Release Of Parent Drug Research Articles

Synthesis, characterization and biochemical study of novel ester prodrugs containing aspirin and ibuprofen

Aspirin and ibuprofen are aryl acids of nonsteroidal anti inflammatory drugs with goodanalgesic. For reducing the gastrointestinal toxicity associated with presence free carboxylicacid functional group in aspirin and ibuprofen, therefore the present work is aimed tosynthesize a novel ester prodrugs of these two drugs. These two novel prodrugs were preparedby the reaction of aspirin or ibuprofen acid chloride with 1,2:5,6-di-O-isopropylidene-α-Dglucofuranose,then deprotection of ester prodrug of aspirin was also accomplished using 70%acetic acid. The purity of the synthesized compounds was established by (TLC), columnchromatography, while their structures were confirmed by (FT-IR, 1HNMR, 13CNMR). Then36 rabbits has been obtained and divided to six groups to show the bioavailability of theprepared prodrugs at some biochemical parameters and compared with the parent drugs andcontrol group. Statistical analysis revealed significant increases in the levels of creatinekinase, alkaline phosphatase, aspartate aminotransferase, alanine amino transferase,glutathione, malondialdehyde, creatinine, uric acid, concentration of Cu, and significantdecreases in the levels of choline esteras, total protein, Zn concentration, while the resultsshowed no significant increases in the activity of lactate dehydrogenase, acid phosphataseand no significant decreases in the levels of albumin, globulin, and iron concentration for theprepared prodrugs compared with the control group. Finally, to ensure the release of parentdrugs(aspirin or ibuprofen), hydrolytic studies of the ester prodrugs were obtained at differentpH (2, 4, 10 and 12) at 25οC, the results showed that the hydrolysis at basic pH were fasterthan acidic pH, so it means that the most hydrolysis will obtain at intestine not at stomach.

Triglyceride-Mimetic Structure-Gated Prodrug Nanoparticles for Smart Cancer Therapy.

Off-target drug release and insufficient drug delivery are the main obstacles for effective anticancer chemotherapy. Prodrug-based self-assembled nanoparticles bioactivated under tumor-specific conditions are one of the effective strategies to achieve on-demand drug release and effective tumor accumulation. Herein, stimuli-activable prodrugs are designed yielding smart tumor delivery by combination of the triglyceride-mimic (TG-mimetic) prodrug structure and disulfide bond. Surprisingly, these prodrugs can self-assemble into uniform nanoparticles (NPs) with a high drug loading (over 40%) and accumulate in tumor sites specifically. The super hydrophobic TG structure can act as a gate that senses lipase to selectively control over NP dissociation and affect the glutathione-triggered prodrug activation. In addition, the impacts of the double bonds in the prodrug NPs on parent drug release and the following cytotoxicity, pharmacokinetics, and antitumor efficiency are further demonstrated. Our findings highlight the promising potential of TG-mimetic structure-gated prodrug nanoparticles for tumor-specific drug delivery.

Oxidation-strengthened disulfide-bridged prodrug nanoplatforms with cascade facilitated drug release for synergetic photochemotherapy

One of the major barriers in utilizing prodrug nanocarriers for cancer therapy is the slow release of parent drug in tumors. Tumor cells generally display the higher oxidative level than normal cells, and also displayed the heterogeneity in terms of redox homeostasis level. We previously found that the disulfide bond-linkage demonstrates surprising oxidation-sensitivity to form the hydrophilic sulfoxide and sulphone groups. Herein, we develop oxidation-strengthened prodrug nanosystem loaded with pyropheophorbide a (PPa) to achieve light-activatable cascade drug release and enhance therapeutic efficacy. The disulfide bond-driven prodrug nanosystems not only respond to the redox-heterogeneity in tumor, but also respond to the exogenous oxidant (singlet oxygen) elicited by photosensitizers. Once the prodrug nanoparticles (NPs) are activated under irradiation, they would undergo an oxidative self-strengthened process, resulting in a facilitated drug cascade release. The IC50 value of the PPa@PTX-S-S NPs without irradiation was 2-fold higher than those of NPs plus irradiation. In vivo, the PPa@PTX prodrug NPs display prolonged systemic circulation and increased accumulation in tumor site. The PPa@PTX-S-S NPs showed much higher efficiency than free PTX or the PPa@PTX-C-C NPs to suppress the growth of 4T1 tumors. Therefore, this novel oxidation-strengthened disulfide-bridged prodrug-nanosystem has a great potential in the enhanced efficacy of cancer synergetic photochemotherapy.

Therapeutic Polymersome Nanoreactors with Tumor-Specific Activable Cascade Reactions for Cooperative Cancer Therapy.

Therapeutic nanoreactors are of increasing interest in precise cancer therapy, which have been explored to in situ produce therapeutic compounds from inert prodrugs or intrinsic molecules at the target sites. However, engineering a nanoreactor with tumor activable cascade reactions for efficient cooperative cancer therapy remains a great challenge. Herein, we demonstrate a polymersome nanoreactor with tumor acidity-responsive membrane permeability to activate cascade reactions for orchestrated cooperative cancer treatment. The nanoreactors are constructed from responsive polyprodrug polymersomes incorporating ultrasmall iron oxide nanoparticles and glucose oxidase in the membranes and inner aqueous cavities, respectively. The cascade reactions including glucose consumption to generate H2O2, accelerated iron ion release, Fenton reaction between H2O2 and iron ion to produce hydroxyl radicals (•OH), and •OH-triggered rapid release of parent drugs can be specifically activated by the tumor acidity-responsive membrane permeability. During this process, the orchestrated cooperative cancer therapy including starving therapy, chemodynamic therapy, and chemotherapy is realized for high-efficiency tumor suppression by the in situ consumed and produced compounds. The nanoreactor design with tumor-activable cascade reactions represents an insightful paradigm for precise cooperative cancer therapy.

Biomimetically engineered Amphotericin B nano-aggregates circumvent toxicity constraints and treat systemic fungal infection in experimental animals

Biomimetic synthesis of nanoparticles offers a convenient and bio friendly approach to fabricate complex structures with sub-nanometer precision from simple precursor components. In the present study, we have synthesized nanoparticles of Amphotericin B (AmB), a potent antifungal agent, using Aloe vera leaf extract. The synthesis of AmB nano-assemblies (AmB-NAs) was established employing spectro-photometric and electron microscopic studies, while their crystalline nature was established by X-ray diffraction. AmB-nano-formulation showed much higher stability in both phosphate buffer saline and serum and exhibit sustained release of parent drug over an extended time period. The as-synthesized AmB-NA possessed significantly less haemolysis as well as nephrotoxicity in the host at par with Ambisome®, a liposomized AmB formulation. Interestingly, the AmB-NAs were more effective in killing various fungal pathogens including Candida spp. and evoked less drug related toxic manifestations in the host as compared to free form of the drug. The data of the present study suggest that biomimetically synthesized AmB-NA circumvent toxicity issues and offer a promising approach to eliminate systemic fungal infections in Balb/C mice.

L-type amino acid transporter 1 utilizing prodrugs: How to achieve effective brain delivery and low systemic exposure of drugs

L-type amino acid transporter 1 (LAT1) is selectively expressed in the blood-brain barrier (BBB) and brain parenchyma. This transporter can facilitate brain delivery of neuroprotective agents and additionally give opportunity to minimize systemic exposure. Here, we investigated structure-pharmacokinetics relationship of five newly synthesized LAT1-utilizing prodrugs of the cyclooxygenase inhibitor, ketoprofen, in order to identify beneficial structural features of prodrugs to achieve both targeted brain delivery and low peripheral distribution of the parent drug. Besides, we studied whether pharmacokinetics and bioconversion of LAT1-utilizing prodrugs in vivo can be predicted in early stage experiments. To achieve these goals, we compared the in vitro brain uptake mechanism of prodrugs, rate of BBB permeation of compounds using in situ perfusion technique, their systemic pharmacokinetics and release of parent drug in brain, plasma and liver of mice. The results revealed that both excellent LAT1-binding ability and transporter utilization in vitro can be achieved by conjugating the parent drug to aromatic amino acids such as phenylalanine in comparison to prodrugs with an aliphatic promoiety. The presence of an aromatic promoiety directly conjugated in meta- or para-position to ketoprofen led to LAT1-utilizing prodrugs capable of delivering the parent drug into the brain with higher unbound brain to plasma ratio and reduced liver exposure than with ketoprofen itself. In contrast, the prodrugs with aliphatic promoieties and with an additional carbon attached between the parent drug and phenylalanine aromatic ring did not enhance brain delivery of ketoprofen. Furthermore, we have devised a screening strategy to pinpoint successful candidates at an early stage of development of LAT1-utilizing prodrugs. The screening approach demonstrated that early stage experiments could not replace pharmacokinetic studies in vivo due to the lack of prediction of the intra-brain/systemic distribution of the prodrugs as well as the release of the parent drug. Overall, this study provides essential knowledge required for improvement of targeted brain delivery and reduction of systemic exposure of drugs via the LAT1-mediated prodrug approach.

Carrier-linked mutual prodrugs of biphenylacetic acid as a promising alternative to bioprecursor fenbufen: design, kinetics, and pharmacological studies

Novel mutual prodrugs of biphenylacetic acid were designed as a promising gastro-protective alternative to fenbufen. Biphenyacetic acid was covalently linked with two non-essential amino acids (D-phenylalanine and glycine) possessing wound healing, analgesic, and anti-inflammatory properties. The prodrugs exhibited good stability in stomach homogenates while hydrolytic release of biphenylacetic acid was observed in phosphate buffer, small intestinal homogenates, and 80% human plasma. In vivo behavior of prodrugs on oral administration to Wistar rats demonstrated 33-45% release of biphenylacetic acid in blood over a period of 24 h indicating passage of intact prodrugs to colon, colonic release of parent drug followed by its absorption through colonic mucosa into systemic circulation. Prodrugs were extensively evaluated for analgesic, anti-inflammatory, anti-arthritic, and ulcerogenic activities. Biochemical, haemetological, histopathological, and radiological studies were also performed. Conversion of bioprecusor fenbufen into mutual carrier-linked prodrugs proved to be promising alternative in terms of reduced ulcerogenic propensity, longer duration of analgesia, enhanced/prolonged anti-inflammatory activity, and superior anti-arthritic effect. These prodrugs could be developed further for chronotherapy of rheumatoid arthritis.

Prodrug Design Targeting Intestinal PepT1 for Improved Oral Absorption: Design and Performance

Oligopeptide transporter 1 (PepT1) plays an essential role in the oral absorption of di-and tripeptides from the digestion of ingested protein. PepT1 has become a striking prodrug-designing target recently, since some poorly absorbed drugs can be modified as peptidomimetic prodrugs targeting intestinal PepT1 to improve membrane permeability, and eventually oral absorption of the parent drug. However, little and no comprehensive attempts have been made to especially focus on the recent developments of prodrugs targeting intestinal PepT1. This article summarized biology, transport mechanism, structure-transport requirements for PepT1 and significant advances on the PepT1-targeted prodrugs within the two decades. The article also aimed to highlight some inspirations and knowledge on the multifunctional PepT1-targeted design, which are necessary for obtaining optimal prodrug candidates. That is the requirements of multifunctional rational PepT1 prodrugs include enough binding affinity for PepT1, controlled or targeted release of parent drug, escapement from P-gp mediated efflux and enhanced chemical/metabolic stability. Several types of peptidomimetic prodrugs reported recently were discussed in detail in this review.

Visible Light Controlled Release of Anticancer Drug through Double Activation of Prodrug.

We designed and synthesized a novel double activatable prodrug system (drug-linker-deactivated photosensitizer), containing a photocleavable aminoacrylate-linker and a deactivated photosensitizer, to achieve the spatiotemporally controlled release of parent drugs using visible light. Three prodrugs of CA-4, SN-38, and coumarin were prepared to demonstrate the activation of deactivated photosensitizer by cellular esterase and the release of parent drugs by visible light (540 nm) via photounclick chemistry. Among these prodrugs, nontoxic coumarin prodrug was used to quantify the release of parent drug in live cells. About 99% coumarin was released from the coumarin prodrug after 24 h of incubation with MCF-7 cells followed by irradiation with low intensity visible light (8 mW/cm(2)) for 30 min. Less toxic prodrugs of CA-4 and SN-38 killed cancer cells as effectively as free drugs after the double activation.

A carbamate-based approach to primaquine prodrugs: Antimalarial activity, chemical stability and enzymatic activation

O-Alkyl and O-aryl carbamate derivatives of the antimalarial drug primaquine were synthesised as potential prodrugs that prevent oxidative deamination to the inactive metabolite carboxyprimaquine. Both O-alkyl and O-aryl carbamates undergo hydrolysis in alkaline and pH 7.4 phosphate buffers to the parent drug, with O-aryl carbamates being ca. 106–1010 more reactive than their O-alkyl counterparts. In human plasma O-alkyl carbamates were stable, whereas in contrast their O-aryl counterparts rapidly released the corresponding phenol product, with primaquine being released only slowly over longer incubation periods. Activation of the O-aryl carbamates in human plasma appears to be catalysed by butyrylcholinesterase (BuChE), which leads to carbamoylation of the catalytic serine of the enzyme followed by subsequent slow enzyme reactivation and release of parent drug. Most of the O-aryl and O-alkyl carbamates are activated in rat liver homogenates with half-lives ranging from 9 to 15h, while the 4-nitrophenyl carbamate was hydrolysed too rapidly to determine an accurate rate constant. Antimalarial activity was studied using a model consisting of Plasmodium berghei, Balb C mice and Anopheles stephensi mosquitoes. When compared to controls, ethyl and n-hexyl carbamates were able to significantly reduce the percentage of infected mosquitos as well as the mean number of oocysts per infected mosquito, thus indicating that O-alkyl carbamates of primaquine have the potential to be developed as transmission-blocking antimalarial agents.

Design, synthesis and biological evaluation of brain-specific glucosyl thiamine disulfide prodrugs of naproxen

Glucosyl derivates exhibited favorable distribution to the brain. However, bidirectional transport of glucose transporter 1 might decrease concentrations of the prodrugs in brain before the release of parent drugs. To overcome this defect, glucosyl thiamine disulfide prodrugs 1a– 1c incorporating naproxen were designed and synthesized. Furthermore, prodrug 2 and 3 were also prepared as control. The favorable physicochemical properties of these prodrugs were verified by stability and metabolism studies. Results from the in vivo distribution study indicated that 1a– 1c, and 1b in particular, significantly increased the level of naproxen in brain when compared to 2 and 3. The study suggested glucosyl thiamine disulfide was a promising carrier to enhance the brain bioavailability of central nervous system active drugs.

Poly(HEMA-Zidovudine) conjugate: A macromolecular pro-drug for improvement in the biopharmaceutical properties of the drug

A macromolecular pro-drug of a known anti-viral agent Zidovudine (AZT) was synthesized and evaluated as a sustained drug delivery system. The pro-drug was synthesized by coupling the drug to 2-hydroxyethyl methacrylate (HEMA) through a succinic spacer to get a monomeric drug conjugate which was polymerized to obtain the polymeric pro-drug. The pr0-drug was subjected for in-vitro drug release study in buffers of pH 1.2 and 7.4. The hydrolytic stability of the pro-drug to pepsin was assessed in simulated gastric fluid (SGF, pH 1.2) and to α-chymotrypsin in simulated intestinal fluid (SIF, pH 7.4). The results showed that the drug release from the polymeric backbone takes place in a sustained manner over a period of 24 h, and the amount of drug released was comparatively higher at pH 7.4. Plasmatic hydrolysis studies of succinylzidovudine showed nearly complete release of AZT. At all pH conditions in the presence and absence of α-chymotrypsin, AZT was released preferentially in comparison with the succinyl derivative. The in-vivo release studies in rabbits after oral administration of AZT conjugate demonstrated a sustained release of parent drug over a period of 24 h. The pro-drug provided a significant increase in the area under the plasma concentration time curve as compared to free drug and extended the plasma half-life from 1.06 h to 8.08 h. This study suggested that, after oral administration, the drug–polymer conjugate can release AZT for prolonged periods, thus improving the pharmacokinetics of AZT and decreasing the fluctuation in plasma drug levels that can lead to toxicity.

Brain uptake of ketoprofen–lysine prodrug in rats

The blood–brain barrier (BBB) controls the entry of xenobiotics into the brain. Often the development of central nervous system drugs needs to be terminated because of their poor brain uptake. We describe a way to achieve large neutral amino acid transporter (LAT1)-mediated drug transport into the rat brain. We conjugated ketoprofen to an amino acid l-lysine so that the prodrug could access LAT1. The LAT1-mediated brain uptake of the prodrug was demonstrated with in situ rat brain perfusion technique. The ability of the prodrug to deliver ketoprofen into the site of action, the brain intracellular fluid, was determined combining in vivo and in vitro experiments. A rapid brain uptake from blood and cell uptake was seen both in in situ and in vivo experiments. Therefore, our results show that a prodrug approach can achieve uptake of drugs via LAT1 into the brain intracellular fluid. The distribution of the prodrug in the brain parenchyma and the site of parent drug release in the brain were shown with in vivo and in vitro studies. In addition, our results show that although lysine or ketoprofen are not LAT1-substrates themselves, by combining these molecules, the formed prodrug has affinity for LAT1.

No Auxiliary, No Byproduct Strategy for Water-Soluble Prodrugs of Taxoids: Scope and Limitation of O−N Intramolecular Acyl and Acyloxy Migration Reactions

Since numerous new taxoids active against multidrug resistant (MDR) tumors have been developed and their poor water-solubility is a very real problem in intravenous administration, we have designed and synthesized a series of novel water-soluble taxoid prodrugs (isotaxoids). These prodrugs, a 2'-O-isoform of taxoids, showed promising results with higher water solubility (0.8-1.1 mg/mL) and proper kinetics for parent drug release by a simple pH-dependent chemical mechanism via O-N intramolecular acyl migration. No additional functional auxiliaries are released during the conversion to parent drugs, which would be an advantage in toxicology and general pharmacology, and the cost for the evaluations of auxiliary units in these fields could be saved in prodrug development. In addition, we demonstrate for the first time the successful application of the O-N intramolecular acyloxy migration reaction in the prodrug design, with the exception of the tert-butyloxycarbonyl group, and that this reaction can be provided with no organic solvent and no side products.

Improvement of warfarin biopharmaceutics by conjugation with poly(ethylene glycol)

One of the most used and useful polymers, poly(ethylene glycol) (PEG) was used as a carrier for warfarin. The drug-polymer conjugate was freely water soluble at room temperature. The hydrolytic stability of the PEG-warfarin was investigated at physiological pH and confirmed the stability of the conjugate. In vivo release studies demonstrated a good release of parent drug, without the initial high plasma level of warfarin.

Improvement of physicochemical and biopharmaceutical properties of theophylline by poly(ethylene glycol) conjugates

In the present paper two theophylline esters with poly (ethylene glycol) (PEG) and methoxy poly (ethylene glycol) (mPEG) were prepared. Quantitative yields of the pure products were obtained. Unlike the free drug, the drug–polymer conjugates are freely water-soluble at room temperature. In vitro release experiments in aqueous buffer demonstrate that both conjugates are stable in buffer of pH 7.4 and 1.2. In vivo release studies after oral administration of theophylline conjugates demonstrate a good release of parent drug.

ChemInform Abstract: Controlled Drug Release: New Water‐Soluble Prodrugs of an HIV Protease Inhibitor.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Controlled drug release: new water-soluble prodrugs of an HIV protease inhibitor

We designed and synthesized a series of highly water-soluble prodrugs of an HIV protease inhibitor, KNI-727 ( 1), containing tandem-linked two auxiliary units, a solubilizing moiety and a self-cleavable spacer. Prodrugs with an ionized amino group at the solubilizing moiety exhibited a remarkable increase of water-solubility (>10 4 fold) compared to the parent drug 1. These prodrugs released 1 not enzymatically, but chemically via an intramolecular cyclization-elimination reaction through an imide formation in physiological conditions. Diversified rates of parent drug release were observed when the chemical structure of both the solubilizing and the spacer moieties were modified. This new approach for water-soluble prodrugs will enable to control chemically the release of parent drug as well as to maintain high water-solubility.

Selective transfer of a lipophilic prodrug of 5-fluorodeoxyuridine from immunoliposomes to colon cancer cells

A monoclonal antibody against the rat colon carcinoma CC531 was covalently coupled to liposomes containing a dipalmitoylated derivative of the anticancer drug FUdR as a prodrug in their bilayers. We investigated the in vitro interaction of these liposomes with CC531 target cells and the mechanism by which they deliver the active drug FUdR intracellularly to the cells by monitoring the fate of the liposomal bilayer markers cholesterol-[ 14C]oleate and [ 3H]cholesteryloleylether as well as the 3H-labeled prodrug and colloidal gold as an encapsulated liposome marker. After binding of the immunoliposomes to the cell surface, only limited amounts were internalized as demonstrated by a low level of hydrolysis of liposomal cholesterol ester and by morphological studies employing colloidal gold-labeled immunoliposomes. By contrast, already within 24 h immunoliposome-incorporated FUdR-dP was hydrolyzed virtually completely to the parent drug FUdR intracellularly. This process was inhibited by a variety of endocytosis inhibitors, indicating that the prodrug enters and is processed by the cells by a mechanism involving an endocytic process, resulting in intracellular FUdR concentrations up to 3000-fold higher than those in the medium. Immunoliposomes containing poly(ethyleneglycol) (PEG) chains on their surface, with the antibody coupled either directly to the bilayer or at the distal end of the PEG chains were able to deliver the prodrug into the tumor cells at the same rate as immunoliposomes without PEG. Based on these observations, we tentatively conclude that during the interaction of the immunoliposomes with the tumor cells the lipophilic prodrug FUdR-dP is selectively transferred to the cell surface and subsequently internalized by constitutive endocytic or pinocytic invaginations of the plasma membrane, thus ultimately delivering the prodrug to a lysosomal compartment where hydrolysis and release of parent drug takes place. This concept allows for an efficient delivery of a liposome-associated drug without the need for the liposome as such to be internalized by the cells.

Drug targeting to the kidney with low molecular weight proteins

This paper reviews the design of a drug targeting strategy for renal specific delivery and endorenal release of drugs using low-molecular-weight proteins (LMWPs). In general, LMWPs are known to be filtered and subsequently reabsorbed by the proximal tubular cells of the kidneys. Within these cells LMWPs are catabolized in lysosomes due to prevalence of proteolytic enzymes and pH of 4-5. As such, these LMWPs might serve as drug carriers that release drugs site-specifically in the kidneys. The ability of the kidney to release the parent drug from drug-LMWP conjugates and drug-spacer derivatives by enzymatic or chemical hydrolysis of the connecting bond has been tested by incubation experiments in renal cortex homogenates and lysosomal lysates. Drug-LMWP conjugates of naproxen, sulfamethoxazole and dopamine have also been studied in vivo. The pharmacokinetics of these conjugates have been examined in freely moving rats and compared to those obtained after injection of equivalent doses of unreacted mixtures of drug and protein. In addition, the disposition of the drug-conjugated LMWP has been studied by radioactive-imaging with a gamma-camera. These studies demonstrated that the kidneys are the main site of uptake of drug-conjugated LMWPs and that the drugs are renally uncoupled and finally excreted in the urine. gamma-Camera experiments revealed a predominant renal uptake of radio-iodinated drug-conjugated LMWPs. Coadministration of an excess of the native LMWP resulted in a pronounced decrease of urinary (parent) drug excretion, suggesting competition for proximal tubular uptake between the LMWP and the drug-conjugated LMWP. Endorenal parent drug release from the LMWP was demonstrated for drugs with carboxyl groups and amino groups. The NSAID, naproxen, was shown to be released from the LMWP conjugate in vivo, provided that coupling via its carboxyl group was performed via an ester bond using a L-lactic acid spacer. If naproxen was directly coupled to the protein via an amide linkage, renal proteolysis of the LMWP-conjugated drug gave rise to the formation of a naproxen-lysine derivative. Interestingly, this product has been demonstrated to be at least as active in inhibiting prostaglandin synthesis as naproxen itself. Sulfamethoxazole was shown to be endorenally released from a drug-LMWP conjugate, if its primary amino group was coupled to the LMWP via an acid-sensitive spacer. Apart from the altered kinetics of the drug itself, the selective renal distribution was further demonstrated by the absence of its hepatically formed metabolite N-4-acetylsulfamethoxazole in urine. This metabolite was abundantly present in the control experiments after injection of the drug in its uncoupled form. Parent drug regeneration in the kidney was further demonstrated for a dopamine-LMWP conjugate, linked through its amino group via a similar acid-sensitive spacer. Within a relatively low dose range of lysozyme, a dose-dependent endorenal dopamine release could be demonstrated. In principle, drugs released within the proximal tubular cell may leave this cell at the basolateral membrane (blood site) or at the brush-border membrane (urine site). Renal delivery of LMWP-conjugated naproxen resulted in detectable plasma levels of the parent drug. In contrast, in the case of LMWP-conjugated sulfamethoxazole and dopamine, no (increase in) plasma levels of the free drugs were measured.