Ali Aghazadeh-Habashi

The Glucosamine Controversy; A Pharmacokinetic Issue

Glucosamine (GlcN) is a naturally occurring aminosugar that is widely used to treat osteoarthritis despite controversial clinical trial results. Animal studies, on the other hand, unequivocally suggest anti-inflammatory and disease modifying effects for GlcN. Many explanations have been offered as to the root of the controversy. They include superiority of a crystalline sulphate salt over HCl, industry bias, insensitive assessment metrics and poor methodology. Herein, we rule out a difference in bioequivalence between GlcN salts and that of chemically equivalent doses and suggest additional factors; i.e., inconsistency in the chemical potency of some products used, under-dosing of patients as well as variable and erratic bioavailability indices for the lack of GlcN efficacy observed in some studies. Clinical trials using higher doses of pharmaceutical grade GlcN or formulations with greater bioavailability should yield positive results.

EXTENT OF RENAL EFFECT OF CYCLO‐OXYGENASE‐2‐SELECTIVE INHIBITORS IS PHARMACOKINETIC DEPENDENT

1 Non‐steroidal anti‐inflammatory drugs (NSAIDs) cause renal side‐effects. In the present study, we tested the hypothesis that the extent of the renal effects of cyclo‐oxygenase (COX)‐2‐selective NSAIDs is linked to their pharmacokinetics. 2 A single oral dose of rofecoxib (10 mg/kg), celecoxib (40 mg/kg), meloxicam (3 mg/kg) or placebo was administered to rats. Urinary excretion of electrolytes, a marker of renal effects, and plasma and kidney concentrations of NSAIDs were measured. Rofecoxib and celecoxib, but not meloxicam, significantly decreased urinary sodium and potassium excretion. There was a significant correlation between the area under the 24 h plasma concentration–time curve (AUC0−24) of rofecoxib and the change in sodium (r = –0.65; P < 0.02) and potassium (r = –0.82; P < 0.0006) excretion. The AUC0−24 of celecoxib was correlated with sodium (r = –0.80; P < 0.05) but not potassium excretion. The ratios of kidney to plasma drug concentrations were 1.72, 3.16 and 0.17 for rofecoxib, celecoxib and meloxicam, respectively. 3 The renal effect of the COX‐2‐selective NSAIDs examined, marked by their ability to reduce the excretion of electrolytes, is influenced by systemic exposure to the drugs. The relatively higher distribution into the kidneys of rofecoxib and celecoxib compared with meloxicam suggests involvement of direct drug exposure in the kidneys in the adverse renal effect.

Pharmacokinetics of meloxicam administered as regular and fast dissolving formulations to the rat: influence of gastrointestinal dysfunction on the relative bioavailability of two formulations.

It is believed that acute pain suppresses nervus vagus, thereby, influencing gastrointestinal secretion and motility, which are the two factors that are necessary for disintegration and dissolution of solid dosage forms. We studied the pharmacokinetics of meloxicam and the effect of vagal suppression on the oral bioavailability and bioequivalence using a marketed (Brand) and a fast dissolving (FD) formulation. In simulated gastric juice, FD was disintegrated in 30s and released 30% of its meloxicam in 15 min and 60% in 2h. Brand was disintegrated in 4.5 min with a dissolution rate of 5.6% in 30 min that stayed plateau for the 2h experiment time. To suppress the vagus nerve, intraperitoneal injection of 20mg/kg propantheline 1 and 2h before meloxicam administration was used. Meloxicam (0.9 mg/kg) was administered to both control and vagally suppressed rats i.v. (n=4-6/group) as well as orally in a paired random fashion as broken pieces of Brand or FD tablets (n=7/ group). Serial (0-48h) blood samples were collected for pharmacokinetic and bioavailability studies. Relative bioavailability was measured according to a method in use for bioequivalence assessments. Systemic pharmacokinetics of meloxicam was not affected by vagal suppression. Absolute bioavailability of meloxicam, based on 0-48h measurement, was >0.68 regardless of the type of formulation and treatment. Vagal suppression, however, significantly reduced AUC(0-24) (microg h mL(-1)) for Brand (control, 58.8+/-22.0 vs treated, 22.1+/-9.7) but not for FD (control, 63.5+/-17.9 vs treated, 64.6+/-8.9) indicating a reduced absorption rate for the former. The peak time for Brand was also significantly delayed by over 20h for Brand and not for FD. Relative bioavailability was confirmed between FD and Brand that were in control but not in the vagally suppressed rats, indicating a disease-dependent bioequivalence. The effect of vagal suppression on the drug absorption rate can be obviated if the disintegration and dissolution become independent of gastrointestinal motility and secretion.

Absorption and Bioavailability of Glucosamine in the Rat

The objective of this study was to determine reasons behind the low oral (p.o.) bioavailability of glucosamine. By using male Sprague-Dawley rats, the movement of glucosamine through everted gut, the effect of dose and glucose, and inhibition of a glucose transporter (GLUT2) by quercetin were studied. Glucosamine pharmacokinetics and the effect of dosing, route of administration, food and antibiotic to eradicate gut microflora was also studied. Both in vitro and in vivo studies demonstrated linear absorption kinetics for glucosamine. Absorption from duodenum was the greatest. Glucose had no effect on the transport, whereas quercetin significantly reduced the extent of glucosamine transport. Intraperitoneal doses were completely absorbed, whereas p.o. doses demonstrated low bioavailability, indicating the gut as the site of presystemic loss. Food had no significant effect on glucosamine pharmacokinetics. Antibiotic treatment resulted in strong trends towards increased bioavailability with significant increase in fecal recovery. Incubation of glucosamine with faeces resulted in a significant loss. Glucosamines low bioavailability is, at least in part, due to its dependence on a transport-facilitated absorption and presystemic loss brought about by the gut microflora.

Glucosamine Dose/Concentration-Effect Correlation in the Rat with Adjuvant Arthritis

There is a debate on the dose dependency, concentration-effect, hence, the beneficial effect of glucosamine (GlcN), a widely used anti-inflammatory natural product. We investigated dose/concentration-effect relationship and determined its minimum effective dose/concentration in rats with adjuvant arthritis (AA, Mycobacterium butyricum in squalene) both as preventive and ameliorating interventions. To control already emerged arthritis, rats received oral doses of placebo or 160 mg/kg.day(-1) GlcN for 6 days. For prevention, rats were orally administered 0, 20, 40, 80, or 160 mg/kg.day(-1) GlcN commencing on the day of adjuvant injection. The arthritis index (AI), serum nitrite, and body weight were recorded. Subsequently, animals were cannulated in the right jugular veins and blood samples were collected for the determination of GlcN. GlcN ameliorated and, dose-dependently, prevented AA. It also controlled nitrite. AI was inversely correlated with GlcN dose, maximum plasma concentration, and the area under the concentration curve. Minimum effective dose was approximately 40 mg/kg.day(-1) that correspond to maximum plasma concentration of 1.37 ± 0.24 mg/L, close to 1.6 mg/L reported for pharmaceutical grades of GlcN to humans. GlcN efficacy is dose and concentration dependent. If the data extrapolated to humans, a higher than the commonly tested 1500 mg/kg dosage regimen may provide more clear treatment outcomes.

Disease specific modeling: Simulation of the pharmacokinetics of meloxicam and ibuprofen in disease state vs. healthy conditions

PURPOSE Studies have shown altered pharmacokinetic patterns (PK) in patient suffering from acute pain. Thus, we aimed to simulate pharmacokinetics of meloxicam and ibuprofen in pain and pain-free states using a physiological based software program to identify the underlining mechanistic changes for the observed differences. METHOD Published in vivo data of meloxicam and ibuprofen were used for the simulations. Two drug formulations were studied: a fast dissolving (FD) and regular release (RR) tablet formulation. The oral bioavailability was compared between these formulations in vagally suppressed rats (gastric dysfunction) and a control group. For ibuprofen additional human data of a control and post dental surgery group were used. All simulations were performed using GastroPlus™. The in vivo drug release and PK of all formulations were estimated for both drugs using the softwares immediate release (IR) or gastric release (GR) models. RESULT For meloxicam, the IR model predicted the in vivo absorption in the control group after administration of the FD and RR formulations. When gastric dysfunction was induced, the IR model did not predict absorption while the GR model did for both formulations, FD and RR. For ibuprofen, the predictions were also very close for both formulations, using the IR model for the control group and the GR model for the vagally suppressed condition in rats and humans. CONCLUSIONS Gastric control of the drug release in pain/disease state was identified as the major factor causing the observed differences in the pharmacokinetics. Computer simulations of disease states can be employed to optimize drug release from dosage forms to overcome the reported shortfalls in the drug absorption.

Simultaneous determination of selected eicosanoids by reversed-phase HPLC method using fluorescence detection and application to rat and human plasma, and rat heart and kidney samples.

Eicosanoids are biologically active lipid-derived oxidative metabolites of arachidonic acid. We, herein, present an improved sensitive, selective and robust high performance liquid chromatography (HPLC)-fluorescence assay for simultaneous quantification of eicosanoids in human plasma and rat tissues. Aliquots of 200 μL of plasma or 30 mg of heart or kidney tissues were spiked with 16-hydroxydecanoic acid as internal standard, and extracted with anhydrous acetonitrile using solid phase cartridges. The eluted samples were dried, reconstituted in anhydrous acetonitrile and labeled with 2-(2,3-naphthalimino)ethyl-trifluoromethanesulphonate in the presence of saturated potassium fluoride solution in anhydrous acetonitrile and N,N-diiospropylethylamine as catalyst. The derivatized eicosanoids were extracted with anhydrous acetonitrile using solid phase cartridges. Chromatographic separation was achieved on a C18 reversed phase column using gradient mobile phase of 0.05% of formic acid:acetonitrile:water at 0.8 mL/min flow rate. The analytes were detected at excitation and emission wavelength of 260 and 396 nm, respectively. The assay was linear (r(2)≥ 0.98) in the concentration range of 0.01-2.5 μg/mL. The intra-day and inter-day coefficients variation was less than 19.8%. Using this assay, we were able to quantify arachidonic acid metabolites simultaneously in human and rat biological samples.

Drug-Disease Interaction: Effect of Inflammation and Nonsteroidal Anti-Inflammatory Drugs on Cytochrome P450 Metabolites of Arachidonic Acid

Inflammatory conditions increase cardiovascular (CV) risk. Some nonsteroidal anti-inflammatory drugs (NSAIDs) that are used to treat pain and inflammation are also associated with CV complications. Inflammation, but not NSAIDs, disrupts the balance of vasodilator and vasoconstrictor components of the renin-angiotensin system within the heart. Herein, we report the effect of both inflammation and NSAIDs (rofecoxib, celecoxib, and meloxicam) on the physiologically active cytochrome P450 metabolites of arachidonic acid (ArA) in the rat with adjuvant arthritis. After oral administration of 7 daily therapeutically equivalent doses of NSAIDs or vehicle, the anti-inflammatory response, as well as the ArA metabolites and drug concentrations in plasma, heart and kidneys were assessed. Inflammation in the form of adjuvant arthritis caused a significant tissue-dependent imbalance of ArA metabolites by elevating the ratio of cardiotoxic 20-hydroxyeicosatetraenoic acid over cardioprotective epoxyeicosatrienoic acids in the heart, and reducing the ratio in the kidney. The observed imbalance was augmented by cardiotoxic rofecoxib but not by other examined NSAIDs with known milder cardiotoxicity. The cardio-renal toxicity of NSAIDs with known severe CV side effects may be due to altered cytochrome P450-mediated ArA acid metabolism. The ArA metabolism profile may be a marker of NSAIDs safety and toxicity.

Transdermal drug delivery: feasibility for treatment of superficial bone stress fractures

Transdermal drug delivery offers the promise of effective drug therapy at selective sites of pathology whilst reducing systemic exposure to the pharmaceutical agents in off-target organs and tissues. However, that strategy is often limited to cells comprising superficial tissues of the body (rarely to deeper bony structures) and mostly indicated with small hydrophobic pharmacological agents, such as steroid hormones and anti-inflammatory gels to skin, muscle, and joints. Nonetheless, advances in transdermal liposomal formulation have rendered the ability to readily incorporate pharmacologically active hydrophilic drug molecules and small peptide biologics into transdermal dosage forms to impart the effective delivery of those bioactive agents across the skin barrier to underlying superficial tissue structures including bone, often enhanced by some form of electrical, chemical, and mechanical facilitation. In the following review, we evaluate transdermal drug delivery systems, with a particular focus on delivering therapeutic agents to treat superficial bone pain, notably stress fractures. We further introduce and discuss several small peptide hormones active in bone (such as calcitonins and parathyroid hormone) that have shown potential for transdermal delivery, often under the added augmentation of transdermal drug delivery systems that employ lipo/hydrophilicity, electric charge, and/or microprojection facilitation across the skin barrier.

The Impact of Implementation of the Canadian Regulatory Requirements on the Quality of Natural Health Products: The Glucosamine Case

PURPOSE We investigated whether the recent implementation of the regulatory requirements for the entry to the Canadian market of natural products has resulted in improved quality of the available glucosamine products. METHODS Eleven available products, of which 8 had been tested in 2002 (7 had contained substantially lower than the label claim of the active ingredient), and a European pharmaceutical grade tablet were assayed for their glucosamine content. The potassium and sodium contents of the products were also tested. RESULTS Nine of the 11 Canadian products and the European tablet had more than 91% of the label claim of the active ingredient, hence, met the criterion. Two products contained 71 and 78% label claim. The electrolyte contents were very variable but constituted only a small fraction of the daily requirements. CONCLUSION Most tested glucosamine products passed the Health Canada requirements. This improvement is likely due to the publicity regarding the low quality of the products in the past and also a result, at least in part, of the introduction of the new regulatory requirements. The sub-standard quality of a few tested products is still of concern.