DISCONTINUOUS ORAL ABSORPTION PHARMACOKINETIC MODEL AND BIOAVAILABILITY OF 1-(2-FLUORO-5-METHYL-β-L-ARABINOFURANOSYL)URACIL (L-FMAU) IN RATS

1-(2-fluoro-5-methyl-β-L-arabinofuranosyl)uracil (L-FMAU), the L isomer of FMAU, has shown potent activity against hepatitis B virus and Epstein--Barr virus. L-FMAU showed double peaks in the plasma concentration versus time profiles following oral administration to rats, indicating discontinuous oral absorption. The objective of this study was to characterize the bioavailability and pattern of L-FMAU absorption using a pharmacokinetic model which incorporated two separate absorption processes following oral administration of the nucleoside in an animal model, the rat. Simultaneous fitting of differential equations to L-FMAU plasma concentrations following oral and intravenous administration was performed using PCNONLIN. Total clearance of L-FMAU was moderate, averaging 0·47±0·16 L h⁻¹ (mean±SD). Distributional clearance averaged 0·18±0·14 L h⁻¹. The volume of the central compartment averaged 0·30±0·09 L, and the volume of the peripheral compartment averaged 0·15±0·08 L. The first-order absorption rate constants describing the first and second absorption phases averaged 1·22±1·56 and 4·14±5·42 h⁻¹, respectively. Oral bioavailability was calculated by three methods: AUC, urinary excretion data, and a discontinuous oral absorption pharmacokinetic model. Bioavailability averaged 0·59±0·16, 0·64±0·23, and 0·63±0·13, respectively, for the three methods. The discontinuous oral absorption pharmacokinetic model is a promising new method for estimating absorption from two phases and for calculating oral bioavailability.     

PHARMACOKINETICS OF THE ENANTIOMERS OF VERAPAMIL AFTER INTRAVENOUS AND ORAL ADMINISTRATION OF RACEMIC VERAPAMIL IN A RAT MODEL

Verapamil is a chiral calcium channel blocking drug which is useful clinically as the racemate in treating hypertension and arrhythmia. The published pharmacokinetic data for verapamil enantiomers in the rat model are limited. Utilizing a stereospecific high-performance liquid chromatographic (HPLC) assay, the enantiomeric disposition of verapamil is reported after intravenous (1·0 mg kg⁻¹) and oral (10 mg kg⁻¹) administration of racemic verapamil to the rat model. After intravenous administration the systemic clearance of R-verapamil was significantly greater than that of S-verapamil; 34·9 ± 7 against 2·7 ± 3·7 mL min⁻¹ kg⁻¹ (mean ± SD), respectively. After oral administration, the clearance of R-verapamil was significantly greater than that of S-verapamil, 889 ± 294 against 351 ± 109 mL min⁻¹ kg⁻¹, respectively. The apparent oral bioavailability of S-verapamil was greater than that of R-verapamil, 0·074 ± 0·031 against 0·041 ± 0·011, respectively. These data suggest that the disposition of verapamil in the rat is stereoselective; verapamil undergoes extensive stereoselective first-pass clearance after oral administration and the direction of stereoselectivity in plasma is opposite to that observed in the human. © 1997 John Wiley & Sons, Ltd.     

PHARMACOKINETICS AND ABSOLUTE BIOAVAILABILITY OF EPRISTERIDE IN HEALTHY MALE SUBJECTS

The objective of the current investigation was to describe the pharmacokinetics and absolute oral bioavailability of epristeride. Twelve healthy male subjects (mean (SD) age, 27 (6·2) years) received a single oral dose of 5 mg and an intravenous infusion of 4·5 mg over 30 min in a crossover fashion. Blood samples were obtained over 72 h for the determination of epristeride plasma concentrations using a sensitive high-performance liquid chromatography assay. The lower limit of quantification was 5 ng mL⁻¹. Pharmacokinetic analysis of the plasma concentration--time data was performed by both non-compartmental and compartmental methods. Absolute bioavailability was determined using dose-normalized AUC values following oral and intravenous administration. Epristeride plasma concentrations declined in a biexponential fashion with secondary peaks evident around 24 h in a majority of subjects following both routes of administration. Maximal plasma concentrations were typically achieved approximately 4 h after oral dosing. The mean apparent terminal elimination half-life estimates were similar following intravenous and oral administration and were 27·3 and 26·2 h, respectively. The mean plasma clearance and steady-state volume of distribution were 0·33 (0·09) mL min⁻¹ kg⁻¹ and 0·54 (0·17) L kg⁻¹, respectively. The mean absolute bioavailability was 93% (95% CI: 84%, 104%). Following compartmental analysis of the intravenous data, the mean (SD) λ₁ and λ₂ half-life estimates were 2·74 (0·48) and 31·8 (19·5) h, respectively. The % AUC associated with the λ₂ exponential phase was approximately 68%. This long half-life allows for once-daily dosing of epristeride.     

PHARMACOKINETICS AND TOXICOKINETICS OF AN ORALLY ACTIVE TRIPEPTIDE,IRI-695, IN ANIMALS

Pharmacokinetics and toxicokinetics of IRI-695, a tripeptide, were investigated in the rat, rabbit, dog, and monkey. Tissue distribution and excretion of [¹⁴C]IRI-695 were determined in the rat. Following a single intravenous (IV) injection, the elimination half-life (t_1/2) of IRI-695 in the rabbit, dog, and monkey was similar (about 65 min) and approximately four times that in the rat (15 min). This difference in t_1/2 can be attributed to about four times higher clearance of the drug in rats (11·2 mL min⁻¹ kg ⁻¹). The volume of distribution (V_ss) in these four species, 132–234 mL kg⁻¹, suggested negligible preferential distribution of IRI-695 to body tissue. After a 5 mg kg⁻¹ oral dose, the absolute bioavailability of IRI-695 was 2·0% in rats and 3·1% in dogs. However, systemic drug exposure in the dog was about five to 10 times that in the rat, which is related to the slower clearance of the peptide in the dog. Toxicokinetic studies in the rat and dog indicated linear kinetics and systemic exposure of IRI-695 up to 300 mg kg⁻¹ d⁻¹ oral doses throughout the 28 d toxicity study. Accumulation of the drug after the repeated oral dosing was negligible. After a single 0·10 mg kg⁻¹ ]¹⁴C[IRI-695 IV injection in rats, almost all of the radioactivity administered was excreted in urine within 24 h postdose.     

Pharmacokinetics and urinary excretion of DMXBA (GTS-21), a compound enhancing cognition

DMXBA (3-(2, 4-dimethoxybenzylidene)-anabaseine, also known as GTS-21) is currently being tested as a possible pharmacological treatment of cognitive dysfunction in Alzheimer's disease. In this study, plasma and brain pharmacokinetics as well as urinary excretion of this compound have been evaluated in adult rats. DMXBA concentrations were determined by HPLC. Following a 5 mg kg⁻¹ iv dose, DMXBA plasma concentration declined bi-exponentially with mean (±SE) absorption and elimination half-lives of 0.71±0.28 and 3.71±1.12 h, respectively. The apparent steady state volume of distribution was 2150±433 mL kg⁻¹, total body clearance was 1480±273 mL h⁻¹ kg⁻¹, and AUC_0–∞ was 3790±630 ng h mL⁻¹. Orally administered DMXBA was rapidly absorbed. After oral administration of 10 mg kg⁻¹, a peak plasma concentration of 1010±212 ng mL⁻¹ was observed at 10 min after dosing. Elimination half-life was 1.740±0.34 h, and AUC_0–∞ was 1440±358 ng h mL⁻¹. DMXBA peak brain concentration after oral administration was 664±103 ng g⁻¹ tissue, with an essentially constant brain–plasma concentration ratio of 2.61±0.34, which indicates that the drug readily passes across the blood–brain barrier. Serum protein binding was 80.3±1.1%. Apparent oral bioavailability was 19%. Renal clearance (21.8 mL h⁻¹ kg⁻¹) was less than 2% of the total clearance (1480±273 mL h⁻¹ kg⁻¹); urinary excretion of unchanged DMXBA over a 96 h period accounted for only 0.28±0.03% of the total orally administered dose. Our data indicates that DMXBA oral bioavailability is primarily limited by hepatic metabolism. © 1998 John Wiley & Sons, Ltd.     

Pharmacokinetics of a new reversible proton pump inhibitor,YH1885, after intravenous and oral administrations to rats and dogs: hepatic first-pass effect in rats

The pharmacokinetics of YH1885 were evaluated after intravenous (iv) and oral administrations of the drug to rats and dogs. The reason for the low extent of bioavailability (F) of YH1885 after oral administration of the drug to rats and the absorption of the drug from various rat gastrointestinal (GI) segments were also investigated. After iv administration of YH1885, 5–20 mg kg⁻¹, to rats, the pharmacokinetic parameters of YH1885 seem to be independent of the drug at the dose ranges studied. After oral administration of YH1885, 50–200 mg kg⁻¹, to rats, the area under the plasma concentration–time curve from time zero to 12 or 24 h (AUC_{0–12 h} or AUC_{0–24 h}) was proportional to the oral dose of the drug, 50–100 mg kg⁻¹, however, the AUC_{0–24 h} value at 200 mg kg⁻¹ increased with less proportion to the dose increase (324, 689, and 815 μg · min mL⁻¹ for 50, 100, and 200 mg kg⁻¹, respectively) due to the poor water solubility of the drug. This was proved by the considerable increase in the percentages of the oral dose remaining in the entire GI tract as unchanged YH1885 at 24 h (11.8, 15.3, and 42.8% for 50, 100, and 200 mg kg⁻¹, respectively). The F value after oral administration of YH1885 to rats was relatively low; the value was approximately 40% at the oral dose of 50 and 100 mg kg⁻¹. The reason for the low F in rats was investigated. The liver showed the highest metabolic activity for YH1885 based on an in vitro rat tissue homogenate study; hence, the liver first-pass effect was estimated. The value of AUC after intraportal administration of the drug, 5 mg kg⁻¹, was approximately 70% (116 versus 163 μg · min mL⁻¹) of that after iv administration of the drug, 5 mg kg⁻¹, to rats; the liver first-pass effect of YH1885 in rats was estimated to be approximately 30%. The total body clearance of YH1885 after iv administration of the drug, 5–20 mg kg⁻¹, to rats were considerably lower than the cardiac output of rats, indicating that the lung and/or heart first-pass effect of YH1885 could be negligible in rats. After oral administration of YH1885, 50 and 100 mg kg⁻¹, to rats, the F value was approximately 40%, and approximately 15% of the oral dose was recovered from the entire GI tract as unchanged YH1885 at 24 h, and 30% of the oral dose disappeared with the liver first-pass effect. Therefore, the remainder, approximately 15% of the oral dose, could have disappeared with the small intestine first-pass effect and/or degradation of the drug in the GI tract. YH1885 was absorbed from ileum, duodenum, and jejunum of rat, however, YH1885 was under the detection limit in plasma when the drug was instilled into the rat stomach and large intestine. After iv administration of YH1885, 5–20 mg kg⁻¹, to dogs, the pharmacokinetic parameters of YH1885 also seemed to be independent of the drug at the dose ranges studied. However, after oral administration of YH1885, 0.5 and 2 g per whole body weight, to dogs, the AUC_{0–10 h} values were not significantly different (96.8 versus 98.2 μg · min mL⁻¹) and this could be due to the poor water-solubility of the drug. YH1885 was not detected in the urine after both iv and oral administration of the drug to both rats and dogs. Copyright © 1998 John Wiley & Sons, Ltd.     

NASAL ADMINISTRATION OF MORPHINE-6-GLUCURONIDE IN SHEEP—A PHARMACOKINETIC STUDY

The pharmacokinetics of morphine-6-glucuronide (M6G) after both intravenous dosing and nasal administration were studied in sheep. The nasal formulation consisted of M6G in combination with an absorption promoting delivery system in the form of chitosan. The mean half-life of M6G after intravenous administration was 51·0±8·2 min and that after intranasal dosing was 45·0±5·5 min. M6G clearance and volume of distribution were 5·4±1·5 mL min^±1 kg^±1 and 0·4±0·1 L kg^±1 respectively. The plasma profile after nasal administration demonstrated rapid absorption of M6G. The bioavailability of M6G in the chitosan formulation was found to be 31·4%. These results suggest that M6G administered in combination with the chitosan delivery system may be considered as a suitable non-parenteral means of administering this analgesic.     

Pharmacokinetics and Cardiovascular Effects of YM-21095, a Novel Renin Inhibitor,in Dogs and Monkeys

Abstract— The pharmacokinetics and cardiovascular effects of YM-21095 ((2 RS), (3S)-3-[N^α-[1,4-dioxo-4-morpholino-2-(1-naphthylmethyl)-butyl]-l-histidylamino]-4-cyclohexyl-1-[(1-methyl-5-tetrazolyl)thio]-2-butanol), a potent renin inhibitor, have been studied in beagle dogs and squirrel monkeys. Plasma levels of YM-21095 after 3 mg kg^?1 intravenous dosing to dogs declined biphasically and fitted a two-compartment model. Kinetics were as follows: t½α = 4·9±0·2 min, t½β = 2·76±0·79 h, Vd_ss = 3·86±1·04 L kg^?1, plasma clearance = 2·22 ± 0·39 L kg^?1, and AUC= 1445 ± 266 ng h mL^?1. After 30 mg kg^?1 oral dose, maximum plasma concentration, t_max and AUC of YM-21095 were 28·8 ± 9·6 ng mL^?1, 0·25 h and 23·6 ± 7·7 ng h mL^?1, respectively. Systemic bioavailability as determined on the basis of the ratio of AUC after intravenous and oral dose was 0·16 ± 0·04%. In conscious, sodium-depleted monkeys, YM-21095 at an oral dose of 30 mg kg^?1 lowered systolic blood pressure and inhibited plasma renin activity without affecting heart rate and plasma aldosterone concentration. Maximum plasma concentration of YM-21095 after 30 mg kg^?1 oral dose to monkeys was 71·8 ± 41·5 ng mL^?1, which was reached 0·5 h after the dose. At equihypotensive doses, captopril and nicardipine increased plasma renin activity markedly and slightly, respectively. These results suggest that oral absorption of YM-21095 is low in dogs and monkeys, and YM-21095 shows a blood pressure lowering effect by inhibiting plasma renin activity in sodium-depleted monkeys.     

Animal pharmacokinetics of inogatran,a low-molecular-weight thrombin inhibitor with potential use as an antithrombotic drug

Pharmacokinetics, excretion, and metabolism of inogatran, a low-molecular-weight thrombin inhibitor, were studied in the rat, dog, and cynomolgus monkey. After intravenous administration the half-life was short in all three animal species, due to a small volume of distribution and a relatively high clearance. At doses of 0.1–5 μmol kg⁻¹, the mean residence time was about 10 min in the rat, 35 min in the dog, and 20 min in the cynomolgus monkey. The oral bioavailability of inogatran was incomplete, presumably due to a low membrane permeability, and dose dependent. The bioavailability was 4.8% at 20 μmol kg⁻¹ and 32–51% at 500 μmol kg⁻¹ in rats, 14% at 10 μmol kg⁻¹ and 34–44% at 150 μmol kg⁻¹ in dogs, and 2.1% at 1 μmol kg⁻¹ in cynomolgus monkeys. The radioactivity excreted in urine and faeces was predominantly unchanged inogatran. After intravenous administration the percentage of the radioactivity recovered in faeces was about equal to or higher than the urinary recovery, which indicates biliary excretion of inogatran. After oral dosing, most of the dose was excreted in faeces, as expected from the estimates of oral bioavailability. The plasma protein binding of inogatran in rat, dog, and human plasma, was 20–28%. The blood–plasma concentration ratio was 0.39–0.56, indicating limited distribution into red blood cells. © 1998 John Wiley & Sons, Ltd.     

RENAL,BILIARY AND INTESTINAL CLEARANCE OF SOTALOL ENANTIOMERS IN RAT MODEL: EVIDENCE OF INTESTINAL EXSORPTION

Biliary clearance (Cl_b ) of sotalol (STL) enantiomers was assessed in anaesthetized Sprague–Dawley rats (419±9 g, mean±SEM, n=4) following administration of a 10 mg kg⁻¹ IV dose of the racemate. Cl_b for S- and R-STL (0·0675±0·0090 and 0·0662±0·0089 mL min⁻¹ kg⁻¹, respectively) represented approximately 0·3% of systemic clearance (Cl_s ) values for S- and R-STL (20·4±2·2 and 20·7±2·0 mL min⁻¹ kg⁻¹, respectively). Bile:plasma concentration ratios at 1, 2, and 3 h post-dose were approximately 1·4, 1·3, and 1·2 for both STL enantiomers. Renal clearance (Cl_r ) and intestinal clearance (Cl_i ) of STL enantiomers were assessed in conscious Sprague–Dawley rats (325 g, n=4) following administration of a 10 mg kg⁻¹ IV dose of the racemate. STL enantiomers were predominantly eliminated intact in the urine: Cl_r for S- and R-STL (26·3±3·2 and 28·7±4·2 mL min⁻¹ kg⁻¹, respectively) accounted for approximately 96% of Cl_s for S- and R-STL (27·5±3·3 and 29·9±4·2 mL min⁻¹ kg⁻¹, respectively). Approximately 4% of the dose was recovered in the faeces, corresponding to Cl_i values of 1·16±0·17 and 1·26±0·19 mL min⁻¹ kg⁻¹ for S- and R-STL, respectively. Total recovery of the administered dose in urine and faeces was 99·7±0·2 and 99·8±0·5% for S- and R-STL, respectively. It is concluded from these results in the rat model that (i) STL enantiomers are predominantly eliminated intact in urine; (ii) STL enantiomers are excreted intact in bile, and to a much larger extent in the faeces, thus suggesting the presence of intestinal exsorption of STL; (iii) STL does not appear to be metabolized; and (iv) Cl_s , Cl_r , Cl_b , and Cl_i are negligibly stereoselective.     

Pharmacokinetics and Absolute Bioavailability of Cyclosporin Following Intravenous and Abomasal Administration to Sheep

Abstract— Cyclosporin A pharmacokinetics were studied following intravenous and abomasal dosing in an open, crossover study in healthy, merino ewes. Five different doses of cyclosporin A were dispersed in milk and administered into the abomasum through a surgically inserted fistula which simulates oral administration. Cyclosporin A was well tolerated. Whole blood concentrations of cyclosporin A were measured by HPLC and mean clearance (0·45 ± 0·05 L h^?1 kg^?1), distribution volume (4·4 ± 2·0 L kg^?1), mean residence time (9·6 ± 4·1 h) and half-life (12·1 ± 3·1 h) were calculated. Negligible cyclosporin A was excreted in urine or bile. Area under the curve increased proportionally with doses up to 26·3 mg kg^?1, but was curvilinear above this dose. Abomasal bioavailability at 6·4 mg kg^?1 was 0·26 ± 0·09, and mean absorption time was 4·7 ± 11·1 h. Considerable pharmacokinetic variability was observed, particularly after abomasal administration. Cyclosporin A pharmacokinetics in sheep lie within the values reported in man after renal, bone marrow and cardiac transplantation.     

Pharmacokinetics and bioavailability of oral ergometrine in male volunteers

The aim of this investigation was to assess the pharmacokinetics and bioavailability of ergometrine in six human male subjects after an oral dose of 0·200 mg and after an intravenous dose of 0·075 mg of ergometrine maleate. A large variation in bioavailability of between 34% and 117% in the six volunteers was observed. The lag time was also subject dependent and ranged between 0·0073 h (0.4 mm) and 0·47 h (28 min). After intravenous administration, the pharmacokinetic profile can be described by a twocompartment model. The distribution half-life t_1/2α is 0·18 ± 0·20 h, the elimination half-life t_1/2β is 2·0 ± 0·90 h, the total body clearance (CL) amounts to 35·9 ± 13·41 h^?1 and the steady-state volume (V_ss) of distribution is 73·4 ± 22·01. After oral administration, the pharmacokinetic profile can be described by a one-compartment model. The absorption half-life t_1/2abs is 0·19 ± 0·22 h, and the elimination half-life t_1/2β 1·90 ± 0·16 h. This study with oral ergometrine shows such a large interindividual variability in bioavailability that the oral route of administration does not seem not to be the most reliable means of accurate dosing in preventing post-partum haemorrhage.     

PHARMACOKINETICS OF SUPEROXIDE DISMUTASE IN RATS AFTER ORAL ADMINISTRATION

The kinetic behaviour of bovine erythrocyte Cu--Zn SOD was investigated in Sprague Dawley male rats after subcutaneous and oral administrations of doses ranging from 0·5 to 20 mg kg⁻¹. Studies have been carried out with SOD and SOD encapsulated into liposomes containing or not containing ceramides. The maximum concentration (C_max) in blood cell pellets ranged from 8·65 to 11·03 U/mg haemoglobin (Hb) after subcutaneous injection, and from 4·48 to 8·23 U/mg Hb after oral administration. The maximum concentrations were reached in 5 h (t _max) for the two routes. Comparison between the areas under the curves (AUCs) obtained after subcutaneous and oral administration allowed the calculation of relative bioavailability (F ′). The maximum bioavailability after oral administration was 14% for free SOD, 22% for SOD encapsulated into liposomes, and 57% when ceramides were added to liposomes. Poor SOD bioavailability was enhanced by liposome encapsulation, and ceramide addition seemed to be beneficial for oral encapsulated SOD administration.     

COMPARISON OF PHARMACOKINETICS OF M1, M2, M3, AND M4 AFTER INTRAVENOUS ADMINISTRATION OF DA-125 OR ME2303 TO MICE AND RATS. NEW ADRIAMYCIN ANALOGUES CONTAINING FLUORINE

The pharmacokinetics of M1, M2, M3, and/or M4 were compared after intravenous (iv) administration of DA-125 and/or ME2303 to mice (25 mg kg⁻¹) and rats (5, 10, 20, 30, and 40 mg kg⁻¹). The mean plasma concentrations of M1 were detected up to 8 h after iv administration of both DA-125 and ME2303 to mice, and were significantly higher for DA-125 than ME2303; this resulted in a considerably greater AUC (303 against 148 μg min mL⁻¹) and a considerably slower CL of M1 (69·3 against 136 mL min⁻¹ kg⁻¹) after iv administration of DA-125. The MRT (371 against 189 min) and CL_NR of M1 (68·7 against 136 mL min⁻¹ kg⁻¹) were considerably greater and slower, respectively, after iv administration of DA-125. The mean plasma concentrations of M2 were detected up to 8 and 4 h after iv administration of DA-125 and ME2303, respectively, to mice and were significantly higher for DA-125 than ME2303, resulting in a considerably greater AUC of M2 (148 against 27·1 μg min mL⁻¹) after iv administration of DA-125. The mean plasma concentrations of M3, being the lowest among M1–M4, were detected only up to 15 min after iv administration of both DA-125 and ME2303 to mice, and were comparable after iv adminstration of DA-125 and ME2303 to mice. The mean plasma concentrations of M4 were detected up to 8 h after iv administration of both DA-125 and ME2303 to mice, and were higher after iv administration of DA-125 than ME2303, resulting in a considerably greater AUC of M4 (197 against 61·9 μg min mL⁻¹) after iv administration of DA-125. Similar results on M1 and M2 were also obtained from rats: the mean plasma concentrations of both M1 and M2 were significantly higher after iv administration of DA-125, 10 mg kg⁻¹, than after ME2303. The plasma concentrations of M1, M2, and M4, and hence their AUCs, were significantly higher after iv administration of DA-125, 5, 10, 20, 30, and 40 mg kg⁻¹, to rats than after ME2303: the mean plasma concentrations of M2, approximately 0·1–0·4 μg mL⁻¹, were maintained from 30 min to 8–10 h after iv administration of DA-125, 20, 30, and 40 mg kg⁻¹, to rats; the plasma concentrations of M3 were the lowest among M1–M4 at all DA-125 doses; and those of M1 and M4 were maintained for a long period of time. However, after iv administration of M2, 5 mg kg⁻¹, to rats, the mean plasma concentrations of M2 were detected up to 60 min with a mean terminal half-life of only 38·8 min, and the concentrations of M3 were negligible. After iv administration of M3, 5 mg kg⁻¹, to rats, the mean plasma concentrations of M3 were detected up to 15 min; the plasma concentrations of M4, reaching their peak at 5 min, decayed more slowly and were higher than those of M3. The AUC of M4 after iv administration of M3, 5 mg kg⁻¹, was comparable to that after iv administration of M4, 5 mg kg⁻¹, to rats, suggesting that M4 is formed fast and almost completely from M3. M1 was not detected in plasma after iv administration of either M2 or M3 to rats. After iv administration of M4, 5 mg kg⁻¹, to rats, the mean plasma concentrations of M4 decayed fast with a mean terminal half-life of 43·9 min and neither M2 nor M3 were detected in plasma. The following disposition mechanisms for M1, M2, M3, and M4 after iv administration of DA-125 to rats could be obtained from the above data: (i) the maintenance of plasma concentrations of M2 for a longer period of time after iv administration of DA-125 than those after iv administration of M2 could be due to the continuous formation of M2 from M1; (ii) the lowest plasma concentrations of M3 among M1–M4 after iv administration of DA-125 could be due to the fast and almost complete formation of M4 from M3 as soon as M3 is formed from M1, and not due to the fast renal excretion of unchanged M3; (iii) M4 was exclusively and continuously formed from M3 and the formation of M4 from M2 was negligible; and (iv) reversible metabolism among M1–M4 did not take place. The following results could also be obtained after iv administration of DA-125 or ME2303 to mice and rats: (i) the lower plasma concentrations of M1 after iv administration of ME2303 than of DA-125 could be due to the greater biliary excretion of unchanged ME2303 (approximately 30% of iv dose) than unchanged DA-125 and (ii) the lower plasma concentrations of M2 and M4 after iv administration of ME2303 than after DA-125 could be due to lower plasma concentrations of M1 and hence less formation of both M2 and M4 from M1. Liver showed the highest metabolic activity for M1 and a considerable amount of M1 was also metabolized in the kidney after 30 min incubation of 50 μg of DA-125 in 9000 g supernatant fraction of rat tissue homogenates. The mean amount of M1 remaining per gram of tissue, the total amount of M1 remaining in whole tissue, and the tissue to plasma ratio of M1 were significantly higher in the heart, lung, large intestine, and kidney at 15 min after iv administration of DA-125, 25 mg kg⁻¹, to mice than after ME2303. M1, the active antineoplastic moiety of DA-125, had higher affinity for the lung after iv administration of DA-125 to mice than after ME2303, indicating that lung tumours could be subjected to a greater exposure to M1 after iv administration of DA-125 than ME2303. The 24 h biliary excretion of M1 was significantly greater after the iv administration of ME2303 than after DA-125 (344 against 79·3 μg). However, reversed results were obtained for M2 (267 against 467 μg). M3 and M4 were under the detection limit in the bile sample after iv administration of either DA-125 or ME2303.     

THE EFFECT OF EXPERIMENTAL RENAL FAILURE ON TOLFENAMIC ACID DISPOSITION IN THE DOG

The pharmacokinetic disposition of tolfenamic acid, an NSAID, after a single administration of tolfenamic acid (4 mg kg⁻¹) by the intravenous (IV) route was compared in eight dogs before and after a surgically induced renal failure. Renal impairment was confirmed by a significant increase ( p <0·001) of water intake, urine volume, and urea and creatinine plasma concentration. PAH and inulin clearances decreased after surgery from 15·2±4·2 to 9·5±0·8 mL kg⁻¹ min⁻¹ ( p <0·05) and from 4·37±1·15 to 2·43±0·88 mL kg⁻¹ min⁻¹ ( p =0·067), respectively. After surgery, clearance of TA was significantly ( p <0·001) increased, from 2·22±1·68 to 3·59±1·81 mL kg⁻¹ min⁻¹. There was no modification of the steady-state volume of distribution ( p >0·05) and the mean residence time was significantly decreased from 606±199 to 373±302 min ( p <0·05). No variation of binding to plasma proteins (<99%) was observed. These results suggest that renal insufficiency could increase hepatic metabolism and/or alter the enterohepatic cycle of TA. © 1997 by John Wiley & Sons, Ltd.     

PHARMACOKINETICS AND SAFETY OF SINGLE INTRAVENOUS AND ORAL DOSES OF DOLASETRON MESYLATE IN HEALTHY WOMEN

Twenty-four healthy women received 2·4 mg kg⁻¹ dolasetron mesylate (1·8 mg kg⁻¹ dolasetron base) by a 10 min intravenous administration and by oral administration. Pharmacokinetics of dolasetron and of its active reduced metabolite MDL 74 156 were monitored for 48 h in plasma. Urine was collected from 0 to 48 h, blood pressure and heart rate were measured at 0, 0·08, 1, 2, 12, 24, and 36 h, and ECGs were measured at 0, 0·08 (intravenous only), 1, 2, and 36 h after dosing. Dolasetron was widely distributed and rapidly reduced (mean t_1/2=0·23 h) to MDL 74 156 (mean t_1/2=8·05 and 9·12 h after intravenous and oral administration respectively). MDL 74 156 was extensively distributed; between 27 (oral route) and 33% (intravenous route) was eliminated unchanged in urine. Safety assessment showed mild to moderate headache, dizziness, and hot flushes after the intravenous administration and headache, abdominal cramps or pain, and constipation after oral administration. Small and clinically non-significant changes in PR, QRS, and QT_c intervals were observed. We conclude that there is no obvious difference in dolasetron pharmacokinetics between healthy women and men and that dolasetron can be used as safely in women as in men. ©1997 by John Wiley & Sons, Ltd.     

Pharmacokinetic and Pharmacodynamic Aspects of Artelinic Acid in Rodents

Abstract— The efficacy of artelinic acid and artemisinin, orally administered at 10 and 50 mg kg^?1 day^?1, was compared in Plasmodium berghei infected mice. Subsequently, the pharmacokinetics of artelinic acid after intravenous, intramuscular, oral and rectal administration of a 20 mg kg^?1 aqueous solution to rabbits were studied in a four-way randomized cross-over experiment. After intravenous administration, artelinic acid concentrations in blood plasma were high (C₀: 76 ± 15 mg L^?1), and the drug was rapidly eliminated from the central compartment, showing linear elimination kinetics with an elimination half-life of 15 ± 3 min. A large inter-subject variation appeared in the absorption rate and the extent of absorption (2–92%) over the 120 min interval after intramuscular administration. Also, a large inter-subject variation in individual rectal bioavailability (17–100%) was shown, which was dependent on the site of absorption in the rectum. The estimated oral bioavailability was low (4·6 ± 1·7%), probably due to a high first-pass effect and possible decomposition in the acidic gastric environment.     

Pharmacokinetics and tissue disposition of danofloxacin in sheep

The plasma pharmacokinetics of danofloxacin administered at 1.25 mg kg⁻¹ body weight by the intravenous and intramuscular routes were determined in sheep. Tissue distribution was also determined following administration by the intramuscular route at 1.25 mg kg⁻¹ body weight. Danofloxacin had a large volume of distribution at steady state (V_ss) of 2.76±0.16 h (mean±S.E.M.) L kg⁻¹, an elimination half-life (t_1/2β) of 3.35±0.23 h, and a body clearance (C1) of 0.63±0.04 L kg⁻¹ h⁻¹. Following intramuscular administration it achieved a maximum concentration (C_max) of 0.32±0.02 μg mL⁻¹ at 1.23±0.34 h (t_max) and had a mean residence time (MRT) of 5.45±0.19 h. Danofloxacin had an absolute bioavailability (F) of 95.71±4.41% and a mean absorption time (MAT) of 0.81±0.20 h following intramuscular administration. Mean plasma concentrations of >0.06 μg mL⁻¹ were maintained for more than 8 h following intravenous and intramuscular administration. Following intramuscular administration highest concentrations were measured in plasma (0.43±0.04 μg mL⁻¹), lung (1.51±0.18 μg g⁻¹), and interdigital skin (0.64±0.18 μg g⁻¹) at 1 h, duodenal contents (0.81±0.40 μg mL⁻¹), lymph nodes (4.61±0.35 μg g⁻¹), and brain (0.06±0.00 μg mL⁻¹) at 2 h, jejunal (10.50±4.31 μg mL⁻¹) and ileal (5.25±1.67 μg mL⁻¹) contents at 4 h, and colonic contents (8.94±0.65 μg mL⁻¹) at 8 h. © 1998 John Wiley & Sons, Ltd.     

In vitro and in vivo α-blocking activity of thymoxamine and its two metabolites

The α-adrenoceptor potency of thymoxamine and its two metabolites deacetylthymoxamine and demethyldeacetylthymoxamine were determined on the contraction of rat vas deferens induced by noradrenaline, the blood pressure increase induced by noradrenaline given i.v. to dogs and the contraction of the nictitating membrane induced by electrical stimulation in cats. In vivo the three drugs were administered at 6·35 times 10^?6 mol kg^?1 intravenously. Deacetylthymoxamine presented nearly the same α-blocking activity as the parent drug. This was ascribed in vivo to the rapid deacetylation of thymoxamine. Demethyldeacetylthymoxamine was less active. In vitro its pA₂ was 6·20 ± 0·09 compared with 6·75 ± 0·20 for thymoxamine and 6·57 ±0·13 for deacetylthymoxamine. In vivo, it was inactive in dog and less active than the other two drugs soon after its administration in the cat. The oral LD 50 values in the mouse for the three drugs were respectively 0·81, 0·71 and 1·14 mmol kg^?1 for thymoxamine, deacetylthymoxamine and demethyldeacetylthymoxamine.     

Oral absorption of anti- AIDS nucleoside analogues. 3. Regional absorption and in vivo permeability of 2′, 3′ - dideoxyinosine in an intestinal–vascular access port (IVAP) dog model

The absolute oral and regional intestinal bioavailabilities (BAs) and pharmacokinetics (PK) of 2′, 3′-dideoxyinosine (ddI), a nucleoside analog used in the treatment of human immunodeficiency virus (HIV) infection, were investigated in an in vivo intestinal–vascular access port (IVAP) dog model. The mean (±SD) absolute regional intestinal BAs of ddI were 49·6±8·8, 42·7±7·9, and 13·6±5·4% after the bolus administration of unbuffered solutions containing 250 mg ddI into the duodenum, ileum, and colon of IVAP beagle dogs, respectively. The BA of the orally administered Videx^™ 250 mg buffered chewable tablets was 44·9±1·6%. ddI absorption and disposition PK were modeled by simultaneously fitting intravenous, oral, and intestinal plasma level versus time data using a physiologically based PK model. The region-specific apparent absorption rates followed the rank order duodenum>ileum>colon. Apparent regional in vivo intestinal permeabilities correlated well with previously determined regional permeabilities in rats. The intestinal pH was monitored using a radiotelemetric pH monitoring system since ddI is unstable in an acidic environment. While the pH was found to be lower in the duodenum and proximal jejunum (∼pH 6) than in the ileum or colon (pH≥7·0), ddI is reasonably stable across the entire pH range of the dog small intestine. These studies demonstrate that the regional reduction in ddI BA is consistent with a reported distal reduction in intestinal permeability and appears to be a significant contributing factor to the high degree of absorption variability reported for ddI. © 1997 John Wiley & Sons, Ltd.