Biomedical subjects

A J McLachlan

Publications and source records attributed to A J McLachlan.

At least 19 recordsLinked to original sources

PubMed2004

Factors affecting variability in distribution of tacrolimus in liver transplant recipients.

AIMS: Therapeutic drug monitoring (TDM) of tacrolimus is complicated by conflicting data on the correlation between tacrolimus trough blood concentrations and the incidence of rejection. The aim of this cross-sectional study was to investigate the blood distribution and protein binding of tacrolimus in liver transplant recipients to explore better predictors of clinical outcome. METHODS: Blood and plasma distribution of 3H-dihydro-tacrolimus was investigated in 40 liver transplant recipients using Ficoll Paque and density gradient ultracentrifugation, respectively, and equilibrium dialysis to investigate plasma protein binding. RESULTS: In blood tacrolimus was mainly associated with the erythrocyte fraction (83.2%, range 74.6-94.9%), followed by diluted plasma (16.1%, range 4.5-24.9%), and lymphocyte fraction (0.61%, range: 0.11-1.53%). In plasma, lipoprotein deficient serum fraction (54.2%, range 38.5-68.2%) was the main reservoir of tacrolimus. The unbound fraction of tacrolimus was found to be 0.47 +/- 0.18% (range 0.07-0.89%). The percentage of tacrolimus associated with the lymphocytes (0.8 +/- 0.4 vs 0.3 +/- 0.1%, P = 0.012) and estimated unbound concentration (0.42 +/- 0.21 ng l-1vs 0.24 +/- 0.08 ng l-1, P < 0.001) of tacrolimus were significantly different in stable transplant recipients and those experiencing rejection. Haematocrit and red blood cell count significantly influenced the percentage of tacrolimus associated with erythrocytes. The fraction unbound of tacrolimus was correlated with alpha1-acid glycoprotein and high density lipoprotein cholesterol concentrations. CONCLUSIONS: Tacrolimus unbound concentration was observed to be lower in liver transplant recipients experiencing rejection and further study is required to evaluate its utility in the TDM of tacrolimus.

Adult↗

PubMed2004

Herb-drug interactions: an evidence based approach.

The increasing use of herbal medicinal products (HMPs) in the community where people are also receiving prescription medicines suggests that adverse herb-drug interactions may be of significant public health consequence. The evidence available to guide practitioners in decision making is complex and consists of a range of sources including adverse event database entries, spontaneous or case reports, in vivo and in vitro drug metabolism studies, and in vivo drug interaction studies in healthy subjects and patients. In the absence of further rigorous studies to assess the clinical significance of herb-drug interactions, an evidence-based appraisal of the current literature is essential to guide practitioners involved in patient care.

Animals↗

PubMed2003

Pharmacokinetics of estradiol, progesterone, testosterone and dehydroepiandrosterone after transbuccal administration to postmenopausal women.

OBJECTIVE: To evaluate the pharmacokinetic profiles of estradiol, progesterone, testosterone and dehydroepiandrosterone in postmenopausal women following single and multiple dosing using a troche and the transbuccal route of administration. METHODS: Each troche contained estradiol (0.5 mg), progesterone (200 mg), testosterone (2.0 mg) and dehydroepiandrosterone (10 mg). A half troche was administered to each of six women and the plasma concentration-time profiles determined over 24 h. Thereafter, a one-half troche was taken twice daily for 2 weeks and concentrations determined over a dosage interval (12 h). Blood and saliva samples were collected at specified time intervals on the first day and again after 2 weeks. RESULTS: Each of the hormones was readily absorbed via the buccal mucous membrane. Peak plasma concentrations of estradiol and progesterone were comparable to those found normally in young menstruating women. CONCLUSION: The transbuccal route is a novel approach to provide therapy for the management of menopause-related symptoms of postmenopausal women without the need to resort to conjugated or synthesized hormones, and may overcome the poor or erratic systemic availability associated with other routes of administration.

Administration, Buccal↗

PubMed2001

Application of a high-performance liquid chromatographic assay for the neuromuscular blocker gallamine to analysis of rat plasma, muscle and microdialysate samples.

A reliable high-performance liquid chromatographic method has been validated for determination of gallamine in rat plasma, muscle tissue and microdialysate samples. A C18 reversed-phase column with mobile phase of methanol and water containing 12.5 mM tetrabutyl ammonium (TBA) hydrogen sulphate (22:78, v/v) was used. The flow-rate was 1 ml/min with UV detection at 229 nm. Sample preparation involved protein precipitation with acetonitrile for plasma and muscle tissue homogenate samples. Microdialysate samples were injected into the HPLC system without any sample preparation. Intra-day and inter-day accuracy and precision of the assay were <13%. The limit of quantification was 1 microg/ml for plasma, 1.6 microg/g for muscle tissue and 0.5 microg/ml for microdialysate samples. The assay was applied successfully to analysis of samples obtained from a pharmacokinetic study in rats using the microdialysis technique.

Animals↗

PubMed2001

Tissue distribution of terbinafine in rats.

Terbinafine is an allylamine antifungal agent that is highly lipophilic and keratophilic. The aim of this study was to investigate terbinafine distribution in peripheral and visceral tissues after intravenous administration to rats. Terbinafine, 6 mg/kg, was administered to 33 male Sprague-Dawley rats via a jugular vein cannula over 30 s. Groups of 3 rats were sacrificed at each of 11 time points (up to 24 h), and plasma and tissues were dissected, sampled, and analyzed by high-performance liquid chromatography. Terbinafine plasma concentrations declined in a triexponential fashion, with an estimated elimination half-life of 10 h. The estimated clearance of terbinafine in rats was 2 L/h/kg and the volume of distribution at steady state was 6 L/kg. The tissue-to-plasma partition coefficient (K(p)) of terbinafine for different tissues was calculated using the ratio of the area under the curve of concentration-time for tissues (AUC(tissue)) to that for plasma (AUC(plasma)), by parametric and semiparametric approaches. There was good agreement between K(p) estimates determined by different approaches. The preferential distribution of terbinafine to adipose and skin (K(p) = 49 and 45, respectively) was consistent with the lipophilicity of the drug. Uptake of terbinafine into brain (K(p) = 1.3) and muscle (K(p) = 1.0) was significantly lower. In conclusion, terbinafine displays extensive uptake to peripheral tissues, which contributes to the long elimination half-life of this drug.

Animals↗

PubMed2001

Pharmacokinetics of cyclosporine in heart transplant recipients receiving metabolic inhibitors.

BACKGROUND: Inhibitors of cyclosporine metabolism are commonly co-administered with cyclosporine in transplant recipients. The aim of this study was to compare cyclosporine pharmacokinetics using the conventional formulation (Sandimmune) and after switching to the microemulsion (Neoral) formulation, in stable heart transplant recipients receiving various cyclosporine metabolic inhibitors. METHODS: Steady-state blood concentration-time profiles of Sandimmune were studied in 47 transplant recipients receiving either cyclosporine alone (Group A, n = 11) or in combination with diltiazem (120 mg/day, Group B, n = 11), ketoconazole (200 mg/day, Group C, n = 13), or both ketoconazole and diltiazem (200 and 120 mg/day, respectively, Group D, n = 12), and restudied 1 week after switching to Neoral. RESULTS: Neoral resulted in more rapid cyclosporine absorption as judged by the shorter absorption half-lives in all groups (p < 0.05). The mean percentage increase in the values of area-under-the-concentration-time curve was 42% and 37.5% higher for Neoral compared with Sandimmune for Groups A and B, respectively, but only 5.4% higher for Group C and 9.5% higher for Group D. The mean morning trough concentration of cyclosporine was not significantly different after administration of Neoral compared with Sandimmune in any of the groups studied (179 vs. 167 microg/liter for Group A; 171 vs. 147 microg/liter for Group B; 189 vs. 194 microg/liter for Group C; and 181 vs 201 microg/liter for Group D). Neoral did not alter serum concentrations of sodium, potassium, creatinine, and urea in any of the study groups. CONCLUSIONS: The faster absorption and improved bioavailability of cyclosporine (around 40%) with Neoral compared with Sandimmune was not seen in patients receiving ketoconazole, where in fact cyclosporine bioavailability was already maximal. Mean morning trough levels of cyclosporine did not reflect the improvement in bioavailability seen in patients switching from Sandimmune to Neoral. Cyclosporine dose adjustment may be needed when switching from Sandimmune to Neoral for patients not receiving sparing agents or who receive diltiazem, but trough levels cannot necessarily be relied upon to determine the degree of adjustment needed. For patientson ketoconazole, the absorption profile is already optimized and no dosage alteration seems necessary.

Calcium Channel Blockers↗

PubMed2001

Population pharmacokinetics of amphotericin B in children with malignant diseases.

AIMS: To construct a population pharmacokinetic model for the antifungal agent, amphotericin B (AmB), in children with malignant diseases. METHODS: A two compartment population pharmacokinetic model for AmB was developed using concentration-time data from 57 children aged between 9 months and 16 years who had received 1 mg kg(-1) day(-1) doses in either dextrose (doseform=1) or lipid emulsion (doseform=2). P-Pharm (version 1.5) was used to estimate the basic population parameters, to identify covariates with significant relationships with the pharmacokinetic parameters and to construct a Covariate model. The predictive performance of the Covariate model was assessed in an independent group of 26 children (the validation group). RESULTS: The Covariate model had population mean estimates for clearance (CL), volume of distribution into the central compartment (V) and the distributional rate constants (k12 and k21) of 0.88 l h(-1), 9.97 l, 0.27 h(-1) and 0.16 h(-1), respectively, and the intersubject variability of these parameters was 19%, 49%, 55% and 48%, respectively. The following covariate relationships were identified: CL (l h(-1)) = 0.053 + 0.0456 weight (0.75) (kg) + 0.242 doseform and V (l) = 7.11 + 0.107 weight (kg). Our Covariate model provided unbiased and precise predictions of AmB concentrations in the validation group of children: the mean prediction error was 0.0089 mg l(-1) (95% confidence interval: -0.0075, 0.0252 mg l(-1)) and the root mean square prediction error was 0.1245 mg l(-1) (95% confidence interval: 0.1131, 0.1349 mg l(-1)). CONCLUSIONS: A valid population pharmacokinetic model for AmB has been developed and may now be used in conjunction with AmB toxicity and efficacy data to develop dosing guidelines for safe and effective AmB therapy in children with malignancy.

Adolescent↗

PubMed2001

Simultaneous administration of a cocktail of markers to measure renal drug elimination pathways: absence of a pharmacokinetic interaction between fluconazole and sinistrin, p-aminohippuric acid and pindolol.

AIMS: Previous studies suggest that estimated creatinine clearance, the conventional measure of renal function, does not adequately reflect changes in renal drug handling in some patients, including the immunosuppressed. The aim of this study was to develop and validate a cocktail of markers, to be given in a single administration, capable of detecting alterations in the renal elimination pathways of glomerular filtration, tubular secretion and tubular reabsorption. METHODS: Healthy male subjects (n = 12) received intravenously infused 2500 mg sinistrin (glomerular filtration) and 440 mg p-aminohippuric acid (PAH; anion secretion), and orally administered 100 mg fluconazole (reabsorption) and 15 mg rac-pindolol (cation secretion). The potential interaction between these markers was investigated in a pharmacokinetic study where markers (M) or fluconazole (F) were administered alone or together (M + F). Validated analytical methods were used to measure plasma and urine concentrations in order to quantify the renal handling of each marker. Plasma protein binding of fluconazole was measured by ultrafiltration. All subjects had an estimated creatinine clearance within the normal range. The renal clearance of each marker (mean+/- s.d.) was calculated as the ratio of the amount excreted in urine and the area-under-the-concentration-time curve. Statistical comparisons were made using a paired t-test and 95% confidence intervals were reported. RESULTS: The renal clearances of sinistrin (M: 119 +/- 31 ml min(-1); M + F: 130 +/- 40 ml min(-1); P = 0.32), PAH (M: 469 +/- 145 ml min(-1); M + F: 467 +/- 146 ml min(-1); P = 0.95), R-pindolol (M: 204 +/- 41 ml min(-1); M + F: 190 +/- 41 ml min(-1); P = 0.39; n = 11), S-pindolol (M: 225 +/- 55 ml min(-1); M + F: 209 +/- 60 ml min(-1); P = 0.27; n = 11) and fluconazole (F: 14.9 +/- 3.8 ml min(-1); M + F: 13.6 +/- 3.4 ml min(-1); P = 0.16) were similar when the markers or fluconazole were administered alone (M or F) or as a cocktail (M + F). CONCLUSIONS: This study found no interaction between markers and fluconazole in healthy male subjects, suggesting that a single administration of this cocktail of markers of different renal processes can be used to simultaneously investigate pathways of renal drug elimination.

Administration, Oral↗

PubMed2001

Analytical validation for a series of marker compounds used to assess renal drug elimination processes.

Renal drug elimination is determined by glomerular filtration, tubular secretion, and tubular reabsorption. Changes in the integrity of these processes influence renal drug clearance, and these changes may not be detected by conventional measures of renal function such as creatinine clearance. The aim of the current study was to examine the analytic issues needed to develop a cocktail of marker drugs (fluconazole, rac-pindolol, para-aminohippuric acid, sinistrin) to measure simultaneously the mechanisms contributing to renal clearance. High-performance liquid chromatographic methods of analysis for fluconazole, pindolol, para-aminohippuric acid, and creatinine and an enzymatic assay for sinistrin were developed or modified and then validated to allow determination of each of the compounds in both plasma and urine in the presence of all other marker drugs. A pilot clinical study in one volunteer was conducted to ensure that the assays were suitable for quantitating all the marker drugs to the sensitivity and specificity needed to allow accurate determination of individual renal clearances. The performance of all assays (plasma and urine) complied with published validation criteria. All standard curves displayed linearity over the concentration ranges required, with coefficients of correlation greater than 0.99. The precision of the interday and intraday variabilities of quality controls for each marker in plasma and urine were all less than 11.9% for each marker. Recoveries of markers (and internal standards) in plasma and urine were all at least 90%. All markers investigated were shown to be stable when plasma or urine was frozen and thawed. For all the assays developed, there were no interferences from other markers or endogenous substances. In a pilot clinical study, concentrations of all markers could be accurately and reproducibly determined for a sufficient duration of time after administration to calculate accurate renal clearance for each marker. This article presents details of the analytic techniques developed for measuring concentrations of marker drugs for different renal elimination processes administered as a single dose to define the processes contributing to renal drug elimination.

Adrenergic beta-Antagonists↗

PubMed2000

Determination of terbinafine in tissues.

Terbinafine and N-demethyl terbinafine concentrations were determined simultaneously in rat tissues by a high-performance liquid chromatography method. This method involved the homogenization of tissues (except for skin) followed by a liquid-liquid extraction. Skin samples were dissolved in sodium hydroxide prior to extraction. Terbinafine and its N-demethylated metabolite were assayed using a C(18) reversed-phase column with a mobile phase of acetonitrile and water (40:60) containing ortho phosphoric acid (0.02 M) and triethylamine (0.01 M), and UV detection (at 224 nm). The standard curve for the assay (constructed using clotrimazole as internal standard) was linear over the concentration range 100-3000 ng/g in skin and 10-600 ng/g in all other tissues. The inter- and intra-day precision for both terbinafine and metabolite was between 0.2% and 16%. The limit of quantification was 10 ng/g in all tissues and 100 ng/g in skin. This assay was found to be reliable and reproducible for the determination of terbinafine and N-demethyl terbinafine concentration in all rat tissues and has been used for tissue distribution studies.

Adipose Tissue↗

PubMed2000

Pharmacokinetics of ciprofloxacin in the human eye: a clinical study and population pharmacokinetic analysis.

Ciprofloxacin, a fluoroquinolone antibiotic active against a wide variety of bacteria, is one of a few antibiotics which enters the human eye after oral administration. However, little is known about its pharmacokinetics in the human eye. One or two oral doses of 750 mg of ciprofloxacin (at a 12-h interval) were administered to 48 patients at various times prior to ocular surgery. Clotted blood, aqueous, and vitreous were collected at surgery, and the concentrations of ciprofloxacin were assayed by high-performance liquid chromatography. Our data were combined with those of others, and a population pharmacokinetic analysis was conducted. The concentrations of ciprofloxacin in both aqueous and vitreous were lower than those in serum and peaked at a later time. The pharmacokinetics of ciprofloxacin in aqueous and vitreous were fitted to a compartmental model in which the antibiotic was transferred into and out of the two compartments (aqueous and vitreous) by first-order processes. Population pharmacokinetic software, P-Pharm, was used to calculate the mean half-lives of the loss of ciprofloxacin from aqueous and vitreous, which were 3.5 and 5.3 h, respectively. At steady state, the mean ratios of then concentrations in aqueous and vitreous to the concentrations in serum were 23 and 17%, respectively. After the administration of one or two doses of 750 mg of ciprofloxacin, the concentrations in both aqueous and vitreous in a number of patients were lower than the MICs at which 90% of isolates are inhibited (0.5 mg/liter) for common intraocular bacterial pathogens. Simulations of concentrations in the eye after the administration of higher doses (1,500 mg of ciprofloxacin as a single dose, two doses of 750 mg 2 h apart, and 750 mg every 6 h) indicated that in approximately 20% of patients the concentrations would still be below 0.5 mg/liter. Although oral ciprofloxacin may be a beneficial adjunctive therapy, the use of oral ciprofloxacin alone may not be adequate for perioperative prophylaxis or for treatment of bacterial endophthalmitis.

Adult↗

PubMed2000

Clinical pharmacokinetics and pharmacodynamics of celecoxib: a selective cyclo-oxygenase-2 inhibitor.

Celecoxib, a nonsteroidal anti-inflammatory drug (NSAID), is the first specific inhibitor of cyclo-oxygenase-2 (COX-2) approved to treat patients with rheumatism and osteoarthritis. Preliminary data suggest that celecoxib also has analgesic and anticancer properties. The selective inhibition of COX-2 is thought to lead to a reduction in the unwanted effects of NSAIDs. Upper gastrointestinal complication rates in clinical trials are significantly lower for celecoxib than for traditional nonselective NSAIDs (e.g. naproxen, ibuprofen and diclofenac). The rate of absorption of celexocib is moderate when given orally (peak plasma drug concentration occurs after 2 to 4 hours), although the extent of absorption is not known. Celexocib is extensively protein bound, primarily to plasma albumin, and has an apparent volume of distribution of 455+/-166L in humans. The area under the plasma concentration-time curve (AUC) of celecoxib increases in proportion to increasing oral doses between 100 and 800mg. Celecoxib is eliminated following biotransformation to carboxylic acid and glucuronide metabolites that are excreted in urine and faeces, with little drug (2%) being eliminated unchanged in the urine. Celecoxib is metabolised primarily by the cytochrome P450 (CYP) 2C9 isoenzyme and has an elimination half-life of about 11 hours in healthy individuals. Racial differences in drug disposition and pharmacokinetic changes in the elderly have been reported for celecoxib. Plasma concentrations (AUC) of celecoxib appear to be 43% lower in patients with chronic renal insufficiency [glomerular filtration rate 2.1 to 3.6 L/h (35 to 60 ml/min)] compared with individuals with healthy renal function, with a 47% increase in apparent clearance. Compared with healthy controls, it has been reported that the steady-state AUC is increased by approximately 40% and 180% in patients with mild and moderate hepatic impairment, respectively. Celecoxib does not appear to interact with warfarin, ketoconazole or methotrexate; however, clinically significant drug interactions with fluconazole and lithium have been documented. As celecoxib is metabolised by CYP2C9, increased clinical vigilance is required during the coadministration of other substrates or inhibitors of this enzyme.

Administration, Oral↗

PubMed2000

[Properties and features of nabumetone].

Nabumetone is a nonsteroidal anti-inflammatory drug (NSAID) of the 2,6-disubstituted naphthylalkanone class. It is a prodrug metabolised to an active metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA), which preferentially inhibits cyclo-oxygenase-2 (COX-2) and has both anti-inflammatory and analgesic properties. The efficacy of nabumetone is comparable to that of other NSAIDs currently marketed in France for the treatment of rheumatoid arthritis and osteoarthritis. Nabumetone is metabolised to 6-MNA by extensive first-pass metabolism. This active metabolite is subsequently conjugated and excreted in urine. 6-MNA does not undergo enterohepatic recirculation, which may have implications for comparative gastrointestinal toxicity. Substantial concentrations of 6-MNA are achieved and maintained in synovial fluid, which is close to the proposed site of action in chronic arthropathies. The long plasma half-life of 6-MNA (20 to 24 hours) and its persistence in synovial fluid facilitate a once-daily dosage regimen. Nabumetone compares favourably with other NSAIDs with respect to its renal and gastrointestinal adverse effect profile, although increased clinical vigilance of drug-related adverse events relating to these organ systems is still recommended. In addition, in vitro experiments have shown this drug to have a good cartilage tolerability profile. Whether nabumetone has clinical utility in cardiovascular disorders remains to be determined. The unique pharmacokinetic and pharmacodynamic properties of nabumetone make it a welcome addition to the growing arsenal of drugs used in the treatment of chronic arthropathies. There may be clinical advantages in terms of the relative tolerability profile of nabumetone, given that this drug has a low COX-2/COX-1 ratio compared with other nonselective NSAIDs.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1999

Criteria for involuntary hospitalisation.

OBJECTIVE: The aim of this paper is to provide an overview of the ethical bases of compulsory commitment legislation. METHOD: The ethical principles of beneficence and autonomy are examined and used to identify criteria for the commitment of mentally ill patients. RESULTS: Two aspects of beneficence, medical paternalism and social paternalism, are discussed. It is argued that social paternalism is insufficient ethically to warrant involuntary admission, and that the basis for compulsory hospitalisation is medical paternalism. CONCLUSION: The central role of autonomy in medical ethics suggests a patient should have a diminished capacity for autonomous decision-making and a potential to benefit from hospitalisation, as well as a risk of harm to self (including self-neglect) to warrant committal. In specific circumstances, the risk of harm to others may also justify committal. These ethical principles may be at odds with public attitudes.

Commitment of Persons with Psychiatric Disorders↗

PubMed1999

Amphotericin B in children with malignant disease: a comparison of the toxicities and pharmacokinetics of amphotericin B administered in dextrose versus lipid emulsion.

In a prospective, randomized clinical trial, the toxicity of 1 mg of amphotericin B (AmB) per kg of body weight per day infused in 5% dextrose was compared with that of AmB infused in lipid emulsion in children with malignant disease. In an analysis of 82 children who received a full course of 6 days or more of AmB (117 courses), it was shown that there were significant increases in plasma urea and creatinine concentrations and in potassium requirement after 6 days of therapy with both AmB infused in dextrose and AmB infused in lipid emulsion, with there being no difference between the two methods of AmB administration. An intent-to-treat comparison of the numbers of courses affected by acute toxicity (fever, rigors) and chronic toxicity (nephrotoxicity) also indicated that there was no significant difference between AmB infused in dextrose (78 courses) and AmB infused in lipid emulsion (84 courses). The pharmacokinetics of AmB were investigated in 20 children who received AmB in dextrose and 15 children who received AmB in lipid emulsion. Blood samples were collected up to 24 h after administration of the first dose, and the concentration of AmB in plasma was analyzed by a high-performance liquid chromatography assay. The clearance (CL) of AmB in dextrose (0.039 +/- 0.016 liter. h-1. kg-1) was significantly lower (P < 0.005) than the CL of AmB in lipid emulsion (0.062 +/- 0. 024 liter. h-1. kg-1). The steady-state volume of distribution for AmB in dextrose (0.83 +/- 0.33 liter. kg-1) was also significantly lower (P < 0.005) than that for AmB in lipid emulsion (1.47 +/- 0.77 liter. kg-1). Although AmB in lipid emulsion is apparently cleared faster and distributes more widely than AmB in dextrose, this study did not reveal any significant advantage with respect to safety and tolerance in the administration of AmB in lipid emulsion compared to its administration in dextrose in children with malignant disease.

Adolescent↗

PubMed1999

Pharmacokinetics of nonsteroidal anti-inflammatory drugs in synovial fluid.

The major site of action for nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of rheumatic diseases is probably within the synovial compartment. There has been little work on the disposition of NSAIDs in the synovium and most studies have involved the measurement of their concentrations in synovial fluid. The concentrations of NSAIDs are more sustained in synovial fluid than in plasma, the difference being particularly noted with NSAIDs with short elimination half-lives. The more sustained concentrations may contribute to the prolonged effect of the short half-life NSAIDs, which are usually administered at intervals longer than their half-lives in plasma. The most widely used method of kinetic analysis of NSAIDs in synovial fluid is a compartmental model in which synovial fluid is a peripheral compartment of distribution of the drug. Repeated samples of synovial fluid from individual patients are difficult to collect, but even 1 sample of synovial fluid and plasma from each patient can provide useful data when analysed using the population approach to pharmacokinetic analysis. According to the compartmental model, the mean half-lives of efflux of the NSAIDs from synovial fluid range from 1.5 to 7 hours. The mean partition coefficient of most NSAIDs between synovial fluid and plasma is approximately 0.6. The NSAIDs are highly protein-bound, and the lower mean concentrations in synovial fluid are largely because of the lower concentrations of the binding protein, albumin. The NSAIDs diffuse into and out of synovial fluid in their unbound forms, but there is some diffusion in the protein-bound forms, particularly out of synovial fluid. The mean rates of diffusion of NSAIDs into and out of skin blisters in humans are similar to the rates of influx and efflux in the synovial fluid of the knee, but there is considerable variation between the pharmacokinetics of transfer at the 2 sites in individual patients. NSAIDs decrease the synthesis of prostaglandins in synovial fluid, but there are few data on the relationship between the kinetics of NSAIDs in synovial fluid and the effects on prostaglandin synthesis.

Animals↗

PubMed1998

Effect of metabolic inhibitors on cyclosporine pharmacokinetics using a population approach.

Drugs known to inhibit the metabolism of cyclosporine are administered concomitantly to those who undergo cardiothoracic transplantation. The aim of this study was to examine in quantitative terms the relationship between cyclosporine oral dose rate and the trough concentration (Css(trough)) at steady state in patients who undergo cardiothoracic transplantation and are administered cyclosporine alone or in combination with drugs known to inhibit its metabolism. Dose and whole blood cyclosporine Css(trough) observations measured using the enzyme-multiplied immunoassay technique (EMIT) (396 observations) or the TDx assay (435 observations) were collected as part of routine blood concentration monitoring from 182 patients who underwent cardiothoracic transplantation. Data were analyzed using a linear mixed-effects modeling approach to examine the effect of metabolic inhibitors on dose-rate-Css(trough) ratio. The mean (and 95% confidence interval) dose-rate-Css(trough) ratio for cyclosporine generated from concentrations measured using EMIT was 94 (82.5-105.5) Lh(-1) for patients administered cyclosporine alone, 66.7 (58.1-75.3) Lh(-1) for patients administered concomitant diltiazem, 47.9 (15.4 -80.4) Lh(-1) for patients administered concomitant itraconazole, 21.7 (14.8-28.5) Lh(-1) for patients administered concomitant ketoconazole, and 14.9 (11.8-18.1) Lh(-1) for patients concomitantly administered diltiazem and ketoconazole. For patients administered concomitant cyclosporine, ketoconazole, and diltiazem, the dosage of cyclosporine, if it is administered alone, should be 20% to achieve the same blood concentrations. This will allow safer drug concentration targeting of cyclosporine after cardiothoracic transplantation.

Administration, Oral↗

PubMed1998

Effect of clofibrate on the chiral disposition of ibuprofen in rats.

A potentially clinically important interaction has been described between clofibrate and ibuprofen in vitro. To determine whether this in vitro interaction is paralleled by a change in pharmacokinetics of ibuprofen in vivo two groups of rats were treated orally with clofibrate (n = 8, 280 mg/kg/day) or vehicle (n = 7) for 3 days. On day 3, 2 hr after the last dose of clofibrate, the rats were given an i.v. dose of pseudoracemic ibuprofen (20 mg/kg, 10 mg R-ibuprofen, 10 mg 13C-S-ibuprofen). Plasma concentrations of the enantiomers were monitored by a stereospecific gas chromatography mass spectrometry assay. The clearance of R-ibuprofen more than doubled in the clofibrate-treated group (mean +/- S.E.M.; 29.4 +/- 4.0 ml/min) as compared to control rats (13.0 +/- 1.4 ml/min; P = .003). This increase was similarly reflected in the clearance by inversion (treated, 23.2 +/- 3.2 ml/min, untreated, 10.0 +/- 1.2 ml/min; P = .003) and there was also an increase in the rate of inversion (treated, t1/2 inversion, 8.3 +/- 1.6 min; untreated, 13.9 +/- 1.4 min; P = .029). By contrast, the estimates of fractional chiral inversion were not affected by clofibrate and were in close agreement whether estimated by the area under the plasma concentration-time curve approach (treated, 0.79 +/- 0.02; untreated, 0.72 +/- 0.02) or by deconvolution (treated, 0.78 +/- 0.02; untreated, 0.73 +/- 0.02). There was a significant increase in volume of distribution at steady-state (treated, 4.42 +/- 1.12 liter/kg; untreated, 1.03 +/- 0.30 liter/kg; P = .017) observed for the R-enantiomer but not the S-enantiomer (treated, 1.04 +/- 0.13 liter/kg; untreated, 1.10 +/- 0.21 liter/kg). Pretreatment of rats with clofibrate significantly increased the concentrations of ibuprofen in fat, lung, brain and liver tissue. With respect to the protein levels of two key enzymes involved in chiral inversion, clofibrate pretreatment significantly induced expression of long chain acyl-coenzyme A synthetase, although the expression of the epimerase was unaltered. It is concluded, that clofibrate may increase the proportion of R-ibuprofen incorporated into long-lived lipid ("hybrid" lipid) stores.

Animals↗