoxides to be virtually inactive in dopamine receptor binding and related pharmacological tests.

Examination of self-crosslinked gelatin as a hydrogel for controlled release

A gelatin matrix crosslinked by extensive dehydration was examined for use in controlled drug delivery in this preliminary investigation. Crosslinking is necessary to prevent gelatin dissolution and immediate drug release at body temperature. Treatment at 105 degrees C and reduced pressure induced crosslinking in discs prepared from Type B gelatin. Crosslinking was evaluated by determining changes in gelatin solubility at 37 degrees C in a USP paddle dissolution apparatus. The crosslinking treatment was reproducible and resulted in 90% of the original gelatin mass remaining after 12 h in water and in phosphate buffer solutions of pH 3 and 6.4. The treated gelatin discs remained intact for greater than 24 h at pH 6.4. Chlorpromazine.HCl (CPZ) was incorporated as a model drug by soaking the treated gelatin discs in an aqueous solution of the drug. Release of CPZ at 37 degrees C in the dissolution apparatus was fitted to an empirical equation. A coefficient of this equation was used as the initial release rate for comparison between different release profiles. The roles of drug solubility, matrix swelling and erosion, and potential drug-matrix interactions were examined by conducting release studies at pH values of 3, 4, 6.4, and 7.4. The insoluble, un-ionized form of the drug had the slowest release rate. The soluble, ionized form under conditions of maximum swelling and a possible drug-matrix repulsive interaction had the fastest release rate. General electrostatic drug-matrix interactions were noted which could influence the drug release rate depending on conditions of the study. The times for 50% release of CPZ ranged from 1.8 to 11.3 h.

Mechanistic aspects of the oxidation of phenothiazine derivatives by methemoglobin in the presence of hydrogen peroxide

Mechanistic aspects of the reaction of hydrogen peroxide with methemoglobin with respect to phenothiazine oxidation have been studied. Three phenothiazines, methoxy- (MoPZ), chlor- (CPZ) and methoxycarbonylpromazine (MaPZ), have been used. These phenothiazines differ only in substitution at the 2-position, which contributes substantially to the electron-donating properties of these compounds. Reaction with hydrogen peroxide oxidizes methemoglobin to ferrylhemoglobin, which contains iron(IV)-oxo porphyrin moiety and a protein radical. The phenothiazines are oxidized by ferrylhemoglobin in the presence of H2O2 mainly to their sulfoxides, with a radical cation as intermediate. The conversion rates (MoPZ greater than CPZ greater than MaPZ) decrease with the electron-withdrawing ability of the 2-substituent, as indicated by Hammett sigma para values. Hydrogen peroxide consumption during the reaction is similar for the three phenothiazines. Denaturation reactions that occur upon exposure of methemoglobin to hydrogen peroxide have been investigated. For this heme-protein cross-linking was studied by means of heme retention by the protein after methyl ethyl ketone extraction. Furthermore, oxygen consumption during the reaction was assayed, which indicates formation of protein-peroxy radicals. The extent of both heme-protein cross-linking and oxygen consumption is decreased by phenothiazines in the same order as the phenothiazine conversion rate. CPZ sulfoxide is not converted by methemoglobin in the presence of hydrogen peroxide, and CPZ sulfoxide shows no effect on heme-protein cross-linking and oxygen consumption. The results are explained by electron transfer from phenothiazine to the protein radical. Stronger electron donors (MoPZ greater than CPZ greater than MaPZ) are converted faster and by reducing the protein radical they better protect hemoglobin against denaturation. A catalytic cycle, that takes into account our observation and the existing knowledge of hemoglobin oxidation states, is presented.

Determination of hemoglobin through its peroxidase activity on chlorpromazine

Chlorpromazine is an excellent chromogen for determining micro-quantities of hemoglobin. The oxidation of chlorpromazine by peroxidase activity of hemoglobin is coupled to a non-enzymatic reaction of second-order. Kinetic analysis of the overall system leads to a discussion about the optimal assay conditions. Spectrophotometric progress curves for the accumulation of the chlorpromazine cation radical during the reaction have been obtained, and further analyzed by non-linear regression. The use of a linear calibration curve of the enzymatic reaction rate against hemoglobin concentration is proposed for its determination.

Hydrophobicity-dependent fluorescence properties and intracellular fluorospectroscopic behavior of phototoxic drugs

Fluorospectroscopic behavior of chlorpromazine, mequitazine, afloqualone and piroxicam, which are known to induce skin photosensitivity, was examined in both homogeneous solutions and human buccal mucosal cells. Each drug showed large Stokes' shifts and their fluorescence intensities increased in hydrophobic solvents. These results indicated that the drugs tested can be used as hydrophobic fluorescence probes. Fluorescence microscopic observations of buccal mucosal cells treated with these drugs showed that all the drugs, especially chlorpromazine and mequitazine, were distributed in intracellular membranous regions.

The influence of charge transfer complex formation on the antibacterial activity of some tricyclic drugs

1. Phenothiazines and structurally related drugs are effective in eliminating bacterial plasmids. 2. Charge transfer complex formation between chlorpromazine and xanthine dyes with different electron acceptor activities (e.g. fluorescein, eosin, erythrosin and rose bengal) was detected by differential spectrophotometry. Charge transfer complexes were formed between the strong electron acceptor rose bengal and various tricyclic drugs. 3. On the basis of the wavelength shift, the binding energies of drugs and dyes were estimated. 4. The temperatures dependence of the reaction indicates charge transfer complex formation rather than a chemical reaction between drugs and dyes. 5. The anti-plasmid action of the phenothiazines was decreased in the presence of xanthine dyes. As a consequence of competitive inhibition between bacterial binding sites and xanthine dyes, the binding energy of drugs in the plasmid replication system could be determined in the presence of dyes. 6. Drugs with binding energies in the range of 0.23-2.31 kcal/mol can inactivate the plasmid replication system.

Interaction of chlorpromazine with DNA

The mechanism of the potential anticancer agent chlorpromazine hydrochloride (CPZ) with DNA was investigated by the techniques of high-performance liquid chromatography (HPLC), viscosity and Raman spectroscopy. It has been suggested from HPLC work that DNA nucleotides (except nucleosides) from either a CPZ-DNA system or a CPZ-nucleotide system. Furthermore, the shear stress of the viscosity of the CPZ-DNA system and the CPZ-nucleotide systems ware shown to be apparently the higher increasing than that of DNA and nucleotide alone. These systems had non-Newtonian properties for the formation of the CPZ-DNA and the CPZ-nucleotide systems under experimental conditions. The Raman spectra showed a dramatic difference at 982 cm-1 due to the symmetric P-O stretching vibration of the PO4(2-) group between dGMP and the CPZ-dGMP system.

Thermodynamics and mathematical modeling of the partitioning of chlorpromazine between n-octanol and aqueous buffer

The distribution of chlorpromazine (CPZ) between aqueous buffer solutions and 1-octanol was studied over a wide range of pH, buffer concentration, and temperature. A mathematical model was developed to simulate the distribution profiles. It is assumed that only monomers of CPZ exist in the organic phase, whereas in the aqueous phase, association equilibria were assumed to occur. The model predicted the formation of dimers and no higher aggregates over most of the concentration range covered in this study. Thermodynamic parameters for the partition equilibria were evaluated from the equilibrium partition coefficients measured as a function of temperature. Positive values of delta H and delta S were obtained for the transfer of CPZ from the aqueous to the organic phase. The process is entropy controlled indicative of a hydrophobic interaction between CPZ and the aqueous solvent.

The determination of chlorpromazine, related impurities and degradation products in pharmaceutical dosage forms

The literature relating to the determination of chlorpromazine, related impurities and degradation products in pharmaceutical preparations is reviewed. Related impurities and degradation products are defined and official methods of analysis are described. Analytical methods including gravimetric, titrimetric ultraviolet-visible spectrophotometric, chromatographic and electrochemical techniques are discussed.

Dissolution studies of drug formulations using ion-selective electrodes as sensors in an air-segmented continuous flow analyzer

The application of drug ion-selective electrodes as sensors for the direct determination of the released drug in a continuous-flow analyzer for automated dissolution studies is described. Flow-through electrodes, selective to chlorpromazine, amitriptyline, propantheline, cimetidine, and ranitidine, have been constructed and used for the dissolution studies of 18 dosage forms using the rotating basket apparatus. The dissolution profiles are obtained in the form of potential peaks versus time.