Nonlinear Pharmacokinetic Properties Research Articles

Benzisothiazolinone: Pharmacokinetics, Tissue Distribution, and Mass Balance Studies in Rats.

Humans are continuously exposed to benzisothiazolinone (BIT), which is used as a preservative, through multiple routes. BIT is known to be a sensitizer; in particular, dermal contact or aerosol inhalation could affect the local toxicity. In this study, we evaluated the pharmacokinetic properties of BIT in rats following various routes of administration. BIT levels were determined in rat plasma and tissues after oral inhalation and dermal application. Although the digestive system rapidly and completely absorbed orally administered BIT, it underwent severe first-pass effects that prevented high exposure. In an oral dose escalation study (5-50 mg/kg), nonlinear pharmacokinetic properties showed that Cmax and the area under the curve (AUC) increased more than dose proportionality. In the inhalation study, the lungs of rats exposed to BIT aerosols had higher BIT concentrations than the plasma. Additionally, the pharmacokinetic profile of BIT after the dermal application was different; continuous skin absorption without the first-pass effect led to a 2.13-fold increase in bioavailability compared with oral exposure to BIT. The [14C]-BIT mass balance study revealed that BIT was extensively metabolized and excreted in the urine. These results can be used in risk assessments to investigate the relationship between BIT exposure and hazardous potential.

Comparative Pharmacokinetic Study of Hesperetin after Oral Administration in Normal and Hyperuricemia Rats by UPLC-MS/MS.

Hesperetin has antihyperuricemia activity, and the pharmacokinetic profiles of hesperetin may be altered by hyperuricemia. This study aimed to develop a highly sensitive and specific method for the determination of hesperetin in normal and hyperuricemia rats, and to compare pharmacokinetic profiles of hesperetin after oral administration between normal and hyperuricemia rats. Sprague-Dawley (SD) rats were randomly divided into one normal group (group A) and four hyperuricemia groups (group B, C, D, and E). Groups A, B, C, and D received a single dose (9-81 mg/kg) of hesperetin on Day 28, respectively, while group E received multiple doses (27 mg/kg) of hesperetin once daily for 28 days. Blood samples were collected at 10 different time points post-dose, and hesperetin was determined by Ultra-high Performance Liquid Chromatography- tandem Mass Spectrometric (UPLC-MS/MS). Compared with normal condition of group A, hyperuricemia of group C induced 48.19% and 19.57% decreases in Cmax and CL/F, and resulted in 58.25% and 19.48% increases in Tmax and AUC0-t for hesperetin, respectively. After 28 days of hesperitin treatment, Cmax of group E was significantly elevated than that of group C (p < 0.05). Hesperetin exhibited nonlinear pharmacokinetic properties in the range of 9-81 mg/kg in hyperuricemia rats. The pharmacokinetic parameters of hesperetin in hyperuricemia rats were reported for the first time. Intestinal injury may be ameliorated by hesperetin in hyperuricemia rats after 28 days' treatment. These findings could provide more beneficial information to the mechanism and clinical applications of hesperetin.

Preclinical Pharmacokinetics of Scoparone, Geniposide and Rhein in an Herbal Medicine Using a Validated LC-MS/MS Method.

The herbal formula Yin-Chen-Hao-Tang has been reported to have anti-fibrosis properties. The aim of this study was to reveal the pharmacokinetic characteristics of bioactive compounds in this herbal formula. A new high-performance liquid chromatography-tandem mass spectrometry method was developed and validated for simultaneous determination of scoparone, geniposide and rhein in rat plasma. A pharmaceutical herbal powder was administered to rats at doses of 1 g/kg and 3 g/kg orally. The method showed excellent linearity (r2 > 0.999) and validation was successfully conducted for the pharmacokinetic study. The results show that the Cmax values and areas under the curve of scoparone, geniposide and rhein were higher and not proportional to the dose in rat plasma, while the Tmax and half-life values were consistent in the group that received 1 g/kg. The clearance of the higher dose (3 g/kg) did not decrease proportionally to that of the low dose. The results showed the nonlinear pharmacokinetic properties of scoparone, geniposide and rhein in Yin-Chen-Hao-Tang that suggested possible accumulation of bioactive compounds through oral administration. This pharmacokinetic study reveals that an increased dose of this herbal formula would largely increase the maximum concentration and bioavailability of scoparone, geniposide and rhein.

Pharmacokinetic and Pharmacodynamic Properties of Cinacalcet (KRN1493) in Chinese Healthy Volunteers: A Randomized, Open-label, Single Ascending–dose and Multiple-dose, Parallel-group Study

PurposeThe aim of this study was to assess the pharmacokinetic (PK) and pharmacodynamic (PD) properties and safety of single and multiple doses of cinacalcet in Chinese healthy volunteers (HVs) for the purposes of a New Drug Application package for the Chinese Food and Drug Administration. MethodsIn this randomized, open-label, single ascending–dose and multiple-dose, parallel-group study, 42 Chinese HVs were randomized to receive a single oral dose of 25, 50, or 100 mg of cinacalcet and multiple doses of 50 mg of cinacalcet once daily for 7 days. Plasma cinacalcet concentrations were analyzed by HPLC-MS/MS. The PK parameters were assessed with noncompartmental analysis. Plasma intact parathyroid hormone, serum calcium, and phosphorus concentrations were measured for PD evaluation. The safety profile was also assessed. Adverse events (AEs) were noted during the study. FindingsOf the 42 randomized HVs, 41 completed the study per protocol; 1 prematurely discontinued the study because of AEs. Cinacalcet has nonlinear PK properties over a dose range of 25 to 100 mg after a single dose. Mean (SD) Cmax values were 7.68 (4.25), 17 (6.33), and 31.3 (16.42) ng/mL with single doses of 25, 50, and 100 mg of cinacalcet, respectively. Mean (SD) AUC0– last values were 58.4 (25.38), 187 (70.7), and 367 (180.03) hr∙ng/mL with single doses of 25, 50, and 100 mg of cinacalcet, respectively. Steady state was attained within 7 doses of successive daily administration of 50 mg of cinacalcet. At steady state, the mean (SD) Cmax and AUC0–last values were 20.6 (9.63) ng/mL and 297 (146.15) ng∙h/mL. The accumulation ratios of Cmax and AUC (AUCτ/AUC0–24) were 1.21 and 1.32. Plasma intact parathyroid hormone and serum calcium concentrations had similar patterns, both decreased after administration of cinacalcet, whether after single dose or multiple doses. A total of 52 AEs were reported in 20 HVs (47.6%). The most frequently reported AEs after single-dose and multiple-dose cinacalcet administration were hypocalcemia, numbness, dizziness, and muscle soreness. No serious AEs were reported. ImplicationsCinacalcet was well tolerated and effective after administration of a single oral dose up to 100 mg and multiple doses of 50 mg of cinacalcet once daily for 7 days. Cinacalcet has nonlinear PK properties over a dose range of 25 to 100 mg after a single dose. PK profiles after multiple doses were similar to those after a single dose with no accumulation. Cinacalcet had similar PK and safety profiles between Chinese and Western HVs at the same dose levels.

Nonlinear pharmacokinetic properties of mildronate capsules: a randomized, open‐label, single‐ and multiple‐dose study in healthy volunteers

Mildronate has been used as antianginal drug in parts of Europe for many years, but its pharmacokinetic (PK) properties in humans remain unclear. This study was designed to assess and compare the PK properties of mildronate capsules after single escalating oral dose and multiple doses in healthy Chinese volunteers. Volunteers were randomly assigned to receive a single dose of 250, 500, 1000, 1250 or 1500 mg of mildronate capsules. Those who received the 500-mg dose continued on the multiple-dose phase and received 500 mg three times a day for 13 days. Plasma drug concentrations were analysed by ultraperformance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Tolerability was assessed throughout the study. A total of 40 Chinese volunteers were enrolled in the study. No period or sequence effect was observed. Area under the concentration and C(max) were increased proportionally with the dose levels, whereas t(1/2) and V(d)/f were dependent on the dose. Nonlinear PK properties were found at doses of 250-1500 mg. There was an accumulation after multiple-dose administration. No serious adverse events (AEs) were reported in the PK study. The formulation was well tolerated.

Nonlinear toxicokinetics of enrofloxacin in rats

The dose-dependent toxicokinetics of enrofloxacin were studied by administering various single subcutaneous doses (5, 10, 20, 40, 70, 100, 150, 200, 300 and 400 mg/kg) in male Sprague-Dawley rats. The blood samples were collected from the tail veins, and the plasma concentration of enrofloxacin was determined by an HPLC-fluorescence detection (FLD) method. The time-concentration profiles of enrofloxacin were well fitted by an one-compartmental model with first order elimination. The absorption half-lives (t₁(/)₂(abs)) ranged from 0.2-0.8 h, and the mean time to maximum plasma concentration (T(max)) ranged from 0.6-1.8 h. On the other hand, marked disproportionate increases of the area under the curve (AUC) and elimination half-lives (t₁(/)₂) were observed from the increase of the doses. This result indicates that the elimination of enrofloxacin has nonlinear pharmacokinetic properties with increasing doses. Therefore, we need to take into consideration the possible occurrence of side effects resulting from greater systemic exposure from high dose therapies.

Enantioselective pharmacokinetic–pharmacodynamic modelling of carvedilol in a NG-nitro-l-arginine methyl ester rat model of secondary hypertension

The role of vascular sympatholytic activity of carvedilol in its antihypertensive effect in N(G)-nitro-l-arginine methyl ester (L-NAME) hypertensive rats was assessed by means of enantioselective pharmacokinetic-pharmacodynamic (PK-PD) modelling. Male Wistar rats were randomly divided into two groups: control rats received tap water to drink for 2 weeks while L-NAME rats received L-NAME solution to drink for 2 weeks. The effects of carvedilol (1 and 5 mg/kg i.v.) on blood pressure, heart rate and blood pressure variability were recorded. Enantioselective carvedilol plasma pharmacokinetics were studied by means of traditional blood sampling. The relationship between carvedilol concentrations and their hypotensive and bradycardic effects was established by means of PK-PD modelling. Vascular sympatholytic activity of carvedilol was assessed by the estimation of drug effects on low frequency blood pressure variability by means of spectral analysis. A dose-dependent increase in volume of distribution, as well as a greater volume of distribution and clearance of S-carvedilol as compared with the R-enantiomer was found in both experimental groups. Although the PK-PD properties of the S-carvedilol chronotropic effect were not altered in L-NAME rats, hypertensive rats showed greater potency and efficacy to the carvedilol hypotensive response. Greater potency of carvedilol for inhibition of sympathetic vascular activity was found in L-NAME rats. Carvedilol showed enantioselective non-linear pharmacokinetic properties in both groups. An enhanced hypotensive activity of carvedilol was found in L-NAME hypertensive rats compared with control rats, which may be explained by the greater potency of carvedilol for sympathetic vascular tone inhibition.

Abstract 2009: ALX-0081 a Novel Anti-Thrombotic: Results of a Single-Dose Phase 1 Study in Healthy Volunteers and Further Development in Patients with Stable Angina Undergoing PCI

Background : ALX-0081 is a bivalent Nanobody ® based on the variable domain of naturally occurring heavy-chain only antibodies. It binds with high affinity to the A1 domain of von Willebrand Factor (vWF) and thereby blocks the interactions between platelets and vascular collagen. It selectively prevents thrombus formation under high shear stress conditions. Aim : Test ALX-0081 single IV infusions (60 minutes) dosed from 0.5mg to 12mg total in 40 male healthy volunteers in double-blind, randomized, placebo controlled study and assess pharmacokinetic (PK), pharmacodynamic (PD), safety and immunogenicity. Results : ALX-0081 displayed non-linear pharmacokinetic properties, following a 2 compartment model. Ristocetin induced platelet aggregation (RIPA) was analyzed as marker for PD effect with full inhibition (defined as measured levels dropping &lt;10%) observed at ALX-0081 concentrations of ~ 400ng/ml. All subjects dosed ≥ 2mg achieved full RIPA inhibition at 1h post-dosing for maximum of 12h. ALX-0081 treatment was well tolerated and safe, no signs of bleeding were reported and no immunogenic response was detected. Target related mild and transient reductions of vWF and FVIII plasma levels were observed and all events were fully reversible. Phase Ib study design : double-blind, randomized, placebo controlled, multiple ascending dose study. ALX-0081 added to standard anti-thrombotic regimen (ASA, clopidogrel, UFH) in patients with stable angina undergoing elective PCI. Single-dose escalation will be followed by multiple dosing (up to 4 doses in 24h). Dose escalation will be guided by safety and efficacy marker. Endpoints: safety, pharmacological profile, biomarker (RIPA, RICO and ACT) and early clinical outcome (MACE, IMR, molecular marker). Conclusion : ALX-0081 can be administered safely over a wide range of dose-regimen. First results of the phase Ib study in stable angina patients will be presented.

Pharmacokinetics and pharmacodynamics of oral cephalosporins as critical factors in choice of antibiotics

The pharmacology of antimicrobial agents can be divided into two major components: pharmacokinetics and pharmacodynamics. They provide a general interrelationship between the concentration of a given antibiotic at a particular site and the activity of the antibiotic against the causative organism. Pharmacodynamics have been upgraded in the last 10 years and the principles that link concentrations of antibiotics within the body system and their effects have been outlined in order to determine the optimal dosing interval [1,2]. Beta-lactam antibiotics have a time-dependent killing activity, and usually do not have large post-antibiotic effects (PAEs). The parameter which better correlate pharmacodynamics with pharmacokinetics is the duration of time with concentrations higher than the minimal inhibitory concentration (MIC) (T\MIC) [1–3]. Different cephalosporins nevertheless, have demonstrated the occurrence of a concentration-dependent PAE, both in vitro and in vivo for Gram-negative organisms, without any difference between oral and parenteral molecules and with constant exclusion of Pseudomonas aeruginosa strain [3–10]. This phenomenon may contribute to the high clinical efficacy of these derivatives [1,4]. (Table 1). From experimental studies on animal models it was demonstrated that cephalosporins do not need to exceed the MIC for the entire dose interval for successful therapy and 40–70% of the interval is probably satisfactory [1,3]. Cephalosporins represent almost half of all beta-lactams and are generally divided into a generational classification of four generations. Among oral derivatives there are compounds of the 1st generation (i.e. cephalexin and cefadroxil), the 2nd generation (i.e. cefaclor, cefprozil and cefuroxime-axetil) and the 3rd generation (i.e. the methoximinic cephalosporins such as cefixime, ceftibuten, cefpodoxime proxetil and cefetamet pivoxil) [11,12] (Table 2). This classification is based mainly on the antimicrobial activity and beta-lactamase behaviour of the different compounds. On the basis of the common causative organisms, the second generation cephalosporins will be preferable for the treatment of respiratory tract infections since they are active against Gram-positive and Gram-negative strains and are partially resistant to beta-lactamase hydrolysis [11,12]. Bioavailability is one of the main criteria for the selection of oral cephalosporins from a pharmacokinetic point of view. Generally, the cephem derivatives with intrinsic bioavailability (cephalexin, cefaclor, and cefprozil) are highly absorbed, while for cefuroxime axetil, the absorption ranges from 36 to 52% of the administered dose. All these cephalosporins however, with the exception of cefatrizine, have linear kinetics. The majority of these antibiotics are eliminated primarily by the kidney, with elimination half-lives generally under 2 h with a dose interval of 8 or 12 h [11–15] (Table 3). A similar behaviour is observed with the 3rd generation cephalosporins. Ceftibuten is highly absorbed, while for pro-drugs and cefixime, the absorption does not normally exceed 50% of the dose. It may also not be uniform, depending on saturable transport [11,16,17]. Many compounds therefore exhibit non-linear pharmacokinetic properties, since increasing doses lead to relatively decreasing peak concentrations and area under the serum concentration–time curve (AUC) values, mainly in relation to proportionally reduced bioavailability [16,17]. * Corresponding author: Tel.: +39-055-4271 ext. 310; fax: +39055-4271 ext. 280. E-mail address: novelli@server1.pharm.unifi.it (A. Novelli).

Pharmacokinetics of a Granulocyte Colony-stimulating Factor (G-CSF). Role of Receptor-mediated Clearance in the Disposition of G-CSF.

Receptor-mediated endocytosis is one of the most important system for determining the disposition of physiologically active peptides. We reviewed the pharmacokinetic properties of granulocyte colonystimulating factor (G-CSF), one of the hematopoietic growth factors, and also the contribution of the receptor-mediated endocytosis in the disposition of G-CSF was discussed. At present, three kinds of recombinant human G-CSF have been on the market in Japan, i.e., rhG-CSF produced by CHO cells, rhG-CSF by E. coli and mutant G-CSF by E. coli which has a different amino acid sequence in the N-terminal region. These G-CSFs commonly show the non-linear pharmacokinetic properties in no relation to the sugar chain or N-terminal sequence. That is, the total clearances of G-CSFs in the experimental animals and humans decrease as the dose increases and those increase after the repeated administrations. Pharmacokinetic analysis of the plasma concentration-time profiles reveals that the total clearance of G-CSF consists of both saturable and nonsaturable clearances. The mean apparent bioavailability of G-CSF after subcutaneous administration is about 60%. The role of a sugar chain in the disposition of G-CSF is not so important, but the negative charges of sialic acids of the sugar chain effect the total clearance and the absorption from the subcutaneous sites. The clinical observations that the total clearance of G-CSF well correlates with the absolute neutrophil counts in the peripheral blood, suggest the contribution of the G-CSF receptor to the saturable clearance of G-CSF. In fact, the several studies using mutant G-CSF have evaluated that the receptor-mediated clearance of the G-CSF receptor in the bone marrow mainly contributes to the saturable G-CSF clearance. On other hand, the glomerular filtration in the kidney is the major mechanism of the nonsaturable clearance of G-CSF.

Clinical pharmacokinetics of newer cephalosporins.

Several new cephalosporins have been developed in recent years. These agents include several oral and parenteral agents with extended activity against Gram-negative pathogens. The pharmacokinetic literature for these agents is quite extensive; therefore, we have summarised this information and presented it in tabular form for critical comparison. With a few exceptions, the newer cephalosporins share similar pharmacokinetic properties. Cefixime, cefetamet pivoxil and ceftibuten differ from the others in that they exhibit nonlinear pharmacokinetic properties. The nonlinear nature of these agents is reflected by decreasing maximal concentrations with escalating doses of cefixime and cefetamet pivoxil, decreasing area under the serum concentration-time curve with increasing doses for cefixime, and a reduced bioavailability with large doses of ceftibuten. Attention to such characteristics aid the clinician in selecting appropriate dosage regimens that will optimise drug absorption. The majority of agents are primarily renally eliminated; however, renal elimination accounts for only 20% of cefixime elimination. The pharmacokinetic parameters noted for the newer cephalosporins are not influenced by multiple-dose administration, suggesting lack of drug accumulation over time. The pharmacodynamics of antimicrobials should be considered when extrapolating pharmacokinetic information into the clinical arena. In the case of the beta-lactams, the time which drug concentrations remain above some critical threshold, such as the minimal inhibitory concentration, appears to have the greatest influence on bactericidal activity. Therefore, it is important to select dosage regimens that will optimise the time serum concentrations remain above this threshold. We present an evaluation of these agents with respect to their activity against a variety of pathogens in an effort to demonstrate a pharmacokinetically-based process of antimicrobial selection.

Bioavailability studies of drugs with nonlinear pharmacokinetics: II. Absolute bioavailability of intravenous phenytoin prodrug at therapeutic phenytoin serum concentrations determined by double-stable isotope technique.

Measurement of the absolute bioavailability of phenytoin (PHT) derived from test doses of phenytoin prodrug (PPD) at therapeutic PHT serum concentrations is complicated by two problems: 1) the area under the serum concentration versus time curve (AUC) produced by a given size of test dose will vary directly with background PHT serum concentration due to the nonlinear pharmacokinetic properties of PHT; 2) PPD is more water soluble than PHT, making renal excretion of PPD more likely. The authors describe a double-stable isotope method that obviates these two problems. Using only six subjects, the authors were able to demonstrate bioequivalence of PHT derived from intravenous PPD with intravenous PHT by current FDA standards for AUC ratio of test/reference formulation (90% confidence intervals between 0.80 and 1.20; ratio > or = 0.80 in > or = 80% of subjects; statistical power to detect a difference of 0.20 with a probability of 0.80).

Bioavailability Studies of Drugs with Nonlinear Pharmacokinetics: I. Tracer Dose AUC Varies Directly with Serum Concentration

The authors show that for a drug cleared by one enzyme the area under the serum concentration-time curve from time 0 to infinity (AUC0-INF) of a test dose can be expressed as AUC0-INF = TD x F x (Km + C)/Vmax where TD is test dose size, F is fraction absorbed, C is drug serum concentration at the time of the study, and Km and Vmax are the Michaelis constant and maximum velocity of the enzyme. This equation predicts the AUC0-INF produced by a given tracer dose of drug will vary directly with C in drugs with nonlinear pharmacokinetic properties (i.e., drugs whose value for C approaches or exceeds Km) if C is held constant by administration of tracer and maintenance doses of drug. The AUC0-INF produced by intravenous tracer doses of 150 mg of 13C15N2-sodium phenytoin was determined in 15 subjects at 30 different values of C. AUC0-INF showed a high degree of direct linear correlation with C (AUC0-INF (ug x hr/mL) = 35.4 + 8.1 x C (ug/mL), r = 0.885, P < .0001). Consequences of this observation for relative bioavailability studies of drugs with nonlinear pharmacokinetic properties are discussed.

New Pharmacokinetic Methods III. Two Simple Tests for “Deep Pool Effect”

If a portion of administered drug is distributed into a "deep" peripheral compartment, the drug's actual elimination half-life during the terminal exponential phase of elimination may be longer than determined by a single dose study or a tracer dose study ("deep pool effect"). Two simple methods of testing for "deep pool effect" applicable to drugs with either linear or nonlinear pharmacokinetic properties are described. The methods are illustrated with stable isotope labeled (13C15N2) tracer dose studies of phenytoin. No significant (P less than .05) "deep pool" effect was detected.

New Pharmacokinetic Methods: L Estimation of Mean Serum Concentration From Trough Serum Concentration

An equation is derived to estimate mean steady state serum concentration (Css) from trough steady state serum concentration (Cmin) which can be used for drugs with either linear or nonlinear pharmacokinetic properties. In 15 subjects receiving phenytoin monotherapy, estimated Css did not differ significantly from measured Css, while Cmin differed significantly (P less than .0001) from measured Css and estimated Css. Clearance (CL) and elimination half-life (t1/2) values determined by stable isotope tracer methods or by standard equations and measured Css or estimated Css did not differ significantly, while CL and t1/2 values calculated with standard equations and Cmin differed significantly (P less than .02) from values obtained by any of the other three methods. We conclude: 1) Cmin values and CL and t1/2 values calculated with Cmin values may differ significantly from Css values and CL and t1/2 values calculated with Css; 2) accurate estimates of Css and of CL and t1/2 can be obtained using our procedure to correct a Cmin value to an estimated Css value.