Transporter-Mediated Hepatic Uptake Plays an Important Role in the Pharmacokinetics and Drug-Drug Interactions of Montelukast.

Montelukast, a leukotriene receptor antagonist commonly prescribed for treatment of asthma, is primarily metabolized by cytochrome P450 (CYP)2C8, and has been suggested as a probe substrate for investigating CYP2C8 activity in vivo. We evaluated the quantitative role of hepatic uptake transport in its pharmacokinetics and drug-drug interactions (DDIs). Montelukast was characterized with significant active uptake in human hepatocytes, and showed affinity towards organic anion transporting polypeptides (OATPs) in transfected cell systems. Single-dose rifampicin, an OATP inhibitor, decreased montelukast clearance in rats and monkeys. Clinical DDIs of montelukast were evaluated using physiologically based pharmacokinetic modeling; and simulation of the interactions with gemfibrozil-CYP2C8 and OATP1B1/1B3 inhibitor, clarithromycin-CYP3A and OATP1B1/1B3 inhibitor, and itraconazole-CYP3A inhibitor, implicated OATPs-CYP2C8-CYP2C8 interplay as the primary determinant of montelukast pharmacokinetics. In conclusion, hepatic uptake plays a key role in the pharmacokinetics of montelukast, which should be taken into account when interpreting clinical interactions.

Pharmacokinetics of sertraline and its N-demethyl metabolite in elderly and young male and female volunteers.

A nonblinded study was conducted to compare the pharmacokinetic properties of the selective serotonin reuptake inhibitor sertraline in 22 young (aged 18 to 45 years) and 22 elderly (> 65 years) volunteers, of whom half were male and half were female. In this study, sertraline was administered at a dosage of 200mg once daily (the maximum recommended daily dosage) for 21 days after upward dosage titration from 50 mg/day over a 9-day period. Thus, this study was designed to measure the effect of age and gender on the pharmacokinetic properties of sertraline at the maximum dosage recommended for clinical use. The terminal elimination half-life (t1/2 beta ) of sertraline was similar in young females, elderly males and elderly females (mean t1/2 beta ranged from 32.1 to 36.7 hours in these groups) but shorter (22.4 hours) in the young males. The mean maximum plasma sertraline concentration (Cmax) and the mean steady-state area under the plasma concentration-time curve from time zero to 24 hours postdose (AUC24) were also similar between the young females, elderly males and elderly females, but were approximately 25% lower in the young males. The time to Cmax was unaffected by age or gender and ranged from 6.4 to 6.9 hours. N-Demethylsertraline is the principal metabolite of sertraline and does not contribute significantly to its serotonergic actions. The mean values for N-demethylsertraline trough plasma concentrations, AUC24 and Cmax were comparable in elderly males and females and young females but lower in young males. The ratios of mean AUC24 and Cmax for N-demethylsertraline to the AUC24 and Cmax for sertraline were similar between the 4 groups.

A study of the potential effect of sertraline on the pharmacokinetics and protein binding of tolbutamide.

The effect of the selective serotonin reuptake inhibitor (SSRI) sertraline 200 mg/day on the metabolism of intravenously administered tolbutamide was examined in a randomised nonblinded parallel-group study in 25 healthy male volunteers. There was a small but statistically significant decrease (16%) in the clearance of tolbutamide in patients receiving the maximum recommended dosage of sertraline. The terminal elimination rate constant was also significantly reduced, corresponding to the increase in the terminal elimination half-life (from 6.9 to 8.6 hours). The decrease in clearance was not associated with any significant changes in plasma protein binding or in the apparent volume of distribution of tolbutamide. This suggests that the change in tolbutamide clearance may be due to a slight inhibition of the cytochrome P450 (CYP) isoenzyme CYP2C9/10 when sertraline was administered in its maximum recommended dosage. However, the small changes in the volume of distribution and plasma binding of tolbutamide after sertraline treatment indicate that there is a minimal interaction between sertraline and tolbutamide.

Effect of sertraline on protein binding of warfarin.

The effect of sertraline on the plasma protein binding of warfarin was investigated in a nonblinded randomised placebo-controlled parallel trial in 12 healthy male volunteers. The study participants received single doses of warfarin before administration of sertraline or placebo and again after sertraline or placebo had been administered for 22 days. Treatment with sertraline for 26 days increased the area under the mean prothrombin time vs time curve by 145 sec *h (7.9%), compared with a decrease of 17 sec *h (-1.0%) in the placebo group. Although statistically significant (p = 0.02), this difference was not felt to be clinically meaningful. There appeared to be a slight delay in the normalisation of the prothrombin time in the sertraline-treated group after the second dose of warfarin, which also would not be expected to be clinically significant. After 22 days, a statistically significant (p = 0.02) increase in unbound warfarin was observed in the sertraline group compared with the placebo-treated individuals. Neither the change in prothrombin time nor the change in plasma protein binding were considered to have any clinical relevance; however, good clinical practice dictates that prothrombin time should be monitored in patients treated concurrently with warfarin and sertraline to ensure that the integrity of coagulation response is maintained. The metabolism of warfarin is principally mediated by the cytochrome P450 (CYP) isoenzyme CYP2C9/10. Thus, sertraline appears to have a minimal effect on the CYP2C9/10 isoenzyme.

Sertraline does not alter steady-state concentrations or renal clearance of lithium in healthy volunteers.

An open-label, placebo-controlled study was conducted to determine the effects of sertraline on the steady-state levels and renal clearance of lithium in 20 healthy volunteers. Subjects received 600 mg of lithium twice daily for 9 days. On the evening of day 8, subjects received orally either placebo or 100 mg of sertraline; these were administered twice, 8 hours apart, beginning 2 hours after the evening dose of lithium. In a comparison of day 8 with day 9 (before administration of the morning doses of lithium), sertraline was associated with only a 0.01 mEq/L (1.4%) decrease in steady-state levels and a 0.11 L/hour (6.9%) increase in the renal clearance of lithium. Neither change was statistically significant relative to placebo. Four subjects were excluded from analysis because of protocol violations or laboratory abnormalities unrelated to sertraline. Seven subjects who received lithium plus sertraline experienced side effects, mainly tremors, possibly related to treatment, whereas none of those administered lithium plus placebo experienced side effects. No sertraline-related laboratory abnormalities were observed.

Metabolism and disposition of the 5-hydroxytryptamine uptake blocker sertraline in the rat and dog.

Sertaline [1S,4S-N-methyl-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1- naphthalenamine] is a potent and selective inhibitor of neuronal serotonin uptake and is currently under development for the treatment of depression and of obesity. The drug is greater than 97% bound to plasma proteins, yet extensively distributes into tissues. The whole brain concentration of sertraline in the rat is more than 40-fold higher than that in plasma, and the volume of distribution is about 25 liters/kg in the rat and dog. Sertraline is extensively metabolized by the rat and dog prior to excretion. The metabolic clearance of sertraline is greater than 35 ml of blood/min/kg in each species, and first-pass metabolism occurs with oral administration. Initial metabolic steps include N-demethylation, N-hydroxylation, oxidative deamination, and glucuronidation of sertraline carbamic acid, which in solution is in equilibrium with sertraline and carbon dioxide. The N-desmethyl metabolite, which is 10-fold less potent as an inhibitor of serotonin uptake, is formed in both species. Plasma AUC for desmethyl-sertraline is 66 to 270% of that for sertraline, and is dependent on the species examined and route of drug administration. Sertraline and desmethyl-sertraline undergo oxidative deamination to the corresponding ketone, which is subsequently hydroxylated at the alpha-carbon, forming a diastereomeric metabolite pair. The glucuronides of sertraline carbamic acid, N-hydroxy sertraline, and the alpha-hydroxy ketone diastereomers comprise 45% and 82% of the total radiolabel excreted in urine and bile of bile duct-cannulated rats and dogs, respectively. Bile is the major route of elimination in both species.

Characterization of a carbamic acid ester glucuronide of the secondary amine sertraline.

In the dog, the major excretory metabolite of the antidepressant sertraline was characterized as sertraline carbamoyl-O-glucuronide. The intact conjugate was isolated from bile by HPLC. The metabolite was labile to beta-glucuronidase and produced sertraline as the single hydrolytic product, based on HPLC and GC-MS analyses. By fast atom bombardment MS analysis, [M+H]+ and [M+Na]+ ions at m/z 526 and 548 were observed, as were the proton and sodium adducts of the aglycone (m/z 350 and 372) due to cleavage of the glycosidic bond and elimination of the glucuronic acid moiety (176 amu). The observed mass of the aglycone was 44 amu greater than sertraline, indicating that a carbamic acid of this secondary amine was conjugated with glucuronic acid. These data suggest that sertraline in solution reversibly associates with CO2 before formation of sertraline carbamoyl-O-glucuronide. This novel amine glucuronide was also identified in human plasma after the oral administration of sertraline to each of seven subjects. The glucuronide was stable in plasma at both acidic and basic pH.

Renal tubular excretory transport of oxalate in the chicken.

By use of the Sperber in vivo chicken preparation, infusion of radiolabeled oxalic acid ([14C]oxalate) into the renal portal circulation indicated net excretory transfer of unchanged oxalate. At infusion rates of 0.1 to 100 nmol/min, approximately 26% of the oxalate reaching the kidney was excreted directly into the urine. The excretory transport of oxalate was not altered by infusion of probenecid or terephthalic acid, at rates that blocked completely the excretory transport of simultaneously infused p-aminohippuric acid. Because probenecid and terephthalic acid are also known to inhibit uric acid excretory transport in the chicken kidney, these findings suggest that the transport system for oxalate in the chicken kidney is separate from those handling p-aminohippuric acid and uric acid. The excretory transport of oxalate was decreased by the infusion of alpha-ketoglutaric acid, suggesting that oxalate competes at least in part with other endogenous dicarboxylic acids for uptake at the peritubular membrane.

Quantitative determination of organ contribution to excretory metabolism.

A method for the quantitative determination of organ contribution to in vivo excretory metabolism is described. By excretory metabolism, we mean metabolism of a compound by an organ with direct excretion. The technique separately and simultaneously quantifies clearance of circulating metabolite and clearance of circulating precursor by excretory metabolism. For xenobiotics, the method involves the simultaneous infusion of radiolabeled precursor and unlabeled metabolite. The method is dependent upon the achievement of steady-state plasma concentrations of precursor and metabolite and on the ability to accurately analyze, both chemically and radioactively, the precursor in plasma, and the metabolite in both plasma and excretory fluid. The technique is not compromised by in vivo conversion of metabolite to precursor. This method is suitable for the simultaneous quantitative determination of the contribution of several organs to the formation of any number of metabolites present in excretory fluids. The simultaneous contribution of excretory metabolism to the urinary and biliary elimination of 1-naphthol in the rat is presented.

The renal handling of terephthalic acid.

By use of the Sperber in vivo chicken preparation method (1948, Ann. R. Agric. Coll. Swed. 15, 317-349), infusion of radiolabeled terephthalic acid ([14C]TPA) into the renal portal circulation revealed a first-pass excretion of the unchanged compound into the urine. This model was utilized further to characterize the excretory transport of [14C]TPA and provide information on the structural specificity in the secretion of dicarboxylic acids. At an infusion rate of 0.4 nmol/min. 60% of the [14C]TPA which reached the kidney was directly excreted. An infusion rate of 3 or 6 mumol/min resulted in complete removal of [14C]TPA by the kidney. These results indicate that TPA is both actively secreted and actively reabsorbed when infused at 0.4 nmol/min and that active reabsorption is saturated with the infusion of TPA at higher concentrations. The secretory process was saturated with the infusion of TPA at 40 mumol/mn. The excretory transport of TPA was inhibited by the infusion of probenecid, salicylate, and m-hydroxybenzoic acid, indicating that these organic acids share the same organic anion excretory transport process. m-Hydroxybenzoic acid did not alter the simultaneously measured excretory transport of p-aminohippuric acid (PAH), suggesting that there are different systems involved in the secretion of TPA and PAH. The structural specificity for renal secretion of dicarboxylic acids was revealed by the use of o-phthalic acid and m-phthalic acid as possible inhibitors of TPA secretion. m-Phthalate, but not o-phthalate, inhibited TPA excretory transport, indicating that there is some specificity in the renal secretion of carboxy-substituted benzoic acids. TPA was actively accumulated by rat and human cadaver renal cortical slices.

In vivo quantification of renal glucuronide and sulfate conjugation of 1-naphthol and p-nitrophenol in the rat.

The simultaneous in vivo renal sulfate and glucuronide conjugations of 1-naphthol (1-N) and p-nitrophenol (PNP) were determined in the rat. In mammals, 1-N and PNP are excreted almost entirely in the urine, mainly as the glucuronide and sulfate conjugates. In male Sprague-Dawley rats, greater than 98% of the infused [14C]1-N (1.0 mumole X min-1 X kg-1) or [14C]PNP (2.0 mumoles X min-1 X kg-1) recovered in urine was identified as the sulfate and glucuronide conjugates. Renal metabolism accounted for a minimum of 20% of the endogenously formed conjugates of either substrate excreted in the urine. The rat kidney formed the glucuronide and sulfate conjugates of PNP at equal rates, whereas the glucuronide: sulfate conjugate ratio for renally formed 1-N conjugates was 3:1. When the conjugates of either 1-N or PNP were infused systemically, in vivo hydrolysis contributed significantly to the amount of circulating parent phenol.

Salicylate enhancement of renal glucuronide conjugation and tubular excretory transfer of phenols.

Salicylate administration increased glucuronyltransferase activity, with o-aminophenol as the substrate, in chicken kidney homogenates, but did not affect glucuronyltransferase activity in chicken liver homogenates. In addition, salicylate administration increased in vivo renal glucuronidation of catechol and p-nitrophenol without affecting renal sulfate conjugation of these compounds. These results suggest that salicylate administration selectively enhances renal glucuronide conjugation, thereby promoting a more rapid metabolism and elimination of circulating phenols, especially at high plasma phenol concentrations. Isolated human kidney perfusion experiments reveal that glucuronide and sulfate conjugates of phenol, p-nitrophenol, and 1-naphthol are formed in the human kidney, suggesting that the effect of salicylate treatment on renal glucuronidation may apply to humans.

Hemoglobin Nigeria (alpha-81 Ser replaced by Cys):a new variant associated with alpha-thalassemia.

Hematologic evaluation of a Nigerian obstetrical patient disclosed the presence of sickle-cell trait as well as evidence of a hemoglobin alpha-chain abnormality. Hemoglobins containing the variant alpha-chain were isolated by DEAE-cellulose column chromatography, and analysis of the purified alpha-chain demonstrated a ser replaced by cys substitution at alpha-81. The abnormal alpha-chain represented approximately 45% of the total, and hemoglobins containing this alpha-chain appeared to have normal stability and functional properties. In addition to the abnormal hemoglobins that were identified in this patient, she also was found to have persistent microcytosis in the absence of iron deficiency, and the percentage of HbS in her erythrocytes was less than that usually present in individuals with sickle cell trait. These findings, together with a reduced alpha/beta globin synthesis ratio from her peripheral blood reticulocytes, indicated that the presence of alpha-thalassemia trait. Hematologic findings from members of the patients's family suggest that an alpha-thalassemia gene may be linked to that of the structurally abnormal alpha-chain.

Sickle cell syndromes. III. Silent-carrier alpha-thalassemia in combination with hemoglobin S and hemoglobin C.

Silent carrier alpha-thalassemia was identified in two individuals, one with sickle-cell trait and the other hemoglobin (Hb) C trait. Both are parents of a child with characteristic hematologic features of the Hb SC-alpha thalassemia syndrome, including microcytosis and an unbalanced pattern of globin synthesis. In contrast to the typical findings that accompany heterozygous Hb S or Hb C with concomitant alpha-thalassemia trait, neither of the parents had microcytosis nor a percent of the abnormal hemoglobin in their erythrocytes that was below the normal range. In both, however, globin synthesis of peripheral blood reticulocytes was unbalanced, consistent with mild alpha-thalassemia. These findings suggest that the alpha-thalassemia silent carrier may be hematologically indistinguishable from the nonthalassemic individual, even when hemoglobin S or C are present.

Unbalanced globin chain synthesis by Hb Lincoln Park (anti-Lepore) reticulocytes.

Hemoglobin synthesis was studied in vitro in reticulocytes from a patient with the anti-Lepore variant Hb Lincoln Park. Incorporation of L-leucine-3H into the alpha and beta delta chains of Hb Lincoln Park was substantially less than the incorporation into the corresponding globin chains of Hb A, with the rate of synthesis of the beta delta chain being similar to that of the delta chain of Hb A2. Synthesis of the alpha and total non-alpha globin components was unbalanced, with a substantial excess of alpha chain synthesis. These findings help to explain the mild hemolytic disease present in individuals with this hemoglobin variant.