Inhibition of autotaxin activity ameliorates neuropathic pain derived from lumbar spinal canal stenosis.

Lumbar spinal canal stenosis (LSS) or mechanical compression of dorsal root ganglion (DRG) is one of the causes of low back pain and neuropathic pain (NP). Lysophosphatidic acid (LPA) is a potent bioactive lipid mediator that is produced mainly from lysophosphatidylcholine (LPC) via autotaxin (ATX) and is known to induce NP via LPA1 receptor signaling in mice. Recently, we demonstrated that LPC and LPA were higher in cerebrospinal fluid (CSF) of patients with LSS. Based on the possible potential efficacy of the ATX inhibitor for NP treatment, we used an NP model with compression of DRG (CD model) and investigated LPA dynamics and whether ATX inhibition could ameliorate NP symptoms, using an orally available ATX inhibitor (ONO-8430506) at a dose of 30 mg/kg. In CD model, we observed increased LPC and LPA levels in CSF, and decreased threshold of the pain which were ameliorated by oral administration of the ATX inhibitor with decreased microglia and astrocyte populations at the site of the spinal dorsal horn projecting from injured DRG. These results suggested possible efficacy of ATX inhibitor for the treatment of NP caused by spinal nerve root compression and involvement of the ATX-LPA axis in the mechanism of NP induction.

Antineutrophil properties of natural gingerols in models of lupus.

Ginger is known to have antiinflammatory and antioxidative effects and has traditionally been used as an herbal supplement in the treatment of various chronic diseases. Here, we report antineutrophil properties of 6-gingerol, the most abundant bioactive compound of ginger root, in models of lupus and antiphospholipid syndrome (APS). Specifically, we demonstrate that 6-gingerol attenuates neutrophil extracellular trap (NET) release in response to lupus- and APS-relevant stimuli through a mechanism that is at least partially dependent on inhibition of phosphodiesterases. At the same time, administration of 6-gingerol to mice reduces NET release in various models of lupus and APS, while also improving other disease-relevant endpoints, such as autoantibody formation and large-vein thrombosis. In summary, this study is the first to our knowledge to demonstrate a protective role for ginger-derived compounds in the context of lupus. Importantly, it provides a potential mechanism for these effects via phosphodiesterase inhibition and attenuation of neutrophil hyperactivity.

A randomized, placebo-controlled, phase 1 study to evaluate the effects of TAK-063 on ketamine-induced changes in fMRI BOLD signal in healthy subjects.

RATIONALE: Phosphodiesterase 10A inhibitor TAK-063 has shown effects that suggest efficacy in schizophrenia treatment. OBJECTIVE: This randomized, double-blind, placebo-controlled, incomplete-crossover study investigated effects of single oral administration of TAK-063 on ketamine-induced changes in blood oxygen level-dependent (BOLD) signal in healthy males. METHODS: Healthy men aged 18 to 45 years with normal magnetic resonance imaging (MRI) scans and electroencephalogram measurements at screening were eligible. Each subject was randomized to one of nine treatment schedules: all subjects received placebo and two of three doses of TAK-063 followed by ketamine. The primary endpoint was ketamine-induced brain activity in select regions of the brain during resting state. Secondary endpoints included pharmacokinetic parameters of TAK-063, proportion of subjects with treatment-emergent adverse events (AEs), and percentage of subjects meeting criteria for abnormal safety laboratory tests and vital sign measurements. RESULTS: The study comprised 27 subjects. Prior to ketamine infusion, TAK-063 exerted region-specific effects on resting state functional MRI (fMRI) BOLD signal. After ketamine administration, TAK-063 reduced the Cohen's effect size for resting-state fMRI BOLD signal in key brain regions examined, and exerted similar effects on BOLD signal during the working memory task across all doses. TAK-063 was safe and well tolerated. CONCLUSIONS: Our results are consistent with non-clinical studies of ketamine and TAK-063 and clinical studies of ketamine and risperidone. It is unknown whether these data are predictive of potential antipsychotic efficacy, and further analyses are required.

Determination of Phosphodiesterase Inhibitors Tadalafil, Roflumilast and Roflumilast N-Oxide Using LC-MS in Guinea Pig Plasma.

Phosphodiesterases are known as a super-family of 11 isoenzymes, which can exert various functions based on their organ distribution. In this work, a rapid and sensitive ultra-high performance liquid chromatography-tandem mass spectrometry method was developed for quantification of tadalafil (phosphodiesterase five inhibitor), roflumilast (RF) (phosphodiesterase four inhibitor) and its active metabolite, RF N-oxide in guinea pig plasma. Chromatographic separation was carried out on UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 µm) at a flow rate 0.5 mL/min, using 0.2% formic acid in acetonitrile and 0.2% formic acid in water as mobile phases within 4 min. Detection was performed using a triple quadrupole mass spectrometer employing electrospray ionization operated in positive mode using multiple reaction monitoring mode. The method utilized deuterium labeled internal standards, and was validated according to European Medicines Agency guidelines. It showed excellent linearity in the range of 0.5-500.0 ng/mL for all analytes with coefficient of determination >0.99. The intra- and inter-day precisions (relative standard deviation %) were within 6.7%, and the recoveries were greater than 73.4%. Using this method, plasma samples from experiments of phosphodiesterase four, and five inhibitors in a model of ovalbumin-induced allergic inflammation in guinea pigs were analyzed.

Hydroxamic Acids Constitute a Novel Class of Autotaxin Inhibitors that Exhibit in Vivo Efficacy in a Pulmonary Fibrosis Model.

Autotaxin (ATX) catalyzes the hydrolysis of lysophosphatidylcholine (LPC) generating the lipid mediator lysophosphatidic acid (LPA). Both ATX and LPA are involved in various pathological inflammatory conditions, including fibrosis and cancer, and have attracted great interest as medicinal targets over the past decade. Thus, the development of novel potent ATX inhibitors is of great importance. We have developed a novel class of ATX inhibitors containing the zinc binding functionality of hydroxamic acid. Such novel hydroxamic acids that incorporate a non-natural δ-amino acid residue exhibit high in vitro inhibitory potency over ATX (IC50 values 50-60 nM). Inhibitor 32, based on δ-norleucine, was tested for its efficacy in a mouse model of pulmonary inflammation and fibrosis induced by bleomycin and exhibited promising efficacy. The novel hydroxamic ATX inhibitors provide excellent tools for the study of the role of the enzyme and could contribute to the development of novel therapeutic agents for the treatment of fibrosis and other chronic inflammatory diseases.

The safety, tolerability and pharmacokinetics of BI 409306, a novel and potent PDE9 inhibitor: Overview of three Phase I randomised trials in healthy volunteers.

Safety, tolerability and pharmacokinetics of BI 409306, a potent and selective phosphodiesterase 9A inhibitor, were assessed in healthy subjects in three Phase I, within-dose group, double-blind trials. Trial 1 randomised young and elderly subjects to receive BI 409306 25, 50, 100 mg, placebo once daily (OD) or BI 409306 50 mg twice daily (young) for 14 days. Trial 2 randomised young poor metabolisers (PM) of cytochrome P450 isoform 2C19 (CYP2C19) and elderly subjects to receive BI 409306 25, 50 mg or placebo OD for 14 days. Trial 3 randomised Chinese and Japanese extensive metabolisers of CYP2C19 to receive single doses (SD) of BI 409306 25, 50, 100 mg or placebo and Chinese (PM) to SD of BI 409306 100 mg or placebo (Part 1). Japanese PM received SD of BI 409306 100 mg or placebo (Day 1) followed by BI 409306 100 mg or placebo OD for 7 days after a 48-hour washout period (Part 2). Reported adverse events (AE) were mild-to-moderate intensity and increased with BI 409306 dose. Eye disorders were most commonly reported (Trial 1: 40.0-41.7%, Trial 2: 29.2-37.5%, Trial 3: 18.2-66.7%) and increased with dose and systemic exposure. PM reported more AEs than other treatment groups, corresponding to higher systemic exposure to BI 409306. Systemic exposure to BI 409306 produced dose-dependent increases and was slightly greater in elderly versus young subgroups (Trial 1). Steady state was achieved by Day 2-3. Overall, BI 409306 demonstrated good safety, tolerability and minor accumulation after multiple dosing.

Effects of a novel phosphodiesterase 10A inhibitor in non-human primates: A therapeutic approach for schizophrenia with improved side effect profile.

Schizophrenia symptoms are associated with alterations in basal ganglia-cortical networks that include the cyclic nucleotides (cAMP/cGMP) signaling pathways. Phosphodiesterase 10A (PDE10A) inhibitors have been considered as therapeutic agents for schizophrenia because the regulation of cAMP and cGMP in the striatum by PDE10A plays an important role in the signaling mechanisms of the striatal-cortical network, and thereby in cognitive function. In the present study we assessed in non-human primates (NHPs) the effects of a novel PDE10A inhibitor (FRM-6308) that has demonstrated high potency and selectivity for human recombinant PDE10A in vitro. The behavioral effects of FRM-6308 in a dose range were determined in rhesus monkeys using a standardized motor disability scale for primates, motor tasks, and the "drug effects on the nervous system" (DENS) scale. The neuronal metabolic effects of FRM-6308 were determined with [(18)F]-fluorodeoxyglucose PET imaging. Results showed that FRM-6308 did not have any specific effects on the motor system at s.c. doses up to 0.32 mg/kg in NHPs, which induced a significant increase in the FDG-SUV in striatum (F 16.069, p < 0.05) and cortical (F 15.181, p < 0.05) regions. Higher doses induced sedation and occasional involuntary movements with clear development of tolerance after repeated exposures. These findings suggest that FRM-6308 has the adequate pharmacological profile to advance testing in clinical trials and demonstrate antipsychotic efficacy of PDE10A inhibition for the treatment of schizophrenia patients.

Validated spectrofluorimetric method for determination of two phosphodiesterase inhibitors tadalafil and vardenafil in pharmaceutical preparations and spiked human plasma.

A valid, sensitive and rapid spectrofluorimetric method has been developed and validated for determination of both tadalafil (TAD) and vardenafil (VAR) either in their pure form, in their tablet dosage forms or spiked in human plasma. This method is based on measurement of the native fluorescence of both drugs in acetonitrile at λem 330 and 470 nm after excitation at 280 and 275 nm for tadalafil and vardenafil, respectively. Linear relationships were obtained over the concentration range 4-40 and 10-250 ng/mL with a minimum detection of 1 and 3 ng/mL for tadalafil and vardenafil, respectively. Various experimental parameters affecting the fluorescence intensity were carefully studied and optimized. The developed method was applied successfully for the determination of tadalafil and vardenafil in bulk drugs and tablet dosage forms. Moreover, the high sensitivity of the proposed method permitted their determination in spiked human plasma. The developed method was validated in terms of specificity, linearity, lower limit of quantification (LOQ), lower limit of detection (LOD), precision and accuracy. The mean recoveries of the analytes in pharmaceutical preparations were in agreement with those obtained from the comparison methods, as revealed by statistical analysis of the obtained results using Student's t-test and the variance ratio F-test.

Synthesis, biological activities and pharmacokinetic properties of new fluorinated derivatives of selective PDE4D inhibitors.

A new series of selective PDE4D inhibitors has been designed and synthesized by replacing 3-methoxy group with 3-difluoromethoxy isoster moiety in our previously reported cathecolic structures. All compounds showed a good PDE4D3 inhibitory activity, most of them being inactive toward other PDE4 isoforms (PDE4A4, PDE4B2 and PDE4C2). Compound 3b, chosen among the synthesized compounds as the most promising in terms of inhibitory activity, selectivity and safety, showed an improved pharmacokinetic profile compared to its non fluorinated analogue. Spontaneous locomotor activity, assessed in an open field apparatus, showed that, differently from rolipram and diazepam, selective PDE4D inhibitors, such as compounds 3b, 5b and 7b, did not affect locomotion, whereas compound 1b showed a tendency to reduce the distance traveled and to prolong the immobility period, possibly due to a poor selectivity.

Evaluation on activity of cytochrome p450 enzymes in turbot via a probe drug cocktail.

Cytochrome P450s (CYPs) are the main catalytic enzymes for metabolism by a variety of endogenous and exogenous substrates in mammals, fish, insects, etc. We evaluated the application of a multidrug cocktail on changes in CYP1, CYP2, and CYP3 activity in Turbot Scophthalmus maximus. The probe drugs were a combination of caffeine (5 mg/kg body weight), dapsone (5 mg/kg), and chlorzoxazone (10 mg/kg). After a single intraperitoneal injection of the cocktail, the concentration of all three probe drugs in the plasma increased quickly to a peak and then decreased gradually over 24 h. Pharmacokinetic profiles of the three probe drugs were determined using a noncompartmental analysis, and the typical parameters were calculated. In the assay for CYP induction, pretreatment with rifampicin significantly reduced the typical pharmacokinetic metrics for caffeine and chlorzoxazone, but not dapsone, indicating that the activity of CYP1 and CYP2 in turbot were induced by rifampicin.

Pharmacokinetics of single oral dose of pimobendan in Hispaniolan Amazon parrots (Amazona ventralis).

Pimobendan is a phosphodiesterase (PDE) inhibitor and calcium sensitizer with inotropic, lusitropic, and rasodilator properties used in the treatment of congestive heart failure. The mechanism of action is by inhibition of PDE III and V and by increasing intracellular calcium sensitivity in the cardiac myocardium. Pharmacokinetic and pharmacodynamic studies have been published in humans, dogs, and cats, but there are no studies in avian species. Pimobendan has been used in birds at the empirical dosage of 0.25 mg/kg q12h. To determine the pharmacokinetic parameters of pimobendan in Hispaniolan Amazon parrots (Amazona ventralis), 3 pilot studies with 2 birds, each receiving 1, 3, and 10 mg/kg PO, provided the basis for the pivotal trials with 6 birds, each receiving 10 mg/kg PO using 2 different suspensions. Blood samples were obtained at 0, 0.5, 1, 1.5, 2, 3, 4, 8, 12, and 18 hours after drug administration. Plasma concentrations were determined by liquid chromatography-tandem mass spectrometry (HPLC/MS) by use of electrospray ionization. Because of the erratic and low concentrations of pimobendan, pharmacokinetic parameters were calculated using naive averaged analysis. Plasma concentrations after commercial pimobendan tablet suspension at 10 mg/kg reached a Cmax of 8.26 ng/mL at 3 hours with a terminal half-life of 2.1 hours, while concentrations after the bulk chemical suspension reached a Cmax of 1.28 ng/mL at 12 hours and had a terminal half-life of 2.3 hours. Further studies evaluating the effect of oral pimobendan in parrots are needed.

Seizures after heart transplantation--two cases of non-immunosuppressant drug interactions in young patients.

BACKGROUND: Neurological complications occur in 30-80% of patients following heart transplantation, and seizures account for 2-20% of these sequelae. The main risk factors are toxicity due to immunosuppression, infections, and brain lesions. We present 2 cases of grand mal type attacks that occurred on the 7th and 15th postoperative days. The origin of the attacks was an unusual interaction between 2 non-immunosuppressive drugs (metoclopramide and theophylline). CASE REPORT: We present 2 cases of seizure episodes during the early postoperative period in young heart transplant recipients (a 26-year-old female and a 33-year-old man). Grand mal type attacks occurred on the 7th and 15th postoperative day, respectively. Both patients were treated with standard triple immunosuppressive therapy including tacrolimus, mycophenolate mofetil, and steroids. Therapy with metoclopramide was started because the patients reported gastrointestinal disturbances. Theophylline was administered due to postoperative bradycardia. Serum theophylline levels were 33 and 34 mcg/ml, respectively. There were no neurological deficits noticed thereafter. The magnetic resonance imaging (MRI) was negative for stroke and central nervous system infection in both cases. CONCLUSIONS: We conclude that theophylline overdose combined with metoclopramide may provoke new-onset seizures, especially in young patients following heart transplantation.

Quantitative analyses of CTP-499 and five major metabolites by core-structure analysis.

CTP-499 is a novel oral multi-subtype selective inhibitor of PDEs that is currently in clinical testing, in combination with angiotensin modulators, as a potentially first-in-class treatment for diabetic kidney disease. The compound was discovered and developed by using Concert's proprietary DCE Platform(®) in which deuterium was incorporated at select positions of 1-((S)-5-hydroxyhexyl)-3,7-dimethylxanthine (HDX). CTP-499 metabolizes to five major metabolites: C-21256, D-M2, D-M3, D-M4 and M5, of which all contains deuterium except M5. During in vivo metabolism, however, H/D exchange takes place. As a result, each analyte, except M5, has multiple molecular masses. To accurately quantify the analytes, we developed an LC-MS/MS method focusing on the core structures of the molecules, termed "core-structure analyses". The core-structure analyses method was then validated under GLP guidance in dog, rat and rabbit plasma, with a sample volume of 50 µL. Results demonstrated that this approach accurately quantifies each of the six analytes despite partial exchange of deuterium with hydrogen atoms in the in vivo samples. The validation parameters included accuracy, precision, sensitivity, stability, dilution integrity, hemolysis, matrix effect, selectivity, and recovery. Acceptable intra-run and inter-run assay precision (%CV ≤ 5.5%) and accuracy (90.1-106.7%) were achieved over a linear range of 10-5,000 ng/mL of each analyte. Various stability tests, including bench-top, freeze/thaw, stock solution, and long-term storage, were also performed. All stability results met acceptance criteria. The robustness of the methods was demonstrated by the incurred sample reproducibility (ISR) tests. After validation, the method was successfully used in support of multiple toxicological studies of CTP-499.

Phosphodiesterase 10A inhibitor MP-10 effects in primates: comparison with risperidone and mechanistic implications.

Phosphodiesterase 10A (PDE10A) is highly expressed in striatal medium spiny neurons of both the direct and indirect output pathways. Similar to dopamine D2 receptor antagonists acting on indirect pathway neurons, PDE10A inhibitors have shown behavioral effects in rodent models that predict antipsychotic efficacy. These findings have supported the clinical investigation of PDE10A inhibitors as a new treatment for schizophrenia. However, PDE10A inhibitors and D2 antagonists differ in effects on direct pathway and other neurons of the basal ganglia, indicating that these two drug classes may have divergent antipsychotic efficacy and side effect profile. In the present study, we compare the behavioral effects of the selective PDE10A inhibitor MP-10 to those of the clinical standard D2 antagonist risperidone in rhesus monkeys using a standardized motor disability scale for parkinsonian primates and a newly designed "Drug Effects on Nervous System" scale to assess non-motor effects. Behavioral effects of MP-10 correlated with its plasma levels and its regulation of metabolic activity in striatal and cortical regions as measured by FDG-PET imaging. While MP-10 and risperidone broadly impacted similar behavioral domains in the primate, their effects had a different underlying basis. MP-10-treated animals retained the ability to respond but did not engage tasks, whereas risperidone-treated animals retained the motivation to respond but were unable to perform the intended actions. These findings are discussed in light of what is currently known about the modulation of striatal circuitry by these two classes of compounds, and provide insight into interpreting emerging clinical data with PDE10A inhibitors for the treatment of psychotic symptoms.

Pharmacokinetics of pentoxifylline and its main metabolites in patients with different degrees of heart failure following a single dose of a modified-release formulation.

Pentoxifylline (PTX) is extensively metabolized in the body, and all its 3 plasma metabolites (M1, M4, M5) are pharmacologically active. The authors evaluated the pharmacokinetics of PTX and its metabolites in 20 patients with chronic heart failure (CHF). Eleven had moderate and 9 severe CHF. The time courses of PTX, M1, M4, and M5 plasma levels were determined after oral administration of a sustained-release 600-mg tablet of PTX, and for each compound, AUC, maximal plasma concentration (C(max)), and time to C(max) (T(peak)) were calculated. Compared with patients with moderate CHF, those with severe CHF showed a significant delay in T(peak) of PTX (3.9 vs 1.6 hours) and M5 (5.6 vs 3.6 hours), a 59% significant increase in M5 AUC, and a 56% nonsignificant increase in PTX AUC. In the whole population, the AUCs of PTX, M4, and M5 were inversely correlated with markers of liver function, whereas the AUCs of M4 and M5 were inversely correlated with the creatinine clearance. In view of the kinetic features of slow-release formulations (flip-flop phenomenon), the delay in T(peak) of PTX in patients with severe CHF compared with moderate CHF should be ascribed to a reduced elimination rate.

The novel phosphodiesterase 10A inhibitor THPP-1 has antipsychotic-like effects in rat and improves cognition in rat and rhesus monkey.

Phosphodiesterase 10A (PDE10A) is a novel target for the treatment of schizophrenia that may address multiple symptomatic domains associated with this disorder. PDE10A is highly expressed in the brain and functions to metabolically inactivate the important second messengers cAMP and cGMP. Here we describe effects of a potent and orally bioavailable PDE10A inhibitor [2-(6-chloropyridin-3-yl)-4-(2-methoxyethoxy)-7,8-dihydropyrido[4,3-d]pyrimidin-6(5H)-yl](imidazo[1,5-a]pyridin-1-yl)methanone] (THPP-1) on striatal signaling pathways, in behavioral tests that predict antipsychotic potential, and assays that measure episodic-like memory in rat and executive function in rhesus monkey. THPP-1 exhibits nanomolar potency on the PDE10A enzyme, demonstrates excellent pharmacokinetic properties in multiple preclinical animal species, and is selective for PDE10A over other PDE families of enzymes. THPP-1 significantly increased phosphorylation of proteins in the striatum involved in synaptic plasticity, including the a-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid receptor (AMPA) GluR1 subunit, extracellular receptor kinase (ERK), and cAMP-response element binding protein (CREB). THPP-1 produced dose-dependent effects in preclinical assays predictive of antipsychotic activity including attenuation of MK-801-induced psychomotor activation and condition avoidance responding in rats. At similar plasma exposures, THPP-1 significantly increased object recognition memory in rat and attenuated a ketamine-induced deficit in the object retrieval detour task in rhesus monkey. These findings suggest that PDE10A inhibitors have the potential to impact multiple symptomatic domains of schizophrenia including positive symptoms and cognitive impairment. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Astragaloside IV inhibited the activity of CYP1A2 in liver microsomes and influenced theophylline pharmacokinetics in rats.

OBJECTIVES: With the growing popularity of herbal and natural medicinal products, attention has turned to possible interactions between these products and pharmaceutical drugs. In this study, we examined whether astragaloside IV (AGS-IV) could inhibit the activity of CYP1A2 in rat liver microsomes in vitro and in vivo. METHODS: The effect of AGS-IV on CYP1A2 activity was investigated using probe substrates: phenacetin in vitro and theophylline in vivo. Phenacetin was incubated in rat liver microsomes with or without AGS-IV, and the mechanism, kinetics and type of inhibition were determined. The inhibitory effect of AGS-IV on CYP1A2 activity in rats was also determined using theophylline in vivo. The pharmacokinetics of theophylline were observed after a single or week-long treatment with AGS-IV. KEY FINDINGS: AGS-IV was found to be a competitive inhibitor with a K(i) value of 6.29 µM in vitro. In the multiple-pretreatment rat group, it was found to have a significantly higher area under the concentration-time curve (AUC) for theophylline, as well as a lower apparent oral total body clearance value (CL/F). In contrast, no significant difference in metabolism of theophylline was found for the single pretreatment group. CONCLUSIONS: These findings suggest that AGS-IV is a potent inhibitor of CYP1A2. This work offers a useful reference for the reasonable and safe use of clinically prescribed herbal or natural products to avoid unnecessary herb-drug interactions.

Ibudilast, a phosphodiesterase inhibitor, in combination with low-dose aspirin potently inhibits guinea pig carotid artery thrombosis without extending bleeding time and causing gastric mucosal injury.

A combination of low-dose aspirin (ASA) and a phosphodiesterase inhibitor has been clinically tried for the secondary prevention of atherothrombotic diseases. The in vivo antithrombotic property of ibudilast (CAS 50847-11-5), a phosphodiesterase 4 (PDE4) inhibitor, was evaluated in a photochemically-induced guinea pig carotid artery thrombosis model in combination with low-dose ASA. The time required to decrease the carotid artery blood flow to the reading "zero" was defined as the time to occlusion (TTO) of the artery through thrombogenesis. Each independent use of ASA (300 mg/kg, p.o.) and ibudilast (3 and 10 mg/kg, p.o.) significantly prolonged the TTO, and ASA (300 mg/kg) significantly increased bleeding time (BT) and gastric mucosal injury. A selective PDE4 inhibitor rolipram (1 and 5 mg/kg, p.o.) tended to prolong the TTO without extending BT. ASA (100 mg/kg) plus ibudilast (3 mg/kg) and ASA (100 mg/kg) plus rolipram (5 mg/kg) markedly prolonged the TTO compared with each agent alone. Interestingly, ASA (100 mg/kg) plus ibudilast (3 mg/kg) caused a longer TTO than ASA (300 mg/kg) alone, without significant extension of BT and gastric mucosal injury as observed in ASA (300 mg/kg). These results indicate that the combination of low-dose ASA and ibudilast has a more potent antithrombotic effect than ASA alone without increasing bleeding tendency and gastric mucosal injury. The potent in vivo antithrombotic effect of this combination may be brought about by an action that is associated with PDE4 inhibition of ibudilast.

A physiologically based pharmacokinetic model characterizing mechanism-based inhibition of CYP1A2 for predicting theophylline/antofloxacin interaction in both rats and humans.

Clinical studies have revealed that some fluoroquinolones may cause severe adverse effects when co-administered with substrates of CYP1A2. Our previous study showed antofloxacin (ATFX) was responsible for mechanism-based inhibition (MBI) of the metabolism of phenacetin in rats. In the clinical setting, ATFX is likely to be administrated with theophylline (TP), which is mainly metabolized by CYP1A2. The aim of the present study was to investigate the possible mechanism of TP/ATFX interaction. In vitro studies showed that the inhibitory effect of ATFX on the formation of three TP metabolites depended on NADPH, the pre-inhibition time, and ATFX concentration, i.e., factors which characterize MBI. In vivo studies demonstrated that single-dose ATFX (20 mg/kg) did not affect the pharmacokinetic behavior of TP, but multidose ATFX (20 mg/kg b.i.d. for 7.5 days) significantly increased the AUC of TP, decreased the amount of three TP metabolites in urine, and suppressed hepatic microsomal activity. A physiologically based pharmacokinetic (PBPK) model characterizing MBI of the three TP metabolites was developed for predicting TP/ATFX interaction in rats; this model was further extrapolated to humans. The predicted results were in good agreement with observed data. All the results indicated that ATFX was responsible for MBI of the metabolism of TP, and the PBPK model characterizing MBI may give good prediction of TP/ATFX interaction.

Relative resistance to oral theophylline treatment in patients with hyposmia manifested by decreased secretion of nasal mucus cyclic nucleotides.

INTRODUCTION: Oral treatment with the phosphodiesterase inhibitor theophylline in an open-label fixed-design clinical trial in 312 patients with hyposmia improved smell function in >50%. Before treatment, all patients had lower than normal levels of nasal mucus cAMP and cGMP. The purpose of this study was to study relationships among changes in smell function, theophylline levels and nasal mucus cAMP and cGMP among patients whose smell function improved (responders) and those who did not improve (nonresponders) on oral theophylline treatment. METHODS: After all data analysis from the clinical trial was completed, data from each of the 31 of the 312 patients in whom nasal mucus cAMP and cGMP and theophylline levels were available before and after theophylline treatment at several drug doses were evaluated. At initiation and at termination of each treatment, dose smell function, nasal mucus cAMP and cGMP and plasma theophylline were analyzed. RESULTS: On the same theophylline dose, although serum theophylline increased among both responders and nonresponders, serum levels were consistently higher among responders. Nasal mucus cAMP and cGMP were also higher among responders than nonresponders. At higher theophylline doses, cGMP reached normal levels among responders, whereas it did not change significantly among nonresponders. CONCLUSIONS: Some patients with hyposmia with initially low nasal mucus cAMP and cGMP levels may be relatively resistant to oral theophylline treatment. This result may offer a mechanism of response lack among some patients whose smell function did not improve after oral theophylline treatment although other factors may influence their response lack.