Anaesthetics, local, determination

Z. Yu and D. Westerlund, Direct injection of large volumes of plasma in a columnswitching system for the analysis of local anaesthetics , II. Determination of bupivacaine in human plasma with an alkyl-diol silica precolumn , ]. Chromatogr. A 725 149-155 (1996). 

Pharmacokinetics. The distribution rate of a single dose of a local anaesthetic is determined by diffusion into tissues with concentrations approximately in relation to blood flow (plasma t] only a few minutes). By injection or infiltration, local anaesthetics are usually effective within 5 min and have a useful duration of effect of 1-1.5 h, which in some cases may be doubled by adding a vasoconstrictor (below). 

Sanger-van de Griend, C. E., Ek, A. G., Widahl-Nasman, M. E., and Andersson, E. K. M. (2006). Method development for the enantiomeric purity determination of low concentrations of adrenaline in local anaesthetic solutions by capillary electrophoresis. /. Pharm. Biomed. Anal. 41, 77—83. 

Stalberg, O., Sander, K., and Sanger-van de Griend, C. (2002). The determination of bromide in a local anaesthetic hydrochloride by capillary electrophoresis using direct UV detection.. Chromatogr. A 977, 265-275. 

Sanger-van de Griend et al. (29) determined the binding constants of several local anaesthetics with DM-/3-CD. These data showed that the achiral separation of analogues is a result of their mobility difference, whereas the resolution of enantiomers results from the difference in their binding constants with CDs. 

New modified polymeric electrodes selective to procaine and other local anaesthetic compounds were reported [72]. The electrode was constructed by incorporating the ion-pair complex of procaine with tungsto-phosphoric acid into ethylene-vinyl acetate copolymer. Best results were obtained with 1 1 nitrobenzene-dioctyl phthalate as a plasticizer. The calibration graph was linear fi om 18 p to 10 mM of procaine. When these electrodes were applied to the determination of the drug in pharmaceutical formulations, the recoveries were found to be quantitative. 

Ambient pH in the extracellular fluid (ECF) is approximately 7.4 but the value varies and this determines the proportions of ionised and unionised local anaesthetic drug. A decrease in ambient pH will increase the amount of ionised drug and reduce the unionised fraction available for transfer across the cell membrane. A common example of this is when infection or inflammation reduces the ambient pH. In the case of lidocaine (lignocaine), a fall in tissue pH from 7.4 to 7.0 will halve the amount of unionised drug. This has obvious implications for efficacy. Similar effects occur following repeated administrations of acidified local anaesthetic solutions. 

Page 49, figure 5.5 Toxicology Letters 100-101 247-254 (1998), French R.J. et al Molecular and kinetic determinants of local anaesthetic action on sodium channels. Reprinted with permission from Elsevier. 

Altun, Z., Abdel-Rehim, M., Blomberg, L.G. New trends in sample preparation On-line microextraction in packed syringe (MBPS) for LC and GC applications. Part III Determination and validation of local anaesthetics in human plasma samples using a cation-exchange sorbent and MEPS-LC-MS-MS. J. Chromatogr. B 813, 129-135 (2004)... 

Shen Y, Mathiasson L, and Jonsson jA. Automated capillary GC determination of local anaesthetics in plasma samples with supported liquid membranes for sample preparation. J. Microcol. Sep. 1998 10 107-113. 

Novocain, the commonly used local anaesthetic, is a weak base with K, = 7 X 10 M. (a) If you had a 0.0200 M solution of Novocain in water, what would be the approximate concentration of OH and the pH (b) Suppose that you wanted to determine the concentration of Novocain in a solution that is about 0.020 M by titration with 0.020 M HCl. Calculate the expected pH at the equivalence point. 

Once inside the neuron dissociation is necessary, because it is the ionized form binds to the sodium ion channel. Local anaesthetic activity is dependent on pH, because pH determines the degree of dissociation into ions. This becomes of clinical importance in inflamed and infected tissue, which often has a more acid pH. Acid conditions result in increased degree of ionization and reduced diffusion of local anaesthetic into neurons. This makes them less effective anaesthetics. 

Local anaesthetics are used to abolish the sensation of pain in a restricted area of the body and for minor surgical operations when loss of consciousness is not desirable. The area is determined by the site and the technique of administration of the anaesthetic agent. The main uses are as follows ... 

Moniero et al.[24] developed an indirect AAS method for the determination of local anaesthetics (lidocaine. tetracaine and procaine hydrochlorides) in pharmaceutical preparations using FI on-line precipitation-dissolution. A cobalt solution is injected into a carrier stream containing the sample, and the precipitate formed is retained on an online stainless steel filter. The determinations were made by measuring the residual cobalt concentration in a similar way as for the indirect determination of sulphonamides (cf. Sec. 9.4.2). A sampling frequency of 100 h was achieved with a precision of 0.6% r.s.d.. 

Anions—direct detection Quantitative determination of alginic acid in pharmaceutical formulatioDS Determination of residual Br in excess of chloride for local anaesthetic analysis Arginine counterion determination for ragaglitazone... 

Baricity and dose of the local anaesthetic along with the patient position determine the anaesthetic block height. 

Gas Chromatographic Determination of Plasma Concentrations of Some Local Anaesthetics Using a Nitrogen Detector... 

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