Dose proportionality of oral etoricoxib, a highly selective cyclooxygenase-2 inhibitor, in healthy volunteers.

To assess dose proportionality of etoricoxib across the anticipated clinical dose range, a single panel of 12 healthy subjects was administered single oral doses of etoricoxib of 5, 10, 20, 40, and 120 mg in an open, two-part, five-period crossover study. Plasma samples were collected aftereach dose and analyzed for etoricoxib concentrations. The pharmacokinetics of etoricoxib appear to be linear over the entire dose range examined, from 5 to 120 mg. Etoricoxib was found to be well tolerated across the 5 to 120 mg dose range.

Lack of pharmacokinetic interaction between rofecoxib and methotrexate in rheumatoid arthritis patients.

Rofecoxib is a highly selective and potent inhibitor of cyclooxgenase-2 (COX-2). Methotrexate is a disease-modifying agent with a narrow therapeutic index frequently prescribed for the management of rheumatoid arthritis. The objective of this study was to investigate the influence of clinical doses of rofecoxib on the pharmacokinetics of methotrexate in patients with rheumatoid arthritis. This was a randomized, double-blind, placebo-controlled study in 25 rheumatoid arthritis patients on stable doses of methotrexate. Patients received oral methotrexate (7.5 to 20 mg) on days -1, 7, 14, and 21. Nineteen patients received rofecoxib 12.5, 25, and 50 mg once daily on days 1 to 7, 8 to 14, and 15 to 21, respectively. Six patients received placebo on days 1 to 21 only to maintain a double-blinded design for assessment of adverse experiences. Plasma and urine samples were analyzed for methotrexate and its major although inactive metabolite, 7-hydroxymethotrexate. The AUC(0-infinity) geometric mean ratios (GMR) and their 90% confidence intervals (90% CI) (rofecoxib + methotrexate/methotrexate alone) for day 7/day -1, day 14/day -1, and day 21/day -1, for rofecoxib 12.5, 25, and 50 mg, were 1.03 (0.93, 1.14), 1.02 (0.92, 1.12), and 1.06 (0.96, 1.17), respectively (p > 0.2 for all comparisons to day -1). All AUC(0-infinity), GMR and Cmax GMR 90% CIs fell within the predefined comparability limits of (0.80, 1.25). Similar results were observed for renal clearance of methotrexate and 7-hydroxymethotrexate at the highest dose of rofecoxib tested (50 mg). It was concluded that rofecoxib at doses of 12.5, 25, and 50 mg once daily has no effect on the plasma concentrations or renal clearance (tested at the highest dose of rofecoxib) of methotrexate in rheumatoid arthritis patients.

Effect of rofecoxib on the pharmacokinetics of digoxin in healthy volunteers.

The authors examined the effect of the cyclooxygenase-2 (COX-2) inhibitor, rofecoxib, at steady state on the pharmacokinetics of digoxin following a single dose in healthy subjects. Each healthy subject (N = 10) received rofecoxib (75 mg once daily) or placebo for 11 days in a double-blind, randomized, balanced, two-period crossover study. A single 0.5 mg oral dose of digoxin elixir was administered on the 7th day of each 11-day period. Each treatment period was separated by 14 to 21 days. Samples for plasma and urine immunoreactive digoxin concentrations were collected through 120 hours following the digoxin dose. No statistically significant differences between treatment groups were observed for any of the calculated digoxin pharmacokinetic parameters. For digoxin AUC(0-infinity), AUC(0-24), and Cmax, the geometric mean ratios (90% confidence interval) for (rofecoxib + digoxin/placebo + digoxin) were 1.04 (0.94, 1.14), 1.02 (0.94, 1.09), and 1.00 (0.91, 1.10), respectively. The digoxin median tmax was 0.5 hours for both treatments. The harmonic mean elimination half-life was 45.7 and 43.4 hours for rofecoxib + digoxin and placebo + digoxin treatments, respectively. Digoxin is eliminated renally. The mean (SD) cumulative urinary excretion of immunoreactive digoxin after concurrent treatment with rofecoxib or placebo was 228.2 (+/- 30.8) and 235.1 (+/- 39.1) micrograms/120 hours, respectively. Transient and minor adverse events occurred with similar frequency on placebo and rofecoxib treatments, and no treatment-related pattern was apparent. Rofecoxib did not influence the plasma pharmacokinetics or renal elimination of a single oral dose of digoxin.

The effect of rofecoxib on the pharmacodynamics and pharmcokinetics of warfarin.

OBJECTIVE: The objective of this study was to examine the effect of 3 doses of rofecoxib (12.5, 25, and 50 mg) on the pharmacodynamics and pharmacokinetics of warfarin. METHODS: Two single-dose (12.5 or 50 mg of rofecoxib with 25 mg or 30 mg of oral warfarin, respectively, on day 7 of each period) trials (N = 12 men) and 1 steady-state warfarin trial (25 mg rofecoxib; N = 15, 13 men and 2 women) were completed as two-period, randomized, balanced, crossover, double-blind designs. The prothrombin time international normalized ratio (INR) and S(-) and R(+) warfarin enantiomers were assessed during 144 hours after the single warfarin doses. In the steady-state warfarin trial, after the attainment of a stable INR (1.4-1.7), the stable warfarin dose was co-administered with rofecoxib (25 mg) and placebo over two 21-day periods. After the dose of warfarin on day 21, INR and S(-) and R(+) warfarin were assessed during 24 hours. RESULTS: Compared with placebo, rofecoxib slightly increased the INR by approximately 5% (90% confidence interval on the geometric ratio, 1.03, 1.08) and 11% (1.04, 1.19) for the two single-dose warfarin trials with 12.5 and 50 mg of rofecoxib, respectively. In the steady-state warfarin study with 25 mg of rofecoxib, the INR was increased by 8% (1.02, 1.15). Rofecoxib had no significant effect (versus placebo) on the pharmacokinetics of S(-) warfarin. However, in the 3 studies, treatment with 12.5, 25, and 50 mg of rofecoxib was associated with a 27%, 38%, and 40% increase in the area under the plasma concentration-time curve of the biologically less active R(+) warfarin. CONCLUSIONS: Rofecoxib increased plasma concentrations of the biologically less active R(+) warfarin, which accounted for a small increase in INR. The approximately 8% increase in INR at steady state with warfarin co-administered with 25 mg of rofecoxib is not likely to be clinically important in most patients taking warfarin. However, standard monitoring of INR values should be conducted when therapy with rofecoxib is initiated or changed, particularly in the first few days, for patients receiving warfarin.

Grapefruit juice has minimal effects on plasma concentrations of lovastatin-derived 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors.

OBJECTIVE: To evaluate the effect of regular-strength grapefruit juice, a cytochrome P4503A4 (CYP3A4) inhibitor, on the pharmacokinetics of a commonly prescribed regimen of oral lovastatin. METHODS: In a randomized crossover study, 16 healthy subjects received a single 40 mg dose of lovastatin in the evening after each consumed an 8-ounce glass of regular-strength grapefruit juice or water with breakfast for 3 consecutive days. The effect of the same grapefruit juice and water regimen on the pharmacokinetics of midazolam (2 mg oral dose given 1 hour after the third day of grapefruit juice and water) was used as a positive control in the same subjects. Plasma concentrations of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors were determined by an enzyme inhibition assay, and concentrations of lovastatin, lovastatin acid, and midazolam were determined by liquid chromatography-tandem mass spectrometry. RESULTS: The area under the plasma concentration-time profiles (AUC) and maximum plasma concentrations (Cmax) of HMG-CoA reductase inhibitors increased slightly (-30% for each) after consumption of grapefruit juice. Similar effects on AUC and Cmax (approximately 40% increase for each) were noted after analysis of samples of hydrolyzed plasma (which converts inactive lactones to active hydroxy acid species). The AUC and Cmax values for lovastatin approximately doubled in the presence of grapefruit juice, whereas the same parameters for lovastatin acid increased 1.6-fold. Grapefruit juice caused the AUC for midazolam to increase by a factor of approximately 2.4. CONCLUSIONS: Daily consumption of a glass of regular-strength grapefruit juice has a minimal effect on plasma concentrations of HMG-CoA reductase inhibitors (approximately 30% to 40% increase) after a 40 mg evening dose of lovastatin.

Pharmacokinetics of alendronate.

Alendronate (alendronic acid; 4-amino-1-hydroxybutylidene bisphosphonate) has demonstrated effectiveness orally in the treatment and prevention of postmenopausal osteoporosis, corticosteroid-induced osteoporosis and Paget's disease of the bone. Its primary mechanism of action involves the inhibition of osteoclastic bone resorption. The pharmacokinetics and pharmacodynamics of alendronate must be interpreted in the context of its unique properties, which include targeting to the skeleton and incorporation into the skeletal matrix. Preclinically, alendronate is not metabolised in animals and is cleared from the plasma by uptake into bone and elimination via renal excretion. Although soon after administration the drug distributes widely in the body, this transient state is rapidly followed by a nonsaturable redistribution to skeletal tissues. Oral bioavailability is about 0.9 to 1.8%, and food markedly inhibits oral absorption. Removal of the drug from bone reflects the underlying rate of turnover of the skeleton. Renal clearance appears to involve both glomerular filtration and a specialised secretory pathway. Clinically, the pharmacokinetics of alendronate have been characterised almost exclusively based on urinary excretion data because of the extremely low concentrations achieved after oral administration. After intravenous administration of radiolabelled alendronate to women, no metabolites of the drug were detectable and urinary excretion was the sole means of elimination. About 40 to 60% of the dose is retained for a long time in the body, presumably in the skeleton, with no evidence of saturation or influence of one intravenous dose on the pharmacokinetics of subsequent doses. The oral bioavailability of alendronate in the fasted state is about 0.7%, with no significant difference between men and women. Absorption and disposition appear independent of dose. Food substantially reduces the bioavailability of oral alendronate; otherwise, no substantive drug interactions have been identified. The pharmacokinetic properties of alendronate are evident pharmacodynamically. Alendronate treatment results in an early and dose-dependent inhibition of skeletal resorption, which can be followed clinically with biochemical markers, and which ultimately reaches a plateau and is slowly reversible upon discontinuation of the drug. These findings reflect the uptake of the drug into bone, where it exerts its pharmacological activity, and a time course that results from the long residence time in the skeleton. The net result is that alendronate corrects the underlying imbalance in skeletal turnover characteristic of several disease states. In women with postmenopausal osteoporosis, for example, alendronate treatment results in increases in bone mass and a reduction in fracture incidence, including at the hip.

Pharmacokinetics of intravenous alendronate.

Alendronate is a potent bisphosphonate that has been studied for the treatment of osteoporosis and Paget's disease of the bone. To examine the pharmacokinetics of this drug, several groups of postmenopausal women were dosed intravenously in several studies. Twelve patients with metastatic bone disease were administered an intravenous dose of 10 mg of 14C-labeled alendronate (approximately 26 muCi), and plasma, feces, and urine samples were collected for 72 hours. Radioactivity was excreted almost exclusively in urine, and all of it was accounted for by alendronate. Overall recovery accounted for 47% of dose, with the remainder presumed to be retained in bone. Metabolism of alendronate was not observed. Renal clearance of alendronate was 71 mL/min. An additional 10 subjects were given repeated i.v. administrations of alendronate to demonstrate that previous exposure does not alter the pharmacokinetic behavior of the drug. Examination of the findings from these and other studies in which alendronate was administered intravenously revealed that disposition of single doses is linear in the range of 0.125 to 10 mg. With the possible exception of a somewhat greater skeletal retention of a systemically administered dose, the pharmacokinetics of i.v. alendronate were found to be similar to those of other bisphosphonates.

Elimination and biochemical responses to intravenous alendronate in postmenopausal osteoporosis.

Postmenopausal women with established vertebral osteoporosis were studied for 2 years to determine the terminal elimination half-life and the duration of response to treatment with intravenous alendronate (30 mg) given over 4 days. The urinary excretion of alendronate followed a multiexponential decline. Approximately 50% of the total dose was excreted over the first 5 days, and a further 17% was excreted in the succeeding 6 months. Thereafter, there was a much slower elimination phase with an estimated mean terminal half-life of greater than 10 years (n = 11). Urinary excretion of hydroxyproline and calcium decreased significantly from pretreatment values by day 3, reaching a nadir by 1 week (40% and 67% decrease, respectively). Thereafter, hydroxyproline remained suppressed for the following 2 years. In contrast, urinary calcium excretion returned gradually toward pretreatment values over the first year and during the second year was comparable to pretreatment values. Serum activity of alkaline phosphatase activity decreased over 3 months (23% reduction), increased gradually thereafter, and returned to pretreatment values at month 24. Bone mineral density measured at the spine increased by approximately 5% during the first year and remained significantly higher than pretreatment values at 2 years. We conclude that a short course of high doses of intravenous alendronate is associated with a prolonged skeletal retention of the agent. This open study also suggests that this regimen has a sustained effect on bone turnover persisting for at least 1 year.

Studies of the oral bioavailability of alendronate.

Clinical studies were performed to examine the oral bioavailability of alendronate (4-amino-1-hydroxy-butylidene-1,1-bisphosphonate monosodium). All studies, with the exception of one performed in men, involved postmenopausal women. Short-term (24 to 36 hours) urinary recovery of alendronate after an intravenous dose of 125 to 250 micrograms averaged about 40% in both men and women. In women, oral bioavailability of alendronate was independent of dose (5 to 80 mg) and averaged (90% confidence interval) 0.76% (0.58, 0.98) when taken with water in the fasting state, followed by a meal 2 hours later. Bioavailability was similar in men [0.59%, (0.43, 0.81)]. Taking alendronate either 60 or 30 minutes before a standardized breakfast reduced bioavailability by 40% relative to the 2-hour wait. Taking alendronate either concurrently with or 2 hours after breakfast drastically (> 85%) impaired availability. Black coffee or orange juice alone, when taken with the drug, also reduced bioavailability (approximately 60%). Increasing gastric pH, by infusion of ranitidine, was associated with a doubling of alendronate bioavailability. A practical dosing recommendation, derived from these findings and reflective of the long-term nature of therapy for a disease such as osteoporosis, is that patients take the drug with water after an overnight fast and at least 30 minutes before any other food or beverage.

Determination of L-691,121, a new class III antiarrhythmic, and its principal metabolite in plasma by differential radioimmunoassay.

A sensitive and specific method based on radioimmunoassay (RIA) has been developed for the analysis of L-691,121, a new antiarrhythmic agent, and its major metabolite, L-692,199, in plasma. Two RIAs using immunogens and radioligands prepared from different derivatives of L-691,121 were used in conjunction to determine both parent compound and metabolite concentrations by solving simultaneous equations, since neither assay alone was adequately specific. Variable cross-reactivity factors were incorporated into the calculations to correct for non-parallel drug and metabolite displacement curves. The direct assay using 30 microliters of plasma is sensitive to 0.1 ng ml-1 and has sufficient precision, accuracy and specificity for the analysis of clinical samples.

Clinical pharmacology of alendronate sodium.

Clinical studies have been performed to investigate the pharmacokinetics and pharmacodynamics of alendronate, an inhibitor of bone resorption for the treatment of osteoporosis. Alendronate is one of the most potent bisphosphonates currently undergoing clinical investigation (> 100-fold more potent than etidronate in vivo). The pharmacokinetics of alendronate are similar to those of other bisphosphonates. After a 2-h intravenous infusion, plasma concentrations of alendronate decline rapidly to approximately 5% of initial values within 6 h. About 50% of a systemic dose is excreted unchanged in the urine in the 72 h following administration. By analogy to its behavior in animals the remainder is assumed to be taken up by the skeleton. After sequestration into bone, the elimination of alendronate is very prolonged. The terminal half-life was estimated to be greater than 10 years. Despite prolonged skeletal residence, the biological effects of alendronate begin to diminish post-treatment, since the duration of effect reflects factors besides dose and cumulative drug exposure. When taken after an overnight fast, 2 h before breakfast, the oral bioavailability of alendronate averages approximately 0.75% of dose with substantial variability (coefficient of variation 55%-75%) both between and within subjects. Reducing the wait before food from 2 h to 1 h, or even 30 min, produces a mean reduction in absorption of 40%. Since the clinical efficacy of alendronate is indistinguishable whether it is given 30 min, 1h, or 3 h before a meal, the observed variability in bioavailability within this range is of little consequence. Dosing up to at least 2 h after a meal dramatically reduces absorption (80%-90%).

Pharmacokinetics and dose proportionality of D2-agonist MK-458 (HPMC) in parkinsonism.

To investigate the pharmacokinetic profile, bioavailability, and dose proportionality of the D2-agonist MK-458 (hydroxypropylmethylcellulose tablet, a sustained release formulation), a 4-period crossover study was conducted in 10 patients with mild to moderate Parkinson's disease (mean age = 63 y; 1 woman, 9 men). Following a titration phase to induce tolerance, each patient was given single oral doses of 6, 12 and 18 mg and a single intravenous 40 micrograms dose (5 micrograms/h over 8h). The maximum concentrations of MK-458 observed in plasma after oral administration were 139, 240 and 344 ng/L for the 6, 12 and 18 mg doses, respectively, and occurred after 8.0, 9.0 and 5.5 h, respectively. Mean areas under the plasma concentration-time curves were 1728, 2849 and 5484 ng/L.h, respectively. The mean plasma half-life was 3.8 h and mean plasma clearance was 3390 ml/min (203.4 L/h). The bioavailability (approximately 5%) was very similar for the 3 tablet formulations tested. The disposition of MK-458 was independent of the dose over the range of doses studied.

Ligand binding to heme proteins. An evaluation of distal effects.

The O2, CO, and alkyl isocyanide-binding properties of a variety of vertebrate and invertebrate heme proteins have been compared in detail to those of protoheme mono-3-(1-imidazoyl)-propylamide monomethyl ester in aqueous suspensions of soap micelles. The proteins examined include: cytochrome P-450cam from Pseudomonas putida, beef heart cytochrome c oxidase, yeast cytochrome c peroxidase, alpha and beta subunits of human hemoglobin, sheep hemoglobin, carp hemoglobin, sperm whale myoglobin, horse heart myoglobin, a monomeric hemoglobin from Glycera dibranchiata, erythrocruorin from Chironomusthummii, soybean leghemoglobin, and several hemoglobins that lack distal histidines. The smallest bimolecular rates were observed for cytochrome P-450 containing bound camphor, cytochrome c oxidase, and cytochrome c peroxidase. In the case of P-450, the extremely low isonitrile binding rates (approximately 1 M-1 S-1 at 20 degrees C) are due to steric exclusion by bound camphor molecules. For the oxidase and peroxidase, inhibition of CO and isonitrile binding appears to be due to the polar nature of the active sites. In the cases of animal hemoglobins and myoglobins, the sixth coordination positions appear to be designed to accommodate diatomic molecules with no steric hindrance by distal protein residues. Protein resistance to the diffusion of CO and O2 does not limit the observed association rate constants. In contrast, ligands containing three or more atoms are sterically hindered both in their final bound positions and during diffusion to the active site. The magnitude of this hindrance (greater than or equal to 2 kcal/mol) exhibits a complex dependence on ligand size and shape. The most important protein residue appears to be His E7. In addition to restricting the size of the sixth coordination position, the distal histidine is also capable of forming a hydrogen bond with bound oxygen molecules. The strength of this hydrogen bond was estimated to be -2 and -1 kcal/mol for mammalian myoglobins and hemoglobins, respectively, and accounts for the smaller CO/O2 partition constants (M values) observed for these proteins in comparison to the constants observed for pentacoordinate model heme compounds.

The room temperature potentiometry of xanthine oxidase. pH-dependent redox behavior of the flavin, molybdenum, and iron-sulfur centers.

A series of potentiometric titrations of xanthine oxidase have been performed at room temperature in the pH range 6.1-9.9. Reduction of the two Fe/S centers was monitored by CD, and that of the FAD and Mo center by EPR. The Fe/S centers behave as centers having a protonable group whose pKa changes with reduction state (E = -344 mV, pKo = 6.4, and pKr = 8.1 for Fe/S I; E = -249 mV, pKo = 6.4, and pKr = 8.0 for Fe/S II). The flavin and the two types of molybdenum centers show varying behavior, but, in all cases, electron addition is accompanied by protonation. The sequence for FAD is reduction, protonation, reduction, protonation with E1 = -398 mV, E2 = -240 mV, pK1 = 9.5, pK2 = 7.4. For "rapid" molybdenum, the sequence is protonation, reduction, protonation, reduction with E1 = -369 mV, E2 = -301 mV, pK1 = 7.9, pK2 = 8.4; and for slow molybdenum, protonation, reduction, protonation with E1 = 320 mV, E2 = -477 mV, pK1 = 7.5, pK2 = 9.5. Comparison to data obtained previously at cryogenic temperatures (Cammack, R., Barber, M. J., and Bray, R. C. (1976) Biochem. J. 157, 469-468 and Barber, M. J., and Seigel, L. M. (1982) in Flavins and Flavoproteins (Massey, V., and Williams, C. H., eds) pp. 796-804, Elsevier/North-Holland, New York) showed the centers to have significant temperature dependence, which calls for a re-evaluation of conclusions reached using cryogenic techniques (e.g. rapid-freeze). The optical absorbance characteristics of the enzyme were also investigated and a possible absorbance for molybdenum was suggested.

The reaction of reduced xanthine oxidase with oxygen. Kinetics of peroxide and superoxide formation.

Product formation during the oxidation of xanthine oxidase has been examined directly by using cytochrome c peroxidase as a trapping agent for hydrogen peroxide and the reduction of cytochrome c as a measure of superoxide formation. When fully reduced enzyme is mixed with high concentrations of oxygen, 2 molecules of H2O2/flavin are produced rapidly, while 1 molecule of O2-/flavin is produced rapidly and another produced much more slowly. Time courses for superoxide formation and those for the absorbance changes due to enzyme oxidation were fitted successfully to the mechanism proposed earlier (Olson, J. S., Ballou, D. P., Palmer, G., and Massey, V. (1974) J. Biol. Chem. 249, 4363-4382). In this scheme, each oxidative step is initiated by the very rapid and reversible formation of an oxygen.FADH2 complex (the apparent KD = 2.2 X 10(-4) M at 20 degrees C, pH 8.3). In the cases of 6- and 4-electron-reduced enzyme, 2 electrons are transferred rapidly (ke = 60 s-1) to generate hydrogen peroxide and partially oxidized xanthine oxidase. In the case of the 2-electron-reduced enzyme, only 1 electron is transferred rapidly and superoxide is produced. The remaining electron remains in the iron-sulfur centers and is removed slowly by a second order process (ks = 1 X 10(4) M-1 s-1). When the pH is decreased from 9.9 to 6.2, both the apparent KD for oxygen binding and the rapid rate of electron transfer are decreased about 20-fold. This result is suggestive of uncompetitive inhibition and implies that proton binding to the enzyme-flavin active site affects primarily the rate of electron transfer, not the formation of the initial oxygen complex.