Impact of Different Mixing Methods on the Performance of Suspension-Based Transdermal Delivery Systems.

Suspension-based matrix transdermal delivery systems (TDSs) are specialized systems that maintain a continuous driving force for drug delivery over prolonged wear. The pressure-sensitive adhesive (PSA) is the most critical constituent of such systems. Our study aimed to determine the effect of different mixing methods on the performance of silicone PSA-based suspension TDSs. Lidocaine suspension TDSs were prepared using conventional slow rotary mixing, high-speed homogenization, bead-mill homogenization, vortex shaking, and by an unguator. Resultant TDSs were tested for tack, shear, and peel properties and correlated to coat weight, content uniformity, microstructure, and in vitro permeation across dermatomed human skin. Every mixing method tested caused a significant reduction in peel. However, bead-mill homogenization resulted in significant loss of all adhesive properties tested, while unguator-mixed TDSs retained most properties. Good linear correlation (R2 = 1.000) between the shear properties of the TDSs with the average cumulative amount of lidocaine permeated after 24 h was observed, with no significant difference between percutaneous delivery from slow rotary-mixed systems (1334 ± 59.21 µg/cm2) and unguator-mixed systems (1147 ± 108.3 µg/cm2). However, significantly lower delivery from bead-mill homogenized systems (821.1 ± 28.00 µg/cm2) was noted. While many factors affect TDS performance, careful consideration must also be given to the processing parameters during development as they have been shown to affect the resultant system's therapeutic efficacy. Extensive mixing with bead-mill homogenization demonstrated crystallization of drug, loss in adhesive properties, coat weight, and film thickness, with reduced transdermal delivery of lidocaine from the prepared system.

In vitro and in vivo studies of micro-depots using tailored microemulsion for sustained local anaesthesia.

In clinical practice, lidocaine is used as local anesthetic for the management of post-operative pain. The commercial formulation including gels, injections and ointments showed short duration of action (1 to 2 h). In this paper, the efforts have being made to develop tailored lidocaine-microemulsion (o/w), which on penetration in the skin layer cause micro-depots formation due to destabilization of the microemulsion system. To identify the microemulsion region, pseudo ternary diagrams were constructed using Capmul MCM as oil, Pluronic F68 as tri-block surfactant, polyethylene glycol 200 as co-surfactant at 1:4 and 1:6 ratios (S:Co-S). The selected 5%w/v lidocaine loaded microemulsion [Ld-ME-2(1:4)] was stable in thermodynamic test and during shelf life period (3 months). In ex vivo permeability study, the lidocaine release from Ld-ME-2(1:4) microemulsion was sustained in comparison to the marketed lidocaine ointment. The skin irritation study confirmed the safety of lidocaine loaded microemulsion. Tail flick test showed improved and sustain local anaesthetic effect in comparison to the market ointment. The improved efficacy of microemulsion system, was due to high penetration in the skin layer due to local precipitation of lidocaine from microemulsion. The findings suggest that the tailored microemulsion could be a potential strategy to prolong the local anaesthesia.

Across-the-World Automated Optimization and Continuous-Flow Synthesis of Pharmaceutical Agents Operating Through a Cloud-Based Server.

The power of the Cloud has been harnessed for pharmaceutical compound production with remote servers based in Tokyo, Japan being left to autonomously find optimal synthesis conditions for three active pharmaceutical ingredients (APIs) in laboratories in Cambridge, UK. A researcher located in Los Angeles, USA controlled the entire process via an internet connection. The constituent synthetic steps for Tramadol, Lidocaine, and Bupropion were thus optimized with minimal intervention from operators within hours, yielding conditions satisfying customizable evaluation functions for all examples.

Synthesis of C2-Symmetric Benzimidazolium Salts and Their Application in Palladium-Catalyzed Enantioselective Intramolecular α-Arylation of Amides.

A series of C2-symmetric chiral benzimidazolium salts, the precursor of N-heterocyclic carbene ligands, were designed and synthesized from 1,2-dibromobenzene. In situ prepared corresponding carbenes were tested in the asymmetric palladium-catalyzed intramolecular α-arylation of amides, affording chiral diarylmethanols with high yields and moderate enantioselectivities.

Rapid Vortex Fluidics: Continuous Flow Synthesis of Amides and Local Anesthetic Lidocaine.

Thin film flow chemistry using a vortex fluidic device (VFD) is effective in the scalable acylation of amines under shear, with the yields of the amides dramatically enhanced relative to traditional batch techniques. The optimized monophasic flow conditions are effective in ≤80 seconds at room temperature, enabling access to structurally diverse amides, functionalized amino acids and substituted ureas on multigram scales. Amide synthesis under flow was also extended to a total synthesis of local anesthetic lidocaine, with sequential reactions carried out in two serially linked VFD units. The synthesis could also be executed in a single VFD, in which the tandem reactions involve reagent delivery at different positions along the rapidly rotating tube with in situ solvent replacement, as a molecular assembly line process. This further highlights the versatility of the VFD in organic synthesis, as does the finding of a remarkably efficient debenzylation of p-methoxybenzyl amines.

ß-Cyclodextrin-Propyl Sulfonic Acid Catalysed One-Pot Synthesis of 1,2,4,5-Tetrasubstituted Imidazoles as Local Anesthetic Agents.

Some functionalized 1,2,4,5-tetrasubstituted imidazole derivatives were synthesized using a one-pot, four component reaction involving 1,2-diketones, aryl aldehydes, ammonium acetate and substituted aromatic amines. The synthesis has been efficiently carried out in a solvent free medium using ß-cyclodextrin-propyl sulfonic acid as a catalyst to afford the target compounds in excellent yields. The local anesthetic effect of these derivatives was assessed in comparison to lidocaine as a standard using a rabbit corneal and mouse tail anesthesia model. The three most potent promising compounds were subjected to a rat sciatic nerve block assay where they showed considerable local anesthetic activity, along with minimal toxicity. Among the tested analogues, 4-(1-benzyl-4,5-diphenyl-1H-imidazol-2-yl)-N,N-dimethylaniline (5g) was identified as most potent analogue with minimal toxicity. It was further characterized by a more favourable therapeutic index than the standard.

Synthesis of ¹³C-lidocaine as a probe of breath test for the evaluation of cytochrome P450 activity.

(13)C-Labeled lidocaine, 2-di[1-(13)C]ethylamino-N-(2,6-dimethylphenyl)acetamide (1), was synthesized from [1-(13)C]acetic acid in six steps, as a probe for a breath test to evaluate in vivo cytochrome P450 activity. The measurement of (13)CO2 in breath was successfully performed following oral administration of (13)C-lidocaine 1 to mice.

Synthesis and characterization of two homologous series of diastereomeric 2-alkoxyphenylcarbamates.

Two homologous series of racemic diastereomeric cis- and trans-(2-dimethylaminomethylcycloheptyl)-2-alkoxyphenylcarbamates with alkyl chain lengths ranging from C1 to C8 were synthesized by stereoselective reactions. The chemical structures of these compounds were confirmed by ¹H-NMR, ¹³C-NMR and IR spectroscopy and their physico-chemical properties were characterized. The two new series of diastereomeric compounds were tested for their local anesthetic activity and parabolic relationship between the local anesthetic activity and lipophilicity was found for both cis- and trans-series. Interestingly, cis-stereoisomers exhibited higher local anesthetic activity.

Synthesis and antispasmodic activity of lidocaine derivatives endowed with reduced local anesthetic action.

The present structure-activity relationship (SAR) study focused on chemical modifications of the structure of the local anesthetic lidocaine, and indicated analogues having reduced anesthetic potency, but with superior potency relative to the prototype in preventing anaphylactic or histamine-evoked ileum contraction. From the SAR analysis, 2-(diethylamino)-N-(trifluoromethyl-phenyl) and 2-(diethylamino)-N-(dimethyl-phenyl) acetamides were selected as the most promising compounds. New insights into the applicability of non-anesthetic lidocaine derivatives as templates in drug discovery for allergic syndromes are provided.

Synthesis of lidocaine-loaded PLGA microparticles by flow focusing. Effects on drug loading and release properties.

In the present work, two methods for the preparation of lidocaine-loaded PLGA microparticles are compared. The differences between the polymeric particles obtained by solvent evaporation (SEVM) or flow focusing (FF) were studied by means of scanning electron microscopy and surface thermodynamics determinations. A detailed investigation of the capabilities of the polymer particles to load this drug is described. The physical state of the drug in the polymeric particles and the existence of interactions between both entities were studied by differential scanning calorimetry. The main factors determining the lidocaine incorporation and the release kinetics were the synthesis procedure followed, the amount of drug dissolved in the organic phase during the synthesis routine, the type of polymer (molecular weight and end chemical groups) and the size and the hydrophobic/hydrophilic properties of the particles. The FF technology allowed higher drug incorporations and slower release kinetics. The release studies showed a biphasic profile probably due to diffusion-cum-degradation mediated processes.

Local Anaesthetic Effect of Methanolic Leaves Extract of Lannea schimperi (Hoschst. Ex Rich) Eng.

BACKGROUND: Local anaesthetics provide relief from pain when applied locally to nerve tissue by blocking conduction of sensory nerve impulse from the receptor to the brain cortex. OBJECTIVE: This study aimed at evaluating local anaesthetic activity of the methanolic leaves extract of Lannea schimperi. METHODS: Six groups of five animals were used; groups I-IV were used for intracutaneous wheal test in guinea pigs for infiltration anaesthesia, while group V and VI were used for guinea pig corneal reflex method of surface anaesthesia. RESULTS: The result indicated a significant ( 0.05) dose dependent local anaesthetic activity of the methanolic leaves extract of Lannea schimperi with faster onset and longer duration of action at 24 mg/ml than at 12 mg/ml of the extract. Additions of 5 µg of adrenaline into the 24 mg/ml preparation also prolonged the duration of local anaesthetic activity of the extract. The extract at 24 mg/ml significantly (0.05) inhibited corneal reflex, lidocaine was used as a standard drug in positive control group, while normal saline was used as negative control in all the treated groups. CONCLUSION: The patent data therefore revealed that the methanolic leaves extract Lannea schimperi possess local anaesthetic principles that may require further scientific elucidation.

Carborane-derived local anesthetics are isomer dependent.

Clinically there is a need for local anesthetics with a greater specificity of action on target cells and longer duration. We have synthesized a series of local anesthetic derivatives we call boronicaines in which the aromatic phenyl ring of lidocaine was replaced with ortho-, meta-, C,C'-dimethyl meta- and para-carborane clusters. The boronicaine derivatives were tested for their analgesic activity and compared with lidocaine using standard procedures in mice following a plantar injection. The compounds differed in their analgesic activity in the following order: ortho-carborane = C,C'-dimethyl meta-carborane > para-carborane > lidocaine > meta-carborane derivative. Both ortho-boronicaine and C,C'-dimethyl meta-boronicaine had longer durations of analgesia than lidocaine. Differences in analgesic efficacies are rationalized by variations in chemical structure and protein binding characteristics.

Mono- and diaryl-2-quinuclidinylcarbinols with local anesthetic and antiarrhythmic activity.

The reaction between 2-carboethoxyquinuclidine and various aryl- and heteroarylithium reagents gave mixtures of aryl 2-quinuclidinyl ketones and diaryl-2-quinuclidinylcarbinols. Diborane reduction of the ketones gave the erythro-carbinols, stereochemically analogous to quinidine. Several of the mono- and diarylcarbinols exhibited potent local anesthetic and antiarrhythmic activity, in some cases greater than that of quinidine. Diphenyl-2-quinuclidinylcarbinol and a (bromomethoxyphenyl)(methoxyphenyl)-2-quinuclidinylcarbinol were particularly active in reverting ouabain-induced arrhythmia in dogs, showing a potency and duration of action equal to or greater than that of propranolol.

Local anesthetics. 2-Diethylamino-2',6'-acylxylidides.

A series of C-alkylated derivatives of lidocaine has been synthesized, and the local anesthetic potencies were determined. Activity reached a miximum with the butyroxylidide (alpha-ethyl group), but toxicity increased regularly with the number of carboons in the side chain. Spectral data showed the compounds to exist as associated H-bonded structures, the free base most likely as intramolecularly bonded trans amides and the hydrochlorides most likely as associated cis amindes.

Quantitative structure-activity relationships for N-[N',N'-disubstituted-amino)acetyl]arylamines for local anesthetic activity and acute toxicity.

The synthesis and physicochemical properties of a series of N-[N',N'-disubstituted-amino)acetyl]arylamines are described. A QSAR method is applied to local anesthetic activity and acute toxicity by means of a "nonclassic" substituent variation involving a modification on both aryl and amino moieties. The choice of the different parameters (partition coefficient, pKa, connectivity index, molar refraction, and molar volume) is discussed and their different methods of determination are described. Molar refraction is the parameter which explains best the variance of the local anesthetic activity, and the quadratic regression with MR leads to a "posteriori" synthesis of one compound with optimized activity. However, the partition coefficient is the most explicative parameter for intravenous toxicity.

Synthesis and study of conformationally defined enantiomers of local anesthetics and conformationally defined enantiomers of fluorescent dyes designed to label electrically excitable membranes.

Conformationally defined enantiomeric local anesthetics and fluorescent dyes were synthesized. Neither the local anesthetics nor the fluorescent probes showed stereospecificity in interacting with nerve membranes. The fluorescence signals generated by the dyes showed excellent correlation with the time course and shape of the nerve action potential.

Analgesic activity of the epimeric tropane analogs of meperidine. A physical and pharmacological study.

Condensation of cis-N-benzyl-2,5-bis(chloromethyl)pyrrolidine (6) and phenylacetonitrile afforded a mixture of epimers 7 and 8. Compound 8 was readily converted to the meperidine analog 1 prepared earlier by Bell and Archer. Compound 7 was converted to a new tropane analog of meperidine, compound 3. The ED50 of 1 and 3 in the D'Amour-Smith "tail flick" test for narcotic type analgesia, which differs by a factor of only 3 or 4 potency, supports the accumulated data that suggest that the analgesic activity of the meperidine type is not very sensitive to the conformation of the phenyl group in 4-phenylpiperidines. A proton and 13C magnetic resonance spectral comparison of 1 and 3, as well as a reevaluation of the conformational requirements of 17-19, leads to the conclusion that the differences in conformation of 1,3,17, and 18 are due to the varying degrees of flattening of piperidine ring. The 1H NMR and 13C NMR data are not consistent with the boat conformation suggested earlier for compound 17.

Oxindole-3-spiropyrrolidines and -piperidines. Synthesis and local anesthetic activity.

The synthesis and local anesthetic properties of five 1-dealkyloxindole-3-spiropyrrolidines and six 1-dealkyloxindole-3-spiropiperidines are described. The compounds studied include members of all five possible positional isomers of the two classes of spirooxindoles; all showed local anesthetic activity by the rat sciatic nerve block method. The coincidence of the least variability in the relative positions of basic nitrogen, amide carbonyl, and aromatic ring (compounds 1 and 6) with lowest normalized toxicity is noteworthy.

Synthesis of (aryloxy)alkylamines. 2. Novel imidazo-fused heterocycles with calcium channel blocking and local anesthetic activity.

A series of imidazo-fused heterocycles substituted with an aryloxy)alkylamine side chain were prepared as modifications to butoprozine (I) and found to possess calcium channel blocking activity similar in potency to that of bepridil in trachea smooth muscle and similar to that of verapamil in nitrendipine binding affinity in rabbit cardiac muscle. Of the various imidazo-fused heterocycles prepared, the imidazo[1,2-a]pyridines were also found to be potent local anesthetic agents. While most compounds in this series were equipotent to lidocaine in our initial screen, compounds 2 and 35 showed local anesthetic activity approximately 100 times more potent than lidocaine in our preliminary assays. These compounds represent a novel structural class of local anesthetic agents, and compound 2 is under further investigation.

Beta-adrenoceptor studies. 2. Effects of alkyl substitution on beta-adrenoceptor blocking, antiarrhythmic, and local anesthetic activities of 1,1'-(o-phenylenedioxy)bis(3-isopropylamino-2-propanol).

A series of bis(2-hydroxy-3-isopropylaminopropyl) ethers of nuclear-substituted catechols (1-7) has been synthesized and examined in vitro for beta-adrenoceptor blocking activity, antagonism of ouabain-induced arrhythmias, and local anesthetic activity. Both tracheal and right atrial beta-adrenoceptor blocking activity are markedly decreased by alkyl substitution in position 3 of parent catechol diether 1. Substitution in position 4 still lowers the affinity to cardiac arrhythmias and local anesthetic activity increases with introduction of alkyl substituents in the 3 as well as in the 4 position. In contrast with biological activities, the partition coefficient 1-octanol-phosphate buffer, pH 7.40, of 1 did not change significantly by 3- and 4-methyl substitution. Stepwise multiple regression analyses were performed using log P or pi values in combination with pKa(m), E8, or sigma. With cardiac beta-adrenoceptor blocking activity the optimal equation contained E8 and pi parameters, tracheal activity appeared to depend mainly on the E8 parameter, whereas for antiarrhythmic and local anesthetic activities the lipophilicity of the substituents appeared to be the determinant factor.