Comparison of pharmacokinetics of gatifloxacin in rats, dogs and humans

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1 Asian Journal of Drug Metabolism and Pharmacokinetics Paper ID Copyright by Hong Kong Medical Publisher Received November 20, 2004 ISSN (1):71-76 Accepted February 5, 2005 Comparison of pharmacokinetics of gatifloxacin in rats, dogs and humans XD Liu 2, L Xie, J Wang, Y Liang, L Li and T Lu Center of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University, Nanjing, 20009, China. Abstract Key words Aim: To compare pharmacokinetic behaviors of gatifloxacin (AM-1155) in rats, dogs and humans. Methods: AM-1155 concentrations in plasma were determined by HPLC after oral administration and intravenous dose in rats, dogs and humans. The pharmacokinetic parameters were estimated using a standard non-compartmental method. Results: AM-1155 was rapidly absorbed in all species, and peak concentrations occurred at about 1, 1.73 and 1.3 h in rat, dog and human after oral administration. The pharmacokinetics of AM-1155 in rats was linear for both oral doses (7.5, 15 and 30 mg/kg) and intravenous doses (3.75, 7.5 and 15 mg kg -1 ). The bioavailability in rat was 60.48%(15 mg kg -1 ) to 78.86%(15 mg kg -1 ). Higher bioavailability, with a mean of 98.47%, was found in dog. The elimination occurs fastest in rats and slowest in dog. After oral administration, the T 1/2 estimated in rats, dogs and humans were 2.11, and 7.32 h. The corresponding oral clearances(cl/f) were 1.42, and 88 l/kg/h, and oral apparent distribution volumes were 4.71, 1.71 and 1.96 l/kg. Exposure AUC normalized by body surface area and dose in dogs was 4.5-fold of that in human. Conclusion: There exists species difference in the pharmacokinetics of AM Dogs have higher exposure than humans and rat do. Pharmacokinetics; species differences; gatifloxacin; exposure Project supported by national 863 item plan(no 2003AA2Z347A) and the Key Laboratory of Jiangsu Drug Metabolism and Pharmacokinetics Correspondence to Dr X.D. Liu. Center of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University, Nanjing, , People s of Republic of China. xdliu1960@hotmail.com Introduction Gatifloxacin (AM-1155), a fluoroquinolone, has potent and broad antimicrobial activity against gram-positive and gram-negative aerobes, anaerobes, Mycoplasma and Chlamydia spp [1,2]. It is more potent than ciprofloxacin and ofloxacin, and is comparable to sparfloxacin and tosufloxacin against gram-positive bacteria and anaerobes in vitro. It has been developed for the therapy of bacterial infections. The aim of the study was to compare pharmacokinetic behavior of AM-1155 following the administration of oral and intravenous of doses in rats, dogs and humans. Chemical and animals Gatifloxacin and ciprofloxacin (internal standard) were obtained from Medicinal Chemistry Institutes of China Pharmaceutical University. Gatifloxacin capsule was presented by Anhui Keyu Pharmaceutical Institute. All other reagents were commercially available. Sprague-Dawley rats, weighing g, and beagle dogs, weighing 9-11 kg, were supplied by Experimental Animal Center of China Pharmaceutical University. The animals fasted, but were given free access to water 12 h prior to experiment. Materials and methods 71

2 Pharmacokinetics of AM-1155 in rats The rats were classified into several groups, each with 3 males and 3 females, and given oral administration 7.5, 15 and 30 mg kg -1 or intravenous administration of 3.75, 7.5 and 15 mg kg -1 of AM The rats were killed by femoral artery bleeding at 0.08, 0.25, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0 and 9.0 h after dose under ether anesthesia. Heparinized blood was collected and centrifuged to obtain plasma. Plasma samples were stored at 20 C until assayed. Pharmacokinetics of AM-1155 in dogs Six beagle dogs, 3 male and 3 female, were classified into two groups. The dogs were given oral or intravenous dose of 5 mg/kg of AM-1155 according to two-way crossover design. Serial blood samples were collected in heparinized tubes at 0.25, 0.5, 1.5, 2, 3, 4, 6, 8, 12, and 48 h. Plasma samples were separated by centrifugation and stored at 20 C until assayed. The wash-out period is was one week. Pharmacokinetics of oral administration of gatifloxacin capsule Twenty male volunteers participated in the study, the average ages, 21.7±1.1 years and weight 64.6±4.9kg, respectively. Prior to the study, each subject was examined to check for the absences of any disease including cardiovascular, epileptic, gastrointestinal, renal, respiratory, and hepatic function. Each subject gave written consent to participate in the study. The protocol was approved by the Local Ethics Committee. After fasted overnight, the subjects received 200 mg of gatifloxacin capsule by oral administration. The heparinized blood samples were obtained at 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24 and 36 h after dose. Plasma samples were separated by centrifugation and stored at 20 C until assayed. Assay procedure AM-1155 concentrations in biological fluids were determined by HPLC with fluorescence detection. (3,4) In brief, twenty µl of ciprofloxacin (0.2 mg/ml) and 500 µl 10% HClO 4 were added to 500 µl of plasma. The samples were mixed 10 min and centrifuged 10 min at rpm. Twenty µl of supernatant was directly injected into the HPLC system(model LC-10A, Shimadzu) with automatic injector (SCL-10 Advp, Shimadzu). A C 18 Hypersil 5µm, 100 mm 4.6 mm column (Shimadzu) was used. The mobile phase was a mixture 0.05 mol L -1 KH 2 PO 4, acetonitrile and triethylamine(830:170:1.4, v/v/v) at flow rate of 1.3 ml min -1. The excitation and emission wavelength of fluorescence detector (Model RF-10 A, Shimadzu) were set at 295 and 495 nm, respectively. The peak areas for the components were recorded, and the ratios of peak areas between AM-1155 and ciprofloxacin were plotted versus concentrations using unweighted linear regression. From the calibration curve obtained, concentrations of unknown samples were calculated. Based on the above conditions, AM-1155 and ciprofloxacin were separated completely from other substances, with retention time of 4.1 and 2.4 min, respectively. The calibration curve of AM-1155 in plasma was linear over µg ml -1, giving an r 2 value of The recoveries were found to be 96.34±5.25, 99.70±2.70 and 94.27±4.30% at concentrations of 0.30, 2.40 and 19.20µg ml -1, respectively. The within-assay coefficients of variation were 4.18, 1.36 and 5.21% at concentrations of 0.30, 2.40 and 19.20µg ml -1, and the between-assay coefficients of variation were 5,44, 2,71 and 4.56%, respectively. Data analysis C max and T max values were obtained directly from the observed concentration vs. time data. AUC was calculated by the trapezoidal method. Terminal half-life(t 1/2 ) was defined as T 1/2 =0.693/k e and the k e was determined by unweighted linear regression of logarithmical plasma concentration versus time for the last 4-5 data points. Mean residence time(mrt) was also calculated using standard noncompartmental analysis. The apparent total body clearance (Cl/F) was calculated as dose/auc. The oral apparent volume of distribution at the elimination phase (V d /F) calculated as Cl/F/k e. Pharmacokinetic parameters and concentrations were given as mean±standard deviation SD). Results and discussion Pharmacokinetics of AM-1155 in rat Figure 1 gives plasma concentration profiles of AM-1155 in rats after oral administration and intravenous administration of three AM-1155 doses. 72

3 The pharmacokinetic parameters estimated are listed in Table A 100 B Level in plasma( g/ml) 1 Level in plasma( g/ml) Fig 1 AM-1155 concentration profiles(mean±sd, n=6) in rats. A, oral dose of 7.5( ), 15 ( )and 30 ( ) mg mg kg -1. B, iv dose of 3.75( ),7.5 ( )and 15 ( ) mg kg -1 Table 1. Pharmacokinetic parameters of AM-1155 in rat after oral and intravenous administration Parameters Oral administration Intravenous injection T max, h C max, µg ml T 1/2 h MRT h AUC 9 µg.h ml AUC µg.h ml Cl/F L kg -1 h V d /F L kg F% The concentration in rat plasma reached a peak at about 1 h and the respective values were 1.26, 2.95 and 5.94µg/ml, after oral administration of 7.5, 15 and 30 mg kg -1. The dose proportionality was calculated by comparison of C max and AUC. A good correlation was found in oral administration between the administrated dose(x) and resulting value(y): y=0.207x for C max and y=0.778x for AUC. The coefficients of correlation were and 0.996, respectively. A good correlation between AUC and dose for iv administration was also found, y=1.148x with the coefficients of correlation The t 1/2 (2.11±0.24) of AM-1155 after oral administration was longer than that(1.25±0.03) after i.v. administration. Pharmacokinetics of AM-1155 in dogs The plasma concentrations of AM-1155 after intravenous and oral administration of 5 mg kg -1 in dogs are shown in Figure 2. The pharmacokinetic parameters are listed in Table 2. 73

4 Concentration in plasma( g/ml) Figure 2. AM-1155 concentration profiles(mean±sd, n=6) in dogs after oral( ) and iv( ) dose of 5 mg kg -1. Table 2. Pharmacokinetic parameters of AM-1155 in dogs after oral and intravenous administration of 5 mg kg -1. Parameters mean ±SD mean ±SD T max h C max µg ml T 1/2 h MRT h AUC 36 µg.h ml AUC µg.h ml Cl/F L kg -1 h V d /F L kg F% High bioavailability (98.47%) of AM-1155 was found in dogs, which indicated that the AM-1155 was almost completely absorbed in dogs after oral administration. Oral distribution volume (Vd/F), oral Clearances (Cl/F) and T 1/2 were similar to those of intravenous administration. Pharmacokinetics of AM-1155 in human The plasma concentration-time course and pharmacokinetic parameters of AM-1155 in healthy human subjects after oral administration of 200 mg are shown in Figure 3 and Table 3, respectively. Level in plamsa ( g/ml) Fig3. AM-1155 concentration profiles(mean±sd) in 20 healthy human subjects after oral dose of 200mg. 74

5 Table 3. Pharmacokinetic parameters of AM-1155 in humans after oral administration of 200 mg Parameters Mean SD T max h C max µg ml T 1/2 h MRT h AUC 24 µg.h ml AUC µg.h ml Cl L h V d L After oral administration of 200 mg of AM-1155 in humans, the peak concentrations (1.89±0.38 µg/ml) occurred between 0.5 and 3 h, with a mean value of 1.3 h. The T 1/2 value was found to be 7.32±0.87 h. These parameters were consistent with those in Japanese subjects [3] after oral administration of 200 mg. The estimated T 1/2 values and T max values were also in a agreement with those in Caucasians, with T 1/2, T max and CL/F mean values were 7.2 h, 1.66 h and 1 L h -1[4], respectively after oral administration of 400 mg. These results suggested that AM-1155 has similar pharmacokinetic behavior in all three populations. The pharmacokinetic behavior in humans is satisfactory, with suitable half-life (about 7 h) and good bioavailability (98.5% absolute bioavailability) [5]. The plasma concentration of AM-1155 at 12 h after oral dose of 200 mg was 0.45±0.08( ) µg ml -1, a concentration is higher than the MICs of Peptostreptococcus micros (MIC = 0.25 µg/ml), H. influenzae (MIC = 0.03 µg/ml), Staphylococcus aureus (MIC = 25 µg/ml) and Peptostreptococcus magnus (MIC = 25 µg ml -1 ) [6]. Comparison of pharmacokinetics of AM-1155 in rats, dogs and humans Species differences in the pharmacokinetics of AM-1155 were found. Compared to rats, AM-1155 has higher bioavailability in dogs and humans (5), which is close to 100%, suggesting that AM-1155 is almost completely absorbed in dogs and humans. Peak concentrations occur at 1, 1.73 and 1.3 h in rats, dogs and humans, respectively. Absorption seems slower in dogs. After oral administration, the T 1/2 values estimated in rats, dogs and humans were 2.11, and 7.32 h. Assuming human weight is 64.6 kg, Cl/F values were normalized to be 1.42, and 88 L kg -1 h -1, and the Vd/F were 4.79, 1.71 and 1.96 L kg -1. In dogs AM-1155 showed lower clearance and longer half-life, compared with those in humans. This result is inconsistent with other quinolones. [7[ In clinical pharmacological studies, health risk assessments and toxicological assessments, C max and AUC are often used as indexes to estimate exposure of drug. The predictions of equivalent safe exposure concentration or dose of drugs for humans from laboratory animals are usually based on body surface area. In order to compare exposure in rats, dog and humans, C max and AUC were normalized by body surface area according to 125 mg of AM-1155 per square meter. Normalized C max in rats, dog and humans were 4.04, 3.74 and 1.88 µg ml -1, respectively. Normalized C max in rats was similar to that in dogs, but higher than that in human. Normalized AUC in rats, dogs and humans were 13.14, and µg.h ml -1, respectively. Normalized AUC in rats was close to that in humans, but AUC in dogs was 4.5-fold higher. These results indicated that although oral bioavailability of AM-1155 and V/F in dogs were similar to those in human, dogs had higher exposure than humans did. As far as exposure was concerned, rats seem to be a better model animal than dogs for predicting AM-1155 exposure in man. 75

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