Piperazinylalkyl prodrugs of naproxen improve in vitro skin permeation.

Novel morpholinyl (4a) and piperazinylalkyl (4b-e) esters were synthesized and evaluated in vitro for their properties as bioreversible topically administered dermal prodrugs of naproxen. These ionizable prodrugs exhibited various aqueous solubilities and lipophilicities, depending on the pH of medium. As indicated by octanol-buffer partition coefficients (logP(app)) at pH 7.4, all of the prodrugs were significantly more lipophilic (logP(app)=0.7-3.9) than naproxen (logP(app)=0.3). Furthermore, the most aqueous of the soluble prodrugs (4b-d) were only 2-3-fold less soluble in an aqueous buffer of pH 7.4 ( approximately 30-50 mM) than was naproxen ( approximately 100 mM). At a pH of 5.0, prodrugs showed a generally higher aqueous solubility and similar logP(app) values, compared to naproxen. The chemical and enzymatic hydrolysis of prodrugs at 37 degrees C was investigated in aqueous buffer solutions (pH 5.0 and 7.4) and in 80% human serum (pH 7.4), respectively. The prodrugs showed moderate chemical stability (t(1/2)=15-150 days at pH 5.0), and they were hydrolyzed enzymatically to naproxen, with half-lives ranging from 0.4 to 77 min. In permeation studies using post-mortem human skin in vitro, the flux of naproxen was 6.5 and 1.6 nmol/cm(2). h in a saturated aqueous buffer vehicle of pH 7.4 and 5.0, respectively. Among the prodrugs, two piperazinyl derivatives (4c and 4d) resulted in a 9- and 4-fold enhancement of permeation, respectively, when compared to naproxen itself at pH 7.4. 4c also resulted in a significantly (4-fold) better permeation than naproxen at pH 5.0. In conclusion, piperazinyl esters improved skin permeation of naproxen and are promising prodrugs of naproxen for topical drug delivery.     

Oligoethylene ester derivatives of ketoprofen,naproxen and diclofenac as oral prodrugs: a pharmacological evaluation

Polyoxyethylene esters of ketoprofen (1a-e), naproxen (2a-e) and diclofenac (3a-e) were tested in vitro to determine their stability in pH 7.4 phosphate buffer and in simulated gastric fluid (pH 2.0 buffer) and their susceptibility in undergoing enzymatic cleavage in human plasma. Furthermore their in vivo antiinflammatory and analgesic activity and GI toxicity were evaluated in rodents. All the prodrugs showed a good stability both in pH 7.4 phosphate buffer and in pH 2.0 buffer. They were readily hydrolyzed by human plasma and, for each group of prodrugs, no significant difference in hydrolysis rate was observed as the length of the oligoethylene chain increased. Esters 1a-e, 2a-e and 3a-e showed an anti-inflammatory activity (expressed as inhibition percent of carrageenan-induced edema in the rat) similar to that of their respective parent drug although at higher doses. The results obtained in the writhing test in mice demonstrated that all the prodrugs tested exhibited, following acute administration, a good analgesic effect. Furthermore these esters were significantly less irritating to the gastric mucosa, although administered at doses higher than the respective parent drug.     

New oligoethylene ester derivatives of 5-iodo-2'-deoxyuridine as dermal prodrugs: synthesis, physicochemical properties, and skin permeation studies.

Five new oligoethylene ester derivatives (9-13) of 5-iodo-2'-deoxyuridine (IDU) were synthesized and assayed to determine their lipophilicity by both experimental lipophilicity indices (log K') and calculated partition coefficients (CLOGP). In vitro experiments were carried out to evaluate the chemical and enzymatic stability and fluxes through excised human skin of these new IDU derivatives. Esters 9-13 showed increased lipophilicity compared with the parent drug (IDU), had good stability in phosphate buffer (pH 7.4), and were readily hydrolyzed by porcine esterase. No correlation between lipophilicity and skin permeation fluxes of synthesized esters 9-13 was observed. Results from in vitro percutaneous absorption studies showed that, among all esters synthesized, only esters 9 and 10 significantly increased the cumulative amount of IDU that penetrated through excised human skin compared with the parent drug (IDU).     

Transport and degradation characteristics of methotrexate dialkyl ester prodrugs across tape-stripped hairless mouse skin

A series of methotrexate dialkyl esters were examined with respect to their permeability across tape-stripped hairless mouse skin. The dialkyl esters showed a parabolic permeability versus side chain length relationship with the dimethyl ester being the most permeable compound. These compounds were also found to undergo an increased degree of degradation with increased ester chain length during the diffusion process, while with substantially reduced degradation occuring with the branched chain diisopropyl ester. No measurable methotrexate was formed during the course of the experiment, apparently due to the chemical and enzymatic stability of the intermediate - and -γ-monoesters.     

Glycosyl derivatives of dopamine and L-dopa as anti-Parkinson prodrugs: synthesis,pharmacological activity and in vitro stability studies

Novel glycosyl derivatives of dopamine and L-dopa (I-IV) are synthesized in order to overcome the problem of blood-brain barrier low permeability of dopamine and of low bioavailability of its precursor L-dopa. Esters synthesized link dopamine and L-dopa, by a succinyl linker, to C-3 position of glucose (I and II) and to C-6 of galactose (II and IV). The chemical and enzymatic stabilities of esters synthesized were evaluated in order to determine both their stability in aqueous medium and their feasibility in undergoing enzymatic cleavage by rat plasma to regenerate the original drug. Furthermore, we have shown the central effects of esters I-IV on classic dopaminergic models, such as morphine induced locomotion and reserpine-induced hypolocomotion. From the result obtained compounds I-IV appeared moderately stable in a pH 7.4 buffered solution and in rat plasma. Furthermore, pharmacological studies showed that both dopamine derivatives (I and II) were equiactive in reversing reserpine-induced hypolocomotion in rats, and both were more active than L-dopa or ester III and IV, while II and III were more potent in reducing morphine-induced locomotion than I and IV. The minimal vascular effects of these derivatives allow us to underline the possibility to use them in pathologies, such as Parkinson disease, characterised by an evident decreasing of dopamine concentration in the brain.     

Ketorolac amide prodrugs for transdermal delivery: stability and in vitro rat skin permeation studies

Various amide prodrugs of ketorolac were synthesized and their rat skin permeation characteristics were determined. The solubility of the prodrugs in propylene glycol (PG) was determined at 37 degrees C while lipophilicity was obtained as 1-octanol/water partition coefficient (logP) and capacity factor (k') using HPLC. Stability of the prodrugs in rat skin homogenate, plasma and liver homogenate was investigated to observe the enzymatic degradation. Rat skin permeation characteristics of the prodrugs saturated in PG were investigated using the Keshary-Chien permeation system at 37 degrees C. The logP value of the prodrugs increased up to 4.28 with the addition of various alkyl chain to ketorolac which has a logP of 1.04. Good linear relationship between logP and capacity factor was observed (r(2)=0.89). Amide prodrugs were converted to ketorolac only in rat liver homogenate. However, the skin permeation rate of amide prodrugs did not significantly increase, probably due to their low aqueous solubility. Chemical modification of the ketorolac amide prodrug and/or the selection of proper vehicle to increase aqueous solubility would be necessary for an effective transdermal delivery of ketorolac.     

An in vitro system for prediction of oral absorption of relatively water-soluble drugs and ester prodrugs

We developed an in vitro system simulating the physiological condition in the gastrointestinal (GI) tract for prediction of oral absorption of relatively water-soluble drugs and ester prodrug pivampicillin. This evaluation system includes a drug-dissolving vessel (DDV, assumed stomach), a pH adjustment vessel (PAV, assumed intestine) and a side-by-side diffusion chamber that is mounted by a Caco-2 monolayer, which is grown on a polycarbonate filter, or by a rat intestine between the donor and receiver compartments. Our proposed system can accommodate large amounts of solid drugs, simulating a drastic pH change process in GI tract, that is, an orally administered solid drug is dissolved in the stomach (pH 1-2) and transferred to the intestine (pH 6), and that dissolution process can also be monitored. The optimal flow rates for our system are 0.35-1.10 ml/min. Using this system, cumulative permeations of eight relatively water-soluble drugs were compared, and these cumulative permeations indicated the ability of drug absorption in humans. Drugs that permeated across a Caco-2 monolayer at cumulative permeation of more than 0.03% or over 0.04% in rat intestine can be almost completely absorbed in humans. If the cumulative permeation across a Caco-2 monolayer is lower than 0.03% or below 0.04% in the rat intestine, there was a good linear correlation between cumulative permeation across a Caco-2 monolayer and oral absorption in humans, or between cumulative permeation across a rat intestine and oral absorption in humans. In the case of relatively water-soluble drugs, a good linear correlation was obtained between cumulative permeation across a Caco-2 monolayer and cumulative permeation across a rat intestine. This result indicates that it is possible to predict the oral absorption of a relatively water-soluble drug in humans based on the cumulative permeation of the drug across a Caco-2 monolayer and/or a rat intestine. The time course of permeation of the ester prodrug pivampicillin, which is metabolized in a Caco-2 monolayer or in a rat intestine, was also evaluated. It stated clearly that it is also possible to predict the oral absorption of pivampicillin in humans based on the cumulative permeation across a Caco-2 monolayer or rat intestine. Our newly developed system enables more kinds of oral preparations and also pH-dependent soluble drugs to be evaluated.     

三环苦参酯类前药的设计、合成及其药动学研究

目的设计合成全新三环苦参酯类前药衍生物,旨在改善其体内药动学行为。方法以苦参碱为原料,经碱水解开环、羧基成酯、12N-苄基取代、甲酯还原得到三环苦参醇母体化合物。采用两种前药制备策略,合成11个酯类前药和2个含有二硫键的前药化合物。选用SD大鼠测定化合物的口服药动学(PK)参数。结果与结论合成了13个未见文献报道的全新结构的三环苦参酯类前药,其结构经HR-MS、~1H-NMR、~(13)C-NMR谱确证。药动学研究表明,不同类型前药的主要药动学参数均低于原药,cLogP值在合理范围内(0~4)的原药可能不适合使用前药策略来改善其药动学行为。     

Development of absorption furosemide prodrugs: synthesis, in vitro and in vivo evaluation.

Six acyloxymethyl esters of Furosemide were synthesized and the structures were determined by chemical and spectroscopic methods. Lipophilicity parameters were analysed by high performance liquid chromatography (HPLC). Hydrolysis performances in human plasma and intestinal fluids anticipate their properties as absorption prodrugs of Furosemide. A bioavailability study carried out with 8 male Wistar rats with one of the synthesized prodrug (acetyloxymethyl 4-chloro-N-furfuryl-5-sulfamoylanthranilate) showed a greater absorption in relation to Furosemide. The percentages of mean urinary recovery of Furosemide for the prodrug and for the standard solution of the drug were 20.84 and 14.36 respectively. The doses were 10 mg/Kg in Furosemide. The analytical determinations of Furosemide in biological fluids were done by HPLC.     

Interactions of C12 surfactants with the skin: studies on enzyme release and percutaneous absorption in vitro

Using an in vitro penetration cell, it has been shown that enzymes (acid phosphatase, lactate dehydrogenase and N-acetylglucosaminidase) are released from rat-skin slices in response to contact with two irritant C12 surfactants, sodium laurate and sodium lauryl sulphate, but not with the non-irritant sodium lauroyl isethionate. About 3-5 hr contact of the stratum corneum with surfactant and a long incubation time (24 hr) were required for enzyme release. Adsorption and penetration of the two effective surfactants was also studied and the results for sodium lauryl sulphate suggested a relationship between enzyme release and adsorption of surfactant. However, no such simple relationship was observed for sodium laurate, emphasizing the complex nature of surfactant interactions with the skin.     

Pharmacokinetic and ulcerogenic studies of naproxen prodrugs designed for specific brain delivery

Naproxen (Nap) is an NSAID used as a neuroprotective agent to treat several neurodegenerative diseases. The observed limited brain bioavailability of the drug prompted the design of several chemical delivery systems. We report the synthesis and preliminary in vitro and in vivo investigations of Nap prodrugs with dihydropyridine (I) and ascorbic acid (II) through an ester spacer to target specific brain delivery of Nap. The purpose of this study was to determine the brain bioavailability of Nap after oral administration of the prodrugs in rats. The results showed moderate oral bioavailability of prodrugs (AUC = 53–94 h · μg/mL) in rats compared with parent Nap (AUC = 155 h · μg/mL) at equimolar doses. Contrarily, there was a twofold increase in Nap levels in the brain with the prodrugs compared to parent Nap. The enhanced brain bioavailability may be attributed to the specific carrier system in addition to the reduced percentage of plasma protein binding of Nap. Plasma protein binding of the tested prodrugs was investigated in vitro using equilibrium dialysis. The percentage of plasma free fraction of prodrugs (9–15%) was significantly greater than that of Nap (about 5%) when tested at 20 μM, illustrating more available prodrug to cross the blood brain barrier. A significant decrease in gastric ulcerogenicity of the prodrugs compared with parent Nap was also noted. In conclusion, oral dihydropyridine and ascorbate prodrugs for brain site-specific delivery of Nap may be promising candidates for safe, chronic use of NSAIDs for the treatment of neurodegenerative diseases.     

Synthesis, characterization and in vitro hydrolysis studies of ester and amide prodrugs of dexibuprofen

Ten prodrugs of dexibuprofen having ester and amide moieties instead of free carboxylic acid which involves in gastrointestinal side effects have been synthesized. Dexibuprofen acid chloride was condensed with different amino acid methyl ester hydrochlorides and five alcohols to afford the amide and ester prodrugs. All of the synthesized prodrugs were characterized by their mp, R _f, elemental analysis, FTIR, ¹H NMR, and ¹³C NMR spectroscopy. The in vitro hydrolysis studies in plasma reflect prodrugs have been varied in terms of reactivity toward hydrolysis, owing to the different chemical structures. In alkyl substitution the branched chain alkyl substituents or aromatic substituents resulted in enhanced lipophilicity but diminished dissolution and hydrolysis rate. The amide prodrugs with branched and aromatic substitution can also be considered for sustained release. Prodrugs are less irritating to gastric mucosa than dexibuprofen.     

萘普生缓释微囊的制备及其体外释药研究

目的 对以壳聚糖和海藻酸钠为囊材,通过复凝聚法将萘普生微囊化的制备工艺和体外释药进行研究.方法 以微囊的药物包封率为制备工艺优化指标,得出成囊的最佳制备工艺条件.结果 最佳工艺条件为:搅拌速度500 r·min-1,pH4.0,壳聚糖浓度3%,反应温度50℃.结论 以最佳制备工艺条件制备了可生物相容,自然降解无毒的载药微囊,重现性好,工艺稳定,同时体外溶出实验表明,该微囊具有较好的缓释作用.     

Paclitaxel-loaded glyceryl palmitostearate nanoparticles: in vitro release and cytotoxic activity

Solid lipid nanoparticles (SLNs) of paclitaxel using glyceryl palmitostearate (GPS) as matrix were prepared by modified hot homogenization method. The SLNs were characterized for mean particle size, percent entrapment efficiency, and zeta potential, which were found to be 207 nm, 96.26%, and ?28.26 mV, respectively. Transmission electron microscopic studies revealed that the prepared SLNs were of spherical shape. Drug retarding efficiency of the lipid (GPS) was better in pH 7.4 compared with pH 3.5. The release profile showed tendency to follow Higuchi diffusion pattern in both the media. Chemosensitivity assay carried out using B16F10 cell lines showed that antiproliferative activity of paclitaxel was not hindered because of encapsulation.     

Straight-chain naltrexone ester prodrugs: diffusion and concurrent esterase biotransformation in human skin

Naltrexone (NTX) is an opioid antagonist used for treatment of narcotic dependence and alcoholism. Transdermal naltrexone delivery is desirable to help improve patient compliance. The purpose of this study was to increase the delivery rate of NTX across human skin by using lipophilic alkyl ester prodrugs. Straight-chain naltrexone-3-alkyl ester prodrugs of 2-7 carbons in chain length were synthesized and evaluated. In vitro human skin permeation rates were measured using a flow-through diffusion cell system. The melting points, solubilities, and skin disposition of the drugs were determined. The prodrugs were almost completely hydrolyzed on passing through the skin and appeared as NTX in the receiver compartment. The mean NTX flux from the prodrug-saturated solutions exceeded the flux of NTX base by approximately 2-7-fold. The amount of drug detected in the skin was significantly greater after treatment with the prodrug solutions compared with treatment with NTX base. The extent of parent drug (NTX) regeneration in the intact skin ranged from 28 to 91%. Higher NTX regeneration percentages in skin appeared to correlate with increased drug delivery rates. Definitively, the highly oil-soluble prodrugs provide a higher NTX flux across human skin in vitro and undergo significant metabolic conversion in the skin.     

Design, synthesis and in vitro evaluation of vinyl ether type polymeric prodrugs of ibuprofen, ketoprofen and naproxen

2-(1-Propene)oxyethyl phthalimide (3) was synthesized from reaction of 1-(2-chloroethoxy)propene (2) with potassium-t-butoxide and polymerized by cationic polymerization method using BF(3).OEt(2) as an initiator at -78 degrees C to obtain polymer 4. Then, polymer 4 was hydrazinolized by hydrazine and gave polymer 5 containing pendent amine groups. Three non-steroidal anti-inflammatory drugs (NSAIDs), ibuprofen, ketoprofen and naproxen were covalently linked to polymer 5 through amide groups by reacting chloroacylated drugs 6a-6c with amine groups of polymer 5 to obtain three polymeric prodrugs 7a-7c. All the synthesized compounds were characterized by FT-IR, (1)H and (13)C NMR spectroscopy techniques. The polymer-drug conjugates were hydrolyzed in cellophane member dialysis bags containing aqueous buffered solutions (pH 1, 7.4 and 10) at 37 degrees C and the hydrolysis solutions were detected by UV spectrophotometer at selected intervals. The results showed that the drugs could be released by hydrolysis of the amide bonds. The release profiles indicated that the hydrolytic behavior of polymeric prodrugs strongly depends on the pH of the hydrolysis solution. The results suggested that the vinyl ether type polymers could be the useful carriers for release of profens in controlled release systems.     

Glyceride derivatives as potential prodrugs: synthesis, biological activity and kinetic studies of glyceride derivatives of mefenamic acid

In order to reduce the gastrointestinal side effect, of mefenamic acid, its carboxylic group was condensed with the hydroxyl group of 1,2,3-trihydroxy propane 1,3-dipalmitate/stearate to give 3a and 3b. These compounds were evaluated for their gastric toxicity, anti-inflammatory activity by the carageenan induced paw oedema test and analgesic activity by the acetic acid induced writhing method. The release of mefenamic acid from the esters 3a and 3b was studied at pH 3, 4, 5 and 7.4 with direct analysis by reverse phase HPLC using acetonitrile:acetate buffer (0.1 M, pH 3.5): methanol (40:25:35) at 1 mL/min. The prodrugs showed less hydrolysis at pH 5 compared to pH 7.4 indicating that the prodrugs do not dissociate at stomach pH but release mefenamic acid at pH 7.4 in adequate amounts. The hydrolysis studies were also performed in rat plasma. A higher plasma concentration of mefenamic acid was observed in animals treated with 3a and 3b compared to the animals treated with the parent drug, and even after 8 h the concentration of mefenamic acid was 2 times higher. The peak plasma concentration of mefenamic acid in animals treated with mefenamic acid was attained in 1.5 h compared with 2 h in the case of prodrugs treated animals. The prodrugs showed less gastric ulceration compared to mefenamic acid at 100 mg/kg, a severity index of 1.10, 1.22 being observed with 3a, 3b and with mefenamic acid a severity index of 2.37 was observed. The prodrugs showed better anti-inflammatory activity compared to the parent drug and analgesic activity comparable to the parent drug. These findings suggest that the prodrugs 3a and 3b synthesized might be used as biolabile prodrugs of mefenamic acid with increased bioavailability and less gastrointestinal side effects.     

Percutaneous absorption and skin decontamination of PCBs: in vitro studies with human skin and in vivo studies in the rhesus monkey

Knowledge of the entry of polychlorinated biphenyls through the skin into the body and subsequent disposition aids estimation of potential for human health hazard. [14C]Aroclor 1242 and [14C]Aroclor 1254 were separately administered intravenously and topically to rhesus monkeys. Following iv administration, 30-d excretion was 39.4 +/- 5.9% urine and 16.1 +/- 0.8% feces (total 55.5 +/- 5.1%) for Aroclor 1242, and 7.0 +/- 2.2% urine and 19.7 +/- 5.8% feces (total 26.7 +/- 7.5%) for Aroclor 1254. Mineral oil and trichlorobenzene are common PCB cosolvents in transformers. Skin absorption of Aroclor 1242 was 20.4 +/- 8.5% formulated in mineral oil and 18.0 +/- 3.8% in trichlorobenzene (p greater than .05). Absorption of Aroclor 1254 was 20.8 +/- 8.3% in mineral oil and 14.6 +/- 3.6% in trichlorobenzene (p greater than .05). PCBs are thus absorbed through skin, and excretion from the body is slow. Vehicle (trichlorobenzene or mineral oil) did not affect percutaneous absorption. In vitro skin absorption in human cadaver skin did not correlate with in vivo findings. This was due to lack of PCB partition from skin into the water receptor fluid, even with addition of 6% Oleth 20 (Volpo 20) solubilizer. Skin decontamination of PCBs showed soap and water to be as effective as or better than the solvent ethanol, mineral oil, and trichlorobenzene in removing PCBs from skin. There is a dynamic time lapse for PCBs between initial skin contact and skin absorption (irreversible removal). Thus initially most PCBs could be removed from skin, but this ability decreased with time to the point where at 24 h only about 25% of the initial PCB skin dose could be recovered with skin washing.     

Chitinosan-drug complexes: effect of electrolyte on naproxen release in vitro

The purpose of this study was to examine the potential use of electrolytes to control naproxen sodium (I) release from chitinosan (II) tablets. An ANOVA was employed to evaluate the effects of molecular weight (MW) of II, electrolyte valence (EV), and pH of the dissolution medium on I's release. The intrinsic dissolution rates and saturation solubilities of I were determined at each of the pHs used. Directly compressed tablets were prepared from admixtures containing: I, NaCl, CaCl(2), or AlCl(3), Mg stearate, and II. The tablets were characterized for their dimensions, crushing strengths, friability, disintegration times, and in vitro dissolution profiles. The slopes of the log-log cumulative percent released-time curves (t=0-5 h) were compared using ANOVA. Based on the ANOVA, each of the variables-chitinosans, EVs, and pHs-significantly affected drug release (P<0.05). Besides the poor aqueous solubility of I, the factors possibly affecting drug release included: (a) the formation of a rate-limiting II gel barrier; (b) the interaction of I with ionized amino groups of II; (c) the effect of electrolyte on the II's gel barrier formation; and/or (d) decreased aqueous solubility of I in the presence of electrolyte.