Structural Chinese medicine: new research field on pharmacodynamic substance basis of traditional Chinese medicine / 中国中药杂志

The research on the pharmacodynamic substance basis of traditional Chinese medicine(TCM) is a key scientific issue for the inheritance and development of TCM. At present, a large number of remarkable achievements have been made in the field of chemical components in Chinese medicine, however, another important aspect, namely the physical structure and mode of action of the multi-component assembly of TCM, has not been clearly understood and deeply studied. From the bottleneck of restricting material ba-sic research, we objectively analyzed the common cause of the existing problems. Based on the new discoveries and advances of active substances from TCM emerging in recent years, we extracted and summarized the concept of structural Chinese medicine, elaborated the basic ideas, main features and research modes, hoping to provide theoretical and practical references for the study on the pharmacodynamic substance basis and other research fields of TCM.

Recent development of natural and reconstituted lipoprotein based nano drug delivery vehicles / 药学学报

Lipoproteins are biological lipids carriers. The natural and reconstituted lipoprotein based drug delivery systems have been extensively developed in recent years. This article reviews the development of natural and reconstituted low-density lipoprotein and high-density lipoprotein based vehicles in the antitumor area.

Solidified mPEG-PDLLA micelles as a novel oral delivery system of indomethacin / 药学学报

In this study, indomethacin (IND) loaded solidified-polymeric micelles (IND-SPM) were prepared. Their in vitro characteristics were investigated. Methoxy-poly(ethylene glycol) poly(D, L-lactide) copolymer (mPEG-PDLLA) was used as IND carrier. The preparation of IND-SPM was conducted by solution-absorption method and evaporation by rotary evaporator. Polyplasdone XL-10 was used as adsorbent. The solution-absorption method was conducted by the following procedure; IND and mPEG-PDLLA were dissolved in acetone, followed by addition of polyplasdone XL-10 and stirred to obtain a suspension. The powder of IND-SPM was simply obtained after the organic solvent was completely evaporated. More than 90% (w/w) of IND (20 mg) in the powder was dissolved in 250 mL PBS within 30 min. DSC, 1H NMR and SEM results proved that IND was encapsulated within mPEG-PDLLA. The solubility of IND in the system increased 4.6 times with the highest amount of copolymer. The solidified particles were found to be suitable for the formulation of tablets or capsules.

Water in oil microemulsions containing NaCl for transdermal delivery of fluorouracil / 药学学报

This study is to prepare the W/O microemulsion containing NaCl and fluorouracil (5-Fu) as a model drug to investigate the transdermal characteristics and skin irritation of the microemulsion in vitro. Isopropylmyristate (IPM) acting as oil phase, Aerosol-OT (AOT) as surfactant, Tween 85 as cosurfactant, NaCl solution was added dropwise to the oil phase to prepare W/O microemulsion at room temperature using magnetic stirring, and then 5-Fu powder was added. According to the area of microemulsion based on the pseudo-tertiary phase diagrams, the optimum formulation was screened initially. And the permeation flux of fluorouracil across excised mice skin was determined in vitro using Franz diffusion cells to study the influence of the amount of water and the drug loading capacity and optimize the formulation further. Refer to 5-Fu cream, the irritation of microemulsion on the rat skin was studied. The optimum formulation was composed of 0.7% (w/v) 5-Fu, 50% NaCl solution (0.05 mol x L(-1)), 20% mix-surfactant (AOT/Tween 85, K(m) = 2) and 29.3% oil (IPM). The cumulative amount of fluorouracil permeated in 12 h was (2 013.4 +/- 41.6) microg x cm(-2), 20.23 folds and 10.38 folds more than 0.7% fluorouracil aqueous solution and 2.5% (w/w) fluorouracil cream, respectively. Microemulsion exhibited some irritation, but could be reversed after drug withdrawal. The addition of NaCl significantly increased the content of water and the drug loading in microemulsion systems. The NaCl/AOT-Tween 85/IPM microemulsion system promoted the permeation of fluorouracil greatly, which may be a promising vehicle for the transdermal delivery of fluorouracil and other hydrophilic drug.

Microemulsion-based gel of fluorouracil for transdermal delivery / 药学学报

This study is to prepare the microemulsion-based gel based on the W/O microemulsion and fluorouracil (5-Fu) as a model drug to study the transdermal characterization and observe its skin irritation of the microemulsion-based gel in vitro. IPM acted as oil phase, AOT as surfactant, Tween 85 as cosurfactant, water was added dropwise to the oil phase to prepare W/O microemulsion at room temperature using magnetic stirring, then 5-Fu powder was added. The gelatin was used as substrate to prepare 5-Fu microemulsion-based gel. The permeation flux of 5-Fu from 5-Fu microemulsion-based gel across excised mice skin was determined in vitro using Franz diffusion cell to study the influence of the amount of gelatin and the drug loading capacity. Refer to 5-Fu cream, the irritation of microemulsion and microemulsion-based gel on the rat skin was studied. Based on the water/AOT/Tween 85/IPM microemulsion, only the gelatin can form the microemulsion-based gel. At 25 degrees C, 32 degrees C and 40 degrees C, the amount of gelatin required for the formation of microemulsion-based gel were 7%, 14% and more than 17%, respectively. The 12 h transdermal cumulated permeation amount of 5-Fu from microemulsion-based gel containing 14% gelatin and 0.5% drug loading were (876.5 +/- 29.1) microg x cm(-2), 12.3 folds and 4.5 folds more than 0.5% 5-Fu aqueous solution and 2.5% (w/w) 5-Fu cream, respectively. Microemulsion-based gel exhibited some irritation, but could be subsided after drug withdrawal. Microemulsion-based gel may be a promising vehicle for transdermal delivery of 5-Fu and other hydrophilic drug.

The effect of polyamidoamine (PAMAM) dendrimers on the solubility and pharmacokinetics of breviscapine / 药学学报

To study the solubilization of breviscapine with polyamidoamine (PAMAM) dendrimers and probe the solubilizing mechanism and investigate the influence of PAMAM dendrimers on the pharmacokinetics of breviscapine, the solubilization of breviscapine by PAMAM dendrimers of generations G1, G1.5, G2 and G2.5 with different concentrations were determined and compared in different pH conditions. Twelve rats randomized into 2 groups were separately orally administered breviscapine and breviscapine combining with PAMAM. Drug in plasma was extracted and determined with HPLC. In pH condition lower than 7.0, the solubilization of breviscapine by PAMAM dendrimers enhanced as the generation and concentration of PAMAM dendrimers as well as the pH increased. Its solubilizing mechanism involves an electrostatic interaction between the carboxyl group of breviscapine and the primary amines and tertiary amines of PAMAM dendrimers. The pharmacokinetics parameters Cmax and AUC0-8 h of breviscapine were (119.65 +/- 9.36) ng x mL(-1) and (370.09 +/- 63.08) ng x h x mL(-1). For breviscapine combined with PAMAM dendrimers, the Cmax and AUC0-8 h were (518.17 +/- 17.07) ng x mL(-1) and (1,219.47 +/- 201.87) ng x h x mL(-1), respectively. There were significant differences of AUC0-8 h between breviscapine and breviscapine combined with PAMAM dendrimers (P < 0.01). PAMAM dendrimers can greatly increase the solubility of breviscapine in water and can improve the oral bioavailability of breviscapine significantly.

Water in oil microemulsions for transdermal delivery of fluorouracil / 药学学报

An Aersol-OT (AOT) included microemulsion containing fluorouracil was prepared by using appropriate proportion of oil, co-surfactant and water for increasing the drug transdermal delivery ability. According to the area of microemulsion basing on the pseudo-tertiary phase diagrams, the optimum formulation was screened initially. And the permeation flux of fluorouracil across excised mice skin was determined in vitro using Franz diffusion cell to optimize the formulation further. The effect of the kind of co-surfactant, the content of water, the content of mixed surfactant, the mass ratio of surfactant/cosurfactant (Km) and the drug load on skin permeation of fluorouracil were evaluated. The optimum formulation was composed of 0.5% (w/v) fluorouracil, 30% water, 20% mix-surfactant (AOT/Tween 85, Km = 2) and 49.5% oil (IPM). The cumulative amount permeated of fluorouracil in 12 hour was 1 355.5 microg x cm(-2), 19.1 folds and 7 folds more than 0.5% fluorouracil aqueous solution and 2.5% (w/w) fluorouracil cream, respectively. The permeation of this microemulsion accorded with first-order model. The water/AOT/Tween 85/IPM microemulsion system promoted the permeation of fluorouracil greatly, which may be a promising vehicle for the transdermal delivery of fluorouracil and other hydrophilic drug.

The enhancing effect of borneol on the absorption of tetramethylpyrazine / 药学学报

To explore the mechanism of the absorption enhancement of borneol, the effect of borneol on the intestinal absorption and the pharmacokinetics of tetramethylpyrazine phosphate after oral administration were investigated. In situ intestinal recirculation was performed to study the effect of various concentrations of borneol on the absorption of tetramethylpyrazine phosphate at duodenum, jejunum, ileum and colon. After oral administration of tetramethylpyrazine phosphate, the mixture of tetramethylpyrazine phosphate and borneol and the mixture of tetramethylpyrazine phosphate and verapamil in rats, the concentrations of tetramethylpyrazine phosphate in plasma were determined by RP-HPLC at predesigned time. The pharmacokinetic parameters were compared based on the results of the three animal experiments, and analyzed with software program 3p97. The result showed that tetramethylpyrazine phosphate could be absorbed at all of the four intestinal segments with increasing absorption amount per unit as follows: colon > duodenum > jejunum > ileum, but without saturation, which demonstrated that tetramethylpyrazine phosphate was absorbed via simple diffusion. Borneol could enhance the intestinal absorption of tetramethylpyrazine phosphate, however, not in proportion. There was no obvious difference between the test group and the control group when 10 microg x mL(-1) borneol was added (P > 0.05), while when the concentration comes to 25 microg x mL(-1) and 50 microg x mL(-1), significant differences were observed (P < 0.05). Borneol and verapamil did enhance the bioavailability of tetramethylpyrazine phosphate after oral administration in rats. The enhancing effect of borneol showed only when the concentration came to a certain level but with no specific sites existed in the intestine. One of the mechanisms of borneol on the enhancing effect on absorption of tetramethylpyrazine phosphate might be the inhibition of the metabolism of CYP 3A and exocytosis of P-gp.

A simple gas chromatographic method for the simultaneous determination and pharmacokinetic study of tetramethylpyrazine phosphate and borneol in mouse plasma and brain tissue after oral administration of the fufang tetramethylpyrazine phosphate tablets.

A rapid, sensitive, and simple gas chromatographic method with flame ionization detection is developed for the simultaneous determination of tetramethylpyrazine phosphate (TMPP) and borneol in mouse plasma and brain tissue. Sample preparations are carried out by deproteinization with an internal standard solution in methanol. The analytes and internal standard (dimethyl sulfoxide) are well-separated on an HP-5 MS capillary column. The analytical curves are linear over a wide concentration range of 0.02-40 microg/mL for both TMPP and borneol in plasma and brain tissue, with the intra- and inter-day precision (the relative standard deviation values) at less than 15%. TMPP and borneol are both stable under different conditions. The method described is successfully applied to the pharmacokinetic study of mouse plasma and brain tissue after oral administration of the Fufang TMPP and TMPP tablets to mice.

Research of oral prodrugs: opportunities and challenges / 药学学报

Prodrug is an effective way to improve the oral absorption of the drugs which belong to Biopharmaceuticals Classification System (BCS) class III and IV. This review addresses the progress of the oral prodrugs in recent years, mainly including classical prodrug design and targeted prodrug design. Classical prodrug design is focused on modification of oil-water partition coefficient or decrease the metabolism of parent drugs. Targeted prodrug design is actively concerned with the physiological characteristics of the gastrointestinal tract to target tissues, enzymes and influx transporters. Intestinal influx transporter, the peptide transporter-targeted prodrug design is a growing field of the research of oral prodrugs recently. Challenges of prodrug strategy, design and investigation in vivo are also discussed.

The enhancing effect of synthetical borneol on the absorption of tetramethylpyrazine phosphate in mouse.

The main purpose of this study was to illustrate the effect of synthetical borneol (SB) on the plasma and brain concentration profile of tetramethylpyrazine phosphate (TMPP) in mice after oral administration of TMPP without or with different amounts of SB. The concentrations of TMPP on the plasma and brain in mice were determined by GC-FID. The pharmacokinetic parameters were computed by software program 3p97. Our data showed that after oral administration of 15, 30, 90 mg kg(-1) of SB, oral bioavailability of TMPP in plasma was 1.52, 2.21, 2.95 times increase, respectively, than that without SB, and 1.12, 1.62, 1.93 times increase, respectively, in brain tissue. The pharmacokinetic data were simulated by non-linear least squares. The results showed that both open two-compartment model and one-order absorption were fitted to TMPP plasma and brain concentration-time course in vivo in mice. The MRT of TMPP showed same results under the conditions without or with SB. SB did enhance the oral absorption of TMPP and the concentration of TMPP in brain tissue, especially in the early period. But the use of SB did not change the behavior in vivo of TMPP.

Characteristics of nobiletin-loaded nanoemulsion and its in vivo distribution in mice / 药学学报

The purpose of this study was to prepare the nobiletin-loaded nanoemulsions (NOB-NE) and study its in vivo distribution in mice. The characteristics and stability of the unloaded and drug-loaded nanoemulsions were investigated. The size, apparent viscosity and pH value of NOB-NE were respectively (15.5 +/- 2.9) nm, (3.10 +/- 0.33) mPa x s and 6.56 +/- 0.05, which were all higher than those of unloaded nanoemulsions. The zeta potential of unloaded and drug-loaded nanoemulsions carried negative charge. The NOB-NE after diluted by 5% glucose solution was stable in 8 h, and there was no significant difference in the size, content and diluted stability of its preconcentrate in long-term storage. The concentration of nobiletin in plasma and tissues was determined by HPLC after intravenous administration of NOB-NE. Based on AUC(0-t), MRT and C(max), the nanoemulsions delivered more nobiletin into the brain and kidney compared to those of nobiletin solution. The brain and kidney targeting efficiency was improved. In addition, the results fitting using SAAM II software show that the higher drug concentration of the NOB-NE in the brain might be owed to the quicker transport rate from the blood to the brain, and that in the kidney relate to the probable accumulation effect. These results indicate that the in vivo distribution of NOB-NE with consistent quality in mice could be changed and its brain and kidney targeting absorption capability was enhanced comparing with nobiletin solution.

The entrapped efficiency of BSA liposome / 药学学报

BSA liposomes were prepared with approximately 100 nm mean particle size under rather gentle experiment conditions, and two-colorimetric coomassie brilliant blue protein was employed to measure the free drug in the entrapped efficiency (EE%) determination of BSA liposomes. Gel filtration was used to measure the EE%, and several Sephadex gels were examined by the separation of liposomes and free drug. To determine the free drug, three methods were compared on two-colorimetric UV spectrophotography, Bradford and two-colorimetric coomassie brilliant blue, separately. Two-colorimetric coomassie brilliant blue process increased the accuracy and improved the sensitivity of the assay about 20-fold comparing with the Bradford method. Two-colorimetric coomassie brilliant blue assay appeared to be more sensitive and showed broader dynamic range to measure the free BSA in the EE% determination of BSA liposome.

Distribution behavior of lipophilic drugs in the oil-in-water microemulsions / 药学学报

Distribution behavior of lipophilic drugs in the oil-in-water (O/W) microemulsions was studied. Fluorescence spectra analysis was performed to investigate the effect of the compositions of microemulsions on the fluorescence spectra of armillarisin and ofloxacin which were used as the model drugs. The fluorescence spectra of the model drugs in the microemulsions with various amount of the compositions were compared. The results showed that the armillarisin were both localized in the interfacial film of microemulsion systems with both phenylmethanol and PEG 400 as the co-surfactants, separately. Ofloxacin was localized in the interfacial film of microemulsion systems with Gradamol GTCC as the oil phase, but in the oil pool of microemulsion systems with oleic acid/olive oil (OA/OO) (1:1) as the oil phase. Besides, it was found that the drug would have the tendency to locate in the microenvironment where the composition with the largest solubility to model drug is located, and its actual localized position would be dependent on the amount of this composition. The results indicate that the localized region of lipophilic drug in the O/W microemulsion systems is related with the solubility of the model drug in various compositions.

Free amino groups on the surface of chitosan nanoparticles and its characteristics / 药学学报

The relationship of free amino groups on the surface and the characteristics of chitosan nanoparticles (CS-NPs) prepared by ionic gelation method was investigated. Free amino groups on the surface of CS-NPs were determined by colloidal titration, and the effects of the amount of free amino groups and its ionizable level on the particle size, zeta potential, appearance, drug entrapment efficiency and drug release profile in vitro of CS-NPs were investigated. The result showed that the surface free amino groups reduced, the average size, zeta potential, stability of nanoparticles, and the drug release rate and degree all decreased while the drug entrapment efficiency was not affected with the increase of tripolyphosphate (TPP) concentration. With the increase of pH, the free amino groups could be deprotonated and the ionizable level was stepped down, correspondingly the particle size and zeta potential of CS-NPs decreased. Additionally, the drug release rate and degree were elevated in acid medium while descended in neutral or base medium. The amount and ionizable level of free amino groups on the surface are affected by the gelation degree and pH, which further affected the volume phase transitions (swelling/shrinking processes) of CS-NPs. The properties of CS-NPs have correlation with the surface free amino groups.

Microstructure of novel solid lipid nanoparticle loaded triptolide / 药学学报

Novel solid lipid nanoparticle (SLN) system is prepared with Compritol ATO 888 and tricaprylic glyceride. DSC, XRD, SAXS and NMR are employed to study the novel carrier property and microstructure. When the peak melting point decreased from 70.8 degrees C to 61.4 degrees C, the enthalpy sharply decreased. It could be concluded that the regular crystal lattices in the novel carriers are broken out for the oil joined in them. Melting behavior is occurred at -17.7 degrees C while novel SLN is composed of oil and solid lipid mixture from the DSC measurement. Most alpha phase and least beta' phase are in the nano carrier system whether drug loading or not from the XRD investigation. There is only 0.1 nm change of long space among the novel SLN made of mixture and the lipid matrix and traditional SLN; therefore, it is impossible of the oil molecular insert into the solid glyceride structure. Since the different melting behavior (DSC measurements) and molecular move state (NMR investigations), two lipid matrix are still in two state of liquid and solid lipid in the novel SLN carrier. Presume the microstructure of the novel SLN prepared by our experiment would be that liquid oil has formed superfine nano accommodation encapsulated with solid lipid, but the whole particle is still in nano size range.

Preparation of silymarin proliposome: a new way to increase oral bioavailability of silymarin in beagle dogs.

The aim of the present study was to find a method to increase oral bioavailability of silymarin, that is to say, by the preparation of silymarin proliposome and to compare the pharmacokinetic characteristics and bioavailability after oral administration of silymarin proliposome and silymarin in beagle dogs. Silymarin proliposome was prepared by the film-deposition on carriers. After the proliposome was contacted with water, the silymarin liposome suspensions formed automatically. The tests of physicochemical properties including SEM, TEM, encapsulation efficiency, dissolution studies, particle size of the reconstituted liposome and stability of the silymarin proliposome were determined by laser-particle-sizer, HPLC, etc. The concentrations of silymarin in plasma of beagle dogs and its pharmacokinetic behaviors after oral administration of silymarin liposome suspensions and silymarin were studied by RP-HPLC. The pharmacokinetic parameters were computed by software program 3p97. The encapsulation efficiency of silymarin liposome could be more than 90%, with an average particle size of about 196.4 nm and the proliposome appeared a very stability at 40 degrees C during 3 months. It was found that mean plasma concentration-time curves of silymarin after oral administration of liposome suspensions and silymarin in beagle dogs were both in accordance with open two-compartments model and first-order absorption. Pharmacokinetic parameters of silymarin proliposome and silymarin in beagle dogs were Tmax both 30 min; Cmax 472.62 and 89.78 ng mL(-1); and AUC0-infinity 2606.21 and 697 ng mL(-1)h, respectively. The high bioavailability of silymarin proliposome could be obtained by oral administration. Silymarin proliposome was stable and did enchance the gastrointestinal absorption of silymarin.

Pharmacokinetics of breviscapine liposomes following intravenous injection in Beagle dogs / 药学学报

<p><b>AIM</b>To prepare the breviscapine liposomes and study the pharmacokinetics of breviscapine liposomes in Beagle dogs.</p><p><b>METHODS</b>The cross-over design (two periods) was employed. Six Beagle dogs were administrated a single intravenous dosage of 28 mg of breviscapine liposomes and reference preparation, respectively, scutellarin in plasma of 6 dogs at different sampling time was determined by RP-HPLC. The pharmacokinetic parameters were calculated by 3P97 program and compared by statistic analysis.</p><p><b>RESULTS</b>The mean concentration-time curves of breviscapine liposomes and reference preparation were both fitted to two-compartment model with the main pharmacokinetic parameters as follows: T 1/2 alpha were (4.4 +/- 0.7) min and (1.8 +/- 1.3) min respectively; T 1/2 beta were (55 +/- 27) min and (28 +/- 23) min respectively; V(c) were (1 580 +/- 265) mL and (2 460 +/- 2 200) mL respectively; CL(s) were (88 +/- 10) mL x min(-1) and (324 +/- 69) mL x min(-1) respectively; and AUC(0-720) were (363 +/- 42) microg x min x mL(-1) and (102 +/- 19) microg x min x mL(-1) respectively. The T 1/2 alpha, CL(s) and AUC(0-720) of breviscapine liposomes all had significant difference from those of reference preparation, after the data were examined by a one-way analysis of variance (ANOVA).</p><p><b>CONCLUSION</b>Compared with the reference preparation, breviscapine liposomes had a much more higher concentration in plasma and contained characteristic of sustained-release, which ameliorated the pharmacokinetic properties of scutellarin.</p>

Effect of preparation technique on in vitro release mechanism of huperzine A microspheres / 药学学报

<p><b>AIM</b>To investigate the effect of preparation technique on in vitro release mechanism of huperzine A-PLGA microspheres.</p><p><b>METHODS</b>Huperzine A-PLGA microspheres were prepared by two kinds of O/O emulsion solvent evaporation method (method A and B). In vitro release mechanism was explained by release profile, degradation rate and swelling rate of microspheres in vitro. The microspheres morphology and drug distribution within microspheres were observed in order to explain further the drug release mechanism.</p><p><b>RESULTS</b>The encapsulation efficiency of huperzine A microspheres prepared by method A and B was 47.60% and 83.50% respectively. Microspheres prepared by method A could sustain release for 35 days with nearly no initial burst release. The release profile fitted well to zero order equation and drug release mainly through degradation and diffusion mechanism. Huperzine A microspheres prepared by method B could sustain release for 21 days with some evidence of initial burst release. The release profile fitted well to the Higuchi equation and drug release was mainly through diffusion mechanism.</p><p><b>CONCLUSION</b>Huperzine A microspheres prepared by method A had more desirable release profile.</p>

Ester prodrug of scutellarin: synthesis, physicochemical property and degradation / 药学学报

<p><b>AIM</b>To establish the fundamentals for the design of scutellarin prodrug and formulation with feasible physicochemical and biopharmaceutical properties by esterifying scutellarin, an active component with poor absorption extracted from Erigeron breviscapus of Chinese medicine.</p><p><b>METHODS</b>With the method of salifying followed by esterifying, ethyl and benzyl ester of scutellarin were synthesized. Glycolamide ester of scutellarin was also synthesized with an improved method. Their structures were confirmed by MS and 1H NMR. The solubility and partition coefficient of the prodrugs were determined and their degradations were investigated in various buffers and in human plasma. The emulsion and cyclodextrin complex of glycolamide ester were prepared and the protection of the ester from degradation was compared in the intestinal tract contents. Furthermore, the degradation of glycolamide ester in the homogenates of various intestinal segments was studied. Results Three prodrugs were synthesized successfully and their structures were confirmed. Glycolamide ester of scutellarin showed better stability in the aqueous solution (t(1/2) approximately =16 d, pH 4.2) and the shortest half-life in the human serum (t(1/2) approximately =7 min). Compared with scutellarin, the solubility of glycolamide ester was increased about ten times in pH 4.0 buffer, and about thirty five times in water. Partition coefficient of the glycolamide ester increased significantly from -2.56 to 1.48. However, the ester degradation in the homogenates of intestinal mucus would be an obstacle for its absorption. The degradation rates were in the order duodenum > ileum > or = jejunum > colon. The emulsion showed a better protection of glycolamide ester from the degradation than cyclodextrin complex.</p><p><b>CONCLUSION</b>Glycolamide ester of scutellarin shows better physicochemical properties than ethyl and benzyl eater of scutellarin, but its stability in intestinal tract needs to be improved. The emulsion or / and colon-targeted delivery may be selected as one of strategies to decrease the presystemic degradation.</p>