Determination of the free fraction and relative free fraction of drugs strongly bound to plasma proteins.

This report describes a new method for the determination of protein binding and relative protein binding (ratio of f(u) for different species) for compounds strongly bound to proteins. The method used is based on the distribution of the drug in plasma water, plasma proteins, and blood cells. Incubations were performed in diluted plasma. In diluted plasma, the erythrocyte/plasma distribution was determined with greater precision than in undiluted plasma. Formulae were derived for calculating f(u) in undiluted plasma based on the f(u) values determined in diluted plasma. These formulae are also valid in the event of more than one independent binding site in plasma. All incubations with plasma of different species were performed using rat erythrocyte suspensions, thereby making it possible for relative f(u) values in different species to be calculated without knowing the absolute free fractions. This method avoids the determination of the erythrocyte/buffer distribution in cases where it is sufficient to know relative f(u) values (e.g., exposure comparisons). Relative protein binding can also be quantified for compounds that tend to adsorb to surfaces of vials or test tubes, thus avoiding errors caused by adsorption when quantifying the drug in a protein-free aqueous solution. This method was validated by making comparisons of free fraction values obtained by the method herein described with those obtained by either ultrafiltration or equilibrium dialysis for two compounds that bind predominantly to albumin and another compound that binds to alpha(1)-acid glycoprotein. The results confirm our method produces identical free fractions in comparison with other established techniques. In addition, the range of applications of our method is much wider.

Pharmacokinetics and metabolism of the new thromboxane A2 receptor antagonist ramatroban in animals. 1st communication: absorption, concentrations in plasma, metabolism, and excretion after single administration to rats and dogs.

The absorption, concentrations in plasma, metabolism and excretion of ramatroban ((+)-(3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9- carbazolepropanoic acid, CAS 116649-85-5, BAY u 3405) have been studied following a single intravenous, oral, or intraduodenal administration of 14C-labeled or nonlabeled compound to rats and dogs (dose range: 1-10 mg.kg-1). After intraduodenal administration of [14C]ramatroban, enteral absorption of radioactivity was rapid and almost complete both in bile duct-cannulated male rats (83%) and female dogs (95%). The oral bioavailability of ramatroban was complete in the dog but amounted to about 50% in the rat due to presystemic elimination. A marked food effect on the rate but not on the extent of absorption was observed in rats. The elimination of the parent compound from plasma occurred rapidly with total clearance of 1.2 l.h-1.kg-1 in male rats and 0.7 l.h-1.kg-1 in dogs. After oral administration to male rats AUC increased dose-proportionally between 1 and 10 mg.kg-1, whereas in Cmax an over-proportional increase was observed. Excretion of total radioactivity was fast and occurred predominantly via the biliary/fecal route in both species. The residues were low, 144 h after dosing less than 0.2% of the radioactivity remained in the body of rats. A considerable sex difference was found in rats following oral administration of ramatroban. In females a 3-fold higher AUC and a 1.7-fold longer half-life of unchanged compound, as well as 3-fold higher renal excretion of total radioactivity was observed. A marked species difference exists in the metabolism of ramatroban. In dogs the drug was almost exclusively metabolized via conjugation with glucuronic acid, whereas in rats oxidative phase I metabolism and glucuronidation were equally important. As a consequence enterohepatic circulation was much more pronounced in dogs (77%) than in rats (17% of the initial dose).

BAY X1005, a new inhibitor of leukotriene synthesis: in vivo inflammation pharmacology and pharmacokinetics.

(R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) (BAY X1005) is an orally active inhibitor of the synthesis of the leukotrienes B4 and C4 in selected animal models that effectively reduces the vascular phenomena of inflammation, i.e., edema formation and leukocyte immigration. The arachidonic acid-induced mouse ear inflammation test allowed the evaluation of the antiedematous effects of BAY X1005 after topical (ED50, 18 micrograms/ear) and oral (ED50, 48.7 mg/kg) administration. Profound inhibition of myeloperoxidase activity as a marker for phagocyte infiltration was seen (ED50, 3 micrograms/ear topically and 7.9 mg/kg p.o.) even 5 hr after application. The platelet-activating factor-induced death of mice was statistical significantly and dose-dependently reduced (100 mg/kg p.o.; mean, 51%). BAY X1005 had no analgesic properties in the phenyl-benzoquinone writhing test in mice and only limited efficacy in the baker's yeast-induced hyperalgesia test in the rat (ED50, 90 mg/kg p.o.), although cyclooxygenase inhibitors (indomethacin ED50, 1.7 mg/kg p.o.) are very potent. In another cyclooxygenase-sensitive test, the carrageenan-induced edema and the baker's yeast-induced fever in the rat, BAY X1005 was virtually devoid of any activity. The rat whole blood ex vivo leukotriene B4 inhibition assay demonstrated that BAY X1005 was potent (ED50, 11.8 and 6.7 mg/kg p.o. at 1 and 5 hr, respectively) and had a long duration of action (16-hr ED40, 70 mg/kg p.o.). Similarly, inhibition of the zymosan-induced exudate leukotrienes B4 and C4 inhibition confirmed these data (ED50, 8.3 and 10.5 mg/kg p.o., respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

BAY X1005, a new selective inhibitor of leukotriene synthesis: pharmacology and pharmacokinetics.

The enantiomer BAY X1005 [(R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid] potently inhibits LTB4 synthesis in isolated PMNL of various species (IC50 mumol/l, human 0.22, rat 0.026, mouse 0.039) and LTC4 synthesis in mouse macrophages (IC50 0.021 mumol/l). Due to high protein binding the in vitro potency for LTB4 synthesis inhibition in whole blood is lowered to 17 mumol/l as determined by RIA. BAY X1005 is selective for the 5-lipoxygenase pathway leaving 12-HETE and HHT unaltered, as determined in human whole blood. After oral application BAY X1005 inhibits edema formation and myeloperoxidase activity in the arachidonate-induced mouse ear inflammation test (ED50 48.7 and 7.9, respectively). Oral activity in the rat ex vivo is found in whole blood for LTB4 synthesis inhibition (ED50 11.8 mg/kg p.o.). BAY X1005 demonstrates a high bioavailability (f 86%) with a Cmax of 13 mg/l and t1/2 of 3.5 h in the rat at 10 mg/kg p.o. Thus, the pharmacodynamic, pharmacokinetic profile and safety aspects of the leukotriene synthesis inhibitor BAY X1005 allow testing in man for its therapeutic potential in inflammatory and allergic diseases.

Biotransformation of nimodipine in rat, dog, and monkey.

14C-labelled (+/-) 3-isopropyl5-(2-methoxyethyl)1,4-dihydro-2,6-dimethyl-4- (3-nitrophenyl)-pyridine-3,5-dicarboxylate (nimodipine, Bay e 9736, Nimotop; CAS 66085-59-4) was administered orally to rat, dog, and monkey (each 5, 10, or 20 mg/kg) and intraduodenally to rat (5 mg/kg). Urine was collected over a period of 24 h (bile 6 h). Dog bile was obtained from the gall bladder 4 h after oral dosing. Rat plasma was taken 1 h p. appl. of the unlabelled compound and additionally at different times following administration of [14C]nimodipine. The metabolite profiles in the excreta were established by TLC (radioscan/autoradiography). The unchanged drug was neither detectable in urine nor in bile, but was present in rat plasma. Nimodipine was extensively metabolized. 18 metabolites were isolated by LC, HPLC, and preparative TLC and identified by comparison with the reference substances using two-dimensional TLC, HPLC, GC/radio-GC, 1H-NMR-spectroscopy, MS, and GC/MS. About 75% of the renally excreted biotransformation products, more than 50% of the metabolites present in the bile (rat, dog) and approx. 80% of the plasma metabolites (rat only) have been identified. The large number of metabolites was produced by some common biotransformation reactions: dehydrogenation of the 1,4-dihydropyridine system, oxidative ester cleavage, oxidative O-demethylation and subsequent oxidation of the resulting primary alcohol to the carboxylic acid, hydroxylation of the methyl groups at 2- or 6-position, hydroxylation of one methyl group of the isopropyl ester moiety, reduction of the aromatic nitro group, and glucuronidation as phase II-reaction.