Synthesis and evaluation of Ketorolac ester prodrugs for transdermal delivery

Recent advances in pain management based on nanoparticle technologies

BACKGROUND

Pain is a vital sense that indicates the risk of injury at a particular body part. Successful control of pain is the principal aspect in medical treatment. In recent years, the advances of nanotechnology in pain management have been remarkable. In this review, we focus on literature and published data that reveal various applications of nanotechnology in acute and chronic pain management.

METHODS

The presented content is based on information collected through pain management publications (227 articles up to April 2021) provided by Web of Science, PubMed, Scopus and Google Scholar services.

RESULTS

A comprehensive study of the articles revealed that nanotechnology-based drug delivery has provided acceptable results in pain control, limiting the side effects and increasing the efficacy of analgesic drugs. Besides the ability of nanotechnology to deliver drugs, sophisticated nanosystems have been designed to enhance imaging and diagnostics, which help in rapid diagnosis of diseases and have a significant impact on controlling pain. Furthermore, with the development of various tools, nanotechnology can accurately measure pain and use these measurements to display the efficiency of different interventions.

CONCLUSIONS

Nanotechnology has started a new era in the pain management and many promising results have been achieved in this regard. Nevertheless, there is still no substantial and adequate act of nanotechnology in this field. Therefore, efforts should be directed to broad investigations.

GSH/enzyme-responsive 2-sulfonyl-1-methylimidazole prodrug for enhanced transdermal drug delivery and therapeutic efficacy against hyperthyroidis

Novel GSH/enzyme-responsive anti-hyperthyroidism prodrugs designed for transdermal delivery of 2-sulfonyl-1- methylimidazole (MMI) were synthesized by a Michael addition reaction of MMI with propiolic acid (PA) followed by esterification with three long chain fatty alcohols and their structures were characterized by ¹H-NMR, ¹³C-NMR and mass spectrometry. Their maximum steady state flux through rat skin in the PG/W solution was found to be more than 37-times faster than that of MMI. The result may be attributed to the improved lipophilicity of prodrug and rapid bioconversion. The prodrugs were hydrolyzed by esterase on passing through the skin and appeared mainly as intermediate MMI-PA in the receiver compartment and accompanied by a small amount of MMI and intact prodrug. The prodrugs did not release any MMI in the media without GSH or with 100 µM GSH, while the obvious MMI release could be observed within 6.4 h in the media containing 2 mM and 10 mM GSH, and their maximum cumulative release rates reached 95.07% for lauryl alcohol ester prodrug (MMI-PA-OLa). MMI-PA-OLa exhibited a significant inhibition effect on lactoperoxidase (LPO) after being incubated in millimolar GSH media, whose inhibition rate was very similar to that of free MMI with an equivalent dose. These results suggested that MMI-PA-OLa could pass efficiently through the skin and release MMI in response to the intracellular environment.

Lipophilic Conjugates of Drugs: A Tool to Improve Drug Pharmacokinetic and Therapeutic Profiles

Lipophilic conjugates (LCs) of small molecule drugs have been used widely in clinical and pre-clinical studies to achieve a number of pharmacokinetic and therapeutic benefits. For example, lipophilic derivatives of drugs are employed in several long acting injectable products to provide sustained drug exposure for hormone replacement therapy and to treat conditions such as neuropsychiatric diseases. LCs can also be used to modulate drug metabolism, and to enhance drug permeation across membranes, either by increasing lipophilicity to enhance passive diffusion or by increasing protein-mediated active transport. Furthermore, such conjugation strategies have been employed to promote drug association with endogenous macromolecular carriers (e.g. albumin and lipoproteins), and this in turn results in altered drug distribution and pharmacokinetic profiles, where the changes can be 'general' (e.g. prolonged plasma half-life) or 'specific' (e.g. enhanced delivery to specific tissues in parallel with the macromolecular carriers). Another utility of LCs is to enhance the encapsulation of drugs within engineered nanoscale drug delivery systems, in order to best take advantage of the targeting and pharmacokinetic benefits of nanomedicines. The current review provides a summary of the mechanisms by which lipophilic conjugates, including in combination with delivery vehicles, can be used to control drug delivery, distribution and therapeutic profiles. The article is structured into sections which highlight a specific benefit of LCs and then demonstrate this benefit with case studies. The review attempts to provide a toolbox to assist researchers to design and optimise drug candidates, including consideration of drug-formulation compatibility.

Transition-metal-free and facile synthesis of 3-alkynylpyrrole-2,4-dicarboxylates from methylene isocyanides and propiolaldehyde

A transition-metal-free, facile and efficient method for the synthesis of 3-alkynylpyrrole-2,4-dicarboxylates was developed.

Fail-safe nano-formulation of prodrug of sulfapyridine: Preparation and evaluation for treatment of rheumatoid arthritis

Aim of the present study was to give a second life to the long-abandoned drug, sulfapyridine (SP) for its anti-arthritic potential by design of nano-vesicular delivery system. For this, intra-articular delivery of its liposomal formulation was tried. As the prepared formulation exhibited rapid drug leakage, an arthritis responsive prodrug of SP showing lability towards synovial enzymes was synthesized to exploit the over-expression of arthritis specific enzymes. Prodrug (SP-PD) exhibited better retention in liposomes as compared to the drug, preventing its escape from synovium. Hydrolysis of SP-PD in human plasma and synovial fluid indicated its high susceptibility to enzymes. The liposomes of SP-PD exhibited larger mean size, less PDI and higher zeta potential as compared to those for SP liposomes. In arthritic rats, prodrug liposomes were found to reverse the symptoms of inflammation, including the levels of biochemical markers. Liposomes of bio-responsive prodrug, therefore, offer a revolutionary approach in the treatment of rheumatoid arthritis.

Magnetic field distribution modulation of intrathecal delivered ketorolac iron-oxide nanoparticle conjugates produce excellent analgesia for chronic inflammatory pain

Background

Nanoparticles have become one of the most promising among the potential materials used for biomedical applications. However, few researchers have focused on their effects on analgesia. Despite the fact that various nanoparticles have been evaluated for drug delivery and MRI imaging contrast enhancement in clinical settings, no reports have investigated the in vivo synergy of ketorolac iron-oxide nanoparticle conjugates to improve the analgesic effect.

Methods

Ketorolac conjugated magnetic iron oxide nanoparticles (Keto-SPIO) were synthesized via two-stage additions of protective agents and chemical co-precipitation. ICR mice were used to develop inflammatory pain models induced by Complete Freund’s adjuvant (CFA) injection in the hind paw. Different magnet field strengths and polarities were applied to the spinal cord after injecting Keto-SPIO into the theca space. Analgesia behavior was evaluated with the up-down method via von Frey microfilament measurement. Spinal cord tissues were harvested at the end analgesia time point upon induction of the inflammatory pain. The presence of the two cyclooxygenases (COX) in the spinal cord was examined via Western blotting to quantify the changes after intra-thecal Keto-SPIO administration.

Results

Intrathecal Keto-SPIO administration demonstrated a magnetic field-dependent analgesia effect in CFA pain model with a significant reduction in COX expression.

Conclusions

Our results indicated that intrathecal administration of the Keto-SPIO combined magnet field modulated delivery significantly promoted an analgesia effect with suppression of COX in the mice inflammatory pain model.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0375-9) contains supplementary material, which is available to authorized users.

Dendritic polymers for dermal drug delivery

Skin-mediated therapeutic delivery is a potential alternative to traditional drug delivery approaches. However, dermal drug delivery is limited to the molecules with optimal physico-chemical properties. To overcome this barrier for delivering ‘nonideal’ drug molecules across the skin, different drug carriers and penetration enhancement methods have been investigated. Conventional chemical and physical approaches for dermal drug delivery are limited by their skin irritation potential, complexity of application and poor patient compliance. In recent years, dendritic polymers have shown potential in improving the dermal delivery of various molecules. With minimal skin irritation potential and high drug loading capacity, dendrimers offer multiple advantages for improving delivery of drugs across the skin. The current review aims to provide an overview of dendritic polymers for dermal (topical and transdermal) drug delivery.

[Formula: see text]

Exploiting the MeDbz Linker To Generate Protected or Unprotected C-Terminally Modified Peptides

C-terminally modified peptides are important targets for pharmaceutical and biochemical applications. Known methods for C-terminal diversification are limited mainly in terms of the scope of accessible modifications or by epimerization of the C-terminal amino acid. In this work, we present a broadly applicable approach that enables access to a variety of C-terminally functionalized peptides in either protected or unprotected form. This chemistry proceeds without epimerization of C-terminal Ala and tolerates nucleophiles of varying nucleophilicity. Finally, unprotected peptides bearing nucleophilic side chain groups can be selectively functionalized by strong nucleophiles, whereas macrocyclization is observed for weaker nucleophiles. The potential utility of this method is demonstrated through the divergent synthesis of the conotoxin conopressin G and GLP-1(7-36) and analogs.

Synthesis of Peptides Containing C-Terminal Esters Using Trityl Side-Chain Anchoring: Applications to the Synthesis of C-Terminal Ester Analogs of the Saccharomyces cerevisiae Mating Pheromone a-Factor

Peptides containing C-terminal esters are an important class of bioactive molecules that includes a-factor, a farnesylated dodecapeptide, involved in the mating of Saccharomyces cerevisiae. Here, results that expand the scope of solid-phase peptide synthetic methodology that uses trityl side-chain anchoring for the preparation of peptides with C-terminal cysteine alkyl esters are described. In this method, Fmoc-protected C-terminal cysteine esters are anchored to trityl chloride resin and extended by standard solid-phase procedures followed by acidolytic cleavage and HPLC purification. Analysis using a Gly-Phe-Cys-OMe model tripeptide revealed minimal epimerization of the C-terminal cysteine residue under basic conditions used for Fmoc deprotection. (1)H NMR analysis of the unfarnesylated a-factor precursor peptide confirmed the absence of epimerization. The side-chain anchoring method was used to produce wild-type a-factor that contains a C-terminal methyl ester along with ethyl-, isopropyl-, and benzyl-ester analogs in good yield. Activity assays using a yeast-mating assay demonstrate that while the ethyl and isopropyl esters manifest near-wild-type activity, the benzyl ester-containing analog is ca. 100-fold less active. This simple method opens the door to the synthesis of a variety of C-terminal ester-modified peptides that should be useful in studies of protein prenylation and other structurally related biological processes.

Impact of ester promoieties on transdermal delivery of ketorolac

Different types of ketorolac ester prodrugs incorporating tert-butyl (KT), benzyl (KB), heptyl (KH), and diketorolac heptyl (DKH) promoieties were synthesized for the comparison of percutaneous penetration. The prodrugs were characterized according to their melting point, capacity factor, lipophilicity, solubility in 30% ethanol/buffer, enzymatic hydrolysis, in vitro skin permeation, hair follicle accumulation, and in vivo skin tolerance. Interactions between the prodrugs and esterases were predicted by molecular docking. Both equimolar suspensions and saturated solutions in 30% ethanol/pH 7.4 buffer were employed as the applied dose. All of the prodrugs exhibited a lower melting point than ketorolac. The lipophilicity increased in the following order: ketorolac < KT < KB < KH < DKH. The prodrugs were rapidly hydrolyzed to the parent drug in esterase medium, skin homogenate, and plasma, with KT and KB exhibiting higher degradation rates. KT exhibited the highest skin permeation, followed by KB. The flux of KT and KB exceeded that of ketorolac by 2.5-fold and twofold, respectively. KH and DKH did not improve ketorolac permeation but exhibited a sustained release behavior. KT and KH revealed selective absorption into follicles and a threefold greater follicular uptake compared with ketorolac. KB, KH, and DKH slightly but significantly increased transepidermal water loss (TEWL) after consecutive administration for 7 days, whereas ketorolac and KT exhibited no influence on TEWL. According to the experimental results, it can be concluded that an optimal balance between lipophilicity and aqueous solubility is important in the design of a successful prodrug. The acceptable skin tolerance for safe application is also an important consideration.

Evaluation of diclofenac prodrugs for enhancing transdermal delivery

Abstract Objective: The purpose of this study was to evaluate the approach of using diclofenac acid (DA) prodrugs for enhancing transdermal delivery.

METHODS

Methanol diclofenac ester (MD), ethylene glycol diclofenac ester (ED), glycerol diclofenac ester (GD) and 1,3-propylene glycol diclofenac ester (PD) were synthesized and evaluated for their physicochemical properties such as solubilities, octanol/water partition coefficients, stratum corneum/water partition coefficients, hydrolysis rates and bioconversion rates. In vitro fluxes across human epidermal membrane (HEM) in the Franz diffusion cell were determined on DA-, MD-, ED-, GD- and PD-saturated aqueous solutions.

RESULTS

The formation of GD and ED led to the prodrugs with higher aqueous solubilities and lower partition coefficients than those of the parent drug. Prodrugs with improved aqueous solubility showed better fluxes across HEM in aqueous solution than that of the parent drug, with GD showing the highest aqueous solubility and also the highest flux. There is a linear relationship between the aqueous solubility and flux for DA, ED and PD, but GD and MD deviated from the linear line.

CONCLUSION

Diclofenac prodrugs with improved hydrophilicity than the parent drug could be utilized for enhancing transdermal diclofenac delivery.

Modeling the human skin barrier--towards a better understanding of dermal absorption

Many drugs are presently delivered through the skin from products developed for topical and transdermal applications. Underpinning these technologies are the interactions between the drug, product and skin that define drug penetration, distribution, and elimination in and through the skin. Most work has been focused on modeling transport of drugs through the stratum corneum, the outermost skin layer widely recognized as presenting the rate-determining step for the penetration of most compounds. However, a growing body of literature is dedicated to considering the influence of the rest of the skin on drug penetration and distribution. In this article we review how our understanding of skin physiology and the experimentally observed mechanisms of transdermal drug transport inform the current models of drug penetration and distribution in the skin. Our focus is on models that have been developed to describe particular phenomena observed at particular sites of the skin, reflecting the most recent directions of investigation.

Synthesis of peptides containing C-terminal methyl esters using trityl side-chain anchoring: application to the synthesis of a-factor and a-factor analogs

A new cysteine anchoring method was developed for the synthesis of peptides containing C-terminal cysteine methyl esters. This method consists of attachment of Fmoc-Cys-OCH(3) to either 2-ClTrt-Cl or Trt-Cl resins (via the side-chain thiol) followed by preparation of the desired peptide using Fmoc-based SPPS. We applied this method to the synthesis of the mating pheromone a-factor and a 5-FAM labeled a-factor analog. The peptides were obtained with high yield and purity and were shown to be bioactive in a growth arrest assay.

The hydrolysis kinetics of monobasic and dibasic aminoalkyl esters of ketorolac

Six aminoethyl and aminobutyl esters of ketorolac containing 1-methylpiperazine (MPE and MPB), N-acetylpiperazine (APE and APB) or morpholine (ME and MB), were synthesized and their hydrolysis kinetics were studied. The hydrolysis was studied at pH 1 to 9 (for MPE, APE and ME) and pH 1 to 8 (for MPB, APB and MB) in aqueous phosphate buffer (0.16 M) with ionic strength (0.5 M) at 37°C. Calculation of k(obs), construction of the pH-rate profiles and determination of the rate equations were performed using KaleidaGraph® 4.1. The hydrolysis displays pseudo-first order kinetics and the pH-rate profiles shows that the aminobutyl esters, MPE, APB and MB, are the most stable. The hydrolysis of the ethyl esters MPE, APE and ME, depending on the pH, is either fast and catalyzed by the hydroxide anion or slow and uncatalyzed for the diprotonated, monoprotonated and nonprotonated forms. The hydrolysis of the butyl esters showed a similar profile, albeit it was also catalyzed by hydronium cation. In addition, the hydroxide anion is 105 more effective in catalyzing the hydrolysis than the hydronium cation. The hydrolysis pattern of the aminoethyl esters is affected by the number and pKa of its basic nitrogen atoms. The monobasic APE and ME, show a similar hydrolysis pattern that is different than the dibasic MPE. The length of the side chain and the pKa of the basic nitrogen atoms in the aminoethyl moiety affect the mechanism of hydrolysis as the extent of protonation at a given pH is directly related to the pKa.

Iontophoretic permeation of lisinopril at different current densities and drug concentrations

PURPOSE

The purpose of the present work was to assess iontophoretic permeation of Lisinopril at different current densities and concentrations for development of patient-controlled active transdermal system.

METHODS

In vitro iontophoretic transdermal delivery of Lisinopril across the pigskin was investigated at three different drug concentrations and three different current densities (0.25- 0.75 mA/cm2) in the donor cell of the diffusion apparatus, using cathodal iontophoresis along with the passive controls.

RESULTS

For passive permeation, the steady state flux significantly increased with the increasing of donor drug concentration. At all concentration levels, iontophoresis considerably increased the permeation rate compared to passive controls. Iontophoretic transport of Lisinopril was to be found increase with current densities. Flux enhancement was highest at the lowest drug load and lowest at the highest drug load.

CONCLUSION

The obtained results indicate that permeation rate of Lisinopril across the pigskin can be considerably enhanced, controlled or optimized by the use of Iontophoresis technique.

Evaluation of salicylic acid fatty ester prodrugs for UV protection

The purpose of this study was to investigate the physicochemical properties and in vitro evaluation of fatty ester prodrugs of salicylic acid for ultraviolet (UV) protection. The physicochemical properties such as lipophilicity, chemical stability and enzymatic hydrolysis were investigated with the following fatty ester prodrugs of salicylic acid: octanoyl (C8SA), nonanoyl (C9SA), decanoyl (C10SA), lauroyl (C12SA), myristoyl (C14SA) and palmitoyl oxysalicylate (C16SA). Furthermore, their skin permeation and accumulation were evaluated using a combination of common permeation enhancing techniques such as the use of a lipophilic receptor solution, removal of stratum corneum and delipidization of skin. Their k' values were proportional to the degree of carbon-carbon saturation in the side chain. All these fatty esters were highly stable in 2-propanol, acetonitrile and glycerin, but unstable in methanol and ethanol. They were relatively unstable in liver and skin homogenates. In particular, C16SA was mostly hydrolyzed to its parent compound in hairless mouse liver and skin homogenates, suggesting that it might be converted to salicylic acid after its topical administration. In the skin permeation and accumulation study, C16SA showed the poorest permeation in all skins, suggesting that it could not be permeated in the skin. Furthermore, C14SA and C16SA were less accumulated in delipidized skin compared with normal skin or stripped skin, suggesting that these esters had relatively strong affinities for lipids compared with the other prodrugs in the skin. C16SA showed significantly higher dermal accumulation in all skins compared with its parent salicylic acid. Thus, the palmitoyl oxysalicylate (C16SA) might be a potential candidate for UV protection due to its absence of skin permeation, smaller uptake in the lipid phase and relatively lower skin accumulation.

Transdermal permeation of novel n-acetyl-glucosamine/NSAIDs mutual prodrugs

The current investigation reports skin permeation of three novel mutual prodrugs (MP) which couple n-acetyl-glucosamine with an NSAID, either ketoprofen or ibuprofen. They were evaluated for transdermal permeation using shed snakeskin, and to our knowledge represent the first MPs synthesized for this purpose, although they also could be used for subcutaneous delivery. MPs are defined as two active drug compounds usually connected by an ester linkage. Glucosamine administration has been linked to damaged cartilage repair, and pain relief in joints afflicted with osteoarthritis. NSAIDs are commonly used orally in transdermal creams or gels for joint pain relief. Two novel compounds we report (MP1 and MP2) covalently link ibuprofen and ketoprofen directly to the amide nitrogen of n-acetyl-glucosamine (NAG); the other compound (MP3) covalently links ibuprofen to the amide nitrogen, using a short chain acetyl linker. Permeability studies show that the ketoprofen mutual prodrug (MP2) permeates shed snakeskin more than three times greater than either ibuprofen derivative, while ethanol markedly increases the permeation for all three. The ketoprofen mutual prodrug appears the most likely candidate for transdermal administration; all three mutual prodrugs may be candidates for subcutaneous injection.

Ester prodrugs of morphine improve transdermal drug delivery: a mechanistic study

Two alkyl esters of morphine, morphine propionate (MPR) and morphine enanthate (MEN), were synthesized as potential prodrugs for transdermal delivery. The ester prodrugs could enhance transdermal morphine delivery. The mechanisms of this enhancing effect were elucidated in this study. Both prodrugs were more lipophilic than their parent drug as evaluated by the skin/vehicle partition coefficient (log P) and capacity factor (log K′). The in-vitro skin permeation of morphine and its prodrugs from pH 6 buffer was in the order of MEN &gt; MPR &gt; morphine. MPR and MEN respectively enhanced the transdermal delivery of morphine by 2- and 5-fold. A contrary result was observed when using sesame oil as the vehicle. The prodrugs were stable against chemical hydrolysis in an aqueous solution, but were readily hydrolysed to the parent drug when exposed to skin homogenate and esterase. Approximately 98% MPR and ∼75% MEN were converted to morphine in an in-vitro permeation experiment. The viable epidermis/dermis contributed to a significant resistance to the permeation of ester prodrugs. According to the data of skin permeation across ethanol-, α-terpineol-, and oleic acid-pretreated skin, MEN was predominantly transported via lipid bilayer lamellae in the stratum corneum. The intercellular pathway was not important for either morphine or MPR permeation.

Design, synthesis and characterization of captopril prodrugs for enhanced percutaneous absorption

Most drugs are designed primarily for oral administration, but the activity and stability profiles desirable for this route often make them unsuitable for transdermal delivery. We were therefore interested in designing analogues of captopril, a model drug with poor percutaneous penetration, for which the sustained steady-state blood plasma level associated with transdermal delivery (and which is unattainable orally) would be particularly beneficial. Quantitative structure—permeability relationships (QSPRs) predicted that ester and thiol prodrug derivatives of captopril would have lower maximal transdermal flux (Jm) than the parent drug, since the increases in permeability coefficient (kp) of prodrugs would be outweighed by the reductions in aqueous solubility. Therefore, the aim of this study was to synthesize a series of prodrugs of captopril and to determine if a QSPR model could be used to design therapeutically viable prodrugs. Molecules with the highest predicted kp values were synthesized and characterized, and Jm measured in Franz diffusion cells from saturated aqueous donor across porcine skin (fresh and frozen). In-vitro metabolism was also measured. Captopril and the prodrugs crossed the skin relatively freely, with Jm being highest for ethyl to butyl esters. Substantial first-order metabolism of the prodrugs was observed, suggesting that their enhanced percutaneous absorption was complemented by their metabolic performance. The results suggested that QSPR models provided excellent enhancements in drug delivery. This was not seen at higher lipophilicities, suggesting that issues of solubility need to be considered in conjunction with any such use of a QSPR model.

Metabolism of captopril carboxyl ester derivatives for percutaneous absorption

Objectives

To determine the metabolism of captopril n-carboxyl derivatives and how this may impact on their use as transdermal prodrugs. The pharmacological activity of the ester derivatives was also characterised in order to compare the angiotensin converting enzyme inhibitory potency of the derivatives compared with the parent drug, captopril.

Methods

The metabolism rates of the ester derivatives were determined in vitro (using porcine liver esterase and porcine ear skin) and in silico (using molecular modelling to investigate the potential to predict metabolism).

Key findings

Relatively slow pseudo first-order metabolism of the prodrugs was observed, with the ethyl ester displaying the highest rate of metabolism. A strong relationship was established between in-vitro methods, while in-silico methods support the use of in-vitro methods and highlight the potential of in-silico techniques to predict metabolism. All the prodrugs behaved as angiotensin converting enzyme inhibitors, with the methyl ester displaying optimum inhibition.

Conclusions

In-vitro porcine liver esterase metabolism rates inform in-vitro skin rates well, and in-silico interaction energies relate well to both. Thus, in-silico methods may be developed that include interaction energies to predict metabolism rates.

Transdermal delivery of ketorolac

A reservoir type transdermal patch for delivery of ketorolac, a potent analgesic agent was studied. The low permeability of skin is the rate-limiting step for delivery of most of the drugs. Studies were carried out to investigate the effect of permeation enhancers on the in vitro permeation of ketorolac across rat skin. The reservoir type transdermal patch was fabricated and the core was filled with gel system of a non ionic polymer HPMC (hydroxypropyl methyl cellulose) formulated in PBS (phosphate buffer saline) solution of pH of 5.4 along with isopropyl alcohol at 25% w/w concentration. Various permeation enhancers' viz. dimethyl sulphoxide, d-limonene, eucalyptus oil and transcutol (diethylene glycol monoethyl ether) were incorporated into the gel system. Permeation enhancement of ketorolac with different enhancers followed the order eucalyptus oil> transcutol> DMSO> d-limonene. Cyclic terpene containing eucalyptus oil was found to be the most promising chemical permeation enhancer for transdermal delivery of ketorolac. The increase in concentration of eucalyptus oil further enhanced drug permeation with maximum flux being achieved at 10% w/w of 66.38 microg/cm(2)/h. Further enhancement of permeation rate of ketorolac across skin was attained by application of abrading gel containing crushed apricot seed onto the skin. There was 5.16 times enhancement and flux of 93.10 microg/cm(2)/h was attained. A reservoir type transdermal patch for delivery of ketorolac thus appears to be feasible of delivering ketorolac across skin.

Synthesis of piperazinylalkyl ester prodrugs of ketorolac and their in vitro evaluation for transdermal delivery

Ketorolac, an NSAID, has low intrinsic permeation capacity through the skin. In this work, seven piperazinylalkyl ester prodrugs of ketorolac were synthesized to enhance its skin permeation. The chemical hydrolysis and the stability in human serum at 37 degrees C were investigated in buffer solutions (pH 5.0 and 7.4) and in 80% human serum (pH 7.4), respectively. The prodrugs were chemically more stable at pH 5.0 than at pH 7.4 with prodrug 8 being the most stable (t(1/2) = 119.75 h and 11.97 h at pH 5 and 7.4, respectively). The prodrugs' t(1/2) in human serum ranged from 0.79 to 3.92 min. The prodrugs' aqueous solubility was measured in buffer solution at pH 5.0 and 7.4 and Log P(app) was measured by partitioning between buffer solution (pH 5.0 and 7.4) and n-octanol. The prodrugs were more lipophilic than ketorolac at pH 7.4. Skin permeation of ketorolac and prodrug 8, the most stable chemically, through rat skin was studied at pH 5.0 and 7.4. Prodrug 8 enhanced permeation by 1.56- and 11.39-fold at pH 5 and 7.4, respectively. This is attributed to higher lipophilicity at pH 7.4 and higher aqueous solubility at pH 5 compared to ketorolac.

In vitro and in vivo evaluation of topical delivery and potential dermal use of soy isoflavones genistein and daidzein

Genistein, daidzein, and glycitein are soy isoflavones. These compounds can be used to protect the skin from oxidative stress induced by UVB radiation. To this end, the feasibility of skin absorption of soy isoflavones was evaluated in the present study. As assayed by flow cytometry, UVB-induced H(2)O(2) production in keratinocytes was inhibited by genistein and daidzein, confirming that these two compounds can act as free radical scavengers when keratinocytes are photodamaged. Glycitein showed no protective activity against photodamage. The effects of vehicles on the in vitro topical delivery from saturated solutions such as aqueous buffers and soybean oil were investigated. The isoflavones in a non-ionized form (pH 6) showed higher skin deposition compared to the ionized form (pH 10.8). Soybean oil reduced the isoflavone amount retained in the skin, especially for genistein. Genistein generally exhibited greater skin absorption than did daidzein. However, daidzein permeation was enhanced when an aglycone mixture was used as the active ingredient. An eutectic effect was proposed as the enhancing mechanism. In vivo skin deposition showed a linear correlation with the in vitro results. The safety profiles suggested no or only negligible stratum corneum disruption and skin erythema by topical application of soy isoflavones. It was concluded that topical delivery may serve as a potent route for soy isoflavones against photoaging and photodamage.

Screening of venlafaxine hydrochloride for transdermal delivery: passive diffusion and iontophoresis

The objective of the study was to investigate in vitro transdermal delivery of venlafaxine hydrochloride across the pigskin by passive diffusion and iontophoresis. For passive diffusion, experiments were carried out in Franz diffusion cell whereas for iontophoretic permeation, the diffusion cell was modified to contain both the donor and return electrode on the same side of skin. Anodal iontophoresis was carried out using a current density of 0.5 mA/cm(2). Donor concentrations used were 585.5 mg/ml (saturated solution) and 100 mg/ml. Experiments initially performed to determine the transport efficiency of venlafaxine ions showed promising results. Iontophoresis increased the permeation rate at both concentration levels over their passive counterparts (P < 0.01), but surprisingly higher steady-state flux was obtained from lower donor drug load (P < 0.01). The favorable pH of the unsaturated solutions is suggested to be the cause for this effect. Mild synergistic effect was observed when iontophoresis was carried out incorporating peppermint oil in the donor but the same was not found in passive diffusion. Highest steady-state flux obtained in the experiment was 3.279 mumol/cm(2)/h when peppermint oil (0.1%) was included in the donor. As the maintenance requirement of venlafaxine hydrochloride is approximately 9.956 mumol/h, the results suggested that the drug is a promising candidate for iontophoretic delivery.

Evaluation of skin permeation and accumulation profiles of a highly lipophilic fatty ester

The aim was to evaluate the skin permeation and accumulation profiles of a highly lipophilic fatty ester using the combination of various permeation enhancing techniques to study the potential of highly lipophilic fatty esters as local topical agents. Permeation and accumulation profiles of ketorolac stearate (C18:0) were studied using solubility improved formulation, supersaturated solution of permeant in enhancer vehicle, lipophilic receptor solution, enhancer pretreatment, and the removal of stratum corneum and delipidization of skins. Impermeability and minimal skin accumulation of ketorolac stearate could delineate a preliminary possibility for designing safer topical agents without systemic absorption.

Evaluation of alternative strategies to optimize ketorolac transdermal delivery

In the present study, 2 alternative strategies to optimize ketorolac transdermal delivery, namely, prodrugs (polyoxyethylene glycol ester derivatives, I-IV) and nanostructured lipid carriers (NLC) were investigated. The synthesized prodrugs were chemically stable and easily degraded to the parent drug in human plasma. Ketorolac-loaded NLC with high drug content could be successfully prepared. The obtained products formulated into gels showed a different trend of drug permeation through human stratum corneum and epidermis. Particularly, skin permeation of ester prodrugs was significantly enhanced, apart from ester IV, compared with ketorolac, while the results of drug release from NLC outlined that these carriers were ineffective in increasing ketorolac percutaneous absorption owing to a high degree of mutual interaction between the drug and carrier lipid matrix. Polyoxyethylene glycol esterification confirmed to be a suitable approach to enhance ketorolac transdermal delivery, while NLC seemed more appropriate for sustained release owing to the possible formation of a drug reservoir into the skin.

Novel Depots of Ketorolac Esters Have Long-Acting Antinociceptive and Antiinflammatory Effects

No long-acting nonsteroidal antiinflammatory drug is clinically available for the treatment of pain. In this study, we evaluated the antinociceptive and antiinflammatory effects and duration of action of several novel depots of ketorolac esters, such as ketorolac propyl ester, pentyl ester, heptyl ester, and decyl ester, and observed whether they had a long-acting effect. Four studies in Sprague-Dawley rats were performed. In Studies 1-3, the antinociceptive and antiinflammatory effects of IM ketorolac tromethamine and its base and propyl ester were evaluated. In Study 4, the antinociceptive and antiinflammatory effects of several other ketorolac esters were evaluated. We found that ketorolac tromethamine 24, 80, and 240 micromol/kg (in saline) produced significant antinociceptive and antiinflammatory effects with duration of action of approximately 6-8 h. The four ketorolac esters at a dose of 240 micromol/kg (in oil) produced significant long-acting antinociceptive and antiinflammatory effects, with duration of action of approximately 52-76 h. We concluded that IM injection of novel depots of ketorolac esters in rats produce long-acting antinociceptive and antiinflammatory effects that are 6.5- to 9.5-fold longer than the traditional dosage form of ketorolac tromethamine.

Pharmacokinetics of Ketorolac Pentyl Ester, a Novel Ester Derivative of Ketorolac, in Rabbits

Ketorolac is a potent nonsteroidal anti-inflammatory drug. Recently, a novel ester of ketorolac, ketorolac pentyl ester, was synthesized. When prepared in injectable oil, the new agent demonstrated a long duration of action. Ketorolac pentyl ester was synthesized using a prodrug design by esterification of ketorolac, and appeared to be a prodrug of ketorolac in vivo, which needed to be confirmed. The aim of the present study was to establish the prodrug's pharmacokinetics in vivo, and to confirm whether or not ketorolac pentyl ester was a prodrug of ketorolac. Pharmacokinetic profiles of intravenous ketorolac and its pentyl ester on an equal-molar basis in six rabbits were evaluated. A high-performance liquid chromatographic method was used to determine the plasma concentrations of ketorolac and its pentyl ester. We found that the plasma concentrations of ketorolac pentyl ester declined rapidly after injection and so did the conversion of ketorolac pentyl ester to ketorolac. Also, the conversion of ketorolac was proved complete when compared with intravenous ketorolac under an equi-molar basis. In conclusion, this in vivo pharmacokinetic study confirmed that keterolac pentyl ester was a prodrug of keterolac.

Selection of topically applied non-steroidal anti-inflammatory drugs for oral cancer chemoprevention

Topical delivery of non-steroidal anti-inflammatory drugs through the oral mucosa has been used for oral cancer chemoprevention. Local permeation of these agents has been one of the major concerns. Here we propose an approach to predict the permeability of topically applied agents for oral cancer chemoprevention. In theory, the total flux through the oral mucosa (Jmax) can be estimated by adding the transcellular flux (JTC) and the paracellular flux (JPC). To target the Cox-2 enzyme in oral epithelial cells, it is desirable to maximize the theoretical activity index, the ratio of JTC and IC50 of a Cox-2 inhibitor (JTC/IC50-Cox-2). Among the 12 commonly used NSAIDs, celecoxib, nimesulide and ibuprofen had the highest values and may be the agents of choice to target Cox-2 in oral epithelial cells through topical application. Based on these calculations, a long-term chemopreventive experiment using celecoxib (3% or 6%) through topical application was performed in a DMBA induced hamster oral cancer model. Both 3% and 6% reduced the incidence of squamous cell carcinoma at the post-initiation stage.

Evaluation of the physicochemical stability and skin permeation of glucosamine sulfate

Glucosamine sulfate (GS) is known to stop the degenerative process of osteoarthritis. Because most of the GS formulation on the market is in the oral form, an alternative formulation such as a transdermal delivery system (TDS) is necessary in order to increase patient compliance. As the initial step to develop a TDS of GS, the physicochemical stability and permeation study in rat skin were examined. Evaluation of the stability of GS at different pHs showed the compound to be most stable at pH 5.0. The degradation rate constant at 25 degrees C was estimated to be 5.93 x 10(-6) hr(-1) (t90 approximately 2.03 years) in a pH 5 buffer solution. Due to its hydrophilic characteristic, low skin permeability was expected of GS. However, the skin permeation rate was determined to be 13.27 microg/cm2/hr at 5% concentration. Results of this study suggest the possibility of developing GS into a transdermal delivery system.

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.

Transdermal Delivery of Ondansetron Hydrochloride: Effects of Vehicles and Penetration Enhancers

The effects of vehicles and penetration enhancers on the in vitro permeation of ondansetron hydrochloride (OS) across dorsal hairless mouse skins were investigated. Various types of vehicles, including ester, alcohol, and ether and their mixtures were used, and then a series of fatty acids and fatty alcohols were employed as enhancers. Among pure vehicles used, water and ethanol showed high permeation fluxes, which were 48.2+/-23.7 and 41.9+/-17.9 microg/cm2 per h, respectively. Even though propylene glycol monocaprylate (PGMC) alone did not show a high permeation rate, the skin permeability of OS was increased by the addition of diethylene glycol monoethyl ether (DGME); the highest flux was achieved at 40% of DGME. Also, the combination of PGMC and ethanol (80:20) or PGMC and propylene glycol (PG) (60:40) increased the permeation flux by six- and two-fold, respectively, compared to PGMC alone. The synergistic enhancement was also obtained by using PG-oleyl alcohol (OAl) cosolvent. The greatest flux was attained by the addition of unsaturated fatty acids at 3% concentration to PG. The enhancement factors with the addition of oleic acid or linoleic acid to PG were about 1250 and 450, respectively. But saturated fatty acids failed to show a significant enhancing effect. When the PGMC-DGME (60:40) cosolvent system was used as a vehicle, all fatty acids, including unsaturated fatty acids, failed to show significant enhancing effects. The results indicate that the combinations of oleic acid, linoleic acid, or oleyl alcohol with PG, or PGMC-DGME (60:40) cosolvent could be used for the design of the OS transdermal system.