Plasma timolol concentrations of timolol maleate: timolol gel-forming solution (TIMOPTIC-XE) once daily versus timolol maleate ophthalmic solution twice daily.

PURPOSE: The objective of this study was to compare plasma concentrations of timolol following multiple dosing of the therapeutic regimens of timolol maleate ophthalmic gel-forming solution (Timolol GS; TIMOPTIC-XE) and timolol maleate ophthalmic solution. Timolol maleate ophthalmic gel-forming solution is also referred to as Timolol GS, i.e. gel-forming solution. METHODS: This was a masked observer, two-period crossover study in six normal male subjects randomized to receive either Timolol GS, 0.5% (TIMOPTIC-XE,) once daily (0530 hours) or timolol maleate ophthalmic solution (0.5% TIMOPTIC) twice daily (0530 and 1730 hours) for 8 days, in both eyes. On Day 8, a blood sample was obtained prior to treatment, as well as 1, 2, 4, 8, 10, 12, 13, 14, 16, and 24 hours following the morning instillation. After a 7-day inter-period washout interval, subjects received the opposite treatment. RESULTS: Timolol GS (TIMOPTIC-XE): Plasma concentrations of timolol rarely exceeded 0.375 ng/ml (the lower limit of assay quantification). For all subjects, peak plasma concentrations of timolol averaged <0.3 ng/ml within 4 hours after the last dose. The highest single observation was 0.49 ng/ml in one subject (at hour 2). Timolol solution: For all subjects, peak plasma concentrations of timolol averaged about 0.5 ng/ml and 0.3 ng/ml within 4 hours following the first and second dose, respectively, on Day 8. The highest single observation was 0.95 ng/ml in one subject (at hour 2). CONCLUSIONS: The data suggest that there is less systemic exposure to timolol following once-daily therapy with Timolol GS 0.5% compared with twice daily therapy with timolol maleate ophthalmic solution 0.5%.

Influence of beta-adrenoceptor antagonists on the pharmacokinetics of rizatriptan, a 5-HT1B/1D agonist: differential effects of propranolol, nadolol and metoprolol.

AIMS: Patients with migraine may receive the 5-HT1B/1D agonist, rizatriptan (5 or 10 mg), to control acute attacks. Patients with frequent attacks may also receive propranolol or other beta-adrenoceptor antagonists for migraine prophylaxis. The present studies investigated the potential for pharmacokinetic or pharmacodynamic interaction between beta-adrenoceptor blockers and rizatriptan. METHODS: Four double-blind, placebo-controlled, randomized crossover investigations were performed in a total of 51 healthy subjects. A single 10 mg dose of rizatriptan was administered after 7 days' administration of propranolol (60 and 120 mg twice daily), nadolol (80 mg twice daily), metoprolol (100 mg twice daily) or placebo. Rizatriptan pharmacokinetics were assessed. In vitro incubations of rizatriptan and sumatriptan with various beta-adrenoceptor blockers were performed in human S9 fraction. Production of the indole-acetic acid-MAO-A metabolite of each triptan was measured. RESULTS: Administration of rizatriptan during propranolol treatment (120 mg twice daily for 7.5 days) increased the AUC(0, infinity) for rizatriptan by approximately 67% and the Cmax by approximately 75%. A reduction in the dose of propranolol (60 mg twice daily) and/or the incorporation of a delay (1 or 2 h) between propranolol and rizatriptan administration did not produce a statistically significant change in the effect of propranolol on rizatriptan pharmacokinetics. Administration of rizatriptan together with nadolol (80 mg twice daily) or metoprolol (100 mg twice daily) for 7 days did not significantly alter the pharmacokinetics of rizatriptan. No untoward adverse experiences attributable to the pharmacokinetic interaction between propranolol and rizatriptan were observed, and no subjects developed serious clinical, laboratory, or other significant adverse experiences during coadministration of rizatriptan with any of the beta-adrenoceptor blockers. In vitro incubations showed that propranolol, but not other beta-adrenoceptor blockers significantly inhibited the production of the indole-acetic acid metabolite of rizatriptan and sumatriptan. CONCLUSIONS: These results suggest that propranolol increases plasma concentrations of rizatriptan by inhibiting monoamine oxidase-A. When prescribing rizatriptan to migraine patients receiving propranolol for prophylaxis, the 5 mg dose of rizatriptan is recommended. Administration with other beta-adrenoceptor blockers does not require consideration of a dose adjustment.

Evaluation of amino acid-based linkers in potent macrocyclic inhibitors of farnesyl-protein transferase.

A series of amino acid-based linkers was used to investigate the effects of various substituents upon the potency, pharmacokinetic properties, and conformation of macrocyclic farnesyl-protein transferase inhibitors (FTIs). As a result of the studies described herein, highly potent FTIs with improved pharmacokinetic profiles have been identified.

Oxo-piperazine derivatives of N-arylpiperazinones as inhibitors of farnesyltransferase.

The evaluation of SAR associated with the insertion of carbonyl groups at various positions of N-arylpiperazinone farnesyltransferase inhibitors is described herein. 1-Aryl-2,3-diketopiperazine derivatives exhibited the best balance of potency and pharmacokinetic profile relative to the parent 1-aryl-2-piperazinones.

Synthesis of conformationally constrained 5,6,7, 8-Tetrahydroimidazo[1,5-a]pyridine inhibitors of farnesyltransferase.

[reaction: see text] Synthesis of the 8-amino-5,6,7,8-tetrahydroimidazo[1,5-a]pyridine ring system was accomplished by intramolecular cyclization of an iminium ion, derived from condensation of an amine and a substituted gamma-(1-imidazolyl)butyraldehyde. The reaction was used to produce conformationally restricted farnesyltransferase inhibitor analogues which exhibit improved in vivo metabolic stability.

In vitro and in vivo evaluation of dihydropyrimidinone C-5 amides as potent and selective alpha(1A) receptor antagonists for the treatment of benign prostatic hyperplasia.

alpha(1) Adrenergic receptors mediate both vascular and lower urinary tract tone, and alpha(1) receptor antagonists such as terazosin (1b) are used to treat both hypertension and benign prostatic hyperplasia (BPH). Recently, three different subtypes of this receptor have been identified, with the alpha(1A) receptor being most prevalent in lower urinary tract tissue. This paper explores 4-aryldihydropyrimidinones attached to an aminopropyl-4-arylpiperidine via a C-5 amide as selective alpha(1A) receptor subtype antagonists. In receptor binding assays, these types of compounds generally display K(i) values for the alpha(1a) receptor subtype <1 nM while being greater than 100-fold selective versus the alpha(1b) and alpha(1d) receptor subtypes. Many of these compounds were also evaluated in vivo and found to be more potent than terazosin in both a rat model of prostate tone and a dog model of intra-urethral pressure without significantly affecting blood pressure. While many of the compounds tested displayed poor pharmacokinetics, compound 48 was found to have adequate bioavailability (>20%) and half-life (>6 h) in both rats and dogs. Due to its selectivity for the alpha(1a) over the alpha(1b) and alpha(1d) receptors as well as its favorable pharmacokinetic profile, 48 has the potential to relieve the symptoms of BPH without eliciting effects on the cardiovascular system.

Combinatorial diversification of indinavir: in vivo mixture dosing of an HIV protease inhibitor library.

An efficient combination solution-phase/solid-phase route enabling the diversification of the P1', P2', and P3 subsites of indinavir has been established. The synthetic sequence can facilitate the rapid generation of HIV protease inhibitors possessing more favorable pharmacokinetic properties as well as enhanced potencies. Multiple compound dosing in vivo may also accelerate the identification of potential drug candidates.

Rizatriptan, a novel 5-HT1B/1D agonist for migraine: single- and multiple-dose tolerability and pharmacokinetics in healthy subjects.

Rizatriptan is a novel 5-HT1D/1B agonist for relief of migraine headache. The pharmacokinetics, metabolite profiles, and tolerability of rizatriptan were examined in a multiple-dose study in healthy subjects. Rizatriptan (N = 24) (or placebo, N = 12) was administered as a single 10 mg dose, followed 48 hours later by administration of one 10 mg dose every 2 hours for three doses on 4 consecutive days, corresponding to the maximum daily dose for a migraine attack. The AUC of rizatriptan and its active N-monodesmethyl metabolite after three 10 mg doses was approximately threefold greater than the plasma concentrations following a single 10 mg dose. Metabolite profiles were similar after single and multiple doses. Adverse events during rizatriptan were mild and transient; similar events occurred during placebo, with a somewhat reduced incidence. Diastolic blood pressure tended to increase compared with placebo (approximately 5 mmHg), particularly on the first multiple-dose day (p < .01 vs. placebo). In conclusion, rizatriptan is well tolerated by healthy subjects during multiple-dose administration, with no unexpected accumulation of drug in plasma.

Pharmacokinetics and tolerability of oral rizatriptan in healthy male and female volunteers.

AIMS: The pharmacokinetics and dose proportionality of rizatriptan single oral doses from 2.5 to 15 mg administered as solutions to healthy volunteers were studied. METHODS: In a randomized, crossover study with four periods, twenty-four healthy volunteers (12 males and 12 females) took single oral doses of 2.5, 5, 10, and 15 mg rizatriptan in Periods 1-4. In a fifth period, subjects received 4 mg intravenous (i.v.) rizatriptan as a reference. Plasma and urine rizatriptan concentrations were determined at several timepoints/intervals for 12 and 24 h, respectively. RESULTS: The arithmetic mean AUC values following single oral doses of 2.5, 5, 10, and 15-mg rizatriptan were 16, 33, 72, and 127 ng ml-1 h, respectively, in males; and 19, 42, 97, and 161 ng ml-1 h, respectively, in females. The overall bioavailability (F ) of rizatriptan was approximately 40% in males. Following the 4 mg reference i.v. dose, the apparent plasma clearance (CL) and renal clearance (CLr ) were 1042 and 225 ml min-1, respectively, in males; and 821 and 174 ml min-1, respectively, in females. CONCLUSIONS: The disposition kinetics of oral rizatriptan were linear for doses of 2. 5-10 mg in males, and for doses of 2.5-5 mg in females. However, the degree of nonlinearity for higher doses was minor for both genders. The plasma concentrations of rizatriptan were slightly greater in women compared to men but the difference was not considered to be clinically meaningful. Also, the clearance of rizatriptan appeared to be mainly nonrenal.

Metabolism of MK-499, a class III antiarrhythmic agent, in rats and dogs.

MK-499 [(+)-N-[1'-(6-cyano-1, 2, 3, 4-tetrahydro-2(R)-naphthalenyl)-3, 4-dihydro-4(R)-hydroxyspiro(2H-1-benzopyran-2, 4'-piperidin)-6-yl]methanesulfonamide] monohydrochloride is an investigational class III antiarrhythmic agent for treatment of malignant ventricular tachyarrhythmias. The disposition of [3H]MK-499 and [14C]MK-499 was studied in rats and dogs after oral and iv administration. MK-499 was concentrated in organs of excretion and the heart. In the rat, urinary radioactivity elimination values after iv (0.5 mg/kg) and oral (6.25 mg/kg) doses were 21 +/- 3% and 10 +/- 2%, respectively. Corresponding fecal recoveries were 68 +/- 6% and 78 +/- 7%. Similar results were found after corresponding doses of [14C]MK-499. In dogs, urine and feces accounted for 16 +/- 3% and 75 +/- 4% of recovered radioactivity after a [3H]MK-499 iv dose (0.1 mg/kg). Corresponding recoveries after an oral dose (1 mg/kg) were 12 +/- 2% and 76 +/- 3%. Biliary (0-24 hr) excretion accounted for 39 +/- 5% and 41 +/- 18% of [3H] and [14C] oral doses in rats, respectively. Dogs excreted 34% of [3H] oral dose in (0-24 hr) bile. The data indicated that a substantial amount of MK-499 was absorbed by rats and dogs. MK-499, metabolite I (formed by loss of N-substitution), and metabolite II (an acid formed by metabolic scission across the benzopyran ring) each represented 30% of rat urinary label. Rat bile contained MK-499 (10%), II (20%), and IV (10%), which was formed by carbon-4 hydroxylation of the tetralin ring. Additionally, rat bile included glutathione (V) and N-acetyl-1-cysteine (VI) conjugates of a ring-opened metabolite. Metabolite III, a positional isomer of IV, was excreted in rat urine. The major labeled species excreted in dog bile were unchanged MK-499 and its glucuronide (VII), which, respectively, represented 50% and 30% of the biliary radioactivity. MK-499 and a small amount of I represented dog urinary radioactivity. The bioavailability of MK-499 was high in dogs (100%) but low in rats (17%). This difference was probably due to the more extensive presystemic metabolism of MK-499 in rats.

The use of stable isotope labeling and liquid chromatography-tandem mass spectrometry techniques to simultaneously determine the oral and ophthalmic bioavailability of timolol in dogs.

Assays have been established for the quantitation of timolol and its 13C3- and 2H9-stable-isotope-labeled analogs in plasma and urine using liquid chromatography with atmospheric-pressure chemical-ionization tandem mass spectrometry. For the analysis of urine, underivatized timolol and its labeled analogs are monitored while timolol in plasma is assayed down to concentrations of 0.2 ng/mL after derivatization with phosgene. The great power of this technique is illustrated by simultaneously assaying three different species of timolol in plasma and urine obtained from dogs receiving simultaneous ophthalmic, oral, and intravenous doses of unlabeled and [2H9]- and [13C3]-labeled timolol. Thus, the ophthalmic and oral bioavailabilities of timolol are measured in a single experiment rather than as a three-phase crossover experiment. This approach yields accurate and precise analytical data, obviates intrasubject variability, and saves both analytical and animal resources.

Pharmacokinetics and tolerability of intravenous rizatriptan in healthy females.

The pharmacokinetics and tolerability of intravenous (i.v.) rizatriptan (MK-0462), a novel 5-HT1D/1B receptor agonist for the acute oral treatment of migraine, were examined in an open, single-dose, four-period, randomized crossover study in healthy females. Results of this study indicated that i.v. rizatriptan (0.5-5 mg) was well tolerated. The disposition kinetics of rizatriptan were linear for i.v. doses up to and including 2.5 mg. Relative to the 0.5 mg dose, geometric mean dose-adjusted AUC ratios were 1.04, 1.09, and 1.18 for 1, 2.5, and 5 mg doses, respectively. Apparent plasma clearance (Cl) ranged between 859 and 941 mL min(-1) from 0.5 to 2.5 mg, but dropped to slightly below 800 mL min(-1) for the 5 mg dose. Therefore, the elimination of rizatriptan appears somewhat dose dependent at the high end of this dose range. Mean plasma half-life (t1/2) was 1.5-2.2 h across all doses while mean residence time in the body (MRT) and steady state volume of distribution (Vss) of rizatriptan remained relatively invariant across doses. Urinary excretion of rizatriptan (Ue) ranged from 14.5 to 34.6% of dose.

3-Pyridyloxypropanolamine agonists of the beta 3 adrenergic receptor with improved pharmacokinetic properties.

Pyridyloxypropanolamines L-749,372 (8, beta 3 EC50 = 3.6 nM) and L-750,355 (29, beta 3 EC50 = 13 nM) are selective partial agonists of the human receptor, with 33% and 49% activation, respectively. Both stimulate lipolysis in rhesus monkeys (ED50 = 2 and 0.8 mg/kg, respectively), with minimal effects on heart rate. Oral bioavailability in dogs, 41% for L-749,372 and 47% for L-750,355, is improved relative to phenol analogs.

A direct technique for the simultaneous determination of 10 drug candidates in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry interfaced to a Prospekt solid-phase extraction system.

New drug candidates are being synthesized at an ever increasing rate and, until recently, the pharmacokinetics of only a few of these could be evaluated. Our laboratory is taking a novel approach to rapid multiple pharmacokinetic screening of potential drug candidates in which mixtures of new substances are co-administered to animals and analyzed simultaneously in plasma using liquid chromatography with tandem MS/MS detection in conjunction with a Prospekt automated on-line solid-phase extraction system. Plasma is sampled via an autosampler and extracted by the Prospekt with the eluent being introduced directly via a reverse phase HPLC column and a heated nebulizer interface to the mass spectrometer. Generic extraction and chromatographic conditions generally give good recoveries. The chromatographic run-times are less than 8 min. The accuracy and precision of these assays are carefully controlled with recoveries generally in the range 80-120% and coefficients of variation less than 20%. Lower quantifiable limits range from 2.5 to 5 ng ml-1. This approach considerably reduces the number of animals needed to screen drug candidates and its power is illustrated by determination of the pharmacokinetics of 10 substances after their simultaneous administration to dogs.

The simultaneous determination of mixtures of drug candidates by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry as an in vivo drug screening procedure.

Liquid chromatography, combined with tandem mass spectrometry (LC/MS/MS) has been rapidly embraced by the pharmaceutical industry as the definitive method for the determination of drug levels in biological fluids obtained from pharmacokinetic and toxicological studies. This technique has proved to be reliable, accurate and precise for the determination of drugs and related substances (e.g. metabolites and isotope-labeled compounds) in support of preclinical and clinical studies. Our group has recently expanded the use of quantitative LC/MS/MS into the area of discovering new substances as potential drug candidates. When used as an accurate mass detector, triple quadrupole instruments have the ability to simultaneously and specifically detect minute quantities of closely-related drug substances in the extracts of biological fluids. Analytical procedures have been developed and validated that simultaneously determine plasma concentrations of up to 12 drug candidates over a concentration range of 1-1000 ng mL-1 in single analytical occasions. This approach is used to support drug discovery by rapidly providing pharmacokinetic data to a wide range of compounds following either the administration of multiple compounds to single animals, or by increasing the speed and efficiency of analyzing samples following the administration of single compounds to multiple animals. Currently, we have screened over 400 compounds in two different target classes in a period of 24 weeks. A standard operating procedure defining the acceptability of quality control data obtained during such screening experiments is described.

Pilot study of MK-462 in migraine.

MK-462 is a potent, selective 5HT1D receptor agonist which may be useful in treating acute migraine. We conducted a double-blind placebo-controlled inpatient study to assess the preliminary efficacy and safety of oral doses of MK-462 20 mg (n = 8) and 40 mg (n = 36) vs placebo (n = 21), administered to 65 male and post-menopausal female migraine patients aged 22-51 with moderate or severe migraine headache. Headache severity and functional disability were measured at 0.5, 1, 1.5, and 2 h post-dose. The 20 mg dose was well tolerated and 4/8 patients obtained relief in headache severity at the 2 h time point. The 40 mg dose was well tolerated and was significantly (p < 0.05) superior to placebo at the 1.5 and 2 h time points (with 27/36 or 75% obtaining relief at 2 h compared to 7/21 or 33% for placebo). Adverse events occurred in 50% of patients on 20 mg MK-462, 72% of those on 40 mg MK-462, and in 52% of placebo-treated subjects. The most common adverse events associated with MK-462 were drowsiness (20 mg 12%; 40 mg 44%; placebo 24%), dry mouth (40 mg 36%; placebo 19%), and lightheadedness/dizziness (40 mg 17%; placebo 10%). Based on these preliminary results, MK-462 appears worthy of continued study for the treatment of acute migraine.

Quantitation of the 5HT1D agonists MK-462 and sumatriptan in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

The 5HT1D agonist sumatriptan is efficacious in the treatment of migraines. MK-462 is a drug of the same class which is under development in our laboratories. Bioanalytical methods of high efficiency, specificity and sensitivity were required to support the preclinical and clinical programs. These assays were based on HPLC with tandem MS-MS detection. MK-462 and sumatriptan were extracted using an automated solid-phase extraction technique on a C2 Varian Bond-Elut cartridge. The n-diethyl analogues of MK-462 and sumatriptan were used as internal standards. The analytes were chromatographed using reversed-phase (nitrile) columns coupled via a heated nebulizer interface to an atmospheric pressure chemical ionization source. The chromatographic run times were less than 7 min. Both methods were precise, accurate and selective down to plasma concentrations of 0.5 ng/ml. The assay for MK-462 was adapted to separately monitor the unlabeled and 14C-labeled species of the drug following intravenous administration of radiolabeled material to man.

Pharmacokinetics and food interaction of MK-462 in healthy males.

A study was conducted to assess the safety, tolerability, and pharmacokinetics of single intravenous (IV) doses of 5-90 micrograms kg-1 of MK-462, and the effect of food on the pharmacokinetics of MK-462 administered orally to healthy males. Results of this study indicate that IV doses of MK-462 from 5 to 90 micrograms kg-1 are well tolerated. The disposition kinetics of MK-462 were linear for IV doses up to and including 60 micrograms kg-1. The values of the plasma clearance (CL), steady-state volume of distribution (Vss), plasma terminal half-life (t1/2), and mean residence time in the body (MRT) of MK-462 averaged 1376 mL min-1, 140 L, 1.8 h, and 1.7 h, respectively, and remained essentially constant over the dosage range of 10-60 micrograms kg-1 of IV MK-462. However, as the dose increased from 60 to 90 micrograms kg-1, the mean value of the apparent CL decreased from 1376 to 807 mL min-1. Thus, elimination of MK-462 was dose dependent in this dosage range. Based on the disposition decomposition analysis (DDA), it was shown that the Vss value of MK-462 remained essentially constant over the dosage range of 10-90 micrograms kg-1 of IV MK-462. The following values of two dose-independent parameters were also calculated by using DDA: distribution clearance (CLd) = 2028 mL min-1, and mean transit time in the peripheral tissues (MTTT) = 0.74 h. The mean values of AUC, Cmax, tmax, and apparent t1/2 of MK-462 in 12 subjects each receiving a 40 mg tablet of MK-462 without breakfast were 330 ng.h mL-1, 77 ng mL-1, 1.6 h, and 1.8 h, respectively. Although administration of a standard breakfast prior to dosing increased the AUC value (by approximately 20%) of MK-462 and delayed its absorption, there were no significant effects of the meal on the values of Cmax and apparent t1/2 of MK-462.

The use of stable isotope labeling and liquid chromatography/tandem mass spectrometry techniques to study the pharmacokinetics and bioavailability of the antimigraine drug, MK-0462 (rizatriptan) in dogs.

MK-0462 (rizatriptan) is a 5HT1D agonist being developed for the treatment of migraine. The assay for this substance in plasma and urine is based on HPLC with tandem mass spectrometry (MS/MS) detection. The procedure has been modified to include the simultaneous determination of the [triazole-13C2, 15N3-] stable-isotope-labelled analogue for which the lower quantifiable limit was 0.1 ng mL-1. The assay has been applied to study the pharmacokinetics of MK-0462 after simultaneous oral and intravenous administration of the drug and its stable-isotope-labelled analogue to dogs. The experiment afforded an estimate of plasma clearance concomitant with a precise measurement of the drug's oral bioavailability. The increasing use of LC-MS/MS in quantitative experiments may renew interest in stable isotopes as tools for pharmaceutical research.