High-performance liquid chromatographic assay for piroxicam in human plasma

Physiologically based pharmacokinetic (PBPK) modeling of piroxicam with regard to CYP2C9 genetic polymorphism

Piroxicam is a non-steroidal anti-inflammatory drug used to alleviate symptoms of osteoarthritis and rheumatoid arthritis. CYP2C9 genetic polymorphism significantly influences the pharmacokinetics of piroxicam. The objective of this study was to develop and validate the piroxicam physiologically based pharmacokinetic (PBPK) model related to CYP2C9 genetic polymorphism. PK-Sim^® version 10.0 was used for the PBPK modeling. The PBPK model was evaluated by predicted and observed plasma concentration-time profiles, fold errors of predicted to observed pharmacokinetic parameters, and a goodness-of-fit plot. The turnover number (k_cat) of CYP2C9 was adjusted to capture the pharmacokinetics of piroxicam in different CYP2C9 genotypes. The population PBPK model overall accurately described and predicted the plasma concentration-time profiles in different CYP2C9 genotypes. In our simulations, predicted AUC_inf in CYP2C9*1/*2, CYP2C9*1/*3, and CYP2C9*3/*3 genotypes were 1.83-, 2.07-, and 6.43-fold higher than CYP2C9*1/*1 genotype, respectively. All fold error values for AUC, C_max, and t_1/2 were included in the acceptance criterion with the ranges of 0.57-1.59, 0.63-1.39, and 0.65-1.51, respectively. The range of fold error values for predicted versus observed plasma concentrations was 0.11-3.13. 93.9% of fold error values were within the two-fold range. Average fold error, absolute average fold error, and root mean square error were 0.93, 1.27, and 0.72, respectively. Our model accurately captured the pharmacokinetic alterations of piroxicam according to CYP2C9 genetic polymorphism.

Enhanced Dissolution and Oral Bioavailability of Piroxicam Formulations: Modulating Effect of Phospholipids

Several biologically relevant phospholipids were assessed as potential carriers/additives for rapidly dissolving solid formulations of piroxicam (Biopharmaceutics Classification System Class II drug). On the basis of in vitro dissolution studies, dimyristoylphosphatidylglycerol (DMPG) was ranked as the first potent dissolution rate enhancer for the model drug. Subsequently, the solid dispersions of varying piroxicam/DMPG ratios were prepared and further investigated. Within the concentration range studied (6.4-16.7 wt %), the dissolution rate of piroxicam from the solid dispersions appeared to increase as a function of the carrier weight fraction, whereas the cumulative drug concentration was not significantly affected by piroxicam/DMPG ratio, presumably due to a unique phase behavior of the aqueous dispersions of this carrier phospholipid. Solid state analysis of DMPG-based formulations reveled that they are two-component systems, with a less thermodynamically stable form of piroxicam (Form II) being dispersed within the carrier. Finally, oral bioavailability of piroxicam from the DMPG-based formulations in rats was found to be superior to that of the control, as indicated by the bioavailability parameters, c_max and especially T_max (53 µg/mL within 2 h vs. 39 µg/mL within 5.5 h, respectively). Hence, DMPG was regarded as the most promising carrier phospholipid for enhancing oral bioavailability of piroxicam and potentially other Class II drugs.

A simple pharmacokinetics subroutine for modeling double peak phenomenon

Double peak absorption has been described with several orally administered drugs. Numerous reasons have been implicated in causing the double peak. DRUG-KNT--a pharmacokinetic software developed previously for fitting one and two compartment kinetics using the iterative curve stripping method--was modified and a revised subroutine was incorporated to solve double-peak models. This subroutine considers the double peak as two hypothetical doses administered with a time gap. The fitting capability of the presented model was verified using four sets of data showing double peak profiles extracted from the literature (piroxicam, ranitidine, phenazopyridine and talinolol). Visual inspection and statistical diagnostics showed that the present algorithm provided adequate curve fit disregarding the mechanism involved in the emergence of the secondary peaks. Statistical diagnostic parameters (RSS, AIC and R2) generally showed good fitness in the plasma profile prediction by this model. It was concluded that the algorithm presented herein provides adequate predicted curves in cases of the double peak phenomenon.

Further Evidence for Interethnic Differences in the Oral Pharmacokinetics of Meloxicam

INTRODUCTION

Meloxicam is a nonsteroidal anti-inflammatory agent used widely in therapeutics. It is mainly metabolised by the cytochrome P450 enzyme (CYP) 2C9, with minor involvement of CYP3A4. So far, no information on the oral pharmacokinetics of this drug in adult Mexicans is available. The purpose of this study was to evaluate the oral pharmacokinetics of meloxicam in Mexican subjects.

METHODS

Twenty-four healthy male subjects received an oral dose of meloxicam 7.5mg after fasting for 10 hours. Blood samples were drawn from a suitable forearm vein and plasma obtained. The meloxicam concentration was evaluated by a high-performance liquid chromatographic method and pharmacokinetic parameters were obtained by non-compartmental techniques. Pharmacokinetic parameters obtained in this study were compared with those reported under similar conditions in other populations in order to establish if interethnic differences in the pharmacokinetics of meloxicam exist.

RESULTS

After administration of meloxicam, plasma levels increased to a maximum concentration (C(max)) of 0.702 +/- 0.027 (mean +/- SEM) microg/mL with a time to reach C(max) of 4.77 +/- 0.65h. The area under the plasma concentration versus time curve was 24.82 +/- 1.23 microg . h/mL. The clearance was about 4.8 mL/min and the volume of distribution 9.8 +/- 0.36L. When these parameters were compared with those reported in German and Indian subjects, a reduced clearance and volume of distribution were evident in Mexicans. However, clearance and volume of distribution obtained in this study were very similar to those reported in Chinese subjects.

CONCLUSIONS

The oral pharmacokinetic parameters of meloxicam in healthy Mexican subjects compared with historic controls reported in other populations showed a reduced clearance and volume of distribution when compared with German subjects, whereas no differences between Mexican and Chinese subjects were observed. These results suggest that there are interethnic differences in the pharmacokinetics of meloxicam.

Stability indicating HPTLC determination of piroxicam

A rapid and sensitive HPTLC method was developed and validated for the estimation of Piroxicam (PM). Spectrodensitometric scanning-integration was performed at an absorbance wavelength of 360 nm. To justify the suitability, accuracy and precision of the proposed method, recovery studies were performed at three concentration levels. One of the degradation products of PM is 2-aminopyridine (2AP). It becomes imperative to separate this compound as it is a precursor during synthesis of the drug. A TLC aluminium plate precoated with silica gel 60F-254 was used as the stationary phase. The solvent system toluene-acetic acid (8:2 v/v) gave a dense and compact spot of PM with a Rf value of 0.58 +/- 0.01 which was well separated from 2AP (Rf 0.23 +/- 0.01). The polynomial regression data for the calibration plots exhibited good linear relationship (coefficient of correlation r = 0.9982) over a concentration range of 400-800 ng. Statistical analysis proves that the proposed method is accurate and reproducible. The method is stability indicating and being economical can be employed for the routine analysis in bulk drug as well as pharmaceutical formulations.

Piroxicam quantitation in human plasma by high-performance liquid chromatography with on- and off-line solid-phase extraction

A comparative study of two analytical methodologies for piroxicam quantitation in plasma by off-line and on-line solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) is described. The SPE cartridges contained C8 for both extraction methods. The analytes piroxicam and tenoxican (internal standard) were separated on a C18 column with a mobile phase consisting of acetonitrile:20 mM phosphate buffer pH 3.1 (50:50, v/v) followed by UV detection at 360 nm. The validation of the methods demonstrated good recoveries (over 90%), sensitivity (limits of quantification of 0.05 microgram/ml with on-line SPE and 0.1 microgram/ml with off-line SPE, based on a 100 microliters and 200 microliters sample volume, respectively), accuracy and precision (better than 9.5%). Both methodologies have been used for bioequivalence studies.

Determination of the novel non-steroidal anti-inflammatory drug lornoxicam and its main metabolite in plasma and synovial fluid

A rapid and sensitive HPLC method for the determination of the non-steroidal anti-inflammatory drug lornoxicam in plasma samples of humans and laboratory animals is described. After addition of the internal standard (tenoxicam) the plasma sample is acidified and extracted either by dichloromethane via Extrelut columns or by solid-phase extraction using C18 columns. After evaporation of the solvent the separation is performed on a C18 column in isocratic mode with a mobile phase consisting of 0.1 M phosphate buffer (pH 6.0)-methanol and detection at 372 nm. The limit of determination was set to 10 ng/ml using 0.5 ml of sample but can be extended down to 2.0 ng/ml plasma. Using solid-phase extraction with C18 columns both lornoxicam and its main metabolite 5'-hydroxylornoxicam can be determined while extraction via Extrelut was used in studies where only lornoxicam was to be determined. This method was used successfully in several thousand samples of pharmacokinetic and bioavailability studies in animals and in humans.

Human intestinal permeability of piroxicam, propranolol, phenylalanine, and PEG 400 determined by jejunal perfusion

PURPOSE

To determine the human jejunal permeabilities of compounds utilizing different transport mechanisms using a regional perfusion approach and to establish a standard procedure for determining drug permeability class to be used for the establishment of drug product bioequivalence standards.

METHODS

Six healthy male volunteers participated in this study. A multi-lumen perfusion tube was inserted orally and positioned in the proximal region of the jejunum. A solution containing piroxicam, phenylalanine, propranolol, PEG 400 and PEG 4000 was perfused through the intestinal segment at a rate of 3.0 ml/min. Perfusate samples were quantitatively collected every 10 minutes for two 100 minute periods with an intermediate wash out period to determine intra and intersubject variation.

RESULTS

The mean P(eff) (+/-SD) of piroxicam, phenylalanine, propranolol, and PEG 400 were 10.40 +/- 5.93, 6.67 +/- 3.42, 3.59 +/- 1.60, 0.80 0.46 x 10(-4) cm/sec, respectively. The coefficient of variation for the intersubject variability, first and second perfusion periods were: piroxicam, 60.5% and 57.1%; phenylalanine, 52.8% and 57.8%; propranolol, 62.1% and 44.6%; and PEG 400, 81.7% and 42.3%, indicating a slightly lower CV for the second perfusion period in the same subject. The intrasubject CV's between the two perfusion periods were: 19.4%, 21.3%, 23.6% and 41.0% respectively, indicating a smaller intraindividual variation for all compounds studied.

CONCLUSIONS

Piroxicam, a nonpolar drug exhibited the highest permeability of the compounds studied. The intrasubject CV was lower than the intersubject CV, indicating consistent permeability estimation within subjects. The methodology is useful for permeability estimation regardless of absorption mechanism and can be used to establish a consistent data base of human permeabilities for estimation of human drug absorption and for establishing the biopharmaceutic permeability class of drugs.

Oxaprozin and piroxicam, nonsteroidal antiinflammatory drugs with long half-lives: effect of protein-binding differences on steady-state pharmacokinetics

The nonsteroidal antiinflammatory drugs (NSAIDs) oxaprozin and piroxicam have long elimination half-lives (t 1/2 approximately 55 hours), permitting once-daily dose regimens. The protein-binding characteristics of these drugs, however, vary widely. This study examines the effect of these binding differences on the drugs' disposition kinetics at steady state. A total of 52 participants (26 young healthy volunteers, and 26 elderly osteoarthritic patients, 15 men and 37 women (2 of them poor metabolizers of debrisoquine [CYP2D6]) completed the two-period, two-treatment, randomized, single-dose and 21-day, once-daily multiple-dose, cross-over study. Doses of oxaprozin and piroxicam were 1,200 mg once daily and 20 mg once daily, respectively. Mean single-dose kinetic parameters of oxaprozin versus piroxicam did not differ more than +/-14% (t1/2, 53.0 versus 57.4 hours; apparent oral clearance adjusted for 70-kg body weight [Clpo], 0.139 versus 0.121 L/hr; apparent volume of distribution adjusted for 70-kg body weight [Vd/F]; 10.2 L versus 9.13 L). Protein binding was plasma-concentration dependent with oxaprozin (range, 10-400 mg/L) but not with piroxicam (range, 1-30 mg/ L). Steady-state conditions were established within 3 days with oxaprozin but took almost 12 days with piroxicam. Compared with the single-dose values, steady-state Clpo (Clpo,ss) and Vd/F of total drug increased with oxaprozin by almost 127% but remained within +/-10% with piroxicam. Post-steady-state apparent t 1/2 of the total and unbound drugs of approximately 62 hours were similarly prolonged with piroxicam but differed substantially with oxaprozin (50.6 hours [total drug] versus 23.8 hours [unbound drug]). Single dose Clpo (Clpo,sd) values of both NSAIDs were significantly correlated in the study populations. With both NSAIDs, Clpo in the two poor metabolizers of debrisoquine was within +/-20% of mean values for the population. Clinically important age- and gender-dependent decreases were not observed in the weight-adjusted, Clpo,sd or Vd/F values of the total drug for either NSAID. Clearances of the two NSAIDs were significantly correlated, suggesting that a common P450 isozyme (most likely CYP2C9, in that piroxicam is a known substrate of this isozyme) may be at least partly involved in the oxidative metabolism of these NSAIDs.

Regional drug delivery II: relationship between drug targeting index and pharmacokinetic parameters for three non-steroidal anti-inflammatory drugs using the rat air pouch model of inflammation

PURPOSE

To quantify the advantage gained by direct administration to a target site for two non-steroidal anti-inflammatory drugs (NSAIDs) piroxicam and diclofenac in the rat air pouch model of inflammation. To derive a model relating drug targeting index (DTI) to the pharmacokinetic parameters of the target and systemic sites, and to compare predictions with observations.

METHODS

DTI was calculated based on area under the concentration time curve at target (pouch) and systemic site (venous blood) following administration into and sampling from both sites. A model was derived relating DTI to systemic clearance, target permeability, plasma protein binding and fraction of the targeted dose that is systemically available.

RESULTS

Both NSAIDs exhibited linear pharmacokinetics over the dose ranges studies. They differed primarily in total body clearance which was approximately 16 fold greater for diclofenac (213 ml hr-1 per 250 g) than piroxicam (13 ml hr-1 per 250 g). Observed DTIs (11, 114 and 276 for piroxicam, S[+]ibuprofen [studied previously] and diclofenac) were ranked in order of total body clearance but were approximately 7.5 fold lower than predicted (101, 700 and 2214 respectively).

CONCLUSIONS

The discrepancy was explained by the influx of the plasma binding protein, albumin, into the target site due to increased vascular permeability associated with the inflammatory response. The originally derived equation for DTI, which assumed only unbound drug diffuses across the target site, was modified to take into account the simultaneous flux of bound drug.

Extractionless high-performance liquid chromatographic method for the simultaneous determination of piroxicam and 5'-hydroxypiroxicam in human plasma and urine

A simple and rapid (extractionless) high-performance liquid chromatographic method with UV detection, at 330 nm, was developed for the simultaneous determination of piroxicam and its major metabolite, 5'-hydroxypiroxicam, in human plasma and urine. Acidified plasma and alkali-treated urine samples are used and naproxen is added as internal standard. The separation is performed at 40 degrees C on a C18 Spherisorb column with acetonitrile--0.1 M sodium acetate (33:67, v/v, pH 3.3) as mobile phase. The retention time is 2.2 min for 5'-hydroxypiroxicam, 2.6 min for piroxicam and 3.2 min for naproxen. The detection limit is 0.05 micrograms/ml using a 100-microliters loop.

Concentration-response relationships for three nonsteroidal anti-inflammatory drugs in the rat intestine

1. The effect of diclofenac, piroxicam and (S+)-ibuprofen upon the rat intestine has been measured at constant drug plasma concentrations in the rat, using (51Cr)-EDTA intestinal permeation as a measure of damage. Initially disposition studies after sc administration of the three NSAIDs were carried out. From these studies it was found that constant-rate iv infusions were necessary to maintain plasma concentrations of diclofenac and (S+)-ibuprofen. Administration of piroxicam by sc bolus gave relatively constant plasma concentrations, thus iv infusions were not necessary to obtain concentration-response data for this drug. Relative potency was found by comparing the concentration-response profiles of the three NSAIDs and the rank order of potency obtained was: diclofenac > piroxicam > (S+)-ibuprofen. 2. The effect of mode of administration upon intestinal damage was also investigated using diclofenac. Intestinal permeability was measured in rats given diclofenac either by sc bolus or iv infusion and dose-response data compared. It was found that for the same dose, administration by sc bolus gave a higher degree of damage than by iv infusion.

Simultaneous high-performance liquid chromatographic determination of lornoxicam and its 5'-hydroxy metabolite in human plasma using electrochemical detection

A selective and sensitive high-performance liquid chromatographic method with coulometric detection is described for the simultaneous quantitation of lornoxicam, a new oxicam class drug, and its 5'-hydroxy metabolite in human plasma. The two analytes and the internal standard are extracted from plasma at pH 4.0 by liquid-liquid extraction and separated on a C18 column. Absolute detection limits using 100 microliters of plasma are found to be 5 and 10 ng/ml for lornoxicam and 5'-hydroxylornoxicam, respectively. The assay described has been successfully applied to samples from clinical studies.

Rapid and sensitive determination of piroxicam in rat plasma, muscle and skin by high-performance liquid chromatography

A rapid and precise high-performance liquid chromatographic method for the determination of piroxicam in a variety of biological samples has been developed. A reversed-phase column, isocratic elution and ultraviolet detection were employed. Calibration curves were reproducible and highly linear, with correlation coefficients typically averaging over 0.992. The detection limit of the assay was 100 ng/ml for all biological samples examined (at a signal-to-noise ratio of 3:1). Validation of the method demonstrated a good sensitivity, accuracy and precision. The method has been adopted for a pharmacokinetic study in rats.

Effects of age on the pharmacokinetics of piroxicam in rats

This study examined the effects of age on the pharmacokinetics of piroxicam in rats. Two groups of rats, aged 5 and 24 months, were administered 1 mg of piroxicam per kg intravenously, and blood samples were withdrawn for up to 120 h. Protein binding studies, with pooled serum from each age group were also performed. Piroxicam concentrations were determined by HPLC analysis, and pharmacokinetic parameters were characterized by area-moment analysis. Plasma piroxicam concentrations declined in both age groups in a biexponential fashion, with half-lives of 5.9 +/- 0.7 h (mean +/- SD) in the young rats and 30.6 +/- 9.9 h in the old rats. Total clearance in the young rats was 0.048 +/- 0.012 L/h/kg, whereas that in the old rats was 0.021 +/- 0.003 L/h/kg. The steady-state volume of distribution in the young rats was 0.42 +/- 0.05 L/kg, and that in the old rats was 0.56 +/- 0.10 L/kg. There was a statistically significant difference between these parameters calculated for each age group. Piroxicam is a highly plasma protein-bound drug; the fraction unbound in the young rats was determined to be 0.067 +/- 0.022, and that in the old rats was determined to be 0.134 +/- 0.065, or twice that in the young rats. Differences in protein binding were due, in part, to a 20% decreased albumin concentration in the old rats; however, there was also a decrease in the number of binding sites and/or the binding affinity with aging.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of piroxicam and its major metabolites in the plasma, urine and bile of humans by high-performance liquid chromatography

A simple and sensitive liquid chromatographic method with ultraviolet detection is described for the determination of the nonsteroidal anti-inflammatory drug piroxicam and its major metabolites in human plasma, urine and bile. Separation of these components occurs on a reversed phase C10CN column with a mobile phase consisting of acetonitrile-water-sodium dihydrogenphosphate solution. The detection limit of the assay was 50 ng/ml with intra- and inter-assay coefficients of variation for piroxicam of the order of 2 and 5%, respectively. The assay linearity was good (typically r = 0.9999). This method can be readily utilised for clinical pharmacokinetic and mass-balance studies.

On-line solid-phase extraction of piroxicam prior to its determination by high-performance liquid chromatography

A direct method for the determination of piroxicam in plasma is described. Plasma is directly injected onto the extraction column (10 mm x 2 mm I.D., packed with 40-microns Bond Elut C2) where proxicam is separated from the plasma concomitants using a solid-phase extraction procedure. Using a laboratory-made on-line column-switching system, the drug is quantitatively transferred and separated on the analytical column (15 cm x 4.6 mm I.D., Supelcosil LC18 DB, 5 microns) followed by determination using ultraviolet absorption at 331 nm. Validation of the method demonstrated a good recovery (100%), sensitivity (limit of determination 0.2 microgram/ml, based on a 20-microliters sample volume), accuracy and precision (better than 5%). The developed method has been adopted for studying the steady-state pharmacokinetics of the drug.

Effects of dose and sex on the pharmacokinetics of piroxicam in the rat

The effects of dose and sex on the pharmacokinetics of piroxicam were studied in the rat. Piroxicam was administered intravenously at doses of 0.50 and 5.0 mg kg-1 to male and female rats. Plasma drug concentrations were determined by a highly sensitive high-performance liquid chromatographic technique. Non-compartmental pharmacokinetic parameters were calculated by area/moment analysis. A prolonged terminal half-life averaging 13.3 h in male rats and 40.8 h in female rats was observed. Dose had no effect on the disposition of piroxicam. The sex of the rat, however, had a marked effect on piroxicam pharmacokinetics, with mean total clearance differing three-fold from 0.0184 l h-1 kg-1 in male rats to 0.00622 l h-1 kg-1 in female rats. The free fraction of piroxicam in serum was greater in male rats than in female rats owing to a higher association constant for piroxicam binding to female rat serum proteins. Free piroxicam clearance differed approximately two-fold with mean values of 0.764 l h-1 kg-1 and 0.418 l h-1 kg-1 in male and female rats, respectively. Thus, protein binding partially explained the sex-dependent disposition of piroxicam. However, sex-dependent metabolism of the drug also appears to be a major determinant of sex-related differences in piroxicam pharmacokinetics. Steady-state volume of distribution was unaffected by sex. Half-life and mean residence time were three-fold greater in female rats owing to the three-fold lower clearance value compared to male rats.