Serum protein binding of lomefloxacin, a new antimicrobial agent, and its related quinolones

The serum protein binding of lomefloxacin (LFLX), a new quinolone (pyridonecarboxylic acid), and its related analogues was studied by an ultrafiltration technique. The extent of binding of quinolones was independent of the concentration of quinolones below 100 micrograms/mL in rat serum; but, above this concentration, the binding decreased with increased drug concentration in the case of nalidixic acid and analogue 3. The extent of binding in rat serum differed widely among the quinolones examined [i.e., from 15% (norfloxacin) to 84% (nalidixic acid) at concentrations of 0.4-10.0 micrograms/mL]. Lomefloxacin was bound to serum proteins to the extent of 28.1, 20.1, and 20.6% in the sera of rats, dogs, and humans, respectively. The binding of nalidixic acid with rat serum albumin, which was very similar to that in rat serum, was concentration dependent. Some quinolone derivatives with a piperazinyl group or a relatively large-sized substituent at the 7-position exhibited a percentage unbound of approximately 70-80%, while some derivatives with small-sized substituents gave a low percentage unbound of 20-30%. This suggests that there is a steric effect of the substituents at the 7-position of quinolones on their binding characteristics with serum proteins. The results of the present study indicate that quinolones bind mainly with albumin among serum proteins and that the remarkable difference of the extent of binding of quinolone analogues is related to the size of the substituent at the 7-position of the molecule, possibly due to its steric effect.     

Human pharmacokinetics of tolfenamic acid,a new anti-inflammatory agent

Summary The pharmacokinetics of tolfenamic acid, a new anti-inflammatory agent was studied in six healthy volunteers after an intravenous dose of 100 mg and oral doses of 100, 200, 400 and 800 mg. The disposition of intravenous tolfenamic acid could be described by two-compartment open model, with a central compartment volume (V_dc) of 5.6±0.31 (mean±SE), volume during -phase (V_d) of 31±21, and a total elimination rate constant (k₁₀) 1.6±0.1 h^–1. The terminal elimination half-life was 2.5±0.6 h and the total plasma clearance 155±15 ml/min. The elimination occured principally by extrarenal mechanisms, the recovery of unchanged drug together with is glucuronide in urine averaging only 8.8% of the intravenous dose. The binding of tolfenamic acid to plasma proteins averaged 99.7%. The gastrointestinal absorption had a mean half-life of 1.7±0.1 h. Based on comparison of areas under the plasma concentration time-curves after intravenous and oral administration, the biovailability of tolfenamic acid capsules averaged 60%. The rate and extent of absorption and the rate of elimination of tolfenamic acid were independent of dose.     

Steady-state pharmacokinetics of a new antipsychotic agent perospirone and its active metabolite, and its relationship with prolactin response

The authors investigated steady-state pharmacokinetics of perospirone and its active metabolite hydroxyperospirone (ID-15036) and its prolactin response in 10 schizophrenic patients receiving 16 mg twice daily. Plasma concentrations of perospirone, hydroxyperospirone, and prolactin were monitored just before and up to 12 hours after the dosing. Thereafter, the dose was decreased to 8 mg twice daily in 8 patients, and drug concentrations were determined. The geometric means of peak concentration (Css(max)), time to Css(max) (tmax), area under the plasma concentration-time curve from 0 to 12 hours [AUC (0-12)], and elimination half-life at steady state were 8.8 ng/mL, 0.8 hours, 22.0 ng x h/mL, and 1.9 hours, respectively, for perospirone, and those of Css(max), tmax, and AUC (0-12) for hydroxyperospirone were 29.4 ng/mL, 1.1 hours, and 133.7 ng x h/mL, respectively. There were no differences in dose-normalized Css(max) or AUC (0-12) perospirone and hydroxyperospirone between 16 mg/day and 32 mg/day of perospirone. Changes in prolactin concentration from 1 to 2 hours after the dosing were parallel with drug concentrations, and almost normal ranges of prolactin concentration were observed before the morning dose despite steady state. The current study indicated that perospirone is rapidly absorbed and rapidly eliminated, which influences the prolactin response. The active metabolite hydroxyperospirone may play an important role in the antipsychotic effect because the plasma concentration of this metabolite is higher than that of the parent compound.     

Dose-dependent pharmacokinetics of a new neuroprotective agent for ischemia-reperfusion damage, KR-31378, in rats

The dose-dependent pharmacokinetic parameters of a new neuroprotective agent for ischemia-reperfusion damage, KR-31378, were evaluated after intravenous and oral administration, 10, 20, and 50 mg/kg, to rats. After intravenous administration of 50 mg/kg, the dose-normalized (10 mg/kg) AUC (994 microg min/mL) was significantly greater than that at 10 (569 microg min/ml) and 20 (660 microg min/mL) mg/kg. This could be due to slower clearance (Cl) with increasing dosage (18.5, 14.6, and 10.2 mL/min/kg for 10, 20, and 50 mg/kg, respectively). The slower Cl with increasing dosage could be due to saturable metabolism of KR-31378 in rats and this could be supported by significantly slower Cl(nr) and significantly greater 24-h urinary excretion of the drug at 50 mg/kg than those at 10 and 20 mg/kg. After oral administration of 50 mg/kg, the dose-normalized (10 mg/kg) AUC (1160 microg min/mL) was significantly greater than that at 10 (572 microg min/mL) and 20 (786 microg min/mL) mg/kg. Note that the AUCs were comparable (not significantly different) between intravenous and oral administration at each dosage, indicating that the absorption from gastrointestinal tract was almost complete and the first-pass (gastric, intestinal, and hepatic) effect was not considerable after oral administration to rats.     

Possible factor for nonlinear pharmacokinetics of TAK-603, a new antirheumatic agent, in rats

A new antirheumatic, TAK-603, shows nonlinear pharmacokinetics in both animals and humans. To elucidate the mechanism of these nonlinear pharmacokinetics, in vivo and in vitro metabolism of 14C-labeled TAK-603 ([14C]TAK-603) was studied using rats as these resemble humans in their metabolic profiles. After intravenous injection of [14C]TAK-603 to rats at doses of 1, 5, and 15 mg kg(-1), the total body clearance of unchanged drug decreased significantly with increasing dose, whereas the apparent distribution volume did not alter remarkably. Thus, saturation in the elimination processes was considered to be a factor responsible for the nonlinear pharmacokinetics. The disappearance of unchanged drug from the circulation, however, followed a dose-dependent first-order process, indicating that the nonlinearity observed was not merely due to saturation of the elimination capacity. In vitro studies using rat liver microsomes showed that TAK-603 competitively inhibited CYP-catalysed nifedipine oxidation and also that the demethylated metabolite M-I, the major metabolite in rats and humans, competitively inhibited the oxidation of nifedipine. These results suggested that inhibition by M-I of the metabolism of the parent drug (i.e. product-inhibition) may be the most likely factor responsible for the nonlinear pharmacokinetics of TAK-603.     

Dose-dependent pharmacokinetics of KR-31378, a new neuroprotective agent for ischaemia-reperfusion damage in dogs

Dose-dependent pharmacokinetic parameters of KR-31378, a new neuroprotective agent for ischaemia-reperfusion damage, were evaluated after intravenous and oral administration of the drug at doses of 5, 10 and 25 mg/kg to male beagle dogs. After intravenous administration, the dose-normalized (based on 5 mg/kg) areas under the plasma concentration-time curve from time zero to time infinity (AUC values, 725, 1450 and 2300 micro g min/ml for 5, 10 and 25 mg/kg, respectively) were significantly different among the three dose ranges studied; the value increased more proportionally as the dose increased. This could be due to slower total body clearance (Cl) with increasing doses (6.90, 3.46 and 2.17 ml/min/kg). The slower Cl value with increasing doses may be due to saturable metabolism of KR-31378 in dogs. After oral administration, the dose-normalized (based on 5 mg/kg) AUC values (833, 1450 and 1920 micro g min/ml) at 5 mg/kg were significantly smaller than those at 10 and 25 mg/kg. Note that the AUC values were comparable (not significantly different) between intravenous and oral administration at all doses studied, indicating that the absorption of KR-31378 from the gastrointestinal tract was essentially complete and the first-pass (gastric, intestinal and/or hepatic first-pass) effects were almost negligible in dogs.     

The effects of KR-10876, a new quinolone antimicrobial agent,on the central nervous system

To evaluate KR-10876, a new fluoroquinolone antibacterial agent, its effects on the central nervous system (CNS) were investigated in mice as part of pharmacological study, and the results were compared with those for ciprofloxacin and ofloxacin, two prototypes of quinolone antibacterial agents. All the parameters indicative of CNS function and acute toxicity were measured by close observation of the animals at regular time intervals after oral treatment of test compounds. KR-10876, ciprofloxacin and ofloxacin exerted a dose-dependent effect on the CNS functions studied. KR-10876 did not have any effects on the parameters measured at lower dose (100, 300 mg/kg, p.o.), but at high dose (1,000 mg/kg, p.o.), it caused ptosis, suppressed spontaneous locomotor activity, hypothermia, and prolonged hexobarbital-induced sleeping time. KR-10876 also had a slight effect on motor coordination only at high dose. Simialr to ciprofloxacin and ofloxacin, KR-10876 did not protect mice from pentylenetetrazol-, strychnine-, and electroshock-inducedl convulsions at doses tested. These findings demonstrate that KR-10876 affects CNS functions only at high doses. The rank order for effects is ofloxacin≥KR-10876>ciprofloxacin.     

High-performance liquid chromatographic analysis of chlorhexidine phosphanilate, a new antimicrobial agent

Chlorhexidine phosphanilate (CHP) is analysed by two separate reversed-phase HPLC methods. CHP was found to be a non-stoichiometric compound with a phosphanilic acid to chlorhexidine ratio of 1.83. By careful choice of solvents, solution pH and HPLC columns, loss of sample due to incomplete dissolution and adsorption to surfaces is avoided. Both methods are shown to be stability-indicating and accurate.     

Synthesis and biological evaluation of new amino acids structurally related to the antitumor agent acivicin

A set of racemic conformationally constrained analogues of the antitumor antibiotic acivicin (+)-1 has been prepared through a strategy based on 1,3-dipolar cycloaddition of bromonitrile oxide to suitable dipolarophiles. The bromo analogue (2) of acivicin was also synthesized and tested as a reference compound, together with its stereoisomer 3. The antitumor properties of novel amino acids 4-7 were evaluated in vitro against human tumor cell lines. Their efficacy to inhibit glutamate synthase (GltS) from Azospirillum brasilense was also assayed. None of the studied compounds, but 2, showed significant activity.     

Single- and multiple-dose pharmacokinetics of nefiracetam, a new nootropic agent, in healthy volunteers.

The pharmacokinetic profile of nefiracetam (N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl)acetamide), a new nootropic agent, was studied in healthy Japanese male volunteers. Nefiracetam was administered orally at doses of 10-200 mg in the single-dose studies, and at doses of 200 mg three times a day for seven days in the multiple-dose study. An HPLC method was used to determine the concentrations of nefiracetam in serum, urine and faecal samples. Linear kinetic behaviour was obtained after single oral administration. Serum concentrations of nefiracetam reached maximum values (Cmax) within 2 h for all dosage groups, and declined monophasically after Cmax with half-lives of 3-5 h. The area under the concentration-time curve (AUC infinity) and Cmax were linearly related to the dose. The apparent clearance (CL) values were 94.4-140.3 mL min-1. Urinary excretion of nefiracetam was independent of the administered dose, and less than 10% of the dose was recovered in urine as the unchanged form within 24 h after administration. Renal clearance (CLR) did not change significantly as dose increased from 10 to 1200 mg. Faecal excretion of nefiracetam was less than 0.1% of the dose up to 24 h after a 300 mg oral dose. Food intake delayed the absorption of nefiracetam but did not significantly modify its pharmacokinetics. No clinically significant accumulation of nefiracetam in the body was observed during and after multiple doses.     

Effects of a standardized meal on the pharmacokinetics of the new cardiotonic agent piroximone.

The influence of food on the pharmacokinetics of piroximone (MDL 19.205, CAS 84490-12-0) was evaluated in two groups of 6 healthy male volunteers receiving either 25 or 50 mg of the drug. Single doses were administered intravenously and orally under fasting conditions or orally with a standard breakfast on 3 different days with a washout period of at least 3 days in-between doses, according to an open, 3-way crossover, randomized design. Pharmacokinetic parameters (Cmax, tmax, AUC, t1/2, Cl, aVd, UEx) were not affected by food administration, but significant differences were found in t1/2 calculated from the decay of plasma concentrations in response to oral administration of 25 mg and 50 mg treatment doses. The urinary excretion of piroximone was significantly reduced after oral administration, when compared with the values obtained after intravenous application. In addition, extra-renal clearance was significantly reduced in the 50 mg treatment group, when compared with the values obtained in response to 25 mg. Bioavailability of piroximone calculated from AUC data compared favorably with data obtained from urinary recovery results.     

Effect of cinacalcet hydrochloride, a new calcimimetic agent, on the pharmacokinetics of dextromethorphan: in vitro and clinical studies

Cinacalcet hydrochloride (cinacalcet) is a positive allosteric modulator of the calcium-sensing receptor indicated for the treatment of secondary hyperparathyroidism in dialysis patients. In vitro study has demonstrated that cinacalcet is a potent inhibitor of cytochrome P450 (CYP) 2D6 with a K(i) value of 0.087 micromol/L, which is comparable to the well-known potent CYP2D6 inhibitor, quinidine (0.064 micromol/L). A clinical study was conducted to assess the inhibitory effect of cinacalcet on CYP2D6 substrates in healthy volunteers. Each subject received 50 mg of cinacalcet or a matched placebo orally once daily for 8 days with 30 mg of dextromethorphan coadministered on day 8. The mean AUC(0-infinity) and C(max) of dextromethorphan increased 11- and 7-fold, respectively, in extensive metabolizers when coadministered with cinacalcet versus placebo. Therefore, during concomitant treatment with cinacalcet, it may be necessary to consider making dose adjustments for drugs with a narrow therapeutic index that are mainly metabolized by CYP2D6.     

Comparative pharmacokinetics and metabolism of levetiracetam,a new anti-epileptic agent,in mouse,rat, rabbit and dog

1.?The pharmacokinetics and metabolism of ¹⁴C-levetiracetam, a new anti-epileptic agent, in mouse, rat, rabbit and dog after a single oral dose were investigated. Moreover, the in vitro hydrolysis of levetiracetam to its major carboxylic metabolite by rat tissue homogenates was investigated to identify tissues involved in the production of the metabolite. Data are also presented on the induction of the enzyme(s) involved in levetiracetam hydrolysis in the rat.

2.?Levetiracetam was rapidly and almost completely absorbed. The unchanged drug accounted for a very high percentage of plasma radioactivity. Levetiracetam did not bind to plasma proteins. Although brain radioactivity concentrations were lower than those of whole blood at early time points, brain-to-blood ratios increased over time. The predominant route of elimination of total ¹⁴C was excretion via urine, accounting for about 81, 93, 87 and 89% of the dose in the mouse, rat, rabbit and dog, respectively. Consequently, levetiracetam was poorly metabolized. It was submitted in vivo to hydrolysis and/or oxidation. Hydrolysis of the amide function of levetiracetam produced the corresponding acid. However, levetiracetam could also be oxidized at positions 3 and 4 of the 2-oxopyrrolidine ring. Finally, the compound and the corresponding acid metabolite could be oxidized at position 5 of the 2-oxopyrrolidine ring and then hydrolysed with the opening of the ring.

3.?All the investigated rat tissues (liver, kidney, lung, brain, small intestine mucosa) had the potential to produce the acid metabolite. By contrast, the acid was undetectable following incubation of levetiracetam with buffer alone or heat-denaturated liver fractions.

4.?No marked species or sex differences were observed in the absorption, disposition and metabolism of levetiracetam.

5.?The hydrolysis of levetiracetam is carried out by an enzymatic process characterized by a broad tissue distribution. In the rat, the enzyme system hydrolysing levetiracetam is not induced by phenobarbital, at least under the experimental conditions used herein, whereas the enzyme system(s) involved in the other metabolic pathways is induced.     

Comparative pharmacokinetics and metabolism of levetiracetam, a new anti-epileptic agent, in mouse, rat, rabbit and dog

1: The pharmacokinetics and metabolism of 14C-levetiracetam, a new anti-epileptic agent, in mouse, rat, rabbit and dog after a single oral dose were investigated. Moreover, the in vitro hydrolysis of levetiracetam to its major carboxylic metabolite by rat tissue homogenates was investigated to identify tissues involved in the production of the metabolite. Data are also presented on the induction of the enzyme(s) involved in levetiracetam hydrolysis in the rat. 2: Levetiracetam was rapidly and almost completely absorbed. The unchanged drug accounted for a very high percentage of plasma radioactivity. Levetiracetam did not bind to plasma proteins. Although brain radioactivity concentrations were lower than those of whole blood at early time points, brain-to-blood ratios increased over time. The predominant route of elimination of total 14C was excretion via urine, accounting for about 81, 93, 87 and 89% of the dose in the mouse, rat, rabbit and dog, respectively. Consequently, levetiracetam was poorly metabolized. It was submitted in vivo to hydrolysis and/or oxidation. Hydrolysis of the amide function of levetiracetam produced the corresponding acid. However, levetiracetam could also be oxidized at positions 3 and 4 of the 2-oxopyrrolidine ring. Finally, the compound and the corresponding acid metabolite could be oxidized at position 5 of the 2-oxopyrrolidine ring and then hydrolysed with the opening of the ring. 3: All the investigated rat tissues (liver, kidney, lung, brain, small intestine mucosa) had the potential to produce the acid metabolite. By contrast, the acid was undetectable following incubation of levetiracetam with buffer alone or heat-denaturated liver fractions. 4: No marked species or sex differences were observed in the absorption, disposition and metabolism of levetiracetam. 5:The hydrolysis of levetiracetam is carried out by an enzymatic process characterized by a broad tissue distribution. In the rat, the enzyme system hydrolysing levetiracetam is not induced by phenobarbital, at least under the experimental conditions used herein, whereas the enzyme system(s) involved in the other metabolic pathways is induced.     

Effect of its demethylated metabolite on the pharmacokinetics of unchanged TAK-603, a new antirheumatic agent, in rats.

A factor in the dose-dependent pharmacokinetics of ethyl 4-(3, 4-dimethoxyphenyl)-6,7-dimethoxy-2-(1,2, 4-triazol-1-yl-methyl)quinoline-3-carboxylate (TAK-603) in rats was shown to be due to the inhibition of metabolic clearance of unchanged TAK-603 by its major metabolite, M-I, in other words, product inhibition. The effect of M-I on the metabolic clearance of TAK-603 was studied using rats continuously infused i.v. with this metabolite at rates of 5.3 and 16.0 mg/h/kg. The total body clearance of TAK-603 was decreased remarkably in M-I-infused rats, and the decline of total body clearance depended on the steady-state plasma concentrations of M-I. The effect of M-I generated from the dosed parent drug on the plasma concentration-time profile of TAK-603 was investigated using bile-cannulated rats after i.v. injection of 14C-labeled TAK-603 at doses of 1 and 15 mg/kg. Elimination rates of TAK-603 from rat plasma increased in the bile-cannulated rats in which systemic M-I levels were reduced by interrupting its enterohepatic circulation. To express, simultaneously, the relationships between TAK-603 and M-I in plasma concentration-time profiles, a kinetic model based on the product inhibition was developed for the bile-cannulated rats. A good agreement between calculated curves and the observed concentrations of both TAK-603 and M-I was found at 1 and 15 mg/kg, and the calculated curves were drawn using constant parameters for the two dosages. These results show that the product inhibition by M-I is one factor responsible for the dose-dependent pharmacokinetics of TAK-603 in rats.     

Age related antihypertensive effect of nitrendipine,a new calcium entry blocking agent

Summary The effect of nitrendipine 20 mg o.d., a new calcium entry blocker similar in structure to nifedipine, on blood pressure has been evaluated in 14 patients (aged 24–62 years) with uncomplicated mild or moderate arterial hypertension. A significant decrease both in systolic (160±12 at baseline vs 141±8 mm Hg, p<0.001) and diastolic (106±8 vs 93±3 mm Hg, p<0.001) blood pressure was observed at the end of 8 weeks of nitrendipine treatment. An inverse correlation was found between age and the reduction in diastolic blood pressure (r=0.772, p<0.001 as absolute reduction; r=0.791, p<0.001 as percentage reduction versus baseline). This peculiar characteristic differentiates the effect of nitrendipine from that of other calcium entry blockers, which appear to be more effective in older patients.     

Radioimmunoassay for mitoxantrone,a new antitumor agent

A sensitive and specific radioimmunoassay for mitoxantrone in serum has been developed. The procedure allows direct measurement of mitoxantrone in unextracted serum samples, by using antisera from rabbits immunized with mitoxantrone-BSA antigen. Tritiated mitoxantrone of high specific radioactivity (ca. 15 Ci/mmol) was used as a radio-tracer ligand. The assay allows the detection of as little as 50 pg/ml and the quantitation of 75 pg/ml in 0.5 ml serum samples. Standard curves were linear in the concentration range of 75–2500 pg/ml, at antiserum dilutions of 1:15,000. The assay shows good reproducibility: coefficients of variation of 3–6% were obtained by analyzing five samples/concentration at 75, 100, 250, 500, and 1000 pg/ml. There was no cross reactivity with the major metabolite in human serum, having concentrations of up to 10,000 pg/ml. Serum samples collected at various time intervals from rats dosed intravenously with mitoxantrone (0.5 mg/kg), were analyzed for unchanged mitoxantrone by RIA. The drug concentrations decreased from 32 ng/ml at 0.5 h to 0.45 ng/ml by 24 h after dosing.Mitoxantrone, a dihydroxyanthracenedione derivative (1), is an antitumor agent currently used in clinical trials with very encouraging results, especially in metastatic breast cancer, and low incidence of adverse reactions (2–4). The drug is being administered intravenously at doses up to 14 mg/m². Preliminary pharmacokinetic studies (to be published separately) indicate rapid distribution, followed by slow clearance rates from the tissues.The sensitivity of the currently available (HPLC) methods (5, 6) is of about 5–20 ng/ml in serum. The purpose of this work was to develop a more sensitive method, such as radioimmunoassay, which can be utilized in pharmacokinetic studies to measure mitoxantrone levels in biological fluids, over extended periods of time after dosing.

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Absorption,distribution and excretion of the new thienopyridine agent prasugrel in rats

Prasugrel is converted to the pharmacologically active metabolite after oral dosing in vivo. In this study, ¹⁴C-prasugrel or prasugrel was administered to rats at a dose of 5?mg?kg^–1. After oral and intravenous dosing, the values of AUC_0–∞ of total radioactivity were 36.2 and 47.1?µg?eq.?h?ml^–1, respectively. Oral dosing of unlabeled prasugrel showed the second highest AUC_0–8 of the active metabolite of six metabolites analyzed. Quantitative whole body autoradiography showed high radioactivity concentrations in tissues for absorption and excretion at 1?h after oral administration, and were low at 72?h. The excretion of radioactivity in the urine and feces were 20.2% and 78.7%, respectively, after oral dosing. Most radioactivity after oral dosing was excreted in bile (90.1%), which was reabsorbed moderately (62.4%). The results showed that orally administered prasugrel was rapidly and fully absorbed and efficiently converted to the active metabolite with no marked distribution in a particular tissue.