Paul J. De Schepper

Characterization of rofecoxib as a cyclooxygenase‐2 isoform inhibitor and demonstration of analgesia in the dental pain model

Nonsteroidal anti‐inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, and indomethacin (INN, indometacin) inhibit both the constitutive (COX‐1) and inducible (COX‐2) isoforms of cyclooxygenase. The induction of COX‐2 after inflammatory stimuli has led to the hypothesis that COX‐2 inhibition primarily accounts for the therapeutic properties of NSAIDs.

Comparative Inhibitory Activity of Rofecoxib, Meloxicam, Diclofenac, Ibuprofen, and Naproxen on COX‐2 versus COX‐1 in Healthy Volunteers

Steady‐state inhibitory activity of rofecoxib (Vioxx™) on COX‐2 versus COX‐1 was compared with that of commonly used nonsteroidal anti‐inflammatory drugs (NSAIDs) in 76 healthy volunteers randomized to placebo, rofecoxib 12.5 mg qd, rofecoxib 25 mg qd, diclofenac 50 mg tid, ibuprofen 800 mg tid, sodium naproxen 550 mg bid, or meloxicam 15 mg qd. All of these doses include the high end of the approved clinical dose range. Ex vivo whole‐blood assays were used to determine the effect on COX‐2 and COX‐1 activity, respectively. Urinary prostanoids were also measured. Mean inhibition of COX‐2 (measured as the weighted average inhibition [WAI] of lipopolysaccharide [LPS]‐induced PGE2 generation over 8 hours on day 6 vs. baseline) was −2.4%, 66.7%, 69.2%, 77.5%, 93.9%, 71.4%, and 71.5% for placebo, rofecoxib 12.5 mg, rofecoxib 25 mg, meloxicam, diclofenac, ibuprofen, and naproxen, respectively. Corresponding values for mean inhibition of COX‐1 (measured as TXB2 generation in clotting whole blood) were −5.15%, 7.98%, 6.65%, 53.3%, 49.5%, 88.7%, and 94.9%. Rofecoxib had no significant effect on urinary excretion of 11‐dehydro TXB2, a COX‐ 1‐derived product. These data support the contention that rofecoxib is the only drug of the regimens tested that uniquely inhibits COX‐2 without affecting COX‐1.

Characterization of Etoricoxib, a Novel, Selective COX‐2 Inhibitor

Etoricoxib is a potent selective COX‐2 inhibitor in man. Ex vivo whole‐blood assays assessed COX‐2 inhibition after oral administration of etoricoxib in single (5–500 mg) and multiple (25–150 mg) once‐daily doses to healthy human subjects. A separate study examined ex vivo gastric mucosal PGE2 synthesis after etoricoxib (120 mg qd), naproxen (500 mg bid), or placebo for 5 days. The effect of etoricoxib 120 mg qd on the COX‐1‐mediated antiplatelet effects of low‐dose aspirin (ASA) was also assessed. The mean (time)–weighted average inhibition (WAI) of lipopolysaccharide (LPS)–stimulated PGE2(COX‐2 assay) versus placebo was dose related after single (range: 3.1%–99.1%) and multiple doses (range: 52.5%–96.7%). PGE2 remained significantly inhibited 24 hours postdose at steady state. Inhibition of LPS‐stimulated PGE2 showed a strong relationship with etoricoxib plasma concentrations; ex vivo, IC50 was almost identical to in vitro. Multiple dosing of etoricoxib (up to 150 mg qd) showed no important effects on serum TXB2, bleeding time, or platelet aggregation (COX‐1‐mediated effects). The nonselective nonsteroidal anti‐inflammatory (NSAID) naproxen significantly inhibited (∼78%) ex vivo prostaglandin synthesis in gastric mucosa; etoricoxib had no effect. Etoricoxib did not interfere with the antiplatelet effects of low‐dose ASA, as assessed by serum TXB2 and platelet aggregation. Etoricoxib was generally well tolerated, even at doses above the clinical dose range. Based on these results, etoricoxib is a potent selective inhibitor of COX‐2 after single and multiple dosing regimens and does not inhibit prostaglandin synthesis in the gastric mucosa, even at doses above the clinical dose range of 60 to 120 mg.

Effect of Montelukast on the Pharmacokinetics and Pharmacodynamics of Warfarin in Healthy Volunteers

Montelukast, a cysteinyl leukotriene receptor antagonist, is being developed for the treatment of asthma and related diseases. This study was designed to evaluate whether montelukast at clinically used dosage levels would interfere with the anticoagulant effect of warfarin. In a two‐period, double‐blind, randomized crossover study, 12 healthy male subjects received a single oral dose of 30 mg warfarin on the 7th day of a 12‐day treatment with montelukast, 10 mg daily by mouth, or a placebo. Montelukast had no significant effect on the area under the plasma concentration‐time curves and peak plasma concentrations of either R‐ or S‐warfarin. However, slight but statistically significant decreases in time to peak concentration of both warfarin enantiomers and in elimination half‐life of the less potent R‐warfarin were observed in the presence of montelukast. These changes were not considered as clinically relevant. Montelukast had no significant effect on the anticoagulant effect of warfarin, as assessed by the international normalized ratio (INR) for prothrombin time (AUC0–144 and INR maximum). The results of this study suggest that a clinically important interaction between these drugs is unlikely to occur in patients requiring concomitant administration of both drugs.

Pharmacokinetics and pharmacodynamics of multiple oral doses of MK‐0591, a 5‐lipoxygenase—activating protein inhibitor

The pharmacodynamics, kinetics, and tolerability of a new orally active 5‐lipoxygenase inhibitor were evaluated in healthy male volunteers. MK‐0591, 50, 125, and 250 mg every morning and 250 mg every 12 hours, was administered for 10 days. Leukotriene B4 biosynthesis ex vivo in ionophore (A23187)‐stimulated whole blood and leukotriene E4 levels in urine were determined. Leukotriene B4 production was inhibited up to 90% of baseline for 12 hours after administration at the highest dose. The degree of leukotriene B4 inhibition ex vivo in whole blood significantly correlated with plasma MK‐0591 concentrations (0 to 1500 ng/ml; r = 0.73). Urinary leukotriene E4 was inhibited by >80% at 24 hours after administration for all dose levels. Pharmacokinetics of MK‐0591 were linear, with a half‐life of approximately 6 hours. Very little accumulation was seen after multiple dosing. MK‐0591 had no effect on testosterone levels, and good tolerability was shown at all dose levels of MK‐0591 administered for up to 10 days.

Hormonal effects, tolerability, and preliminary kinetics in men of MK-906, a 5α-reductase inhibitor

The hormonal effects following the acute (single dose) administration of a 4-azasteroid inhibitor of 5 alpha-reductase (MK-906) were evaluated in 10 healthy male volunteers. Marked suppression of serum dihydrotestosterone (DHT) was observed after the administration of single doses as low as 12.5 mg. The mean percent decrease in DHT at 24 hours in the group treated with a single 25-mg dose was 56% +/- 10% compared with the baseline. The suppression of plasma DHT levels continued for up to 72 hours. This study demonstrates that administration of single oral doses (12.5 to 400 mg) of MK-906 results in a significant decrease in the conversion of testosterone to DHT.

Influence of chronic renal failure and hemodialysis on diflunisal plasma protein binding

Diflunisal protein binding was studied by equilibrium dialysis at 37° in plasma from healthy, uremic, and geriatric subjects. Binding data were computer analyzed assuming 2 classes of independent binding sites (Scatchard model). K1, the primary association constant for the diflunisal‐albumin interaction, was substantially lower in uremic plasma (2.39 ± 0.29 × 105M−1) than in normal plasma (6.86 ± 0.59 × 105 M−1). No difference was found between the number of primary diflunisal binding sites (N1) in uremic and normal plasma. In geriatric plasma neither K1 nor N1 differed from the normal values, indicating that decreased diflunisal plasma protein binding in the elderly is a result of lower plasma albumin concentration. Binding studies with plasma from uremic patients during hemodialysis revealed that free diflunisal rose from 0.46 ± 0.04% at the start to 0.61 ± 0.06% at the end of dialysis. Plasma free fatty acid concentrations rose similarly. In vitro displacement studies showed that oleic acid is a competitive inhibitor for the binding of diflunisal to human serum albumin. This may explain the decrease in diflunisal plasma binding at the end of hemodialysis treatment.

Effect of Multiple Doses of Montelukast, a CysLT1 Receptor Antagonist, on Digoxin Pharmacokinetics in Healthy Volunteers

The effect of multiple oral doses of montelukast, a cysLT1 receptor antagonist, on the pharmacokinetics of oral digoxin was studied in healthy male volunteers in a randomized double‐blind two‐period crossover study. Subjects received 10 mg of montelukast or placebo daily for 11 days. On day 7, they received a single 0.5 mg oral dose of digoxin elixir. The pharmacokinetic parameters of digoxin (AUC0→24, AUC0→…, Cmax, tmax, t1/2) and cumulative urinary excretion over 120 hours were not affected by the multiple doses of montelukast. The 90% confidence interval for each of these parameters fell within prespecified clinically acceptable bounds. Side effects were mild and transient. This suggests that concurrent administration of montelukast and digoxin was well tolerated. Concurrent treatment with montelukast has no effect on the pharmacokinetics of digoxin.

Metabolic effects of hypoglycemic sulfonylureas. 3. Effect of chlorpropamide on energy metabolism and ketogenesis in the isolated perfused rat liver.

Abstract The effects of 1 and 5 mM chlorpropamide were studied in the isolated perfused liver from fasted rats in the absence of exogenous substrate. 1 mM chlorpropamide caused a slight, but not significant, decrease in ATP content and in ATP/ADP ratio in the liver; 5 mM chlorpropamide caused a significant decrease in ATP, total adenine nucleotides and ATP/ADP ratio and an increase in ADP, AMP and inorganic phosphate content. The redox states of both cytosol and mitochondria, as measured by the lactate/pyruvate and β-hydroxybutyrate/acetoacetate ratios, respectively, were unaffected. However, there was a significant and dose dependent decrease in acetoacetate and β-hydroxybutyrate content. Livers perfused with 1 mM chlorpropamide showed a slight, but not significant, increase in oxygen uptake; 5 mM chlorpropamide had a biphasic effect: an initial stimulation, followed by a progressive inhibition of oxygen uptake. Ketone body production measured in the perfusion medium was inhibited by 1 and 5 mM chlorpropamide. No influenee could be seen on ureogenesis. The measured rates of oxygen uptake by the liver compared with the changes in oxygen uptake calculated from the reduced ketogenesis indicate a mixed effect of chlorpropamide on the perfused liver; (1) a decreased oxidation of endogenous triglycerides and (2) an increased oxidation of acetyl coenzyme A through the tricarboxylic acid cycle. The present findings suggest that chlorpropamide acts on the perfused liver as an uncoupling agent and as an inhibitor of the hepatic triglyceride lipase. (Glycerol ester hydrolase, EC 3.1.1.3.) Both effects could be related.

Metabolic effects of hypoglycemic sulfonylureas-VI. Effects of chlorpropamide and carbutamide on ketogenesis and on mitochondrial redox state in the isolated perfused rat liver.

Abstract The effect of 5 mM chlorpropamide and 5 mM carbutamide on fatty acid oxidation in the perfused rat liver was studied. Chlorpropamide as well as carbutamide inhibited endogenous lipid oxidation to ketone bodies. Chlorpropamide had no effect on ketogenesis from exogenously added octanoate, but inhibited ketone body production from a single dose of oleate. Ketogenesis from a continuous oleate infusion was reduced by chlorpropamide during the first 15 min of infusion but was unaffected during the next 45 min studied. Carbutamide did not decrease ketogenesis during oleate infusion. The uptake of octanoate and oleate remained unchanged in the presence of both drugs. Chlorpropamide caused a stimulation of oxygen consumption in the absence of fatty acid substrates but was unable to alter oleate-stimulated respiration. Chlorpropamide, but not carbutamide, stimulated oligomycin-inhibited respiration although to a lesser degree than 2,4-dinitrophenol. Krebs cycle flux during oleate infusion was slightly stimulated by chlorpropamide. Mitochondrial redox state, as measured by the β-hydroxybutyrate/acetoacetate ratio in the perfusate, was markedly lowered by chlorpropamide in the octanoate and oleate experiments. The lactate/pyruvate ratio was unaffected by chlorpropamide. Carbutamide did not produce any change compared with control experiments. From these experiments it is concluded that chlorpropamide and carbutamide inhibit endogenous lipid oxidation by interfering with hepatic triglyceride lipase activity. Changes in oxygen uptake and in mitochondrial redox state caused by chlorpropamide are attributed to the uncoupling activity of this drug.