Pharmacokinetics of theophylline metabolites in 8 Chinese patients

AIM

To study theophylline metabolites pharmacokinetics in patients after a therapeutic dose.

METHODS

Eight adult patients with mild bronchial asthma and normal liver function were infused aminophylline intravenously (6.6 mumol.kg-1). The plasma concentrations of theophylline and its 4 metabolites: 1,3-dimethyluric acid (DMUA), 3-methylxanthine (3-MX), 1-methyluric acid (MUA), and the intermediate 1-methylxanthine (1-MX) were monitored by HPLC throughout 24 h.

RESULTS

The plasma concentration of DMUA was the highest one among the 4 metabolites. 3-MX showed the slowest elimination rate. The plasma concentration of 1-MX throughout a 24-h period showed that there was a picking up of 1-MX (from 0.04 mumol.L-1 to 1.05 mumol.L-1) in the next morning.

CONCLUSION

The formation of DMUA was the main metabolites. During night there was an accumulation of 1-MX.

Pharmacokinetics of bambuterol in subjects homozygous for the atypical gene for plasma cholinesterase

AIMS

It has been assumed that both plasma cholinesterase (EC 3.1.1.8) and oxidative enzymes are needed for optimum formation of the bronchodilator terbutaline from its biscarbamate prodrug bambuterol. The present study aimed at investigating the fate of bambuterol in subjects with deficient plasma cholinesterase but with normal oxidative (CYP2D6) capability.

METHODS

The pharmacokinetics of bambuterol and terbutaline were studied in four healthy subjects (two men and two women) being homozygous for the atypical gene for plasma cholinesterase. Their oxidative metabolism was apparently good as they were all rapid metabolizers of debrisoquine. Bambuterol hydrochloride 20 mg was given orally once daily for 10 days, and plasma and urine samples were taken for 1.5 days (plasma) and 4.5 days (urine) after administration of the last dose.

RESULTS

The pharmacokinetic parameters in the present study were grossly similar to those found in a study of bambuterol in subjects with normal plasma cholinesterase activity (N). However, subjects with atypical cholinesterase had a shorter terminal half-life of bambuterol (a measure of uptake rate), 4.8-12.6 h vs 8.3-22.3 h in N, and slightly higher plasma concentrations of bambuterol (average concentrations 1.9-3.7 nmol l(-1) vs 1.5-3.1 nmol l(-1) in N). Peak/trough terbutaline plasma concentrations ratios (2.1-3.2) were somewhat increased, but average plasma concentrations (8.3-14.5 nmol l(-1)) and terminal half-life (16.5-21.8 h) of terbutaline did not differ.

CONCLUSIONS

In Caucasian populations, one subject out of 2500 is homozygous for the atypical gene for plasma cholinesterase. The atypical enzyme has a much lower affinity for bambuterol than the normal enzyme. Nevertheless, the subjects with atypical cholinesterase were able to produce terbutaline as efficiently as normal subjects. This might be explained by an altered uptake and metabolism in the absence of plasma cholinesterase, or the importance of this enzyme for the formation of terbutaline from bambuterol in vivo may have been overestimated.

Stereoselective sulphate conjugation of fenoterol by human phenolsulphotransferases

1. The objective of this study was to determine (1) the molecular site(s) of sulphoconjugation of fenoterol; (2) the human phenolsulphotransferase (PST) isoform(s) involved; and (3) the stereochemistry of the enzymatic reaction. 2. Using the human Hep G2 cell line, hplc isolation and FAB/ms/ms, it was determined that fenoterol is sulphated both in the 4'-hydroxyphenyl position and in one of the 3',5'-dihydroxyphenyl positions. 3. Recombinant human M-PST preferentially sulphated the 4'-hydroxyphenyl position. In contrast, recombinant P-PST exclusively sulphated the 3',5'-hydroxyphenyl position. 4. The M-PST-catalysed sulphation of the 4'-hydroxyphenyl position was highly selective for the active RR-enantiomer, whereas the sulphation of the 3',5'-dihydroxyphenyl position was slightly selective for the opposite SS-enantiomer. 5. The P-PST-catalysed sulphation of the 3',5'-hydroxyphenyl position was selective for the inactive SS-enantiomer.

Griseofulvin and fluvoxamine interactions with the metabolism of theophylline

Theophylline is predominantly metabolized by cytochrome P4501A2 (CYP1A2). A possible interaction between griseofulvin and theophylline was reported to our laboratory, which led us to form the hypothesis that griseofulvin induces the metabolism of theophylline. One purpose of this study was to investigate this hypothesis. The study was carried out as a randomized crossover study of 12 healthy volunteers. In period A of the study, each volunteer received a single dose of 300 mg theophylline ethylenediamine orally. In period B, the subjects took fluvoxamine, 50 mg for 1 day and 100 mg for 6 days, and on day 4, the subjects ingested 300 mg theophylline ethylenediamine. Fluvoxamine is a potent inhibitor of CYP1A2, and period B was included as a positive control. In period C, the subjects took 500 mg griseofulvin for 9 days; on day 8 the subjects again ingested 300 mg theophylline ethylenediamine. Theophylline and its metabolites (1-methyluric acid [IMU], 3-methylxanthine [3MX], and 1,3-dimethyluric acid [13DMU]) in plasma and urine were assayed by high-performance liquid chromatography. During fluvoxamine intake, the median of the total clearance of theophylline decreased from 80 ml/min to 24 ml/min, and the half-life increased from 6.6 to 22 h. The partial formation clearances of the metabolites decreased from 17 to 1.7 ml/min, from 8.9 to 0.9 ml/min, and from 21 to 6.8 ml/min for 1MU, 3MX, and 13DMU, respectively. The results confirm that assessment of theophylline metabolism indeed serves as a biomarker for CYP1A2. During griseofulvin ingestion, the median of the total and partial clearances of theophylline were 84 ml/min, 22 ml/min (1MU), 9.4 ml/min (3MX), and 25 ml/min (13DMU). The half-life decreased significantly from 6.6 to 5.7 h. The increase in partial formation clearances of 1MU and 13DMU, but not of 3MX, were statistically significant. The increase in the total clearance reached only borderline significance. In four subjects a marked induction was seen for all pharmacokinetic parameters, suggesting that the susceptibility to induction is more pronounced in some subjects. This susceptibility could theoretically be explained by a polymorphism in the inducibility of the gene coding for the CYP1A2 enzyme.

Nitric oxide and the lung: an overview

This brief discussion focuses on the effects of nitric oxide (NO) in the lung. A short introduction of some of the physical characteristics of the NO gas molecule and the endogenous production of NO by the vascular endothelium is addressed first. This is followed by a review of inhaled NO use as a bronchodilator of the airway and recent findings of the endogenous production of NO during positive end-expiratory pressure and the possible role of NO produced in the paranasal sinuses. Next, the use of inhaled NO for both pulmonary hypertension and improvement in oxygenation under a variety of clinical situations is discussed. Finally, some suggestions are given regarding the safe delivery of inhaled NO during clinical applications using a face mask, an anesthesia circuit, and a mechanical ventilator.

Delivery of metered dose inhaler aerosols to paralyzed and nonparalyzed rabbits

OBJECTIVE

To assess whether paralysis alters pulmonary deposition of albuterol delivered by metered dose inhaler and spacer to small animals.

DESIGN

A parallel group study of intubated and ventilated rabbits.

INTERVENTIONS

Animals in group 1 (n = 7) were paralyzed with intravenous pancuronium, and ventilated at a rate of 30 breaths/ min. The animals in group 2 (n = 6) were ventilated at a rate of 10 breaths/min under light anesthesia without paralysis. In this latter group, spontaneous respiration continued at a rate of 40 to 50 breaths/min. Both groups were maintained at PaCO2 of 35 to 40 torr (4.7 to 5.3 kPa), and other ventilatory settings were identical.

MEASUREMENTS AND MAIN RESULTS

Technetium-99m labeled albuterol aerosol was delivered by metered dose inhaler via a spacer device to both groups. Pulmonary deposition of the aerosol, determined by measuring the radioactivity in the lung tissues at autopsy, was expressed as percent of the total radioactivity dispensed by the metered dose inhaler. Group 2 showed significantly greater lung deposition than group 1 (0.510 +/- 0.076 [SEM]% vs. 0.226 +/- 0.054%, p = .0094). Deposition in the airway, the endotracheal tube, and the ventilator circuit did not differ significantly.

CONCLUSION

Metered dose inhaler delivery of aerosolized medications to ventilated rabbits is significantly enhanced if respiration is not controlled. This observation might have implications for the delivery of therapeutic aerosols to newborns and young infants receiving slow, intermittent, mandatory ventilation.

Relation between plasma and saliva concentrations of enoxacin, ciprofloxacin, and theophylline

To assess the reliability of predicting plasma concentrations of enoxacin, ciprofloxacin, and theophylline from drug concentrations in saliva, six healthy volunteers received single oral doses of enoxacin, ciprofloxacin, and theophylline administered in combination on each of four separate study days, with different, doses separated by at least 5 days. Drug concentrations were determined by a newly developed high-performance liquid chromatography (HPLC) assay, which could measure simultaneously all three drugs in plasma or saliva. Saliva data from the postabsorptive phase after drug administration were used to minimize the effects of variation in absorption. There were good correlations between saliva and plasma concentrations of enoxacin, ciprofloxacin, and theophylline (r = 0.91, 0.88, and 0.98, respectively). The mean (+/-SD) saliva-to-plasma (S/P) ratio for theophylline was 0.63 +/- 0.06 with a coefficient of variation (CV) of 7.9 +/- 2.7%. In contrast, the S/P ratios and CV values for enoxacin and ciprofloxacin were 0.72 +/- 0.21 and 28.9 +/- 11.1%, and 0.58 +/- 0.15 and 25.3 +/- 6.7%, respectively. Because of the large inter- and intraindividual variability, saliva concentrations of enoxacin and ciprofloxacin are not reliable for predicting plasma concentrations. However, saliva may be used reliably for predicting plasma concentrations of theophylline.

Clinical pharmacokinetics of bambuterol

Bambuterol, a biscarbamate ester prodrug of the beta 2 adrenergic agonist terbutaline, has been approved for the treatment of asthma in 28 countries. It is available in 10 and 20mg (25 and 50 mumol) tablets as the hydrochloride salt. Bambuterol is stable to presystemic elimination and is concentrated by lung tissue after absorption from the gastrointestinal tract. The prodrug is hydrolysed to terbutaline primarily by butyrylcholinesterase, and lung tissue is capable of this metabolic pathway. It is also oxidatively metabolised to products which can be hydrolysed to terbutaline. Peak terbutaline plasma concentrations occur 3.9 to 6.8 hours after bambuterol ingestion, and the peak: trough terbutaline concentration ratio is lower than that after ingestion of terbutaline. Older patients have a greater area under the plasma concentration-time curve for terbutaline over a dose interval at steady-state. Whether genetic variations in the expression of butyrylcholinesterase alter therapeutic response remains to be determined. The efficacy of bambuterol has been demonstrated to last for 24 hours after ingestion; once-daily administration in the evening is recommended. Maximum therapeutic benefit requires more than 1 week of treatment. Except for the suppression of plasma butyrylcholinesterase, the adverse effect profile of bambuterol is essentially that of a beta 2 agonist and is best correlated with circulating terbutaline concentration in plasma. Plasma butyrylcholinesterase activity returns to control values approximately 2 weeks after discontinuation of treatment with bambuterol. This new drug provides oral beta 2 agonist therapy in a more convenient form than was available previously, and may have a better therapeutic: toxic ratio than terbutaline.

Adrenomedullin is inactivated in the lungs of neonatal piglets

Adrenomedullin, a novel 52 amino acid peptide normally present in adult human plasma, has been shown to induce systemic hypotension in the adult rat, pig and cat, and in the new-born piglet. Little is known about the site (s) of adrenomedullin inactivation in adults or neonates. Groups of five 0-2-day old and 2-week old anaesthetized piglets were prepared to enable continuous monitoring of cardiac output, mean systemic arterial pressure, mean pulmonary artery pressure, mean systemic vascular resistance and mean pulmonary vascular resistance. In both age groups, injections of human adrenomedullin1-52 into the left atrium produced significant (P < 0.05) reductions in mean systemic arterial pressure and mean pulmonary artery pressure. Although injections of similar doses of human adrenomedullin1-52 into the right atrium produced significant (P < 0.05) decreases in mean pulmonary artery pressure, there were no appreciable alterations in mean systemic arterial pressure in either age group. These results suggest that the systemic vasodilator properties of human adrenomedullin1-52 are reduced upon first pass through the pulmonary circulation in 2-week old piglets, a phenomenon that is present at birth.

Functional and binding characteristics of long-acting beta 2-agonists in lung and heart

Salmeterol and formoterol, two new long-acting beta 2-agonists were equipotent (values of negative log molar concentration eliciting half-maximal effect [pD2] 9.2 +/- 0.03 and 8.9 +/- 0.03, respectively) in relaxing maximally contracted guinea pig tracheal spirals (histamine, 100 microM). Both agonists were 10 times more potent than L-isoproterenol and fenoterol and 100 times more potent than albuterol. L-Isoproterenol and fenoterol induced > 90% relaxation (percentage of maximal aminophylline relaxation). Formoterol and albuterol were equally efficacious. Formoterol was more efficacious (86 +/- 5%) than salmeterol (62 +/- 3%) or soterenol (59 +/- 3%). In minimally contracted tissues (10 microM histamine), agonist potencies increased 10-fold and relaxation was complete. In [125I]iodocyanopindolol-labeled bronchial membranes, formoterol and salmeterol induced high-affinity states of the beta 2-receptor (pKh 9.6 +/- 0.4 and 10.4 +/- 0.7, respectively), the former inducing a higher percentage (57 +/- 6 versus 28 +/- 4, p < 0.05). Only low-affinity binding (pKI) was observed when guanine nucleotide was present. pD2 values were similar to pKh values and relative efficacies significantly correlated with percentage of pKI sites. Formoterol and salmeterol were highly selective for the beta 2 versus beta 1-subtype (pKI values were 8.2 +/- 0.09 and 6.25 +/- 0.06 and 8.3 +/- 0.04 and 5.7 +/- 0.04, respectively). Albuterol (5.83 +/- 0.06 and 4.71 +/- 0.16) and fenoterol (6.33 +/- 0.07 and 5.67 +/- 0.05) were less selective. These results can explain the potencies and efficacies of salmeterol and formoterol in humans.

The effect of ipriflavone and its main metabolites on theophylline biotransformation

The effect of ipriflavone and its major metabolites, 7-hydroxy-isoflavone and 7-(1-carboxy-ethoxy)-isoflavone on theophylline metabolism was examined in vitro in human liver microsomes. The compounds inhibited the N-demethylation to 1- or 3-methylxanthine, the major pathway of theophylline metabolism. The effect showed concentration dependence. The oxidation of theophylline to 1,3-dimethyluric acid was slightly affected by ipriflavone and its metabolites and the effect was non-specific. Results indicate that the reduction of theophylline clearance by concomitant ipriflavone administration observed by Takahashi et al. [Takahashi J., Kawakatsu K., Wakayama T., Sawaoka H. (1992): Elevation of serum theophylline levels by ipriflavone in a patient with chronic obstructive pulmonary disease. Eur. J. Clin. Pharmacol., 43, 207-208] is primarily due to an interaction of the inhibitory ipriflavone and/or its metabolites with cytochrome P450 enzyme(s) that mediate N-demethylation of theophylline.

Cloning and expression of cDNA encoding a rat adrenomedullin receptor

Adrenomedullin is a potent vasodilator peptide that exerts major effects on cardiovascular function. Its actions are mediated through an abundant class of specific binding sites that activate adenylyl cyclase through a G protein-coupled mechanism. We report here the identification of a cDNA clone for the adrenomedullin receptor that was originally isolated as an orphan receptor from rat lung. The cDNA encodes a polypeptide of 395 residues that contains seven transmembrane domains and has a general structural resemblance to other members of the G protein-linked receptor superfamily. When expressed in COS-7 cells, this receptor mediates a cAMP response to adrenomedullin with an EC50 of 7 x 10(-9) M, and binds 125I-adrenomedullin with a KD of 8.2 x 10(-9) M, properties that are consistent with those observed in cardiovascular and other target tissues. The receptor gene is expressed as several mRNA species of which the most prominent is a 1.8-kilobase transcript found in the lung, adrenal, heart, spleen, cerebellum, and other sites. Identification of this receptor cDNA should facilitate further investigation of the cellular actions of adrenomedullin and its regulatory effects in normal and disordered states of cardiovascular function.

Verlukast (MK-0679) conjugation with glutathione by rat liver and kidney cytosols and excretion in the bile

Verlukast (MK-0679) is a potent leukotriene D4 antagonist that was under development for the treatment of bronchial asthma. A previously uncharacterized metabolite of verlukast was formed in incubations using rat liver cytosol fortified with glutathione (GSH). The metabolite was detected by HPLC and characterized by UV spectroscopy (photodiode array detection after HPLC) and capillary HPLC continuous flow-liquid secondary-ion mass spectrometry. After a large-scale incubation and isolation, it was further characterized by 500 MHz proton NMR. The metabolite is a 1,4-Michael addition product in which GSH has added to position 12 of the styryl quinoline double bond of verlukast. There is no apparent stereoselectivity because a mixture of the two possible isomers, in equal amounts, was observed by NMR. Although there was spontaneous chemical addition of GSH to verlukast (0.18 nmol/min), the reaction was shown to be enzyme-catalyzed in studies using three different preparations of rat liver cytosol at pH 7.4. Using Lineweaver-Burk analysis of experiments in which the effect of verlukast concentration on the rate of conjugation was studied, the apparent KM and Vmax were determined to be 107 +/- 22 microM (SD, N=3) and 0.66 +/- 0.21 nmol/min/mg protein, respectively. In similar studies with GSH as the variable substrate, the apparent KM and Vmax were 2.32 +/- 0.68 mM and 0.69 +/- 0.14 nmol/min/mg protein, respectively. Incubations with kidney cytosol produced the GSH, cysteinylglycine, and cysteine conjugates of verlukast. In bile collected from rats dosed intravenously with 50 mg/kg of verlukast, approximately 80% of the dose was recovered up to 4 hr postdose. The GSH conjugate accounted for 16.5% of the dose. The cysteinylglycine, cysteine, and N-acetylcysteine conjugates were observed and together accounted for 7.5%. Verlukast accounted for 14.5%, and the remainder of the metabolites (40.5%) were oxidation or acyl glucuronide metabolites.

Effects of lansoprazole on pharmacokinetics and metabolism of theophylline

The effect of the new substituted benzimidizole proton pump inhibitor, lansoprazole, on pharmacokinetics and metabolism of theophylline has been studied in healthy adults given oral lansoprazole 30 mg once daily for 11 days. On Days 4 and 11 of 300 mg aminophylline was simultaneously administered orally and blood samples for theophylline analysis were taken over 24 h. Urine samples were collected for up to 24 h and were assayed for theophylline and its major metabolites 1,3-dimethyluric acid (1,3-DMU), 1-methyluric acid (1-MU) and 3-methylxanthine (3-MX). The pharmacokinetic parameters of theophylline were determined, and the urinary recovery of unchanged theophylline and its major metabolites were calculated. After administration of lansoprazole for 4 days, no significant alteration in the terminal elimination half-life (t1/2beta) or the mean resistance time (MRT) was detected. However, there was a significant decrease of about 13% in the area under the plasma concentration-time curve (AUC) and a significant increase of about 19% in the apparent clearance (CLapp). Lansoprazole treatment for 11 days caused a significant decrease of approximately 12% in t1/2beta and about 10% in the MRT of theophylline, although neither AUC nor CLapp showed a significant alteration. The excretion of 3-MX in the urine was significantly increased by about 20% after lansoprazole treatment for 4 and 11 days, although there was no significant alteration in the excretion of unchanged theophylline, 1,3-DMU or 1-MU. The results indicate that repeated administration of lansoprazole to humans induces the hepatic microsomal P-450-dependent drug oxidation system that mediates N-1-demethylation of theophylline, consequently increasing its metabolism.

The effect of delay, multiple actuations and spacer static charge on the in vitro delivery of budesonide from the Nebuhaler

A multistage liquid impinger was used to determine the amount of budesonide available from the Nebuhaler spacer device following alteration of spacer static charge, delay in sampling from the spacer, and multiple actuations of the metered dose inhaler into the spacer prior to sampling. The mean amount of budesonide (s.d.) recovered per 200 micrograms actuation in particles smaller than 5 microns increased from 30.5 micrograms (8.8) to 69.3 micrograms (17.9) with a low static spacer. A 20 s delay between actuation and inhalation reduced the amount recovered to 10.9 micrograms (3.2), but no reduction was seen when using a low static spacer after the same delay. Multiple actuations into the spacer before sampling also reduced the recovery to 24.8 micrograms (3.4) after two actuations, and 13.5 micrograms (7.6) after five actuations. When using a Nebuhaler with budesonide metered dose inhalers, more respirable drug will be obtained if the aerosol is inhaled immediately after actuation, and multiple actuations into the spacer device are avoided. Low static spacers may also improve drug delivery. Attention to the details of spacer use may reduce the incidence of therapeutic failure and the cost of inhaled medications.

Alterations in the pharmacokinetics and protein binding of enprofylline in Eisai hyperbilirubinemic rats

Mutant rats possessing conjugated hyperbilirubinemia have recently been established from Sprague-Dawley rats (SDRs) and are called Eisai hyperbilirubinemic rats (EHBRs). The effects of hyperbilirubinemia on the disposition, renal handling, and protein binding behavior of enprofylline, which is mainly excreted into the urine by an active tubular secretion mechanism, were investigated in 9- and 19-week-old EHBRs and compared with their age-matched normal SDRs. Enprofylline was administered intravenously at a dose of 2.5 mg/kg, which exhibits linear kinetics. Pharmacokinetic parameters for both total and unbound enprofylline were estimated by model-independent methods. Both systemic clearance and volume of distribution at steady state of enprofylline significantly increased in 19-week-old EHBRs. However, there were no differences in the glomerular filtration rate estimated as inulin clearance and fraction of urinary excretion as unchanged drug between EHBRs and normal SDRs. Significant decreases in both the binding capacity and number of binding sites were observed in 19-week-old EHBRs, but no such changes were observed between 9-week-old EHBRs and SDRs. Hyperbilirubinemia in EHBRs had no effect on the pharmacokinetics and renal handling of unbound enprofylline. These results indicate that the pharmacokinetics of enprofylline, but not renal handling, glomerular filtration, or tubular secretion are modified in EHBRs by changes in protein binding behavior.

Characterization of [3H]Ba 679 BR, a slowly dissociating muscarinic antagonist, in human lung: radioligand binding and autoradiographic mapping

Ba 679 BR [7(S)-(1 alpha, 2 beta, 4 beta, 5 alpha, 7 beta)-7-[(hydroxydi(2-thienyl) acetyl)oxy]-9,9-dimethyl-3-oxa-9-azoniatricyclo[3.3.1.0(2,4)]nonan e bromide] is a new long-acting muscarinic antagonist developed as a bronchodilator drug. In this study, we have evaluated its affinity, its selectively, and the distribution of its binding sites in human lung. [3H]Ba 679 BR binds to a homogeneous population of muscarinic receptors in human lung membranes, with affinities in the subnanomolar concentration range. Like ipratropium bromide, Ba 679 BR showed no selectivity in its interactions with rat cerebrocortical M1 receptors (labeled with [3H]telenzepine) or heart M2 and salivary gland M3 receptors [labeled with [N-methyl-3H]scopolamine ([3H)]. Ba 679 BR displayed 6-20-fold higher affinity, compared with ipratropium bromide. We also studied the rate of Ba 679 BR and ipratropium bromide dissociation from human lung muscarinic receptors, by monitoring [3H]NMS association. Unlike ipratropium bromide (100 nM), which dissociated so quickly that there was little difference in the [3H]NMS association, compared with vehicle-treated membranes, Ba 679 BR (1 nM) had a strong protective effect against [3H]NMS binding ( > 70%) that lasted for 90 min. Kinetic experiments conducted with [3H]Ba 679 BR confirmed the slow dissociation profile of this compound. The dissociation rate constant (k-1) for [3H]Ba 679 BR was 3.29 +/- 0.18 x 10(-3) min-1, corresponding to a half-life of the complex of 212 +/- 11 min. Autoradiographic studies revealed that [3H]Ba 679 BR binding sites were densely distributed in alveolar walls and submucosal glands. These results suggest that the slow dissociation profile of Ba 679 BR from human lung muscarinic receptors might be the underlying mechanism by which this drug achieves its long duration of action observed in functional tests.

Disposition of salmeterol xinafoate in laboratory animals and humans

The disposition of [14C]salmeterol xinafoate, a new inhaled beta 2-adrenoceptor agonist with both bronchodilator and antiinflammatory activity, has been studied in laboratory animals and humans following intravenous and oral administration. [14C]Salmeterol was rapidly absorbed in animal species and humans with Cmax observed within 2 hr. Cmax was similar for normalized oral dose level in mice, rats, and rabbits. In dogs, Cmax was higher and reflected the greater oral bioavailability in this species. The plasma t1/2, after intravenous administration, was 5 hr in rats and 2 hr in dogs. The volume of distribution of salmeterol was significantly greater than total body water in both rats (40 liters/kg) and dogs (6 liters/kg) and indicated high tissue uptake of the compound. Plasma clearance was high in rats (95 ml/min/kg) and dogs (30 ml/min/kg). Radioactive drug-related material was widely distributed throughout body tissues in rats. The highest concentrations were present in kidney, liver, gastrointestinal tract, pituitary, lung, heart, and bone marrow. Transfer of radioactive drug-related material across the placental barrier or into milk, studied in rats, was low. In all species the majority of an oral or intravenous dose (55-75%) was excreted in feces. Biliary excretion in rats and dogs accounted for 53% (0-27 hr) and 40% (0-8 hr) of an oral dose, respectively, indicating good absorption across the gastrointestinal tract. Enterohepatic circulation was significant in rats. Salmeterol was cleared predominantly by metabolism in animals and humans.(ABSTRACT TRUNCATED AT 250 WORDS)

CYP1A1 specificity of Verlukast epoxidation in mice, rats, rhesus monkeys, and humans

It has previously been shown that Verlukast is converted to Verlukast dihydrodiol in microsomes from beta-naphthoflavone (BNF)-treated, but not uninduced Swiss Webster mice and Sprague-Dawley rats. We have examined the involvement of CYP1A1 in this reaction in more detail. It is concluded that this reaction is catalyzed exclusively by CYP1A1 in rats, mice, and humans based on the following criteria: 1) the epoxidation of Verlukast is negligible in uninduced rats, which express CYP1A2 but not CYP1A1; 2) Verlukast epoxidation is highly inducible by BNF treatment (60- to 200-fold); 3) Verlukast epoxidation in BNF-treated rat microsomes was inhibited by alpha-naphthoflavone (ANF) treatment, indicating that this activity was mediated by the CYP1A subfamily; 4) > 95% of Verlukast epoxidation in BNF-treated rat microsomes was inhibited by antibodies raised against CYP1A1; and 5) Verlukast was epoxidized by human CYP1A1 but not CYP1A2. Thus, Verlukast epoxidation appears to be specific for rat, mouse, and human CYP1A1. Additional studies showed that Verlukast was metabolized to Verlukast dihydrodiol in microsomes from uninduced rhesus monkeys. This reaction was inhibited by nanomolar concentrations of ANF in rhesus monkey microsomes implicating the involvement of the CYP1A subfamily. In addition, the 8-hydroxylation of R-warfarin, a pathway that is selective for rodent and human CYP1A1 activity, was also catalyzed at significant rates by rhesus monkey microsomes. These findings indicate that, unlike rats, mice, and humans, which have very low constitutive levels of hepatic CYP1A1 activity, the uninduced rhesus monkey is able to catalyze reactions specific to CYP1A1 in rodents and humans.(ABSTRACT TRUNCATED AT 250 WORDS)