The development and evaluation of dose-prediction tools for allopurinol therapy (Easy-Allo tools)

AIMS

Dose escalation at the initiation of allopurinol therapy can be protracted and resource intensive. Tools to predict the allopurinol doses required to achieve target serum urate concentrations would facilitate the implementation of more efficient dose-escalation strategies. The aim of this research was to develop and externally evaluate allopurinol dosing tools, one for use when the pre-urate-lowering therapy serum urate is known (Easy-Allo1) and one for when it is not known (Easy-Allo2).

METHODS

A revised population pharmacokinetic-pharmacodynamic model was developed using data from 653 people with gout. Maintenance doses to achieve the serum urate target of <0.36 mmol L-1 in >80% of individuals were simulated and evaluated against external data. The predicted and observed allopurinol doses were compared using the mean prediction error (MPE) and root mean square error (RMSE). The proportion of Easy-Allo predicted doses within 100 mg of the observed was quantified.

RESULTS

Allopurinol doses were predicted by total body weight, baseline urate, ethnicity and creatinine clearance. Easy-Allo1 produced unbiased and suitably precise dose predictions (MPE 2 mg day-1 95% confidence interval [CI] -13-17, RMSE 91%, 90% within 100 mg of the observed dose). Easy-Allo2 was positively biased by about 70 mg day-1 and slightly less precise (MPE 70 mg day-1 95% CI 52-88, RMSE 131%, 71% within 100 mg of the observed dose).

CONCLUSIONS

The Easy-Allo tools provide a guide to the allopurinol maintenance dose requirement to achieve the serum urate target of <0.36 mmol L-1 and will aid in the development of novel dose-escalation strategies for allopurinol therapy.

Population pharmacokinetics, pharmacodynamics and pharmacogenetics modelling of oxypurinol in Hmong adults with gout and/or hyperuricemia

AIMS

The aim of this study was to quantify identifiable sources of variability, including key pharmacogenetic variants in oxypurinol pharmacokinetics and their pharmacodynamic effect on serum urate (SU).

METHODS

Hmong participants (n = 34) received 100 mg allopurinol twice daily for 7 days followed by 150 mg allopurinol twice daily for 7 days. A sequential population pharmacokinetic pharmacodynamics (PKPD) analysis with non-linear mixed effects modelling was performed. Allopurinol maintenance dose to achieve target SU was simulated based on the final PKPD model.

RESULTS

A one-compartment model with first-order absorption and elimination best described the oxypurinol concentration-time data. Inhibition of SU by oxypurinol was described with a direct inhibitory Emax model using steady-state oxypurinol concentrations. Fat-free body mass, estimated creatinine clearance and SLC22A12 rs505802 genotype (0.32 per T allele, 95% CI 0.13, 0.55) were found to predict differences in oxypurinol clearance. Oxypurinol concentration required to inhibit 50% of xanthine dehydrogenase activity was affected by PDZK1 rs12129861 genotype (-0.27 per A allele, 95% CI -0.38, -0.13). Most individuals with both PDZK1 rs12129861 AA and SLC22A12 rs505802 CC genotypes achieve target SU (with at least 75% success rate) with allopurinol below the maximum dose, regardless of renal function and body mass. In contrast, individuals with both PDZK1 rs12129861 GG and SLC22A12 rs505802 TT genotypes would require more than the maximum dose, thus requiring selection of alternative medications.

CONCLUSIONS

The proposed allopurinol dosing guide uses individuals' fat-free mass, renal function and SLC22A12 rs505802 and PDZK1 rs12129861 genotypes to achieve target SU.

Mechanisms of theaflavins against gout and strategies for improving the bioavailability

BACKGROUND

Gout is a crystal related arthropathy caused by monosodium urate deposition. At present, the identification of appropriate treatments and new drugs to reduce serum uric acid levels and gout risk is a major research area.

PURPOSE

Theaflavins are naturally occurring compounds characterized by a benzodiazepine skeleton. The significant benefits of theaflavins have been well documented. A large number of studies have been carried out and excellent anti-gout results have been achieved in recent years.

STUDY DESIGN

A comprehensive analysis of the mechanism of the anti-gout effect of theaflavins is presented through a literature review and network pharmacology prediction, and strategies for increasing the bioavailability of theaflavins are summarized.

METHODS

In this review, the active components and pharmacological mechanisms of theaflavins in the treatment of gout were summarized, and the relationship between theaflavins and gout, the relevant components, and the potential mechanisms of anti-gout action were clarified by reviewing the literature on the anti-gout effects of theaflavins and network pharmacology.

RESULTS

Theaflavins exert anti-gout effects by down regulating the gene and protein expression of glucose transporter 9 (GLUT9) and uric acid transporter 1 (URAT1), while upregulating the mRNA expression levels of organic anion transporter 1 (OAT1), organic cation transporter N1 (OCTN1), organic cation transporters 1/2 (Oct1/2), and organic anion transporter 2 (OAT2). Network pharmacology prediction indicate that theaflavins can regulate the AGE-RAGE and cancer signaling pathways through ATP-binding cassette subfamily B member 1 (ABCB1), recombinant mitogen activated protein kinase 14 (MAPK14), telomerase reverse tranase (TERT), signal transducer and activator of transcription 1 (STAT1), matrix metalloproteinase 2 (MMP2), B-cell lymphoma-2 (BCL2), and matrix metalloproteinase 14 (MMP14) targets for anti-gout effects.

CONCLUSION

This review presents the mechanisms of anti-gout action of theaflavins and strategies for improving the bioavailability of theaflavins, as well as providing research strategies for anti-gout treatment measures and the development of novel anti-gout drugs.

Biopharmaceutical characterization of a novel sustained-release formulation of allopurinol with reduced nephrotoxicity

The present study was aimed to develop a novel sustained-release formulation for allopurinol (ALP/SR) with the use of a pH-sensitive polymer, hydroxypropyl methylcellulose acetate succinate, to reduce nephrotoxicity. ALP/SR was evaluated in terms of crystallinity, the dissolution profile, pharmacokinetic behavior, and nephrotoxicity in a rat model of nephropathy. Under acidic conditions (pH1.2), sustained release behavior was seen for ALP/SR, although both crystalline ALP and ALP/SR exhibited rapid dissolution at neutral condition. After multiple oral administrations of ALP samples (10 mg-ALP/kg) for 4 days in a rat model of nephropathy, ALP/SR led to a low and sustained plasma concentration of ALP, as evidenced by half the maximum concentration of ALP and a 2.5-fold increase in the half-life of ALP compared with crystalline ALP, possibly due to suppressed dissolution behavior under acidic conditions. Repeated-dosing of ALP/SR resulted in significant reductions in plasma creatinine and blood urea nitrogen levels by 73% and 69%, respectively, in comparison with crystalline ALP, suggesting the low nephrotoxic risk of ALP/SR. From these findings, a strategic SR formulation approach might be an efficacious dosage option for ALP to avoid severe nephrotoxicity in patients with nephropathy.

Low-Dose Allopurinol Promotes Greater Serum Urate Lowering in Gout Patients with Chronic Kidney Disease Compared with Normal Kidney Function

OBJECTIVES

Gout patients with chronic kidney disease (CKD) accumulate the active allopurinol metabolite oxypurinol, suggesting that allopurinol may promote greater serum urate (sU) lowering in CKD patients.

METHODS

We identified all patientswith gout diagnoses on either 100 mg or 300 mg of allopurinol daily, with available pre- and on-treatment sU levels, in our system in a 1-year period. Mean sU decrement by dosing per CKD groups was determined by CKD stage.

RESULTS

Of 1,288 subjects with gout, 180 met entry criteria, with 83 subjects receiving 100 mg and 97 receiving 300 mg allopurinol. Subjects with CKD stage 1 experienced less sU lowering with 100 mg than 300 mg of allopurinol. Subjects with stage 4 and 5 CKD had equivalent sU decreases across the 100 mg and 300 mg allopurinol groups. However, the 100 mg group started at a higher pre-treatment sU and ended at a higher final sU than the 300 mg group.

CONCLUSIONS

The strategy of titrating allopurinol to sU in patients with kidney impairment may result in greater sU lowering at lower doses than in patients without CKD but may also pose a treatment challenge from a possible drug ceiling effect.

Effect of steady-state atorvastatin on the pharmacokinetics of a single dose of colchicine in healthy adults under fasted conditions

BACKGROUND AND OBJECTIVE

Colchicine is commonly prescribed for gout. While minimally metabolized by the cytochrome P450 (CYP) 3A4 isoenzyme, colchicine is a substrate for P-glycoprotein (P-gp). Atorvastatin is metabolized primarily by CYP3A4 and is a P-gp inhibitor. Patients with gout often have dyslipidemia; therefore, the potential for co-administration of atorvastatin and colchicine exists. The objective of this study was to determine the effect of oral atorvastatin on the pharmacokinetics of a single, oral dose of colchicine.

METHODS

Twenty-four healthy adult subjects were enrolled in this single-center, open-label, non-randomized, one-sequence, two-period drug-drug interaction study. On day 1, subjects received a single oral dose of colchicine 0.6 mg. After a 14-day washout, subjects received atorvastatin 40 mg once daily for 14 days followed by a single dose of colchicine 0.6 mg co-administered with atorvastatin 40 mg on day 28. Main outcome measures were colchicine maximum plasma concentration (C max), area under the plasma concentration-time curve (AUC) from time zero to the last measurable concentration (AUC last), and AUC from time zero to infinity (AUC∞), which were compared with and without concurrent atorvastatin.

RESULTS

Colchicine AUC last, AUC∞, and C max increased by 27, 24, and 31 %, respectively, when co-administered with atorvastatin. Corresponding 90 % confidence intervals around the ratios were outside the established no-effect 80-125 % interval.

CONCLUSION

Increased colchicine exposure was observed after a single dose of colchicine was administered with steady-state atorvastatin. Additional studies with multiple dosing of both drugs are needed to further determine the clinical implications of these results.

Colchicine in clinical medicine. A guide for internists

Colchicine (COL) has been used in medicine for a long time. It is well recognized as a valid therapy in acute flares of gouty arthritis, familial Mediterranean fever (FMF), Behçet's disease, and recurring pericarditis with effusion. It has also been used to treat many inflammatory disorders prone to fibrosis, mostly with disappointing therapeutic results. The pharmacotherapeutic mechanism of action of COL in diverse diseases is not fully understood, thought it is known that the drug accumulates preferentially in neutrophils, and this effect is useful in FMF. COL shows a large interindividual bioavailability. Furthermore, interactions with drugs interfering with CYP3A4 dependent enzymes and P-glycoprotein occur and are clinically important. The dosage of COL must be reduced in patients with relevant hepatic and/or renal dysfunction. However, when appropriately used and contraindications have been excluded, oral COL is a safe treatment.

Colchicine update: 2008

OBJECTIVES

To review recent advances in the understanding of molecular mechanisms of drug disposition and cellular mechanisms of action and targets of colchicine, and disease applications and guidelines for oral colchicine use.

METHODS

Summarized and interpreted here is the pertinent English and non-English language literature on MEDLINE since the last update of colchicine in this journal in 1998 and published up to July 2008 regarding colchicine pharmacology, toxicology, mechanisms of action, and clinical applications in gout and other medical conditions.

RESULTS

Assessment, after review of 1512 publications, is that oral colchicine therapy is being refined by attention to novel targets such as NALP3 and pyrin. The drug has a narrow therapeutic-toxicity window, and potentially serious drug-drug interactions (eg, with clarithromycin and cyclosporine) are better recognized and therefore preventable. Reviewed here are recent advances in colchicine pharmacogenomics, and recognition of drug-drug interactions and predictors of potential toxicities, including alterations in the P-glycoprotein multidrug transporter ABCB1, cytochrome P450 3A4 isoenzyme, and hepatobiliary and renal function. Current understanding of optimization of colchicine dosing is reviewed, as are recent findings on colchicine therapy of nonrheumatic cardiovascular, hepatic, and renal diseases (eg, lowering of C-reactive protein, and treatment of acute and recurrent pericarditis). Finally, the article reviews the recent U.S. Food and Drug Administration-mandated cessation of marketing of injectable colchicine.

CONCLUSIONS

Oral colchicine has unique anti-inflammatory and antiproliferative effects with broad ramifications for rheumatic and nonrheumatic disease applications. Significant advances in the last decade have increased understanding of predictors of both colchicine efficacy and toxicity.

Pegloticase, a polyethylene glycol conjugate of uricase for the potential intravenous treatment of gout

Savient Pharmaceuticals Inc (formerly Bio-Technology General Corp), under license from Duke University, is developing pegloticase, PEG conjugates of uricase (urate oxidase), for the potential treatment of gout. The in-life portion of the phase III trials have been completed.

Gout and related morbid conditions: pharmacological and SPA therapy

Gouty arthritis is estimated to be the most frequent manifestation of inflammatory arthritis in men aged over 40. Hyperuricemia occurs because of both exogenous and genetic factors, which are particularly influential in some populations such as Taiwan aborigines. Current understanding of the disease etiopathogenesis, its clinical manifestations and the stages of its progression are presented here. The criteria for a correct diagnosis of the disease are also reported, pointing out how to distinguish gout from clinical events of different origin but with a very similar symptomatology. A distinction is made between the agents used to relieve the acute attack (colchicine, nonsteroidal anti-inflammatory drugs, corticosteroids) and those used with the purpose of correcting hyperuricemia and preventing recurrences and complications (allopurinol, uricosurics). Mecha-nisms of action, administration routes, doses, side effects and contraindications of every drug are described. Besides pharmacological therapy, the importance and the efficacy of spa therapy is underlined. Finally, perspectives opened by gene therapy are mentioned.

A study of the pharmacokinetic interactions of the direct renin inhibitor aliskiren with allopurinol, celecoxib and cimetidine in healthy subjects

OBJECTIVE

Aliskiren is the first in a new class of orally effective direct renin inhibitors approved for the treatment of hypertension. This multiple-dose study investigated the potential for pharmacokinetic interactions between aliskiren and three drugs, each predominantly eliminated by a different clearance/metabolic pathway: allopurinol (glomerular filtration), celecoxib (cytochrome P450 metabolism) and cimetidine (P-glycoprotein and organic anion/cation transporters).

RESEARCH DESIGN AND METHODS

Three open-label, multiple-dose studies in healthy subjects investigated possible pharmacokinetic interactions between aliskiren 300 mg od and allopurinol 300 mg od (n = 20), celecoxib 200 mg bid (n = 22), or cimetidine 800 mg od (n = 22). Subjects received aliskiren alone or co-administered with allopurinol, celecoxib or cimetidine. Allopurinol and celecoxib were also administered alone and in combination with aliskiren. Plasma drug concentrations were determined by LC/MS/MS.

RESULTS

Co-administration of aliskiren with allopurinol had no effect on allopurinol AUC(tau) (ratio of geometric means 0.93 [90% CI, 0.88, 0.98]) or oxypurinol AUC(tau) (mean ratio 1.12 [90% CI, 1.08, 1.16]) and C(max) (mean ratio 1.08 [90% CI, 1.04, 1.13]), with 90% CI within the bioequivalence range 0.80-1.25, and a minor effect on allopurinol C(max) (mean ratio 0.88 [90% CI, 0.78, 1.00]). Aliskiren co-administration had no effect on AUC(tau) or C(max) of celecoxib (mean ratios and 90% CI within range 0.80-1.25). Neither allopurinol nor celecoxib significantly altered aliskiren AUC(tau) or C(max) (geometric mean ratios 0.88-1.02 with 90% CI including 1.00, but with some 90% CI outside the 0.80-1.25 range due to high variability). Co-administration of aliskiren with cimetidine increased aliskiren AUC(tau) by 20% (mean ratio 1.20 [90% CI, 1.07, 1.34]) and C(max) by 25% (mean ratio 1.25 [90% CI, 0.98, 1.59]).

CONCLUSIONS

In this multiple-dose study, aliskiren showed no clinically relevant pharmacokinetic interactions when co-administered with allopurinol, celecoxib or cimetidine in healthy subjects.

Studies on bi-layer osmotic pump tablets of water-insoluble allopurinol with large dose: in vitro and in vivo

Controlled release bi-layer osmotic pump tablets (BOPT) of water-insoluble allopurinol with large dose (150 mg/BOPT) were successfully prepared merely with sodium chloride as osmotic promoting agent and polyethylene oxide (PEO) as suspending agent. Formulations of the two kinds of agents were investigated in order to discuss their effects on the release behavior of BOPT, and then the optimal formulation was evaluated. The pharmacokinetics studies of allopurinol and its active metabolite oxypurinol in two-preparation and two-period crossover design relative to the equivalent dose of commercially common allopurinol tablets were evaluated in six Beagle dogs. And the pharmacokinetics results showed that allopurinol BOPT were able to provide a slow release of allopurinol, and oxypurinol were bioequivalent between allopurinol BOPT and common allopurinol tablets. A good in vitro-in vivo correlation of allopurinol was also proved. In conclusion, water-insoluble drugs with large dose can be designed to BOPT for efficacy and safety use.

Allopurinol dosing in renal impairment: walking the tightrope between adequate urate lowering and adverse events

Allopurinol is the mainstay of urate-lowering therapy for patients with gout and impaired renal function. Although rare, a life-threatening hypersensitivity syndrome may occur with this drug. The risk of this allopurinol hypersensitivity syndrome (AHS) is increased in renal impairment. The recognition that AHS may be because of delayed-type hypersensitivity to oxypurinol, the main metabolite of allopurinol, and that oxypurinol concentrations are frequently elevated in patients with renal impairment prescribed standard doses of allopurinol has led to the widespread adoption of allopurinol-dosing guidelines. These guidelines advocate allopurinol dose reduction according to creatinine clearance in patients with renal impairment. However, recent studies have challenged the role of these guidelines, suggesting that AHS may occur even at low doses of allopurinol, and that these guidelines lead to under-treatment of hyperuricemia, a key therapeutic target in gout. Based on current data, we advocate gradual introduction of allopurinol according to current treatment guidelines, with close monitoring of serum uric acid concentrations. In patients with severe disease and persistent hyperuricemia, allopurinol dose escalation above those recommended by the guidelines should be considered, with careful evaluation of the benefits and risks of therapy. Further work is needed to clarify the safety and efficacy of allopurinol dose escalation, particularly in patients with renal impairment.

Pharmacokinetics and pharmacodynamics of intravenous PEGylated recombinant mammalian urate oxidase in patients with refractory gout

OBJECTIVE

To evaluate the efficacy, immunogenicity, and tolerability of intravenous (IV) PEGylated recombinant mammalian urate oxidase (PEG-uricase) for the treatment of severe gout.

METHODS

Single infusions of PEG-uricase (at doses ranging from 0.5 mg to 12 mg) were administered to 24 patients (6 cohorts of 4 patients each) in a phase I clinical trial. Plasma uricase activity (pUox), the plasma urate concentration (pUAc), and the uric acid-to-creatinine ratio (UAc:Cr) in urine were monitored for 21 days after dosing. Adverse events and the IgG antibody response to PEG-uricase were followed up for 35 days.

RESULTS

All patients completed the trial. Maximum pUox was linearly related to the IV dose of PEG-uricase, the area under the curve (AUC) value increased linearly (up to a dose of 8 mg), and the pUox half-life was 6.4-13.8 days. After doses of 4-12 mg, the pUAc fell within 24-72 hours, from a mean +/- SD value of 11.1 +/- 0.6 mg/dl to 1.0 +/- 0.5 mg/dl; the AUC value for the pUAc was equivalent to maintaining the pUAc at 1.2-4.7 mg/dl for 21 days postinfusion. The UAc:Cr ratio in urine fell in parallel with the pUAc. IgG antibodies to PEG-uricase, mostly IgG2 and specific for PEG, developed in 9 patients, who had more rapid enzyme clearance but no allergic reactions. All adverse events were mild to moderate, with gout flares being most common.

CONCLUSION

The bioavailability, efficacy, and tolerability of IV PEG-uricase were greater than the bioavailability, efficacy, and tolerability observed in a previous phase I trial of subcutaneous PEG-uricase. Infusing 4-12 mg of PEG-uricase every 2-4 weeks should maintain the pUAc well below the therapeutic target of 6 mg/dl and greatly reduce renal uric acid excretion. This treatment could be effective in depleting expanded tissue urate stores in patients with chronic or tophaceous gout.

In den Gärten der Medea

Es werden zwei Fälle beschrieben, wo Colchicin als Entzündungshemmer eingesetzt wurde. Im ersten Fall wurde ein unklares, rezidivierendes Fieber erfolgreich behandelt, der dankbare Patient wurde geheilt nach Hause entlassen. Im zweiten Fall kam es zu einer fatalen Colchicinvergiftung. Der Wirkmechanismus und Abbauweg des Colchicin werden erläutert, mit besonderem Hinweis auf die Interaktion zwischen Colchicin und Makroliden. Die Symptome und Behandlungsmöglichkeiten bei Colchicinvergiftung werden zusammengefasst.

Pharmacokinetic interactions of concomitant administration of febuxostat and NSAIDs

To evaluate the effect of febuxostat on the pharmacokinetics of indomethacin and naproxen and vice versa, 2 multiple-dose, 3-period crossover studies were performed in healthy subjects. In study 1, subjects received febuxostat 80 mg once daily, indomethacin 50 mg twice daily, or both. In study 2, subjects received febuxostat 80 mg, naproxen 500 mg twice daily, or both. Twenty-four-hour blood samples were collected on day 5 in study 1 and day 7 in study 2. In study 1, 90% confidence intervals of geometric mean ratios for maximum plasma concentration (Cmax) and area under the curve (AUC) were within the 0.80 to 1.25 no-effect range for febuxostat and indomethacin. In study 2, 90% confidence intervals for febuxostat C(max) and AUC extended above that range, with increases of 28% and 40% in Cmax and AUC24, respectively. However, 90% confidence intervals for naproxen C(max) and AUC were within the 0.80 to 1.25 range. Febuxostat had no effect on the plasma pharmacokinetics of indomethacin and naproxen. Similarly, indomethacin had no effect on the plasma pharmacokinetics of febuxostat. Although naproxen caused an increase in plasma exposure to febuxostat, this increase is not expected to be clinically significant. Therefore, based on the plasma pharmacokinetic data in healthy subjects, febuxostat may be administered with indomethacin or naproxen with no dose adjustments for febuxostat, indomethacin, or naproxen.

Colchicine today

Colchicine is used chiefly in the treatment of gout but is also valuable in other inflammatory diseases such as familial Mediterranean fever (FMF). Three proteins play pivotal roles in colchicine pharmacokinetics: the colchicine receptor, tubulin, which governs the plasma elimination half-life of the drug; intestinal and hepatic CYP3A4, which is key to the biotransformation of colchicine; and P-glycoprotein, a cell efflux pump that regulates the tissue distribution of colchicine, as well as its excretion via the biliary tract and kidneys. Pharmacokinetic studies have been performed using a radioimmunology assay to measure blood colchicine levels. Absorption after oral ingestion varies widely (from 24% to 88% of the dose), the volume of distribution is extremely large (7 l/kg), and binding to albumin is moderate. Colchicine is excreted chiefly through the liver and has an elimination half-life of 20-40 hours. With repeated doses of about 1mg/day, the steady-state is achieved within 8 days and concentrations range from 0.3 to 2.5 ng/ml. Studies of associations between pharmacokinetic parameters and pharmacodynamics show that effects are correlated, not to plasma levels, but to levels in leukocytes. Adverse events are not uncommon, most notably when colchicine is used in combination with drugs that interact with CYP3A4 and/or P-glycoprotein, thereby decreasing the renal and/or hepatic elimination of colchicine. Careful monitoring in this situation is effective in preventing the development of toxicity.

Pharmacokinetics, Pharmacodynamics and Safety of Febuxostat, a Non-Purine Selective Inhibitor of Xanthine Oxidase, in a Dose Escalation Study in Healthy Subjects

BACKGROUND

Febuxostat is a novel non-purine selective inhibitor of xanthine oxidase currently being developed for the management of hyperuricemia in patients with gout.

OBJECTIVE

To investigate the pharmacokinetics, pharmacodynamics and safety of febuxostat over a range of oral doses in healthy subjects.

METHODS

In a phase I, dose-escalation study, febuxostat was studied in dose groups (10, 20, 30, 40, 50, 70, 90, 120, 160, 180 and 240 mg) of 12 subjects each (10 febuxostat plus 2 placebo). In all groups, subjects were confined for 17 days and were administered febuxostat once daily on day 1, and days 3-14. During the course of the study, blood and urine samples were collected to assess the pharmacokinetics of febuxostat and its metabolites, and its pharmacodynamic effects on uric acid, xanthine and hypoxanthine concentrations after both single and multiple dose administration. Safety measurements were also obtained during the study.

RESULTS

Orally administered febuxostat was rapidly absorbed with a median time to reach maximum plasma concentration following drug administration of 0.5-1.3 hours. The pharmacokinetics of febuxostat were not time dependent (day 14 vs day 1) and remained linear within the 10-120 mg dose range, with a mean apparent total clearance of 10-12 L/h and an apparent volume of distribution at steady state of 33-64 L. The harmonic mean elimination half-life of febuxostat ranged from 1.3 to 15.8 hours. The increase in the area under the plasma concentration-time curve of febuxostat at doses >120 mg appeared to be greater than dose proportional, while the febuxostat maximum plasma drug concentration was dose proportional across all the doses studied. Based on the urinary data, febuxostat appeared to be metabolised via glucuronidation (22-44% of the dose) and oxidation (2-8%) with only 1-6% of the dose being excreted unchanged via the kidneys. Febuxostat resulted in significant decreases in serum and urinary uric acid concentrations and increases in serum and urinary xanthine concentrations. The percentage decrease in serum uric acid concentrations ranged from 27% to 76% (net change: 1.34-3.88 mg/dL) for all doses and was dose linear for the 10-120 mg/day dosage range. The majority of adverse events were mild-to-moderate in intensity.

CONCLUSION

Febuxostat was well tolerated at once-daily doses of 10-240 mg. There appeared to be a linear pharmacokinetic and dose-response (percentage decrease in serum uric acid) relationship for febuxostat dosages within the 10-120 mg range. Febuxostat was extensively metabolised and renal function did not seem to play an important role in its elimination from the body.

Pharmacological and Clinical Basis of Treatment of Familial Mediterranean Fever (FMF) with Colchicine or Analogues: An Update

Familial Mediterranean Fever (FMF), an autosomal recessive disorder, is characterised by recurrent attacks of fever and serositis, lasting 24-72 hours. Since 1972 colchicine has become the drug of choice for prophylaxis against FMF attacks and amyloidosis FMF-associated. Colchicine, an alkaloid neutral, is absorbed in the jejunum and ileum. It metabolised by liver and only small amounts are recovered unchanged in the urine. Really plasma half-life is prolonged in patients with liver or renal failure. Colchicine is able to prevent activation of neutrophils, binding beta-tubulin and making beta-tubulin-colchicine complexes; this way inhibits assembly of microtubules and mitotic spindle formation; moreover its mode of action includes modulation of chemokines, prostanoids production, inhibition of neutrophil and endothelial cell adhesion molecules. The minimal daily dose in adults is 1.0 mg/die, but in children there is not a definite dose. Since in vitro high dosages of colchicine stop mitosis, this drug might interfere with male and female fertility and with children growth, but, according to current guidelines and because of rare side effects of the drug, FMF patients are recommended to take colchicine. Since colchicine treatment is often complicated by frequent gastrointestinal side effects, by our experience, in order to improve colchicine tolerance we recommend: lactose-free diet and treatment of intestinal bacterial overgrowth and/or Hp-infection, assessed by breath tests. Since our data showed that 10-15% of FMF patients seem are non-responders or intolerant to colchicine, today we are working in the design of colchicine analogues which may have lesser toxicities and a larger therapeutic window.

Facile and rapid high-performance liquid chromatography method for simultaneous determination of allopurinol and oxypurinol in human serum

OBJECTIVE

To develop a rapid and sensitive assay for the simultaneous determination of allopurinol and oxypurinol in serum.

METHOD

High-performance liquid chromatography (HPLC) with UV-detection. Sample preparation consists of protein precipitation by an addition of trichloracetic acid.

RESULTS

Percentage recovery and intra-assay coefficient of variation (CV%) for allopurinol were 97.4-101.3 and 0.66-5.13, respectively, in the concentration range 0.5-5.0 microg/mL. For oxypurinol, the percentage recovery and the intra-assay CV% were 93.2-98.1 and 0.88-5.62, respectively, in the concentration ranges 0.4-20 microg/mL. There was no interference of endogenous compounds in this assay.

CONCLUSION

This method is useful for routine therapeutic drug monitoring of allopurinol in a clinical setting.

Application of LC-MS analysis to a colchicine fatality

A 73-year-old man developed nausea, vomiting, and diarrhea 20-30 min after receiving a 1.0 mg intravenous dose of colchicine for the treatment of severe pain due to gouty arthritis in his physician's office. He was hospitalized 8 h later, and his condition deteriorated as he developed renal and respiratory failure. He subsequently died 10 h later, or a total of 18 h after he received the original 1 mg colchicine injection. The patient received a prescription for oral 0.6 mg colchicine tablets 8 days previously and consumed eight tablets during that period, an average of 0.6 mg/day (42 of 50 tablets remained at the time of death). Colchicine concentrations were measured by liquid chromatography-mass spectrometry in selected ion monitoring mode using positive ionization. Chromatography was performed using an Eclipse XDB C8 analytical column (30 mm x 2.1-mm i.d., 3-microm particle size) and a programmed mobile phase consisting of 50 mM pH 4 ammonium acetate buffer and acetonitrile. Colchicine concentrations were as follows: 50 microg/L in cardiac blood, 10 microg/L in vitreous humor, 575 microg/kg in liver, 12,000 microg/L in bile, and 4.4 microg in 60 g received gastric contents (estimated total gastric contents 100 g). The cause of death was ruled to be "acute colchicine toxicity" and the manner of death "accidental."

Update on colchicine and its mechanism of action

Colchicine is a unique anti-inflammatory drug with respect to its limited clinical usefulness and its mode of action. Colchicine is mainly indicated for the treatment and prophylaxis of gout and familial Mediterranean fever. Its mode of action includes modulation of chemokine and prostanoid production and inhibition of neutrophil and endothelial cell adhesion molecules by which it interferes with the initiation and amplification of the joint inflammation. This paper discusses its adverse effects and indications.

[Aspects of colchicine therapy. 2. Additional classical indications and new therapeutic aspects]

The complex actions of colchicine, which are attributable to its stabilising action on the cytoskeleton and cell membranes and its special pattern of distribution, form the basis of the results presented here; results that relating to the prophylactic and/or therapeutic actions of colchicine in a whole range of other diseases.

[Aspects of colchicine therapy. 1: Pharmacology, toxicology, classic indications]

Colchicine has been traditionally used for the treatment of gout. Many observations discuss the prophylactic and/or therapeutic action of colchicine upon a whole range of other diseases. The first part of the overview deals with the pharmacology, and toxicology and the classical indications.

Bioequivalence of allopurinol-containing tablet preparations

AIM

The study was undertaken to prove the bioequivalence of two allopurinol tablet preparations.

SUBJECTS, MATERIALS AND METHODS

The relative bioavailability of allopurinol from two tablet preparations (Uribenz vs. Zyloric 300) was estimated on 18 volunteers of both sexes in an open randomized study by administering one tablet of each preparation at an interval of 2 weeks. The plasma concentrations of allopurinol and its active metabolite oxypurinol were measured over a time-period of 72h by HPLC.

RESULTS

While the mean AUC(0-72) values of allopurinol and oxypurinol after the test and reference preparations are entirely identical (5.33 vs. 5.21 and 137.95 vs. 137.96 microg h ml(-1), respectively), the C(max) values of oxypurinol unlike those of allopurinol show small differences (4.59 vs. 4.78 and 1.91 vs. 193 microg/ml, respectively). According to the parametric and non-parametric analysis, the quotients AUC(T)/AUC(R) and C(maxT)/C(maxR) lie within the confidence intervals 0.8 to 1.2 and 0.7 to 1.3 respectively With regard to the t(max) of allopurinol, the differences of test and reference preparations are between 0.10 to 0.05h and of oxypurinol between -0.10 to 0.87h (parametric analysis). Both, Uribenz 300 and Zyloric 300 caused a maximum decrease of the uric acid concentration in the volunteers by 18% after 10 and 24h, respectively.

CONCLUSION

Thus the bioequivalence of the allopurinol tablet preparations is demonstrated.

Mrp1 multidrug resistance-associated protein and P-glycoprotein expression in rat brain microvessel endothelial cells

Two membrane glycoproteins acting as energy-dependent efflux pumps, mdr-encoded P-glycoprotein (P-gp) and the more recently described multidrug resistance-associated protein (MRP), are known to confer cellular resistance to many cytotoxic hydrophobic drugs. In the brain, P-gp has been shown to be expressed specifically in the capillary endothelial cells forming the blood-brain barrier, but localization of MRP has not been well characterized yet. Using RT-PCR and immunoblot analysis, we have compared the expression of P-gp and Mrp1 in homogenates, isolated capillaries, primary cultured endothelial cells, and RBE4 immortalized endothelial cells from rat brain. Whereas the mdr1a P-gp-encoding mRNA was specifically detected in brain microvessels and mdr1b mRNA in brain parenchyma, mrp1 mRNA was present both in microvessels and in parenchyma. However, Mrp1 was weakly expressed in microvessels. Mrp1 expression was higher in brain parenchyma, as well as in primary cultured brain endothelial cells and in immortalized RBE4 cells. This Mrp1 overexpression in cultured brain endothelial cells was less pronounced when the cells were cocultured with astrocytes. A low Mrp activity could be demonstrated in the endothelial cell primary monocultures, because the intracellular [3H]vincristine accumulation was increased by several MRP modulators. No Mrp activity was found in the cocultures or in the RBE4 cells. We suggest that in rat brain, Mrp1, unlike P-gp, is not predominantly expressed in the blood-brain barrier endothelial cells and that Mrp1 and the mdr1b P-gp isoform may be present in other cerebral cells.

Colchicine: 1998 update

OBJECTIVE

To present an update of the use of colchicine in patients with familial Mediterranean fever (FMF) and other rheumatic and nonrheumatic diseases.

DATA SOURCES

Published studies on colchicine retrieved from MEDLINE searches from 1987 to 1997 and reports presented at national and international meetings. STUDIES SELECTION AND EXTRACTION: All studies were reviewed by the authors. Reports addressing the topics of colchicine pharmacokinetics, biological effects, indications for use, and side effects were selected.

DATA SYNTHESIS

Colchicine is an alkaloid that may interfere with microtubule formation, thereby affecting mitosis and other microtubule-dependent functions. It has a bioavailability of 25% to 50% when administered orally. Colchicine and its metabolites are excreted through the urinary and biliary tracts. It may be used while breast feeding; however, amniocentesis should be performed when used in pregnancy. The drug may be given to children with FMF. The efficacy of colchicine has been proved in FMF, gout, Behcet's disease, and cirrhosis. Its place in the treatment of scleroderma, sarcoidosis, and skin disorders remains to be determined. Gastrointestinal side effects occur early and are most common manifestations of colchicine toxicity. Severe colchicine toxicity results in multiple organ failure, convulsions, coma, and death. Potentially, effective treatment with Fab anti-colchicine antibodies unfortunately is unavailable; therefore, treatment is supportive.

CONCLUSIONS

Colchicine is a relatively safe and effective medication for several disorders when used in appropriate dosage in patients with normal kidney and liver function.

P-glycoprotein is more efficient at limiting uptake than inducing efflux of colchicine and vinblastine in HL-60 cells

PURPOSE

To investigate the role of the P-glycoprotein (P-gp) drug efflux pump in the intracellular disposition of colchicine and vinblastine.

METHODS

Uptake and efflux kinetics were studied in vitro in human lymphocytes and in HL-60 cells with or without the P-gp modulator, verapamil.

RESULTS

In human lymphocytes, colchicine was slowly taken up (uptake half-life was 18.9+/-1.1 hr.) and verapamil increased colchicine uptake by 37%, whereas it did not modify colchicine efflux from cells. In HL-60 cells, colchicine uptake was non-linear and slower than that of vinblastine, the colchicine uptake half-life (11.1+/-0.5 hr.) being 25-fold longer than that of vinblastine at 25 nM. Verapamil did not significantly modify colchicine uptake half-life, but increased its intracellular accumulation by 23% and that of vinblastine by 81%. Immuno-flow cytometry showed that P-gp expression in HL-60 cells increased significantly from 24 hr. following colchicine or vinblastine exposure. The significant increase in colchicine uptake induced by verapamil at 24 hr. was correlated with this enhanced P-gp expression. The drug efflux half-life was 11.5-fold higher for colchicine (23+/-0.9 hr) than vinblastine, indicating a much slower elimination of colchicine from cells that could be related to its longer dissociation half-life from the tubulin receptor. Verapamil treatment did not modulate either colchicine or vinblastine efflux kinetics, suggesting that the intracellular drugs are not available to the transmembrane P-gp binding sites.

CONCLUSIONS

P-gp may not be the main reason for the slowness of colchicine uptake. It may be more efficient at controlling entry of colchicine and vinblastine through the plasma membrane than at mediating their efflux from HL-60 cells.

Encapsulation, stability and in-vitro release characteristics of liposomal formulations of colchicine

The severe toxicity and low therapeutic index of colchicine limit its therapeutic use. Encapsulation in liposomes might reduce these toxic effects. The objective of this study was to determine the factors influencing encapsulation of colchicine in liposomes and to optimize the encapsulation parameters. Colchicine was encapsulated in multilamellar liposomes and large unilamellar liposomes prepared using various phospholipids. The effects of method of preparation, type of vesicle, charge, and concentration of cholesterol on encapsulation of colchicine in liposomes were investigated. Also, stability of colchicine under stress conditions and at various temperatures, and in-vitro release characteristics were determined. A significant difference in encapsulation of colchicine in multilamellar liposomes was observed when prepared by two different methods. Induction of charge on the liposome surface increased encapsulation of colchicine in multilamellar liposomes, but did not affect large unilamellar liposomes. The liposome preparations could withstand simulated transport conditions and frequent changes in temperature. Particle size and concentration of colchicine did not change significantly during storage at various temperatures for six months. In order to retain encapsulated colchicine in liposomes, storage at or below room temperature was found to be suitable. In-vitro release of colchicine from large unilamellar liposomes was biphasic and was influenced by two rate-limiting barriers, the dialysis membrane and the liposome bi-layers. For optimum encapsulation and stability of colchicine liposomes were prepared from a mixture of 1,2-distearoyl-sn-glycero-3-phosphocholine, cholesterol and either stearylamine or dicetyl phosphate.

Colchicine biotransformation by human liver microsomes. Identification of CYP3A4 as the major isoform responsible for colchicine demethylation

Colchicine disposition involves both active biliary and renal excretion of parent drug, and at least in mammals a substantial fraction undergoes hepatic demethylation prior to excretion. We investigated the biotransformation of [3H]colchicine in a panel of microsomal preparations obtained from sixteen human liver samples. The production rate of the main metabolites of colchicine's 3-demethylcolchicine (3DMC) and 2-demethylcolchicine (2DMC), was linear in relation to incubation time, cytochrome (P450) content, and substrate concentration. Following the incubation of colchicine (5 nM) with microsomes in the presence of an NADPH-generating system for 60 min, 9.8% and 5.5% of the substrate were metabolized to 3DMC and 2DMC, respectively. The formation rate of colchicine metabolites exhibited a marked variation between the different microsomal preparations. The formation rates of both colchicine metabolites were correlated significantly with nifedipine oxidase activity, a marker of CYP3A4 activity (r = 0.96, P < 0.001), but not with the metabolic markers of CYP2A6, CYP2C19, CYP2C9, CYP2D6, and CYP2E1 activities. Chemical inhibition of CYP3A4 by preincubation with gestodene (40 microM) or troleandomycin (40 microM) reduced the formation of 3DMC and 2DMC by 70 and 80%, respectively, whereas quinidine, diethyldithiocarbamate, and sulfaphenazole had no inhibitory effect. Similarly, antibodies raised against CYP3A4 almost completely abolished colchicine demethylation and nifedipine oxidase activity, but preimmune IgG had no effect. In conclusion, colchicine was metabolized to 3DMC and 2DMC by human liver microsomes. The production of colchicine metabolites was mediated by CYP3A4, and its rate varied greatly between microsomal preparations obtained from different liver samples. The coadministration of colchicine with known inhibitors or substrates of CYP3A4 may inhibit colchicine metabolism, resulting in concentration-related toxicity.

Colchicine poisoning: report of a fatal case and presentation of an HPLC procedure for body fluid and tissue analyses

A case involving a suicidal overdose resulting from the ingestion of colchicine tablets is presented. The drug was quantitated using liquid chromatography. The femoral blood level was 62 ng/mL, and the maximum concentration found in bile was 2921 ng/mL. Therefore, bile appears to be the sample of choice for toxicological analysis when a poisoning case involving colchicine is suspected.

Oral absorption characteristics and pharmacokinetics of colchicine in healthy volunteers after single and multiple doses

Colchicine is an antimitotic drug used to treat gout and familial Mediterranean fever. Absolute bioavailability, pharmacokinetics, and absorption characteristics of colchicine after single 1.0-mg doses in oral solution or tablet form or 0.5-mg intravenous doses were compared in 6 subjects. This study was combined with 14 days of multiple-dose administration of 1.0-mg colchicine tablets in 6 subjects. Serial blood samples were collected for 48 hours after administration of single doses and for 120 hours after the last dose in the multiple-dose regimen. Plasma colchicine profiles as measured by radioimmunoassay were analyzed using deconvolution and compartmental methods. After intravenous bolus injection of colchicine, the area under the concentration-time curve (AUC) was 61.2 +/- 12.7 ng.hr/mL, steady-state volume of distribution (Vss) was 419 +/- 95 L, systemic clearance (Cl) was 8.5 +/- 1.8 L/hr, and the terminal half-life (t1/2) was 57.8 +/- 10.7 hours. After oral administration in solution form, peak plasma concentrations (Cmax) of 6.50 +/- 1.03 ng/mL were reached at time (tmax) 1.07 +/- 0.55 hours, with a rate of 0.109 +/- 0.024 hr-1 (Cmax/AUC); bioavailability was 47 +/- 14%. Oral tablets yielded similar Cmax, tmax, and Cmax/AUC values, but AUC was significantly lower. Most participants exhibited a secondary peak within 6 hours of administration, possibly in relation to a second absorption site or enterohepatic recirculation. This second absorption process was significantly longer than the first one, and accounted for a similar amount of colchicine absorbed. From the multiple-dose study, a model including an alteration of colchicine absorption due to possible drug-induced gastrointestinal modifications allowed better determination of steady-state plasma concentrations of colchicine.

Disposition and uric acid lowering effect of oxipurinol: comparison of different oxipurinol formulations and allopurinol in healthy individuals

We have investigated the disposition and plasma uric acid lowering effect of oxipurinol in ten healthy individuals following oral administration of three different formulations of oxipurinol and of allopurinol in equimolar doses. The reduction of plasma uric acid was clearcut up to 48 h. As estimated from plasma AUC0-infinity, Cmax, tmax, tlag, and urinary drug excretion, a conventional rapid release preparation of oxipurinol sodium was clearly superior to oxipurinol as free acid and to enteric coated microtablets of oxipurinol sodium. Plasma oxipurinol concentrations following a single dose of the conventional formulation of oxipurinol sodium were approximately 25% lower than those observed after an equimolar dose (300 mg) of allopurinol, but mean Cmax reached the value reported to be necessary for 90% inhibition of xanthine oxidase. Since prolonged administration will result in accumulation of oxipurinol because of its slow elimination, this type of oxipurinol formulation can be expected to meet the therapeutic requirements for a drug to lower plasma uric acid.