High-performance liquid chromatographic determination of ibuprofen in human plasma and urine by direct injection

In vivo evaluation of matrix granules containing microcrystalline chitosan as a gel-forming excipient

Interest in drug delivery to the gastrointestinal tract by means of chitosan has been increasing. In the study reported, the biopharmaceutical properties of granules containing microcrystalline chitosan (MCCh; molecular weight 150 kDa, degree of deacetylation 75%) were evaluated via bioavailability tests in human volunteers. Ibuprofen and furosemide were used as model drugs. With ibuprofen, granules containing 40% of MCCh behaved as a slow-release formulation (t(max) 2.9 h). With furosemide, the most marked difference between a conventional dosage form and granules containing 40% MCCh was a marked lag time (0.5 h) before absorption from the latter. This difference was reflected in t(max) values for furosemide. Despite the lag time, AUC values for furosemide were high, indicating that the granules containing MCCh had remained in the stomach and that drug release had taken place in the stomach rather than in the intestine. The results of the bioavailability studies indicate that MCCh matrix granules allow a simple preparation of slow-release and perhaps stomach-specific dosage forms. Use of model drugs differing in relation to sites of absorption in the gastrointestinal tract aided identification of sites of absorption of drugs from the granules. Further studies, including gamma-scintigraphic evaluations, will be performed on how the granules behave in the stomach.

Validation of a liquid chromatographic method for the determination of ibuprofen in human plasma

A simple, rapid method of determining the ibuprofen concentration in small volumes of human plasma (50 microl) by HPLC was developed. The sample was prepared for injection using a solid-phase extraction method, with naproxen as the internal standard. A 96-well extraction plate was used, easing sample preparation and allowing the simultaneous extraction of multiple plasma samples directly into the HPLC injection vials. Samples were stable at room temperature for at least 48 h prior to injection. The HPLC method used an ultraviolet detector with a 5-min run time and measured concentrations across the range typically seen with the clinical use of this drug. The calibration curve was linear across the concentration range of 0.78-100 microg/ml with a limit of quantitation (LOQ) of 1.56 microg/ml. The coefficient of variation for intra-day and inter-day precision was 6% or less with accuracies within 2% of the nominal values for low (4.5 microg/ml), medium (40 microg/ml) and high (85 microg/ml) ibuprofen concentrations. For ibuprofen concentrations at the LOQ, the intra-day and inter-day precision and accuracy were within 10 and 15%, respectively. Recovery was 87% or greater for ibuprofen. This method was used to analyze plasma samples for unknown ibuprofen concentrations in bioequivalence and limited food effect studies of different formulations of ibuprofen. Thus, this method has been fully validated and used in the analysis of unknown plasma samples for ibuprofen.

Bioavailability and in vitro oesophageal sticking tendency of hydroxypropyl methylcellulose capsule formulations and corresponding gelatine capsule formulations

The overall aim of the present study was to widen our knowledge about the biopharmaceutical behaviour of novel hydroxypropyl methylcellulose (HPMC)-based two-piece capsules by comparing them with the classic hard gelatine capsules. Firstly, the tendency of the HPMC capsules to stick to isolated porcine oesophageal preparation was evaluated. The force needed to detach the HPMC capsules from the oesophagus was significantly lower than that for the gelatine capsules (P<0.001), which is evidently an advantage of this new dosage form. The second aim was to investigate the possibility of preparing sustained-release capsules using different powdered HPMCs as diluents (K100, K4M and K15M) and the effect of the molecular weight of HPMC powder on the in vitro and in vivo behaviour of the capsules. In addition to peroral drug administration also rectal dosing was applied. Two groups of eight healthy volunteers participated in randomised, cross-over, single-dose studies. One group was administered capsules orally and the other rectally. There were no marked differences in the bioavailability properties of either the oral or rectal HPMC capsules containing ibuprofen as model drug as compared with corresponding gelatine capsule formulations. Using different viscosity grades of HPMC powders as diluents it was possible to control the absorption rate of the model drug both from gelatine and HPMC capsules as far as the oral route was concerned. After rectal administration there were no statistically significant differences between the formulations containing different grades of HPMC powder. Only partial correlation was observed between the results of the bioavailability studies and the in vitro dissolution studies. From a biopharmaceutical point of view these two shell materials can be regarded as interchangeable.

Citric acid as excipient in multiple-unit enteric-coated tablets for targeting drugs on the colon

Delivery of drugs to the large bowel has been extensively investigated during the last decade. The aim of this study was to investigate whether enteric-coated tablets could be made from enteric-coated matrix granules and drug release targeted to the colon. Whether in vitro drug release rate and in vivo absorption could be delayed by adding citric acid to the granules and/or to the tablet matrix was also studied. Ibuprofen was used as model drug because it is absorbed throughout the gastrointestinal tract. Eudragit S and Aqoat AS-HF were used as enteric polymers. Drug release rates were studied at different pH levels and drug absorption was studied in bioavailability tests. The conclusion was that citric acid retarded in vitro drug release when used in multiple-unit tablets. In vivo absorption of ibuprofen was markedly delayed when citric acid was included in both granules and tablet matrix. Further studies are needed to determine the optimal amount of citric acid in formulations.

Enteric polymers as binders and coating materials in multiple-unit site-specific drug delivery systems

The aim of this study was to develop a multiple-unit, site-specific drug formulation allowing targeting of drug release in the colon. Initially, characteristics of matrix pellets containing various enteric polymers as binders were tested. An enteric coating was then added to the formulations. Ibuprofen and furosemide were used as model drugs. The former is absorbed throughout the gastrointestinal tract, the latter only from upper parts. Methacrylate copolymers, hydroxypropyl methylcellulose acetate succinates and cellulose acetate phthalate were used as enteric polymers. The properties of the products were initially tested via dissolution studies at different pHs, then via bioavailability studies in healthy volunteers. The main conclusion was that drug release can be targeted on the distal part of the small intestine and the colon by preparing film-coated matrix pellets in which enteric polymers dissolving at pH approximately 7 have been used both as binders in the pellets and as coating material. This conclusion is based on the finding that absorption of ibuprofen from the formulations developed was adequate, with a lag-time of about 2 h and tmax values at 4-5 h, where as absorption of furosemide from the analogous products was negligible. It was also found that uncoated pellets as such could represent a slow-release formulation for furosemide, a problem drug as far as modified-release products are concerned.

Biopharmaceutical evaluation of time-controlled press-coated tablets containing polymers to adjust drug release

This paper deals with press-coated modified release tablets in which the drug dose is situated in the core or is divided between the core and the coat. The coat contains polymer (sodium alginate or hydroxypropylmethyl cellulose, HPMC) to control drug release. The main objective was to investigate how the pharmacokinetic profile of the model drug could be modified by altering the proportion of the drug between the core and the coat. The effect of the amount of the polymer in the coat was also studied. Bioavailability tests were carried out on healthy volunteers. In the absorption curves of the tablets containing 50%, 67% and 80% of the drug in the core and 180 mg HPMC in the coat a bimodal profile was observed. No bimodal release pattern in the in vitro dissolution studies was found. If the whole dose was incorporated in the core the absorption curve has only one clear t(max) value at about 10 h. Doubling the amount of HPMC in the coat dramatically decreased drug absorption. It was concluded that, if a slightly reduced t(max)-value was required, the viscosity grade of HPMC used should be lowered.

Controlled release gel of ibuprofen and lidocaine in epidural use--analgesia and systemic absorption in pigs

PURPOSE

Reduction of the frequency of injections and localization of the absorption of drug molecules to the injection site would be of great advantage in epidural pain treatment. The epidural use of a controlled release gel of lidocaine and ibuprofen was studied.

METHODS

The effect of a poloxamer gel (25%) containing 2% lidocaine.HCl and 2% ibuprofen.Na on the duration of analgesia after epidural administration to pigs was compared with drug in solution. Analgesia was assessed by observing the motor function and the nociceptive reflex-withdrawal response to painful pressure stimulation on the feet. Pharmacokinetic and histological examinations were performed.

RESULTS

Analgesia lasted significantly longer after epidural lidocaine gel injection in comparison with the solution. The gel prolonged the systemic absorption, thereby increasing the epidural availability of lidocaine for spinal analgesia. Although the absorption of ibuprofen was prolonged after epidural gel injection, the duration of analgesia as compared with the solution was not prolonged. After epidural injection, only slight inflammatory changes were observed in the tissue structures of the epidural space, but none in the spinal cord.

CONCLUSIONS

These results demonstrate poloxamer gel to be a promising controlled-release, injectable epidural formulation for the management of pain.

Determination of ibuprofen in erythrocytes and plasma by high performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method is described for the determination of ibuprofen in isolated erythrocytes and plasma. Before HPLC analysis ibuprofen was isolated by liquid-liquid extraction from these biological matrices; methylene chloride proved to be the best of the organic solvents tested. For the sample of erythrocytes it was necessary to carry out haemolysis prior to their extraction. HPLC was performed on a C-18 column with a mobile phase of methanol-water (220:100, v/v) acidified with perchloric acid to pH 3. Ultraviolet detection was at 222 nm. This method has been applied to the quantification of ibuprofen in rabbit erythrocytes and plasma for a pharmacokinetics study.

High-performance liquid chromatographic assay for ibuprofen in whole blood using solid-phase extraction

A precise, accurate, reproducible one-step method for the high-performance chromatographic determination of ibuprofen in whole blood is described. Samples were, after haemolysis, prepared by solid-phase extraction. Analyses were performed using reversed-phase chromatography on a Separon SGX C18 column with a mobile phase of methanol-water (pH 3) and ultraviolet detection at 222 nm. The method was used for pharmacokinetic studies in rabbits.

Direct determination of ibuprofen and ibuprofen acyl glucuronide in plasma by high-performance liquid chromatography using solid-phase extraction

A method for the simultaneous determination of ibuprofen and its labile, reactive metabolite, ibuprofen acyl glucuronide, in plasma is described. Reversed-phase high-performance liquid chromatography (HPLC) employed a C18 column using methanol-10 mM trifluoroacetic acid as the mobile phase with ultraviolet detection at 225 or 214 nm. It is essential that blood is handled rapidly and plasma is acidified upon collection prior to freezing. Plasma samples first are deproteinated with acetonitrile, the supernatant is diluted with phosphate buffer, and ibuprofen, ibuprofen glucuronide, and ibufenac (internal standard) are initially isolated by solid-phase extraction on C18 cartridges. Upon elution, the residue is evaporated, dissolved and injected onto the HPLC system. Recovery is 94 +/- 8 and 70 +/- 9% for ibuprofen glucuronide and ibuprofen, respectively. The measurable concentration range is linear from 0.1 to 10 micrograms/ml for ibuprofen glucuronide and from 0.5 to 100 micrograms/ml for ibuprofen. The method is satisfactory for the analysis of ibuprofen and ibuprofen glucuronide from pharmacokinetic studies in humans. The direct determination of ibuprofen glucuronide allows accurate measurement of this conjugate at low levels relative to the parent compound, ibuprofen, a distinct advantage compared to previously employed indirect methods.

Analysis of drugs and other toxic substances in biological samples for pharmacokinetic studies

The importance of the role of analysis of drugs and other toxic substances in biological samples (bioanalysis) in medicine, toxicology, pharmacology, forensic science, environmental research and other biomedical disciplines is self-evident. Among these disciplines, bioanalysis plays a special pivotal role in pharmacokinetics. The pharmacokinetic parameters, such as half-life, volume of distribution, clearance and bioavailability, of drugs and other compounds are derived from the concentrations of these analytes assayed in the biological samples collected at specified time points. The capability of analysts to develop sensitive and specific analytical methods for the assay of low concentrations of drugs and other toxic compounds in small amounts of biological samples has contributed significantly to the theoretical advances in pharmacokinetics and its applications in clinical pharmacology and the management of drug therapy in patients. The increased demands for pharmacokinetic applications in turn have stimulated the innovation and improvement in bioanalytical technologies. The reliability of the pharmacokinetic conclusions depends on the accuracy and precision of the analytical methods employed to assay the biological samples. Factors that affect the integrity of the bioanalytical data should therefore be controlled in analysis of biological samples for pharmacokinetics studies. The biological samples for drug concentration determination should be collected as specified in the study protocol with respect to the time and site of sampling. These samples should be processed to avoid extraneous interactions between the analytes and sampling devices or additives resulting in the redistribution of the analytes between components of the biological samples, such as displacement of drug binding and changes in the distribution of the analytes between plasma and red blood cells. The stability of the drugs and other analytes in the samples should also be evaluated to establish the conditions suitable for the transportation and storage of the samples to avoid chemical, photochemical and enzymatic degradation of the analytes. Various technologies have been utilized to assay biological samples for pharmacokinetic studies. The most frequently used are chromatography (high-performance liquid chromatography, gas chromatography and thin-layer chromatography), immunoassays and mass spectrometry.(ABSTRACT TRUNCATED AT 400 WORDS)

Application of micellar mobile phases for the assay of drugs in biological fluids

Although micellar chromatography has been used for the determination of drugs in biological fluids since 1985, relatively few researchers have applied the technique to therapeutic monitoring. The reasons for this are rather unclear. It may be that most of the present extraction/reconstitution techniques are well established or that the method development procedure is unfamiliar. Significantly lower detection limits can be obtained with micellar mobile phases and column switching than with micellar mobile phases alone. Only two groups have used micellar mobile phases in conjunction with column switching for the determination of drugs in biological fluids. Since column switching with micellar mobile phases is a relatively new and untried technique, it will take some time before the full range of its applicability and limitations are known.

Rapid high-performance liquid chromatographic methods for the determination of overdose concentrations of some non-steroidal anti-inflammatory drugs in plasma or serum

Separate methods are described for the determination of the non-steroidal anti-inflammatory drugs diflunisal, indomethacin, fenoprofen, ibuprofen, ketoprofen, naproxen, mefenamic acid and piroxicam at overdose concentrations in human plasma or serum, using high-performance liquid chromatography and ultraviolet detection. A common extraction, involving protein precipitation with acetonitrile, is employed for all methods. A 25 cm Hypersil ODS (5 mu particle size) analytical column is used for all chromatographic separations, with a mobile phase of acetonitrile-acetate buffer (pH 4.2 or 4.8). The methods are all reproducible and can also determine concentrations that fall within the normal therapeutic range for each drug.

Use of micellar mobile phases and microbore column switching for the assay of drugs in physiological fluids

The feasibility of directly assaying drugs in physiological fluids using on-line preconcentration and microbore high-performance liquid chromatography has been demonstrated. The untreated sample is injected onto a hydrophobic pre-column, using micellar sodium dodecyl sulfate (SDS) in the case of serum or phosphate buffer in the case of urine, as the load mobile phase. This traps the components of interest which are then backflushed onto a microbore analytical column using a stronger mobile phase. This procedure was then applied to diazepam in serum and phenobarbital in urine. Recovery was linear and quantitative over the range 30-3000 ng/ml for diazepam in serum and 2-200 micrograms/ml for phenobarbital in urine. The diazepam method was specific against caffeine and the three major metabolites of diazepam: oxazepam, temazepam, and nordiazepam. The effects of varying pre-column dimensions, pre-column loading time, and SDS concentration volume were evaluated.

Determination of the enantiomeric composition of ibuprofen in human plasma by high-performance liquid chromatography

A normal-phase high-performance liquid chromatographic method, using a hexane-ethyl acetate solvent system, for the determination of the enantiomeric composition of ibuprofen in human plasma is described. The method is based on the resolution of the diastereoisomeric amides formed on reaction of the ibuprofen enantiomers with S-1-(naphthen-1-yl)ethylamine using p-chlorophenoxy-acetic acid as internal standard. The application of the method for the determination of the enantiomeric composition of ibuprofen in human plasma following the repeated oral administration of the drug to two volunteers is reported. The plasma concentrations of the S-(+) enantiomer were always greater than that of the R-(-), the ratio of the areas under the enantiomer plasma concentration-time curves (S/R) being 1.8 and 1.6.