Liraglutide attenuates nicotine self-administration as well as nicotine seeking and hyperphagia during withdrawal in male and female rats.

RATIONALE: Nicotine cessation is associated with increased consumption of highly palatable foods and body weight gain in most smokers. Concerns about body weight gain are a major barrier to maintaining long-term smoking abstinence, and current treatments for nicotine use disorder (NUD) delay, but do not prevent, body weight gain during abstinence. Glucagon-like peptide-1 receptor (GLP-1R) agonists reduce food intake and are FDA-approved for treating obesity. However, the effects of GLP-1R agonist monotherapy on nicotine seeking and withdrawal-induced hyperphagia are unknown. OBJECTIVES: We screened the efficacy of the long-lasting GLP-1R agonist liraglutide to reduce nicotine-mediated behaviors including voluntary nicotine taking, as well as nicotine seeking and hyperphagia during withdrawal. METHODS: Male and female rats self-administered intravenous nicotine (0.03 mg/kg/inf) for ~21 days. Daily liraglutide administration (25 µg/kg, i.p.) started on the last self-administration day and continued throughout the extinction and reinstatement phases of the experiment. Once nicotine taking was extinguished, the reinstatement of nicotine-seeking behavior was assessed after an acute priming injection of nicotine (0.2 mg/kg, s.c.) and re-exposure to conditioned light cues. Using a novel model of nicotine withdrawal-induced hyperphagia, intake of a high fat diet (HFD) was measured during home cage abstinence in male and female rats with a history of nicotine self-administration. RESULTS: Liraglutide attenuated nicotine self-administration and reinstatement in male and female rats. Repeated liraglutide attenuated withdrawal-induced hyperphagia and body weight gain in male and female rats at a dose that was not associated with malaise-like effects. CONCLUSIONS: These findings support further studies investigating the translational potential of GLP-1R agonists to treat NUD.

Therapeutic Differences in 24-h Ambulatory Blood Pressures in Patients Switched Between Bioequivalent Nifedipine Osmotic Systems With Differing Delivery Technologies.

Comparing modified-release formulations can be difficult using current bioequivalence criteria. Two 60-mg-once-daily nifedipine formulations are deemed bioequivalent in Canada. This study examined the validity of the assumption that these interchangeable, but different, delivery technologies are therapeutically equivalent in maintaining systolic blood pressure (SBP) control throughout the entire dosing interval. We used 24-h Ambulatory Blood Pressure Monitoring to objectively examine whether formulation switches changed population SBP >2 mmHg (reflecting 6% increased stroke mortality) and in what proportion of patients SBP changed ≥6 mmHg (risking unnecessary therapeutic alterations). When 20 patients, previously receiving 60-mg-once-daily Nifedipine-GITS, were switched to Mylan-Nifedipine-XL, population-mean ± SE 24-h SBP increased 3 ± 1.1 mmHg (P = 0.0173) and 8-h nocturnal SBP increased 4 ± 1.6 mmHg (P = 0.0098). Thus, interchange of nifedipine formulations can affect therapeutic consistency. These data support existing calls to improve criteria for establishing bioequivalence between formulations employing differing modified-release technologies.

Drug interactions and the statins.

Drug interactions commonly occur in patients receiving treatment with multiple medications. Most interactions remain unrecognized because drugs, in general, have a wide margin of safety or because the extent of change in drug levels is small when compared with the variation normally seen in clinical therapy. All drug interactions have a pharmacokinetic or pharmacodynamic basis and are predictable given an understanding of the pharmacology of the drugs involved. Drugs most liable to pose problems are those having concentration-dependent toxicity within, or close to, the therapeutic range; those with steep dose-response curves; those having high first-pass metabolism or those with a single, inhibitable route of elimination. Knowing which drugs possess these intrinsic characteristics, together with a knowledge of hepatic P-450 metabolism and common enzyme-inducing and enzyme-inhibiting drugs, can greatly assist physicians in predicting interactions that may be clinically relevant. This article reviews the pharmacology of drug interactions that can occur with hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) to illustrate the scope of the problem and the ways in which physicians may manage this important therapeutic class of drugs.

A cardiovascular risk factor reduction clinic.

OBJECTIVE: To describe a cohort of patients referred to a cardiovascular risk factor reduction unit (CRFRU). DESIGN: Prospective cohort study. SETTING: Out-patients referred to a specialty clinic in a tertiary care hospital. PATIENTS: Seven hundred and four consecutive male and female patients with one or more cardiovascular risk factors, of whom 388 were reassessed after one year. INTERVENTIONS: Standard risk factors were measured in all participants. The probability of coronary artery disease (CAD) was assessed according to the Framingham equation and results were compared with data from the Saskatchewan Heart Health Survey for the general population of Saskatchewan. Patients received dietary and fitness advice, as well as drug therapy when indicated. For follow-up studies, the change in probability of CAD and selected variables after one year were measured. MAIN RESULTS: Patients referred to the CRFRU were at considerably higher risk for CAD than the general population. One hundred and sixty-eight of 235 men and 77 of 153 women seen in follow-up had a reduced risk score. Those who improved had a favourable change in systolic blood pressure and in their lipid profile, as well as greater weight loss. CONCLUSIONS: A CRFRU is feasible and appears to reduce risk in a considerable proportion of patients.

Changes in the position and angulation of incisura during contractions of the isolated cat stomach.

Contractions change the configuration of the lesser curvature of the stomach while they indent the greater curvature. We studied these lesser curvature changes by measuring the position and angle of the gastric incisura on still frames captured from videotapes of isolated cat stomachs suspended in physiologic solution. In response to filling with 100 mL Krebs' solution stomachs generated a tonic contraction of the fundus/body segment and gave rise to a peristaltic contraction that spread from the body and through the antrum to the pylorus. In preparations where we left the duodenal cannula open we found that the incisura moves toward the gastro-oesophageal (GO) junction and the angle of the incisura widens as the contraction passes through the stomach and empties its contents. Furthermore, the angle of the incisura is most acute when the full stomach starts contracting in its fundic segment and again when the contraction involves the gastric sinus (the wedge-shaped segment adjacent to the incisura which forms the transition between the body and the antrum of the stomach). In preparations where the duodenal cannula was kept closed, the angle of the incisura becomes most acute when the contraction involves the gastric body and when the luminal pressure peaks. We conclude that changes in the position and angulation of the incisura are part of the mechanical response of the stomach to filling and emptying; unlike the peristaltic contraction along the greater curvature the net movement of the incisura goes in the orad direction. Movements of the incisura profoundly affect the configuration of the stomach and hence the distribution of luminal contents between various gastric segments. The gastric sling muscles are responsible for the formation of the gastric incisura but their role in any movements of the incisura remains to be defined.

Contractions move contents by changing the configuration of the isolated cat stomach.

To understand how contractions move gastric contents, we measured, in isolated cat stomachs, the effects of contractions on gastric length, diameters, pressures, and emptying. Movements of the stomach and of gastric contents were monitored by video camera and ultrasound and were related to mechanical events. Based on pressures, we defined the following four phases of contractions: 1) Po, a steady pressure associated with tonic contraction of proximal stomach; 2) P', a pressure wave during which the contraction indents the gastric body; 3) a pressure nadir while the contraction lifts the gastric sinus toward the incisura; and 4) a second pressure wave, P", as the contraction advances through the antrum. In open preparations, liquid output and shortening of the greater curvature are large during Po, stop during P', and resume with P". Contractions generate higher pressures when gastric volume is held steady. Contractions increase wall thickness and decrease gastric diameters at sites they involve and have opposite effects at remote sites. Contractions move the incisura and hence redraw the borders between gastric segments and shift volumes back and forth within the gastric lumen. Contractions furthermore stir up, compress, and disperse particulate beans without moving them to the pylorus. We conclude that gastric contractions 1) reverse changes in gastric length that occur during gastric filling, 2) move gastric contents directly through local contact and indirectly by changing the configuration of the stomach, and 3) interact with structures such as the incisura in retaining and breaking up solid gastric contents.

Disposition of diazepam in young and elderly subjects after acute and chronic dosing.

1. The pharmacokinetics of diazepam were examined in seven young (20-30 years) and six elderly (60-75 years) males prior to and also after chronic oral dosing of diazepam. 2. Following intravenous administration, the half-life and volume of distribution of 14C-labelled diazepam in the elderly were approximately twofold greater than corresponding estimates in younger subjects (mean +/- s.d., 71.5 +/- 27.6 vs 44.5 +/- 16.5 h and 1.39 +/- 0.32 vs 0.88 +/- 0.30 1 kg-1, respectively). Clearance did not differ between the two groups (0.26 +/- 0.09 vs 0.29 +/- 0.09 ml min-1 kg-1). 3. The accumulation of diazepam and its major metabolite, desmethyldiazepam, were extensive during chronic administration. A radioreceptor assay that measured total benzodiazepine activity, including diazepam and its active metabolites, indicated that the accumulation of 'benzodiazepine equivalents' was similar to the sum of the accumulated diazepam and desmethyldiazepam concentration levels. However, the level of 'benzodiazepine equivalents' on multiple-dosing was about double that of the predicted steady-state 'equivalent' concentration from single-dose studies. This was due to the insensitivity of the radioreceptor assay for desmethyldiazepam following single-dose diazepam administration. 4. There were no age- or dosing-related differences in diazepam clearance (0.37 +/- 0.22 vs 0.32 +/- 0.18 ml min-1 kg-1, young vs elderly, single-dose; 0.37 +/- 0.11 vs 0.27 +/- 0.12 ml min-1 kg-1, young vs elderly, multiple-dose) and no age-related differences in the levels of accumulated 'benzodiazepine equivalents' (243.7 +/- 60.1 vs 288.0 +/- 125.8 ng ml-1, young vs elderly). 5. Thus, changes that occur in diazepam disposition with ageing after acute administration do not appear to be important during chronic dosing. On the other hand, accumulation of diazepam and desmethyldiazepam are considerable and would be expected to be clinically relevant.

Disposition of lorazepam in diabetes: differences between patients treated with beef/pork and human insulins.

The pharmacokinetics of lorazepam was examined in 10 male patients with insulin-dependent diabetes mellitus before and following treatment with neomycin and cholestyramine. Neomycin and cholestyramine were given in an attempt to block the enterohepatic circulation of lorazepam and so to permit an in vivo estimate of hepatic glucuronidation. The volume of distribution and clearance of free lorazepam in diabetic patients were not significantly different from the corresponding estimates in 14 normal controls. Neomycin and cholestyramine increased the clearance of lorazepam by 63% consistent with their effect in non-diabetic controls. However, patients on beef/pork insulin exhibited a greater than normal increase on this interupting regimen (125%), and had a significantly greater neomycin/cholestyramine cycling-interrupted clearance of lorazepam than either normal controls or patients on human insulin (15.4 vs. 6.96 and 7.87 ml.min-1.kg-1). The clearance was correlated positively and significantly with HbA1c and glycated proteins (fructosamine), but only in patients on human insulin. Thus, the pharmacokinetics of lorazepam was not altered in patients with insulin-dependent diabetes mellitus. However, it is possible that there are differences in the rate and extent of hepatic glucuronidation and enterohepatic circulation of lorazepam between patients treated with beef/pork and human insulins and between diabetics treated with beef/pork insulin and non-diabetic controls.

Effect of probenecid on the formation and elimination kinetics of the sulphate and glucuronide conjugates of diflunisal.

The effect of probenecid on the pharmacokinetics of diflunisal and its glucuronide and sulphate conjugates was studied in 8 healthy volunteers. Diflunisal 250 mg b.d. was administered p.o. for 15 days and its steady state pharmacokinetics was evaluated on Day 16 after the last dose (control phase). Probenecid 500 mg b.d. was co-administered throughout the entire study period in the treatment phase of the study. The steady state plasma concentration of diflunisal was significantly higher during the probenecid treatment phase as compared to the control phase (104.0 vs. 63.1 micrograms.ml-1). This was the result of a significant decrease in the plasma clearance of diflunisal from 5.8 (control) to 3.4 ml.min-1 (probenecid co-administration). The metabolite formation clearances of both glucuronides were significantly decreased by probenecid, -45% and -54% for the phenolic and acyl glucuronide, respectively. The metabolite formation clearance of the sulphate conjugate was not affected by probenecid coadministration. Steady state plasma concentrations of the sulphate and glucuronide conjugates of diflunisal were 2.5- to 3.1-fold higher during probenecid co-administration, due to a significant reduction in the renal clearance of the three diflunisal conjugates. Probenecid also reduced the plasma protein binding of diflunisal, but only to a minor extent; the unbound plasma fraction of diflunisal at steady state averaged between 5 and 30% higher during probenecid co-administration.

Disposition of lorazepam in Gilbert's syndrome: effects of fasting, feeding, and enterohepatic circulation.

The effects of fasting and feeding of a high-carbohydrate, low-fat diet on the glucuronidation and enterohepatic circulation (EHC) of lorazepam were examined in seven healthy men (age 18-30 years) and seven matched patients with Gilbert's syndrome. A simultaneous intravenous/oral dosing regimen was used, with half of each group receiving treatment with neomycin and cholestyramine (neo/chol) to block the EHC of the drug. Feeding increased the clearance of free lorazepam from 10.96 +/- 0.56 (mean +/- SD) to 14.11 +/- 1.21 mL/min/kg (P = 0.05) in patients with Gilbert's syndrome when examined in the presence of neo/chol. Clearances, on the other hand, decreased with feeding in control Gilbert's patients (7.61 +/- 0.54 versus 8.82 +/- 0.48 mL/min/kg), although the differences were not significant (P = 0.09). In contrast to both of these groups, feeding decreased lorazepam clearances (13.33 +/- 0.32 to 12.45 +/- 0.52 mL/min/kg, P = 0.17) in neo/chol-treated normals and increased clearances (9.95 +/- 1.84 to 12.38 +/- 2.05 mL/min/kg, P = 0.04) in control normals. Lorazepam clearances were also 20-40% lower in patients with Gilbert's syndrome compared with normals when studied fasting and with neo/chol, or fed and in the control state (P < 0.05 for both). Thus, the glucuronidation and EHC of lorazepam is sensitive both to diet and to the presence or absence of the Gilbert's trait.

Analysis of polymorphic variation in drug metabolism: I. Kernal density estimation.

Kernel density estimation was examined as an objective, nonparametric approach to the detection of polymorphic variation in distributions containing multiple complex data sets. Power curves were constructed for the kernel density estimate based on its ability to detect worked bimodality in stimulated distributions as a function of the distribution size, the fraction contained within a particular subdistribution, and the location of the mean of that subdistribution with respect to the mean of the overall distribution. Comparisons were then made between kernel density estimation and the Kolmogorov-Smirnov test of maximal differences. Results showed that kernel density estimation performed as well or better than the Kolmogorov-Smirnov test and offered a number of advantages, including identification of the frequency and placement of individual modes and antimodes. The Kolmogorov-Smirnov test, on the other hand, examined normality of a distribution rather than modality or inherent polymorphism, and the outcome was highly dependent on the subdistribution location and total distribution size. We conclude that kernel density estimation is an excellent method for analysis of polymorphic variation in drug metabolism.

Analysis of polymorphic variation in drug metabolism: II. Effects of data transformation on the sensitivity and specificity of modal detection.

Simulations were conducted for a model of drug metabolism involving 2 parallel competing pathways of elimination, wherein the effects of variability in 1 enzyme pathway were examined with respect to variability in recovery of its metabolite and recovery of metabolite through the second, nonvaried, co-eliminating route. Expression of metabolite recoveries as fractions of the total recoverable drug yielded a statistic possessing variability similar to the pattern of variability induced in the enzyme itself. However, the transformation was subject to a "distributive" effect, in that the magnitude of variation in the downstream metabolite was reduced and transferred through reciprocal variations in availability of unmetabolized drug to other nonvaried pathways. The sensitivity and specificity of the fractional recovery statistic were thereby diminished. Expression of recoveries as metabolic ratios, on the other hand, limited variability to the pathway in which it was originally induced. The pattern of variation was skewed and exaggerated, particularly towards the rightward, "poor metabolizer" tail of the distribution, and this caused problems with visual interpretations as well as more objective approaches like the kernel density estimate. Additional transformation to the log metabolic ratio provided considerable improvement in this regard. Thus, log metabolic ratios are the most sensitive and specific of the data transformations and are the preferred manner of expression in all multipathway metabolite analyses.

Analysis of polymorphic variation in drug metabolism: III. Glucuronidation and sulfation of diflunisal in man.

The urinary excretion of diflunisal (D) and its metabolites diflunisal sulfate (DS), diflunisal phenolic glucuronide (DPG), and diflunisal acyl glucuronide (DAG) were measured in 110 healthy, drug-free Caucasian volunteers given 50 mg of diflunisal by mouth. When expressed as fractional recoveries, DS, DPG, and DAG were strongly negatively correlated with one another. Metabolic ratios, on the other hand, correlated positively and tended to localize variability within a single enzyme pathway. Thus, females using estrogen-containing oral contraceptives were shown to excrete 50% less DS and 20% more DAG than non-users, and recoveries of DS were reduced by about 30% in cigarette smokers. Kernel density analyses of the log metabolic ratios of DS and DPG were broad-based and unimodal. However, kernel density estimates of the distribution of log metabolic ratios of DAG showed 3 peaks, 1 of which (an extensive metabolizer polymorph) could be removed by excluding contraceptive-using females. Similarly, there were 2 poor metabolizer peaks in the distribution of log metabolic ratios of DS attributable to cigarette smoking and, in females, use of an oral contraceptive. Thus, we conclude that the metabolism of diflunisal is altered by cigarette smoking and oral contraceptives, and that kernel density estimation, as applied to log metabolic ratios, is a sensitive and specific method for detection of polymorphic variation in drug metabolism.

High glucose attenuates peptide agonist-evoked increases in cytosolic free [Ca2+] in rat aortic smooth muscle cells.

Incubation of cultured rat aortic smooth muscle cells (ASMCs) in a medium containing high glucose concentrations (25 mM) did not affect the basal cytosolic free calcium ([Ca2+]i) but led to significant reductions in peak [Ca2+]i response evoked by arginine vasopressin, angiotensin II, and endothelin-1 (ET-1). This was observed in both the presence and absence of extracellular Ca2+. Maintenance of rat ASMCs in a medium containing mannose (an osmotic control for high glucose) did not affect either the basal or peptide agonist-evoked increase in [Ca2+]i. However, pretreatment with either the nonselective protein kinase C (PKC) inhibitor staurosporine or the selective PKC inhibitor 2,6-diamino-N-([1-(1-oxotridecyl)-2 piperidinyl] methyl) hexanamide reversed the attenuating effect of high glucose on peak [Ca2+]i response evoked by ET-1. Also, short-term incubation of ASMCs with the active phorbol ester, phorbol 12-myristate 13-acetate, led to a reduction in peak [Ca2+]i response to all three agonists, whereas the inactive phorbol ester, 4 alpha-phorbol 12,13-didecanoate, which does not activate PKC, had no such effect. Although high-glucose treatment of rat ASMCs led to significant reductions in the maximal number of binding sites to the extent of 39% of [125I]ET-1 specific binding, no significant differences in the affinity (Kd approximately 110 pM) characteristics were evident between control and high-glucose treatment groups. It is proposed that incubation of rat ASMCs with high glucose enhances the de novo synthesis of diacylglycerol and activates membrane-bound PKC and that this, in turn, impairs agonist-mediated intracellular Ca2+ mobilization.

Multiple-dose lorazepam kinetics: shuttling of lorazepam glucuronide between the circulation and the gut during day- and night-time dosing intervals in response to feeding.

Lorazepam kinetics were examined in seven healthy males age 18 to 30 years after single- and multiple-dose lorazepam administration and in the presence and absence of neomycin and cholestyramine to block the enterohepatic circulation of the drug. Methods used a simultaneous i.v./p.o. dosing regimen with provision to measure lorazepam clearance during day- and night-time dosing intervals. The day-time steady-state clearance of free lorazepam measured 7.55 +/- 1.95 ml/min/kg (mean +/- S.D.) and was identical to that observed after single-dose administration (7.68 +/- 3.19 ml/min/kg). Neomycin and cholestyramine increased lorazepam clearances 5 to 45% (P < or = .05) as would be expected for interruption of an enterohepatic circulation and in keeping with previous observations under nonsteady-state conditions. Lorazepam clearances were the same during the day as during the night, except in the presence of neomycin and cholestyramine, where night-time clearances were significantly greater (10.16 +/- 3.52 vs. 8.77 +/- 2.43 ml/min/kg, P < or = .05). Urinary recoveries of lorazepam glucuronide, on the other hand, were greater during the day than during the night (114 +/- 11 vs. 77 +/- 15%, P < or = .05) and in all cases were greater than 100% of the administered dose for that interval. Thus, there is a diurnal variation in lorazepam elimination consistent with a fasting-induced increase in hepatic glucuronidation during the night. This, combined with the relative inactivity of the gut during this period, serves to trap the glucuronide and delay its transfer back to the systemic circulation and urine.

The effect of multiple dosage on the kinetics of glucuronidation and sulphation of diflunisal in man.

1. The single (250 and 500 mg) and multiple dose (250 and 500 mg twice daily for 15 days) pharmacokinetics of diflunisal were compared in young volunteers. 2. The plasma clearance of diflunisal was lowered significantly after multiple dose administration (5.2 +/- 1.2 and 4.2 +/- 0.7 ml min-1 for the 250 and 500 mg twice daily regimens, respectively) as compared with single dose administration 11.4 +/- 3.1 and 9.9 +/- 2.0 ml min-1 for the 250 and 500 mg single doses, respectively). 3. The partial metabolic clearances of diflunisal by acyl and phenolic glucuronide formation were lowered significantly (greater than 50%) after multiple dose administration. 4. The urinary recovery of diflunisal sulphate increased as a function of dose: 6.1 +/- 2.8 and 9.1 +/- 3.5% following the 250 and 500 mg single dose, respectively, and 10.9 +/- 3.1 and 15.9 +/- 3.6% following the 250 and 500 mg twice daily regimens. The partial metabolic clearance of diflunisal by sulphate conjugation was unchanged following multiple dose administration. 5. The plasma protein binding of diflunisal was concentration-dependent. Analysis of unbound plasma clearances of diflunisal showed that its total plasma clearance following 500 mg twice daily was affected by both saturable glucuronidation and concentration-dependent plasma binding.

Sex-difference and the effects of smoking and oral contraceptive steroids on the kinetics of diflunisal.

The single dose pharmacokinetics of diflunisal were studied in 4 groups of 6 young volunteers: control men, control women, women taking low estrogen oral contraceptive steroids (OCS), and women smokers (10-20 cigarettes day). The plasma clearance of diflunisal was significantly higher in men (0.169 ml.min-1.kg-1) and in women on OCS (0.165 ml.min-1.kg-1) as compared to control women (0.108 ml.min-1.kg-1). Partial metabolic clearances of diflunisal by the three conjugative pathways (phenolic and acyl glucuronide formation, sulphate conjugation) were all increased in men and women OCS users as compared to control women. Statistically significant increases, however, were only observed for the partial metabolic clearance of diflunisal by phenolic glucuronidation between men and women (2.91 vs. 1.85 ml.min-1 respectively), and for the partial clearance by acyl glucuronidation between OCS users and control women (4.81 vs. 3.01 ml.min-1 respectively). Smoking resulted in a moderate increase (35%) in plasma diflunisal clearance. However, a significant reduction in total urinary recovery of diflunisal and its glucuronide and sulphate conjugates was found in smokers (70.5% in smokers as compared to 84.2-87.2% in the 3 other study groups). Consequently, smoking may have induced hydroxylation, a minor oxidative metabolic pathway of diflunisal recently discovered in man.

Disposition of lorazepam in human beings: enterohepatic recirculation and first-pass effect.

The effects of neomycin and cholestyramine on the disposition of lorazepam was examined in seven healthy drug-free men. Half-life as determined for the oral route was, in all subjects, 15% to 35% less than that determined for the intravenous route. Free oral clearance was slightly but not significantly less than free systemic clearance, but the ratio of the AUC of lorazepam glucuronide corrected for dose was twofold greater by the oral route. Urinary recoveries also differed (71.6% and 50.4%, oral versus intravenous). Neomycin and cholestyramine treatment resulted in a 19% to 26% reduction in half-life attendant on a 34% increase in free oral clearance and a 24% increase in free systemic clearance. This suggests that lorazepam undergoes significant enterohepatic recirculation in human beings and that there exists an extrahepatic pathway, at least for the intravenous route. Since pharmacokinetic measurements do not take these physiologic processes into account, the drug cannot properly be used as a marker of conjugative metabolism.

Effect of dose on the glucuronidation and sulphation kinetics of diflunisal in man: single dose studies.

1. The effect of dose (100 mg, 250 mg, 500 mg, 750 mg and 1000 mg) on the glucuronidation and sulphation of diflunisal was studied in six healthy volunteers. 2. Total urinary recovery ranged from 78.9 +/- 11.9% to 91.5 +/- 18.7% of the administered dose. Urinary recovery (normalized for total urinary recovery) of diflunisal sulphate (DS) significantly increased with dose from 9.3 +/- 3.7% to 18.1 +/- 4.8%. 3. Normalized urinary recovery for diflunisal phenolic glucuronide (DPG) was unaffected by dose (range: 30.6 +/- 3.8% to 40.6 +/- 6.6%). Normalized urinary recovery for the acyl glucuronide (DAG) significantly decreased from 52.3 +/- 4.6% to 40.2 +/- 3.4% as the dose increased. 4. Total plasma clearance of diflunisal significantly decreased from 14.4 +/- 1.4 ml min-1 to 8.7 +/- 1.4 ml min-1 as the dose increased from 100 mg to 750 mg. A further increase in dose to 1000 mg resulted in an unexplained increase in total plasma clearance to 10.3 +/- 1.8 ml min-1. 5. Dose-dependent plasma clearance of diflunisal was caused mainly by saturation of the formation of DAG, whereas the formation of DS and DPG were relatively unaffected by dose.