Scanning laser Doppler flowmeter study of retinal blood flow in macular area of healthy volunteers.

AIM: To compare the interocular and intraocular differences of capillary perfusion, and the intraocular regional differences of retinal blood flow in the macular area of healthy volunteers. METHODS: Tissue blood flow in the macula was examined in both eyes of 20 healthy volunteers with the Heidelberg retinal flowmeter. Blood flow measurements were made in a 10 degrees x 2.5 degrees area superior and inferior to the macula. The mean blood flow (MBF) was calculated by an automatic full field perfusion image analyser program. The MBF in the right and left eyes and in the superior and inferior macular areas of the same eye were compared. RESULTS: The ratios of the MBF in the right eye to the left eye in the macular areas were 1.00, and 1.03, respectively. The ratio of the MBF in the superior macular area to the inferior area was 1.01 for the right eyes and 1.04 for the left eyes. CONCLUSIONS: Because no significant differences were found in the MBF between the two eyes and between the superior and inferior macular areas in the same eye, interocular (for example, affected eye versus fellow eye) and intraocular (superior versus inferior macular areas) comparisons of MBF can be made to determine if changes in retinal perfusion have occurred.

Phenotype of cytochrome P4501B1 gene (CYP1B1) mutations in Japanese patients with primary congenital glaucoma.

AIM: To investigate the phenotypes associated with cytochrome P4501B1 gene (CYP1B1) mutations in Japanese patients with primary congenital glaucoma (PCG). METHODS: 66 Japanese patients with PCG were screened for sequence mutations in the CYP1B1 gene using single strand conformation polymorphism analysis followed by automated DNA sequencing. 11 cases had a CYP1B1 mutation in both alleles (the mutation group) and 21 cases did not have a CYP1B1 mutation (the "no mutation" group). The clinical features, such as age of onset, sex, intraocular pressure, and Descemet's membrane rupture, of the two groups were compared. RESULTS: The clinical symptoms and signs did not differ for the two groups. The mean age at onset was 1.7 months in the mutation group and 3.1 months in the no mutation group, and the male:female ratio was 6:5 in the mutation group and 19:2 in the no mutation group. Both of these differences were statistically significant. CONCLUSIONS: In clinically diagnosed cases of PCG, a subgroup shows a CYP1B1 gene mutation. Age at onset was earlier in PCG patients with CYP1B1 mutations than in patients without mutations. Women were more prevalent among patients with mutations than those without mutations.

Novel cytochrome P4501B1 (CYP1B1) gene mutations in Japanese patients with primary congenital glaucoma.

PURPOSE: To investigate CYP1B1 gene mutations in Japanese patients with primary congenital glaucoma (PCG). METHODS: Sixty-five unrelated Japanese patients with PCG were screened by PCR-single-strand conformational polymorphism (SSCP) analysis followed by direct sequencing. No patients were offspring of consanguineous marriages, a common occurrence among patients in previous reports. PCG haplotypes were constructed with intragenic polymorphisms in affected individuals. Three-dimensional atomic structures of human CYP1B1 and four mutant CYP1B1 sequences representing missense mutations were assembled using homology modeling and were regularized by an energy-minimization procedure. RESULTS: Eleven novel mutations, including seven definite and four probable mutations, were detected in 13 (20%) of the 65 unrelated patients. Of the seven definite mutations, three were predicted to truncate the CYP1B1 open reading frame. The other four were missense mutations (Asp192Val, Ala330Phe, Val364Met, and Arg444Gln), all located in conserved core structures determining proper folding and heme-binding ability of cytochrome P450 molecules. Molecular modeling demonstrated that two of four mutations in positions 330 and 364 were structurally neutral, but Arg444Gln caused significant structural change. Of the four probable mutations, three were missense (Val198Ile, Val320Leu, and Glu499Gly); the other was a base substitution in the noncoding region of exon 1. CONCLUSIONS: The 11 varied CYP1B1 mutations found in 13 unrelated Japanese patients with sporadic occurrence of PCG represent an allelic heterogeneity and may be unique to a specific population.

Pharmacokinetics of epinastine and a possible mechanism for double peaks in oral plasma concentration profiles.

The pharmacokinetics of epinastine (EPN), an anti-allergic agent, was investigated in rats. The plasma concentration-time profile of EPN after intravenous (i.v.) administration was triexponential. After oral administration of EPN (7.5 and 20 mg/kg), the drug was rapidly absorbed, and Cmax was reached 2 h after dosing. A minor secondary peak was observed in EPN plasma concentration-time profiles at both doses. The bioavailability of EPN after oral dosing was 41 and 40%. The kinetic parameters (T 1/2, AUC and MRT) for unlabeled EPN were much smaller than those for 14C-EPN, which has already been reported. The total biliary excretion of EPN at a 7.5 mg/kg dose was 15.5% of the dose, but the percentage of conjugates in bile was extremely low and about 11% of the total biliary excretion. The increase in the plasma concentration in bile duct-linked rats after oral administration of EPN (20 mg/kg) was not observed, indicating that a secondary increase in drug concentration based on enterohepatic circulation was ruled out. When the gastrointestinal (GI)-transit of phenol red (PR) after oral administration of EPN (20 mg/kg) was estimated, the GI-transit of PR was significantly delayed, and at 3-4 h after dosing half of the PR dose reached the jejunum. The remaining EPN in the small intestine after oral administration (7.5 mg/kg) reached peak levels 2 h after dosing, but then partly increased again at 4 h. As a result, it was clarified that the double peaks observed after oral doses are mainly due to the delayed absorption of a part of EPN, based on the reduction in gastric motility caused by the drug.

Oral delivery of synthetic eel calcitonin, elcatonin, in rats.

This study was designed to develop an oral dosage form of elcatonin (EC), a hypocalcemic peptide. The EC absorption was estimated by the reduction in plasma calcium concentrations. When EC was orally coadministered with nitroso-N-acetyl-D,L-penicillamine (SNAP, 4.0 mg) and 0.02% Carbopol solution or with taurocholate (20 mM) and 0.02% Carbopol solution, the lowering effect was increased compared with that after EC alone, but the F values (0.32 and 0.30%) were extremely small. The oral administration of the mucoadhesive emulsion, which was prepared by coating the W/O/W emulsion with 0.1% Carbopol, enhanced the calcium lowering effect, with the F value of 0.43%. The strong mucoadhesion of the mucoadhesive emulsion to the gastrointestinal mucosa was observed. A capsule containing EC (500 microg), taurocholate (6 mg) and lyophilized Carbopol (3.5 mg) administered orally gave a sustained but comparatively small calcium lowering effect. In the in vitro enzymatic hydrolysis experiment, EC was more rapidly hydrolyzed in the intestinal fluid than in the mucosal extract. The combination of 20 mM taurocholate with 0.02% Carbopol showed the greatest inhibitory effect in both fluid and extract. These data indicated that EC was effectively absorbed through the intestinal wall, but the peptide was dominantly degraded by proteolytic enzymes in the GI tract. These results will offer a potential approach to the oral delivery of EC.

Transdermal absorption of bupranolol in rabbit skin in vitro and in vivo.

This study was designed to clarify the percutaneous penetration of bupranolol (BP), a beta-adrenoceptor antagonist, through rabbit skin and to compare the in vitro penetration with the in vivo absorption. BP penetrated across the skin slowly in the absence of enhancers in vitro. Isopropyl myristate and N-methyl-2-pyrrolidone enhanced the in vitro penetration, with a 3.6 times higher flux compared with that without enhancers. However, in the in vivo percutaneous absorption, the maximal penetration was obtained with the formulation added dlimonene, with a 3.0 times higher area under the concentration-time curve (AUC) than that for the formulation without enhancers. The plasma levels of BP determined, however, were extremely lower than the theoretical plasma steady-state concentrations predicted. The plasma levels of BP after application of these formulations were maintained in the range of 7-22 ng/ml for 30 h, of which concentrations were above the therapeutically effective concentration (1.5-4 ng/ml). Therefore, the transdermal systems will offer an efficient drug delivery system for the treatment of angina pectoris and tachycardia.

Effect of positively and negatively charged liposomes on skin permeation of drugs.

To clarify the effect of the surface charge of liposomes on percutaneous absorption, the permeation of liposomal drugs through rat skin was investigated in vitro and in vivo. Liposomes were prepared using egg yolk lecithin (EPC, phase transition temperature, -15 to -17 degrees C), cholesterol and dicetylphosphate (DP) or stearylamine (SA) (10:1:1, mol/mol). Also examined was the penetration behavior of positively and negatively charged liposomes, using a fluorescent probe (Nile Red). The in vitro penetration rate of melatonin (MT) entrapped in negatively charged liposomes was higher than that of positively charged ones (p<0.05). When the percutaneous absorption of ethosuximide (ES) encapsulated was estimated in vivo, the absorption of ES from negatively charged liposomes was slightly higher than that from positively charged liposomes. Additionally, the absorption of ES from both types of liposomes was superior to that from the lipid mixtures consisting of the same composition as the vesicles. The percutaneous absorption of betahistine (BH) from a gel formulation containing negatively charged liposomes of BH was much more than that from the formulation with positively charged ones, with 2-fold higher AUC (p<0.05). Histological studies revealed that the negatively charged liposomes diffused to the dermis and the lower portion of hair follicles through the stratum corneum and the follicles much faster than the positive vesicles at the initial time stage after application. Thus, the rapid penetration of negatively charged liposomes would contribute to the increased permeation of drugs through the skin.

In vitro skin penetration and degradation of peptides and their analysis using a kinetic model.

The main purpose of this study was to estimate the net percutaneous absorption of physiologically active peptides in vitro. The degradation of two peptides, Leu-enkephalin (Enk) and Tyr-Pro-Leu-Gly amide (TPLG), during skin penetration and on the dermal side following penetration, and the prevention of degradation by some protease inhibitors, were investigated using rat skin in vitro. In addition, these permeation and degradation data were analyzed using a kinetic model. These peptides were rapidly degraded in the receptor fluid of a Franz diffusion cell (rate constant: 0.977 h(-1) for Enk and 0.250 h(-1) for TPLG). The addition of phenylmethylsulfonyl fluoride (PMSF) and phenanthroline and the pretreatment of skin with these inhibitors prevented almost completely any degradation in the receptor fluid and skin, respectively. The pretreatment of skin with PMSF and phenanthroline had no effect on the penetration of dextran (1000 Da). The degradation rate constant during skin penetration, calculated from the difference in the penetration rate constants via pretreated and untreated skins, was also high (0.037 h(-1) for Enk and 0.050 h(-1) for TPLG). A kinetic model including an input rate (zero-order), the permeation rate across the viable skin (first-order) and the degradation rate in skin (first-order) was sufficient to describe the apparent steady-state flux of the peptides through skin. We have, thus, established a method for measuring the true flux of peptides across skin in vitro and a kinetic model which simply describes the skin penetration of peptides.

Novel mutations in the myocilin gene in Japanese glaucoma patients.

Myocilin is a gene responsible for juvenile onset primary open angle glaucoma (POAG) mapped as the GLC1A locus and, many mutations have been reported worldwide. Some mutations were found not only in patients with juvenile onset POAG, but also in patients with late onset POAG and in patients with normal tension glaucoma. To investigate the mutation prevalence in Japan, we performed a mutation analysis in 140 unrelated Japanese patients. We have identified the 10 sequence variants, of which four were highly probable for disease-causing mutations (Arg46ter, Arg158Gln, Ile360Asn, and Ala363Thr), and six polymorphisms (Gln19His, Arg76Lys, Asp208Glu, Val439Val, Arg470His, and Ala488Ala). Thus, myocilin mutations were found at the rate of 4/140 (2.9%) probands, similar to previous reports with other ethnic populations.

Percutaneous penetration of ozagrel and the enhancement produced by saturated fatty acids.

The effects of a series of fatty acids on the percutaneous penetration of ozagrel (OZ), a selective thromboxane A2 synthetase inhibitor, through rat skin and the mechanism by which fatty acids enhance the skin penetration of OZ were examined in vitro. Lauric acid, at the fatty acid: OZ molar ratio of 2 : 1, was the most potent agent as far as increasing the skin penetration was concerned, with a flux 24-fold higher than that without fatty acid. A molar ratio of 3 : 1 also produced a large enhancing effect, comparable with that of a molar ratio of 2 : 1. When the gel formulation with lauric acid (molar ratio of 2 : 1) was applied to the skin for 6 h, the amount of drug penetrating into the skin was significantly increased compared with that after the formulations without lauric acid and with capric and palmitic acids. However, lauric acid did not change the apparent partition coefficient of OZ between n-heptane and phosphate buffer (pH 7.4). The 13C-NMR spectra of OZ was also unaffected by the addition of lauric acid, indicating that a complex or ion pair with lauric acid was not formed. A possible mechanism for the enhancing effect is the increased incorporation of lauric acid with OZ into the bulk lipid phase of the stratum corneum, where the fatty acid would act as a co-penetrant enhancing passage through the stratum corneum.

Granulation of acetaminophen by a rotating fluidized-bed granulator.

The purpose of this research was to evaluate the use of a rotating fluidized-bed granulator to produce acetaminophen granules with sufficient binding force between particles and good plasticity in tablets. Ethenzamide and ascorbic acid were used to compare the relationship between granulation and the sample wetness. It was revealed that a blade rotation rate of 300 rpm, inlet air flow rate of 42 m3/hr, and spraying pressure of 1.5 kg/cm3 produced tablets with the best properties. The granule and tablet properties of ethenzamide and ascorbic acid were compared to those of acetaminophen. These compounds showed different wetting behaviors with water and different compression behaviors. With an increase in medicament content, tablet hardness increased except for the ascorbic acid formulation. Capping and sticking were observed in acetaminophen and in ascorbic acid, respectively, and acetaminophen and ethenzamide showed prolonged disintegration time.

[Transdermal delivery of drugs and enhancement of percutaneous absorption].

This paper describes 1) the drug delivery through the skin to produce systemic effects, 2) the enhancement of percutaneous absorption by absorption enhancers, heating and complex formation, 3) the mechanism for the enhancement effect by enhancers, 4) the percutaneous absorption of peptides, and 5) the pharmacokinetic analysis for percutaneous absorption. 1,3-Dinitroglycerin, indomethacin (IND) and many drugs were efficiently absorbed via rat and rabbit skins in the presence of some enhancers, and using a microporous membrane therapeutic plasma concentrations were maintained for a long time. Enhancement of percutaneous absorption by the complex formation with fatty acid was observed for propranolol (PL) in vitro and in vivo. Heating at 42-45 degrees C also enhanced the percutaneous absorption dramatically, with decreased activation energies. The following mechanisms for the enhancement effect by enhancers were found: a) an increase in the fluidity of the stratum corneum lipids and reduction in the diffusional resistance to permeants, b) the removal of intercellular lipids and dilation between adherent cornified cells, c) an increase in the thermodynamic activity of drugs in vehicles, d) the exfoliation of stratum corneum cell membranes, the dissociation of adherent cornified cells and elimination of the barrier function. Peptides such as enkephalin, elcatonin and insulin were effectively absorbed through the skin in the presence of some enhancers and specific inhibitors, with no proteolytic degradation. The pharmacokinetic model with two parallel absorption processes, lipidic and aqueous pore transport pathways, in skin could adequately describe the percutaneous absorption of IND, PL and valproic acid. With peptides, a kinetic model including zero-order input rate, first-order permeation rate and first-order degradation rate was able to describe well the steady-state flux of peptides.

Pharmacokinetics of aniracetam and its metabolites in rat brain.

The pharmacokinetics of aniracetam (AP) and its main metabolites, 4-p-anisamidobutyric acid (ABA), 2-pyrrolidinone (PD) and p-anisic acid (AA), in 3 brain regions (cerebral cortex, hippocampus and thalamus) was investigated after single intravenous (i.v.) and oral administrations of AP to rats. AP, AA and PD were rapidly distributed into the 3 brain regions after i.v. administration of AP, but the amounts of AP were low. The concentrations of AP and AA in brain regions rapidly declined, whereas PD levels were higher and more sustained than those of AP and AA. ABA levels in the regions were below the detection limit. There were no significant differences in the distribution of these compounds in the 3 brain regions. The AUCbrain/AUCplasma ratio of PD was 53--55%, in contrast to the low ratio of AP (2.4--3.2%) and AA (3.9--4.2%). On oral administration of AP, the AUCbrain/AUCplasma ratio of PD was also higher than that of AA. When the transport of PD was tested using the in situ brain perfusion technique, it was clarified that PD was not transported across the blood-brain barrier (BBB) by a neutral amino acid carrier system. The high brain levels of PD and the low levels of AP suggest that the clinical efficacy of dosed AP may partly result from PD penetrating into the brain.

The myocilin (MYOC) gene expression in the human trabecular meshwork.

PURPOSE: We previously reported a novel cytoskeletal protein with a myosin-like domain which is localized in the ciliary rootlet and basal body of connecting cilium of photoreceptor and hence we named it 'myocilin'. It was soon realized that myocilin is identical to a protein called TIGR (trabecular meshwork inducible glucocorticoid response protein) which was found to be responsible for the pathogenesis of juvenile open angle glaucoma. In this study, we employed in situ RNA hybridization to examine the myocilin (MYOC)/ TIGR gene expression in the trabecular meshworks of glaucomatous and nonglaucomatous eyes. METHODS: The glaucomatous specimens were obtained by trabeculectomy from the patients with primary open angle glaucoma (POAG), chronic angle closure glaucoma (CACG) and steroid glaucoma, respectively, and the nonglaucomatous specimens were obtained from a victim of traffic accident at autopsy and from a patient with maxillary sinus carcinoma at enucleation for the operation. The in situ RNA hybridization was carried out with digoxigenin-labeled sense and antisense RNA probes. RESULTS: In all cases, hybridization signals were detected primarily in the trabecular meshwork cells and secondarily in the fibroblast-like cells of corneoscleral wall. CONCLUSIONS: Myocilin gene is expressed clearly in the trabecular meshwork cells of both glaucomatous and nonglaucomatous eyes.

Release characteristics of endogenous constituents by exposure of small intestine to modified beta-cyclodextrins.

The aim of the present research is to characterize the leakage of intestinal constituents induced by beta-cyclodextrin (beta-CyD) derivatives using an in situ perfusion and an in vitro everted sac. The efficacy of 6-O-alpha-D-glucosyl (G1)- and 6-O-alpha-D-maltosyl (G2)-beta-CyDs as oral carriers was also compared with that of 2-hydroxypropyl-(HP1; average molar degree of substitution, 0.9) and 2,6-di-O-methyl (DM)-beta-CyDs. In the in situ studies, phenol red (PR) penetration and the release profiles of intestinal constituents for G2-beta-CyD were fairly close to those for HP1-beta-CyD. However, the ability of G2-beta-CyD to include cholesterol was greater than that of HP1-beta-CyD. To characterize the release of intestinal constituents induced by modified beta-CyDs, the capability of including cholesterol was held constant between DM- and branched beta-CyDs. The everted sac study showed that the amount of DM-beta-CyD transferred to the serosal side was not significantly different from the branched beta-CyDs. On the serosal side, the amount of cholesterols released was approximately 3 times higher for DM-beta-CyD than for the branched beta-CyDs at 60 min. The cumulative amounts of cholesterols for DM-beta-CyD increased approximately 6 times at 60 min compared with at 30 min, predominating over the leakage (average 2.6-fold) on the mucosal side. In contrast, the exposure of the branched beta-CyDs resulted in an insignificant increase over the period of this experiment. The present study suggests that permeable beta-CyD derivatives play an important role in the leakage of intestinal components. G2-beta-CyD is preferably recommended as a drug solubilizer in oral formulations as well as HP1-beta-CyD, based on the lower release of intestinal constituents.

Effect of sugar-modified beta-cyclodextrins on dissolution and absorption characteristics of phenytoin.

Inclusion complexes of phenytoin (DPH) with 6-O-alpha-D-glucosyl (G1)- and 6-O-alpha-D-maltosyl (G2)-beta-cyclodextrins (beta-CyDs) were prepared in a molecular mixing ratio of 1:1. The advantages of these preparations in terms of dissolution characteristics and the oral absorbency of DPH were evaluated in comparison with the known solid dispersions of polyvinylpyrrolidone K-30 and sodium deoxycholate (DC-Na). The results of a phase-solubility study indicated that G1- and G2-beta-CyDs provided higher solubility for DPH than 2-hydroxypropyl (HP)-beta-CyD. Irrespective of inclusion ability, the DPH/beta-CyD complexes allowed faster dissolution rates than those of the known dispersions in JP 1st and 2nd mediums. The dissolution behavior of the DPH/DC-Na dispersion was considerably different between the 1st and 2nd mediums. The complexation by the sugar-modified derivatives yielded a higher stability of dissolved DPH in the JP 2nd medium than that yielded by K-30 or DC-Na. The safe estimation of carriers themselves indicated that G1- and G2-bet-CyDs did not damage the small intestine, while 10 mM DC-Na showed some damage. Compared with the DPH/K-30 dispersion, the preparations with the sugar-modified beta-CyDs were more effective in enhancing the absorbability of DPH after oral administration. These results clearly suggest that complexation with G1- and G2-beta-CyDs are useful forms for the oral delivery of DPH. The advantage of these complexes is that they produce an increased level of DPH available for gastrointestinal absorption. Additionally, G2-beta-CyD is recommended as a safe and potent additive for DPH.

Pharmacokinetic drug interactions between ampiroxicam and sulfaphenazole in rats.

The aim of the present study was to determine the effect of sulfaphenazole (SP) on the pharmacokinetics of ampiroxicam (AM) which is metabolized by cytochrome P-450 (CYP) 2C9, since SP is a potent inhibitor of CYP 2C9, and so a dramatic pharmacokinetic drug interaction between both drugs is assumed after dosing. Single intravenous and oral administrations of AM (5 and 7.5 mg/kg piroxicam equivalent, respectively) and SP (80 and 120 mg/kg, respectively) to rats did not significantly alter the elimination kinetics of AM and piroxicam (PX) converted from AM. When SP was preloaded orally at 2 h before the dosing of AM, and when AM and SP were orally coadministered for 7 d, the elimination of PX from plasma was slightly retarded and the area under the plasma concentration-time curve (AUC) was increased 77 and 53%, respectively, but not significantly, compared with those after AM alone. On the other hand, a significantly decreased metabolic conversion of PX to 5'-hydroxyPX in plasma was observed by these treatments (p<0.05). In order to clarify the mechanism for the interaction, hepatic and intestinal metabolizing enzyme activities, CYP, uridine 5'-diphosphoglucuronyltransferase (UDPGT) and aryl esterase, were assayed after single and multiple oral administrations of AM or AM and SP. The enzyme activities were hardly inhibited by the treatment, indicating that the inhibition of CYP and hydrolytic enzymes by SP was approximately denied. These results suggest that SP does not significantly affect the pharmacokinetics of AM and PX in rats. However, the pharmacokinetic drug interaction between both drugs in man may not always be ignored.

Enhancement of the oral bioavailability of phenytoin by N-acetylation and absorptive characteristics.

To improve the absorbability of phenytoin (DPH), a prodrug, N-acetyl-DPH (EDPH), was synthesized, and the absorptive characteristics and pharmacokinetics of the prodrug were evaluated in rats. EDPH was rapidly hydrolyzed to DPH in the intestinal fluid and the mucosa (rate constant, 0.055 and 0.169 min(-1), respectively). The plasma concentrations of DPH after intravenous dosing of EDPH declined in a biexponential manner, although two different elimination patterns were observed in these rats. When dosed orally (25 mg/kg, DPH equivalent), the plasma levels of DPH converted from the prodrug were significantly higher and more sustained than those after DPH alone, giving bioavailability 11.4 (rapid decay) and 9.1 times (slow decay) as high, respectively, as that after DPH alone. The concentrations of DPH distributed into the mucosa of the duodenum and jejunum 1 and 5 h after oral dosing of EDPH were significantly higher than those after DPH alone. The prodrug and DPH converted from the prodrug dissolved 2-4 fold more than DPH alone in bile salt solution and bile salt-oleic acid mixed micelles, indicating the increased solubility of the prodrug in the intestinal fluid. It is concluded from the data that such high solubility of EDPH enhanced the intestinal absorption of the prodrug, part of which would be absorbed in the amide form, and thus gave the high bioavailability.

Pharmacokinetics of aniracetam and its metabolites in rats.

The pharmacokinetics of aniracetam (AP), a new cognitive performance enhancer, and its main metabolites was investigated after intravenous (iv) and oral administrations to rat. The plasma levels of AP, 4-p-anisamidobutyric acid (ABA), and p-anisic acid (AA) were determined simultaneously by the HPLC method. The plasma concentrations of the parent drug and ABA quickly declined in a biexponential manner, with rapid terminal decay and a small mean residence time. However, AA yielded nonlinearly high levels at the initial times and the plasma concentrations of 2-pyrrolidinone (PD) were sustained over a relatively long time. When AA was administered intravenously, nonlinearity of the plasma concentrations was also found at higher doses. To describe the time course of the plasma levels of AP and its metabolites after iv administration, a pharmacokinetic model with seven compartments was applied, which included 10 first-order rate constants and one Michaelis-Menten constant. An approximate fit was obtained between the observed and calculated curves based on the model, except for the plasma concentrations of ABA. The plasma concentration-time profiles of AP and its metabolites following oral administration of AP (50 and 100 mg/kg) were similar to those after iv dosing, with the exception of PD, which showed much lower plasma levels than those after iv administration. Elimination of AP and ABA was rapid after oral dosing, and the bioavailability of AP was extremely small (11.4 and 8.6%). As a result, AP was largely metabolized to ABA, AA, and PD in rat.