THE PHARMACOKINETICS OF 1954U89, 1, 3-DIAMINO-7-(1-ETHYLPROPYL)-8-METHYL-7H-PYRROLO-(3, 2-f )QUINAZOLINE,IN DOGS AND RATS AFTER INTRAVENOUS AND ORAL ADMINISTRATION

1954U89, 1, 3-diamino-7-(1-ethylpropyl)-8-methyl-7H-pyrrolo-(3, 2-f )quinazoline, is a potent, lipid-soluble inhibitor of dihydrofolate reductase. The pharmacokinetics and bioavailability of 1954U89 were examined in male beagle dogs and male CD rats. Dogs received single intravenous (2·5 mg kg⁻¹) and oral (5·0 mg kg⁻¹) doses of 1954U89 with and without successive administration of calcium leucovorin. Single intravenous (5·0 mg kg⁻¹) and oral (10 mg kg⁻¹) doses of [1,3-¹⁴C₂]1954U89 were administered to rats. Plasma concentrations of total radiocarbon were determined by scintillation counting, and intact 1954U89 was measured by HPLC. The mean plasma half-life was 3·2 ± 0·62 and 4·2 ± 0·68 h after intravenous and oral administration, respectively, to dogs. The pooled plasma half-life after intravenous administration to rats averaged 1·2 h; a reliable plasma half-life value after oral administration could not be determined. Mean total-body clearance was 2·4 ± 0·39 and 4·5 ± 1·1 L h⁻¹ kg⁻¹ after intravenous and oral administration, respectively, to dogs, and averaged 12 and 77 L h⁻¹ kg⁻¹ after intravenous and oral administration, respectively, to rats. Neither clearance nor bioavailability of 1954U89 in dogs was affected significantly by administration of calcium leucovorin. Absolute bioavailability was 54 ± 12% in dogs and 16% in rats. © 1997 John Wiley & Sons, Ltd.     

COMPARATIVE ABSORPTION OF BISMUTH IN SPRAGUE–DAWLEY RATS FOLLOWING ORAL ADMINISTRATION OF PREPARATIONS CONTAINING BISMUTH SUCROSE OCTASULFATE,BISMUTH SUBSALICYLATE,AND BISMUTH SUBCITRATE

The absorption of bismuth from De-Nol (bismuth subcitrate, DN), Pepto-Bismol (bismuth subsalicylate, PB) and bismuth sucrose octasulfate (BISOS) was examined in male Sprague–Dawley rats after a single oral dose of each compound (60 mg bismuth). Bismuth was analysed in blood, urine, kidney, brain, liver, and lung using graphite furnace atomic absorption spectrophotometry. Bismuth C_max averaged 18·4±11·6 ng mL⁻¹ for BISOS, 292±130 ng mL⁻¹ for DN, and 21·5±9·63 ng mL⁻¹ for PB. C_max was significantly lower for BISOS compared to DN (p <0·05) but not significantly different for BISOS compared to PB (p >0·05). Bismuth AUC was 1356±474 ng h⁻¹ mL⁻¹ for BISOS, 2129−452 ng h⁻¹ mL⁻¹ for DN, and 1824−919 ng h⁻¹ mL⁻¹ for PB, which indicated a lower extent of absorption from BISOS compared to DN. Kidney, liver, and lung levels of bismuth were also significantly lower for BISOS compared to DN (p <0·05). Bismuth urinary excretion was significantly lower for BISOS (0·04±0·02%) compared to DN (0·27±0·15%) but not significantly different compared to PB (0·07±·03%). These data suggest that the absorption of bismuth following oral administration of bismuth sucrose octasulfate is significantly lower than that from De-Nol and similar to that from Pepto-Bismol. © 1997 by John Wiley & Sons, Ltd.     

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 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 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.     

Mass balance of 14C-bismuth sucrose octasulfate in Sprague-Dawley rats: evidence for dissociation of bismuth from sucrose octasulfate

The mass balance of ¹⁴C bismuth sucrose octasulfate (BISOS) was investigated in eight male Sprague–Dawley rats after single oral doses of 1·0 g kg⁻¹. Bismuth and radioactivity were monitored in blood, urine, and feces for up to 144 h post-dose, while kidneys, brain, liver, and lungs were assayed for bismuth at 144 h post-dose. In a separate experiment, bismuth was monitored in bile of bile-duct-cannulated animals for 48 h post-dose. Fecal excretion of bismuth averaged 95·8±5·30% bismuth dose, while 99·2±3·63% of the radiolabel was excreted in feces. Urinary excretion of bismuth averaged 0·051±0·028% bismuth dose, and 1·83±1·08% radioactive dose. Biliary excretion of bismuth averaged 0·0003±0·0006% bismuth dose, and 0·026±0·030% radiolabeled dose. An average 0·005±0·002% of the bismuth dose was present in kidney, liver, and lung. Bismuth levels in brain were below quantifiable limits. Though BISOS contains 57·3% by weight of bismuth, peak blood concentrations of bismuth were three orders of magnitude lower than for BISOS equivalents (C_max for BISOS averaged 110±55·4 μg eq mL⁻¹, while for bismuth it was 26·1±10·3 ng mL⁻¹). This data indicates that bismuth dissociates from sucrose octasulfate, probably during the absorption phase, and exhibits differential pharmacokinetic characteristics from sucrose octasulfate. The low biliary and urinary excretion of both bismuth and BISOS equivalents is indicative of low systemic absorption. Greater than 96% recovery in feces, bile, and urine indicates that mass balance was achieved following oral administration. © 1997 John Wiley & Sons, Ltd.     

THE EFFECT OF FOOD ON THE BIOAVAILABILITY OF IBUPROFEN AND FLURBIPROFEN FROM SUSTAINED RELEASE FORMULATIONS

The effect of food on the plasma concentration–time profile of sustained release dosage forms of ibuprofen and flurbiprofen has been investigated in healthy Asian Indian volunteers, in two separate studies. In study 1, 20 volunteers were administered a single 200 mg multiple-unit sustained release capsule of flurbiprofen (Froben SR^™), after an overnight fast or a heavy vegetarian breakfast. Food produced a statistically significant increase in the mean (±SE) maximal plasma concentration (C_max ) and area under the plasma concentration–time curve (AUC_0–48 . C_max (±SE) increased from 9·88± 0·48 mg L⁻¹ (fasting) to 11·36±0·88 mg L⁻¹ (postprandial) and AUC_0–48 (±SE) increased from 120·78±9·64 mg h L⁻¹ (fasting) to 149·73±12·24 mg h L⁻¹ (postprandial). The mean (±SE) time to peak (t_max ) was also significantly delayed from 3·85±0·27 h to 8·70±0·89 h. In study 2, 18 volunteers were administered a single 800 mg erodible sustained release matrix tablet of ibuprofen (Brufen Retard^™), after an overnight fast or along with a heavy vegetarian breakfast. The formulation exhibited multiple peaks (n≥2) on the plasma concentration–time curve. Although food did not affect the bioavailability of this formulation, there was a statistically significant increase in the mean (±SE) concentration of the first peak (C_peak1 ) from 14·21±1·38 mg L⁻¹ (fasting) to 20·14±1·38 mg L⁻¹ (with food). The time at which C_peak1 was reached was not influenced by the intake of food. Results indicate that while qualitative changes in the plasma concentration versus time curves are primarily influenced by the nature of the formulation and the type of meal, bioavailability is influenced by the absorption characteristics of the drug as well. Thus, despite a significant increase in peak plasma concentrations of both drugs with a meal, the bioavailability of flurbiprofen alone was enhanced.     

A LIMITED SAMPLING METHOD FOR THE ESTIMATION OF FLUNARIZINE AREA UNDER THE CURVE (AUC) AND MAXIMUM PLASMA CONCENTRATION (CMAX)

A limited sampling model has been developed for flunarizine following a 30 mg oral dose in epileptic patients who were receiving phenytoin or carbamazepine or both, to estimate the area under the curve (AUC) and maximum plasma concentration (C_max). The model was developed using training data sets from 30, 20, 15, or 10 patients at one or two time points. The equations describing the models for AUC using two time points (3 and 24 h) and C_max for the training data set of 30 subjects were AUC_predicted=11·1 C_{3 h}+121·4 C_{24 h}–157 (r =0·80) C_{max(predicted)}=0·036 AUC+42·9 (r =0·74) The model was validated on 64 patients who received flunarizine orally. The model provided reasonably good estimates for both AUC and C_max. The mean predicted AUC of flunarizine was 1230±717 ng h mL⁻¹, whereas the observed AUC was 1203±900 ng h mL⁻¹. The bias of the prediction was 2% and precision was 28%. The mean predicted C_max of flunarizine was 86±32 ng mL⁻¹ as compared to an observed mean C_max of 90±42 ng mL⁻¹. The bias and precision of the prediction were 4% and 24%, respectively. The method described here may be used to estimate AUC and C_max for flunarizine without detailed pharmacokinetic studies. © 1997 by John Wiley & Sons, Ltd.     

Effect of addition of hyaluronic acid to highly concentrated insulin on absorption from the conjunctiva in conscious diabetic dogs

Abstract— Insulin absorption from the conjunctiva was investigated in five pancreatectomized diabetic mongrel dogs, with the nasolacrimal ducts occluded by micro plugs to prevent insulin absorption from nasolacrimal membrane. In the anaesthetized state, highly concentrated porcine insulin (1000 units mL^?1, pH7·4) was absorbed rapidly and significantly from the conjunctiva. Plasma immunoreactive insulin concentrations increased significantly up to 3 h after insulin administration to conjunctival membranes. Plasma glucose concentration decreased significantly compared with saline control experiments after insulin administration (10 units kg^?1) at 3 h (8·3 ± 0·1 vs 15·6 ± 0·6 mmol, P < 0·01). However, in the conscious state, there was no significant increase in the plasma insulin levels after topical insulin administration. To improve insulin absorption in the conscious state, we examined the effect of increasing viscosity of insulin preparation with hyaluronic acid. In anaesthetized experiments, there were no significant changes in the bioavailability of insulin after addition of hyaluronate (0·84 ± 0·11 vs 0·87 ± 0·05%). In the conscious state, with addition of hyaluronic acid, the area under the curve of plasma insulin concentration was significantly increased (1842 ± 383 vs 75 ± 24 m units min L^?1, P < 0·01). The bioavailability of insulin absorption was significantly increased after addition of hyaluronate (0·68 ± 0·14 vs 0·03 ± 0·01%, P < 0·01). From this study we could demonstrate that the conjunctiva is a potential route for insulin administration, and increased viscosity by the addition of hyaluronate was found effective in increasing the bioavailability of insulin absorption from conjunctival membrane in the conscious state.     

Pharmacokinetics and bioavailability of montelukast sodium (MK-0476) in healthy young and elderly volunteers

A study was conducted to (i) characterize the multiple-dose pharmacokinetics of oral montelukast sodium (MK-0476), 10 mg d⁻¹ in healthy young subjects (N =12), (ii) evaluate the pharmacokinetics of montelukast in healthy elderly subjects (N =12), and (iii) compare the pharmacokinetics and oral bioavailability of montelukast between elderly and young subjects. Following oral administration of montelukast sodium, 10 mg d⁻¹ (the therapeutic regimen for montelukast sodium) for 7 d, there was little difference in the plasma concentration–time profiles of montelukast in young subjects between day 1 and day 7 dosing. On average, trough plasma concentrations of montelukast were nearly constant, ranging from 18 to 24 ng mL⁻¹ on days 3–7, indicating that the steady state of montelukast was attained on day 2. The mean accumulation ratio was 1·14, indicating that this dose regimen results in a 14% accumulation of montelukast. In elderly subjects, mean values of plasma clearance (Cl), steady-state volume of distribution (V_ss), plasma terminal half-life (t_1/2), and mean residence time in the body (MRT^IV) following a 7 mg intravenous (5 min infusion) administration of montelukast sodium in the elderly were 30·8 mL min⁻¹, 9·7 L, 6·7 h, and 5·4 h, respectively. Following a 10 mg oral dose, the bioavailability of montelukast in healthy elderly averaged 61%, very close to that (62%) determined previously in healthy young subjects. Also following the 10 mg oral administration, the mean values of AUC_0→∞, C_max, t_max, and t_1/2, and the mean plasma concentration–time profile of montelukast in the elderly, were generally similar to those in young subjects, indicating that age has little or no effect on the pharmacokinetics of montelukast. There is no need to modify dosage as a function of age. © 1997 John Wiley & Sons, Ltd.     

PHARMACOKINETICS AND HAEMATOLOGICAL PARAMETERS OF RECOMBINANT HUMAN ERYTHROPOIETIN AFTER SUBCUTANEOUS ADMINISTRATIONS IN HORSES

The pharmacokinetics of recombinant human Epo (rHuEpo) were investigated after subcutaneous administration to horses. Four horses received a single 30 IU kg⁻¹ dose of rHuEpo. One horse received three repeated doses of 120 IU kg⁻¹ at 48 h intervals. Plasma erythropoietin (Epo) was measured by radioimmunoassay. In both cases pharmacokinetic parameters were evaluated using a one-compartment open model and first-order input and output rates. The mean values (±SD) for elimination half-life, CL/F, and V_d/F after a single dose were 12·9±3·34 h, 11·8±4·96 L h⁻¹, and 233±126 L, respectively. After repeated doses, elimination half-life, CL/F, and V_dss/F were 11·3 h, 8·94 L h⁻¹, and 145·6 L, respectively. No significant differences were observed between the haematological parameters after a single 30 IU kg⁻¹ administration compared to baseline values. Multiple and high doses of rHuEpo modified red blood cells, haemoglobin, and hematocrit. According to our results, plasma Epo assay can help, during an antidoping control procedure, to support a positive result only up to 72 h after the last rHuEpo     

Effects of Ageing on the Oral Absorption of D-Xylose in Rats

The effects of ageing on the oral absorption of d -xylose were investigated in rats. The pharmacokinetic analysis of d -xylose concentration in plasma after oral administration showed that the fraction absorbed was increased to 0·998 ± 0·002 and 0·950 ± 0·049, respectively, in old (52 weeks) and very old (102 weeks) rats, compared with 0·768 ± 0·052 in young (9 weeks) rats, while the absorption rate constant was not significantly changed: 0·944 ± 0·233, 0·844 ± 0·143 and 0·725 ± 0·004 h^?1, respectively, in young, old and very old rats. The absorbed fractions estimated from faecal and urinary excretion were in agreement with those by the pharmacokinetic analysis. Thus, the present study demonstrated an increase in the extent of the oral absorption of d -xylose with ageing. The increase in the extent of absorption might be caused by a delay in the intestinal transit, because the absorption rate constant was unchanged. These results suggest potential increases with ageing in the fractions absorbed of hydrophilic drugs such as d -xylose where oral absorption is incomplete.     

AN INVESTIGATION OF THE DOSE PROPORTIONALITY OF DEFLAZACORT PHARMACOKINETICS

The dose proportionality of deflazacort was assessed following single-dose oral administration at doses of 3, 6, and 36 mg to 24 healthy young adult volunteers. The active metabolite of deflazacort (21-desacetyl deflazacort) was monitored in plasma using a sensitive, semi-microbore liquid chromatographic method. C_max averaged 10·4±5·0, 19·8±7·5, and 132·6±52·5 ng mL⁻¹ for the 3, 6, and 36 mg doses, respectively. AUC(0–∞) averaged 38·5±37·1, 64·9±20·8, and 411·7±148·5 ng h mL⁻¹ for the same three doses, respectively. Elimination half-life ranged from 1·9±0·5 h at the 6 mg dose to 2·4±1·5 h at the 36 mg dose. Regression analyses of dose versus C_max and AUC(0–∞) yielded intercepts which were not significantly different from zero (p>0·05) and slopes which were significant (p<0·05). Regression analysis of dose versus apparent oral clearance yielded a slope which was not significantly different from zero (p>0·05). These data indicate that deflazacort exhibits dose-proportional pharmacokinetics.     

Pharmacokinetic analysis and antiepileptic activity of two new isomers of N-valproyl glycinamide

Valproyl glycinamide (TV 1901-VPGD) is a new antiepileptic drug, which is currently undergoing clinical trials. The present study explored the pharmacokinetics and pharmacodynamics (anticonvulsant activity and neurotoxicity) of two new isomers of valproyl glycinamide: valnoctyl glycinamide (VCGD) and diisopropylacetyl (DIGD). Both VCGD and DIGD showed anticonvulsant activity and a safety margin in mice similar to those of VPGD. Following iv administration (556 mg) to six dogs, VCGD had a clearance (Cl) value of 3·8±1·1 L h⁻¹ (mean±SD), a volume of distribution (V_ss) of 15±2 L, and a half-life (t_1/2) of 1·9±0·3 h. DIGD had Cl, V_ss, and t_1/2 values of 10±0·8 L h⁻¹, 19±3 L, and 1·6±0·2 h, respectively. Neither VCGD nor DIGD operated as chemical drug delivery systems (CDDSs) of glycine, valnoctic acid, or diisopropyl acetic acid and both showed antiepileptic profiles different from that of valproic acid (VPA). Both glycinamides were biotransformed to their glycine analogues with similar fractions metabolized ( f_m): 59±5% (VCGD) and 62±15% (DIGD). The two glycine metabolites, valnoctyl glycine (VCGA) and diisopropylacetyl glycine (DIGA), were also administered to the same dogs in order to calculate the above f_m values. Both VCGA and DIGA had higher Cl and lower V_ss values than VCGD and DIGD and therefore their mean t_1/2 values were 0·43±0·02 and 0·30±0·07 h, respectively. VCGA and DIGA were excreted mainly intact in the urine, with fractions excreted unchanged ( f_e) of 60±9 and 55±7%, respectively. The improved pharmacokinetic profile of VCGD and DIGD relative to their glycine analogues may explain the similarity of their anticonvulsant activity to that of valproyl glycinamide. The current study demonstrates the benefit of the structure–pharmacokinetic–pharmacodynamic relationship (SPPR) approach in developing and selecting a potent antiepileptic compound in intact animals based not only on its intrinsic pharmacodynamic activity but also on its improved pharmacokinetic profile. © 1997 John Wiley & Sons, Ltd.     

PHARMACOKINETIC–PHARMACODYNAMIC MODELLING FOR CAPTOPRIL IN HEALTHY ANAESTHETIZED PIGLETS

The use of the angiotensin converting enzyme inhibitor, captopril, specially in children, has been empirical. This is because the relationship between the pharmacokinetics and pharmacodynamics of captopril has not been clearly defined. It is not usually feasible to obtain the serial kinetic–dynamic data necessary to study this relationship in infants. The piglet was therefore investigated as an animal model in which to study the relationship between the kinetics and dynamics of captopril. The standard pharmacokinetic parameters for captopril in healthy anaesthetized piglets were found to be within the range reported for humans. Cl_TB was estimated to be 1·42±0·33 L h⁻¹ kg⁻¹; t_1/2 was 0·44±0·08 h; V_dss was calculated to be 0·64±0·13 L kg⁻¹; t_1/2 and AUC_0–∞ was estimated to be 145±27 ng h mL⁻¹. The observed haemodynamic response was qualitatively similar to that in humans. Aortic pressure was reduced by 42±18%; heart rate was reduced by 21±11%. A parametric pharmacokinetic (two-compartment)–pharmacodynamic (linear) model has been established to describe plasma captopril concentration and aortic pressure relationship. Based on the observed results, the piglet was considered to be a viable model for our purpose.     

Pharmacokinetics of the 5-hydroxytryptamine1A agonist 8-hydroxy-2-(N,N-di-n-propylamino)tetralin (8-OHDPAT) in the rat after intravenous and oral administration

1. Plasma levels of ³H and unchanged drug were measured in the non-anaesthetized male rat after intravenous (i.v.) or oral administration of (±)-(R,S)-[propyl-³H]-8-OHD-PAT, at three dose levels per route of administration. The excretion of conjugated metabolites in bile was also studied following i.v. administration.

2. For unchanged 8-OHDPAT following i.v. administration, terminal t_1/2 was 1.56 ± 0.01?h (mean ± SD, n±4), k_elim 0.45 ± 0.01 h^?1, volume of distribution 0.14 ± 0.02 litres and clearance 1.10 ± 0.17 ml min^?1. After oral administration, terminal t_1/2, k_elim apparent volume of distribution and clearance were essentially the same when bioavailability was taken into account. Neither dose size nor route of administration had any significant effect on either terminal t_1/2 or k_elim. Comparison of AUCs following i.v. and oral administration yielded a mean for absolute oral bioavailabiltty of 2.60 ± 0.24%.

3. Comparison of AUCs for total plasma ³H showed that the extent of absorption was 80.1%, indicating that the low oral bioavailability of 8-OHDPAT is due to first-pass metabolism, rather than poor absorption from the GI tract.

4. Following i.v. administration, irrespective of dose, some 10% of the ³H dose was excreted in the bile in 6h, 8.5% as 8-OHDPAT-glucuronide and 1.5% as the glucuronide of the N-despropylated metabolite, 8-OHDPAT. The majority of the biliary excretion occurred within 3?h of dosing.     

间尼索地平控释微丸Beagle犬体内药动学研究

目的建立间尼索地平血药浓度的高效液相色谱-质谱联用方法,研究Beagle犬单剂量口服间尼索地平控释微丸的药动学。方法用HPLC-MS法测定健康Beagle犬单剂量口服间尼索地平控释微丸和普通微丸的血药浓度,以DAS 2.0软件计算药动学参数。结果单剂量给药后,控释微丸和普通微丸的tmax分别为(11.154±0.5077)h和(2.213±0.3225)h,Cmax分别为(79.40±10.60)ng.mL1和(116.7±20.35)ng.mL1,AUC分别为(1227.8±296.0)ng.h.mL1和(867.8±146.7)ng.h.mL1,控释微丸的相对生物利用度为141.5%。结论本方法准确、灵敏,间尼索地平控释微丸血药浓度平稳,可较长时间保持血药浓度。     

咪达唑仑片在中国维吾尔族和汉族健康人体的药动学比较

目的研究健康维吾尔族和汉族志愿者单剂量口服咪达唑仑片的药动学。方法维吾尔族、汉族健康志愿者各10名,男、女各半,单剂量口服15 mg咪达唑仑片后,用HPLC法测定咪达唑仑的血浆浓度,运用DAS 2.0程序以非室模型拟合药动学参数,并对药动学参数进行独立样本t检验和非参数Mann-Whitney U test检验,以判断药动学是否存在显著性的民族差异。结果单剂量口服15 mg咪达唑仑片后,维吾尔族志愿者的主要药动学参数分别为:ρmax(124.8±50.0)μg.L-1,tmax(0.8±0.5)h,t1/2z(1.9±0.7)h,MRT0-12 h(2.8±0.8)h,CL/F(0.9±0.4)L.h-1.kg-1,Vz/F(2.3±0.7)L.kg-1和AUC0-12 h(343.2±150.9)μg.h.L-1。汉族健康受试者的主要药动学参数分别为:ρmax(103.1±26.4)μg.L-1,tmax(1.5±0.7)h,t1/2z(3.0±0.8)h,MRT0-12 h(3.6±0.4)h,CL/F(0.7±0.2)L.h-.1kg-1,Vz/F(2.7±0.8)L.kg-1和AUC0-12 h(368.8±103.4)μg.h.L-1。经检验,维吾尔族的tmax、t1/2z和MRT0-12 h比汉族的短,差异有显著性统计学意义,其余参数的民族差异无显著性统计学意义。两个民族的部分受试者的药-时曲线有双峰。结论单剂量口服咪达唑仑片后,汉族和维吾尔族健康志愿者的药动学存在较大的个体差异,且消除速率的民族差异有显著性统计学意义,临床应用时应注意个体化给药。     

THE EFFECT OF CHANGES IN GASTRIC pH INDUCED BY OMEPRAZOLE ON THE ABSORPTION AND RESPIRATORY DEPRESSION OF METHADONE

The effect of omeprazole (2 mg kg⁻¹ i.v.) on respiratory depression induced in rats by acute oral methadone administration (5 mg kg⁻¹) was examined and compared with control animals that only received methadone. Quantitative assessments of arterial p_CO2, p_O2, pH, and respiratory rate were employed as criteria for evaluation. Intragastric pH was measured in each rat immediately before and 2 h after methadone. Plasma concentration of methadone was measured for 3 h. The relationship between drug effect and the systemic bioavailability of methadone, measured as the area under the plasma concentration–time curve (AUC_0–180 ), was also evaluated. The intensity of the methadone-induced respiratory depression was significantly greater in the omeprazole group than in control rats. A significant variation (p<0·01) in all respiratory parameters was detected from 30 to 120 min after methadone. Omeprazole caused a significant increase in methadone levels (C_max=156± 6·5 ng mL⁻¹ against 51±5·8 ng mL⁻¹ in control; p<0·05). AUC_0–180 was higher (p<0·05) after omeprazole treatment (18·6±1·4 μg mL⁻¹ min) than in control (6·8± 0·6 μg mL⁻¹ min). Two hours after treatment with omeprazole, intragastric pH values were significantly elevated (4·7±0·1 against 2·2±0·04) and continued increasing, being 6·4±0·1 at the end of the experiment. Correlation was observed between intragastric pH and the area under the effect– (respiratory depression–) time curve (r=0·74; p<0·001). A relationship between plasma methadone levels at 120 min and gastric pH (r=0·92; p<0·001) was detected. A significant correlation between the area under the effect–time curve (0–120 min) and AUC_0–180 has been also observed (r=0·90; p<0·01). These pharmacokinetic and pharmacodynamic changes could be gastric pH dependent because they were mimicked when gastric pH was experimentally modified by bicarbonate whereas opposite results were obtained with acidic pH 2 solution.