Gas-liquid chromatographic determination and pharmacological studies of six clinically-used local anesthetics.

A gas-liquid chromatographic method was developed for the simultaneous assay of six local anesthetics, including amethocaine, bupivacaine, etidocaine, lignocaine, mepivacaine and prilocaine, in biological samples. These drugs and internal standard (clomipramine) in basified samples were extracted into 5 ml n-hexane, and the extract was analyzed by a temperature programming method (the column temperature was kept at 210 degrees C for 5 min, then raised to 280 degrees C at the rate of 10 degrees C/min) using a 3% W/W SP 2250 glass column (2 m x 2 mm i.d.) connected to a nitrogen sensitive detector. The injector and detector temperature were maintained at 300 degrees C. The pKa values, partition coefficients (K) and buccal absorptions of six local anesthetics were determined. The results showed that the onset of action and duration could be shown to be dependent on the pKa values and partition coefficients, respectively. A relatively good positive correlation (r = 0.991) was observed between the percentage of buccal absorption at pH 7.4 and the logarithms of K in n-hexane-S?rensen buffer system, and hence the more lipid soluble the local anesthetic, the greater the buccal absorption. The buccal absorption test supplemented by the n-hexane-buffer partition coefficient could be used as indicators for the ability of the anesthetics to penetrate biological barriers. The lipid penetration of the drugs, and thus their pharmacological action, is also influenced by the pKa values of the anesthetics.     

Study of anaesthetic agents for their ability to elicit porphyrin biosynthesis in chick embryo liver

Effects of some anaesthetic drugs on the activity of delta-aminolevulinate synthetase and on the formation of porphyrins and cytochrome P-450 were studied in 18-day-old chick embryo livers in ovo. The drugs were either tested alone or with a small dose of 1,4-dihydro-3,5-dicarbethoxycollidine, which reproduces in the embryo liver a partial block in the heme biosynthesis pathway similar to that found in cells of human patients with porphyrias. Two series of local anaesthetics were tested: procaine and its derivatives (proxymetacaine, oxybuprocaine, butacaine and tetracaine) had no (or very slight) porphyrogenic effects. In contrast, lidocaine and its derivatives (bupivacaine, mepivacaine, etidocaine, pyrrocaine and prilocaine) were found to induce delta-aminolevulinate synthetase and to cause accumulation of porphyrins and cytochrome P-450. Some other drugs used in anaesthesiology were tested: fentanyl, morphine, sodium oxybate, pancuronium, pethidine and phenoperidine were found to be non-porphyrogenic; alcuronium was a slight inducer. It is suggested that the inducing drugs should be avoided in patients with hepatic porphyrias.     

Effect of cutaneously applied nonionic surfactants and local anesthetic bases on thermal sensations

With cutaneously applied local anesthetic bases various effects may be observed, such as a decrease in pricking pain and a change in burning, itch, and thermal sensations. These effects occur after skin penetration and may be attributed to the action of the anesthetics on nociceptors and thermoreceptors, i.e., on C and A delta nerve fibers, respectively. As little is known about the pharmacodynamic response of nonionic surfactants with a potentially anesthetic action such as polidocanol, this study characterizes nonionic surfactants pharmacodynamically by measuring thermal thresholds with a thermal sensory analyzer after cutaneous application. The results obtained with the nonionic surfactants were compared with data resulting from the cutaneous application of local anesthetic bases such as mepivacaine, bupivacaine, prilocaine, lidocaine, the 1:1 mixture of lidocaine and prilocaine contained in EMLA and a triple mixture consisting of lidocaine, prilocaine and tetracaine (1:1:1). The results show that none of the investigated surfactants affect thermal thresholds probably due to their high molecular weight. The same was observed with the anesthetics mepivacaine and bupivacaine. In contrast, prilocaine, lidocaine, the 1:1 mixture of lidocaine and prilocaine and the triple mixture consisting of lidocaine, prilocaine and tetracaine (1:1:1) proved to be potent local anesthetics. However, their pharmacodynamic responses do not differ significantly from each other.     

Prilocaine elimination by isolated perfused rat lung and liver

Prilocaine is assumed to undergo significant elimination by extrahepatic organs and to differ in this respect from other commonly used local anaesthetics. In order to clarify whether the lung may play an important role as a site of elimination of prilocaine, the kinetic parameters were studied in isolated perfused rat lungs and were compared to those of isolated livers. Furthermore, the structurally related compounds bupivacaine and mepivacaine were also investigated in this system. Prilocaine was dispersed into a relatively large apparent distribution volume in perfused rat lung (139 ml versus 97 ml in controls). In single-pass perfused lungs the observed maximum of concentration was decreased by about 60% compared to controls. The mean residence time was prolonged by about 40%. These observations suggest that prilocaine is substantially retained by rat lung and that this effect occurs particularly during first-pass.However, the ability of rat lung to degrade prilocaine was relatively low. The clearance values were about 0.3 ml/min equal to about 20% of the hepatic capacity calculated per g of tissue. Thus it must be assumed that prilocaine is only transiently retained by the lung and will gain systemic availability later on. In rat lungs the kinetics of prilocaine elimination were not substantially different from those of bupivacaine and mepivacaine (16 and 12%). These observations do not support the assumption that especially prilocaine undergoes extrahepatic elimination.For low (2 g/ml) and intermediate (10 g/ml) drug concentrations isolated rat liver exhibited clearance values close to the perfusion flow rate. Accordingly, prilocaine was removed from the perfusion medium of isolated livers already during first-pass. At very high concentrations of 100 g/ml, the clearance dropped to about half of the control values. Thus under these conditions approximately half of the dose escaped first-pass extraction which is probably caused by saturated metabolic clearance. Such an effect was not observed for bupivacaine and mepivacaine.Part of the doctoral thesis of Markus Ebke, Medical Faculty of the University of Göttingen     

Displacement of lidocaine from serumα 1-acid glycoprotein binding sites by basic drugs

Since little is known of the number and types of binding sites on alpha 1-acid glycoprotein (AAG) and because drug-drug protein binding interactions often fail to fit a simple model, a study of the effect of 9 known AAG binding drugs on lidocaine free fraction (LFF) was performed. Serum was obtained from 10 healthy males, pooled and various concentrations (from 0.15 to 1000 micrograms/ml) of amitriptyline, bupivacaine, chlorpromazine, disopyramide, imipramine, meperidine, nortriptyline, propranolol and quinidine were added. LFF was determined by equilibrium dialysis at an initial lidocaine concentration of 2.0 micrograms/ml. LFF increased from 0.30 +/- 0.019 (mean +/- SD) in the absence of displacing agents to maximum values ranging from 0.59 (nortriptyline) to 0.73 (bupivacaine). Plots of LFF vs. the logarithm of displacing drug concentration yielded simple sigmoidal curves in all cases. LFF was increased 50% by an initial bupivacaine concentration of 6.0 micrograms/ml with all other drugs requiring more than 10 micrograms/ml to increase LFF to that extent. Lidocaine binding in a 4.5 g/dl albumin solution was unaffected by concentrations of quinidine, meperidine, nortriptyline and bupivacaine up to 200 micrograms/ml. Addition of AAG to serum reduced LFF as expected. A plot of the reciprocal of bound drug concentration vs. the reciprocal of free drug concentration in the presence and absence of quinidine suggested a competitive binding interaction. These data indicate that the binding interactions between lidocaine and the various displacing compounds are not significantly complicated by cooperative effects and that, with the possible exception of bupivacaine, displacement of lidocaine by any of these drugs is likely to be of clinical significance.     

Effects of local anaesthetics on responses of human saphenous vein and bovine coronary artery to neurotransmitters, acetylcholine, noradrenaline and 5-hydroxytryptamine

The effects of 5 different local anaesthetics, lignocaine, etidocaine, prilocaine, mepivacaine, bupivacaine, and 3 different neurotransmitters, acetylcholine (ACh), noradrenaline (NA), 5-hydroxytryptamine (5-HT) on tone and contractility of human saphenous vein and bovine coronary artery were studied and compared in vitro. The experiments were carried out to see if there were species or tissue differences in the action of local anaesthetics and neurotransmitters at vascular smooth muscle, i.e. saphenous vein and coronary artery. Another important aspect was to see if local anaesthetics modified cholinergic (ACh), adrenergic (NA) and serotoninergic (5-HT) responses in vascular smooth muscle. Among the local anaesthetics studied, lignocaine and etidocaine produced prolonged relaxations, whereas prilocaine, mepivacaine, bupivacaine produced contractions in the saphenous vein and coronary artery. High concentrations of the latter drugs produced relaxations in the blood vessels. Among the local anaesthetics, lignocaine produced differential effects on saphenous vein and coronary artery, its effect on the latter was 3 times larger than on the saphenous vein. ACh, NA and 5-HT contracted the saphenous vein. In the coronary artery, ACh and 5-HT contracted whereas NA relaxed the vessel. On a molar basis, ACh was less effective than NA in contracting the saphenous vein. 5-HT was equipotent on both the saphenous vein and coronary artery. Lignocaine reduced ACh, NA and 5-HT-induced contractions in the saphenous vein and those of ACh and 5-HT in the coronary artery, and shifted the control curves, non-competitively, to the right. The relaxation produced by NA in the coronary artery was enhanced by lignocaine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spinal hyperbaric prilocaine vs. mepivacaine in perianal outpatient surgery

Background

The aim of this randomised, clinical trial was to compare safety and efficiency of hyperbaric prilocaine and mepivacaine at a dosage of 0.5 ml each for perianal outpatient surgery in terms of transient neurologic symptoms (TNS) and postoperative recovery.

Methods

160 patients aged 18–80 years were randomized to receive a spinal anaesthesia (SPA) with 0.5ml of mepivacaine or prilocaine. We measured the expansion of the block, evaluated postoperative recovery times and determined the incidence of TNS one week after surgery.

Results

160 patients (93 male / 67 female) were available for analysis. Prilocaine led to shorter times from SPA to micturition (prilocaine: 178 (110–254) min vs. mepivacaine: 195 (130–305) min, p=0.0008) and discharge (prilocaine: 192 (126–267) min vs. mepivacaine: 220 (140–320) min, p<0.0001). 152 / 160 patients were available for the telephone follow-up. Six patients (9%) receiving mepivacaine compared to zero patients of the prilocaine group announced typical symptoms of TNS (p=0.0284).

Conclusion

Both, hyperbaric mepivacaine 40 mg/ml and hyperbaric prilocaine 20 mg/ml can be used at a dosage of 0.5 ml each for SPA in perianal outpatient surgery. Due to the faster recovery profile and a lower incidence of TNS, we recommend the use of 10mg hyperbaric prilocaine 20 mg/ml for this indication.     

Determination of lidocaine in hair of drug fatalities by headspace solid-phase microextraction

The local anesthetic lidocaine was determined in hair by hydrolysis of the samples with 4% NaOH in the presence of excessive Na2SO4 and subsequent headspace solid-phase microextraction with a 65-microm Carbowax/divinylbenzene fiber, and gas chromatography-mass spectrometry measurement with etidocaine as the internal standard. The calibration curve was linear between 0.1 and 1000 ng/mg. The detection and quantitation limits were 0.1 and 0.4 ng/mg, respectively. The method was applied to hair samples of 49 drug fatalities, and positive results were obtained in 32 cases with lidocaine concentrations between 0.4 and 400 ng/mg and 675 ng/mg in one extreme case. For comparison, morphine, 6-acetylmorphine, codeine, dihydrocodeine, methadone, cocaine, and benzoylecgonine were also determined by usual methods. From segmental investigations in four of the cases and from comparison with the hair concentrations of the other drugs, it follows that lidocaine was consumed for a longer period of time as an adulterant of cocaine and heroin preparations.     

Pharmacological profile of RWJ 20085: A new,potent, long-acting local anesthetic

RWJ 20085 is a potent, long-acting local anesthetic that has been studied in vivo and in vitro relative to several clinically active agents. In mice, RWJ 20085 [ED₅₀ = 0.0078% (0.0053–0.011%)] was more potent by perineural infiltration than bupivacaine [ED₅₀ = 0.035% (0.026–0.046%)], etidocaine [ED₅₀ = 0.025% (0.016–0.035%)], or lidocaine [ED₅₀ = 0.18% (0.13–0.26%)]. The onset of action of each compound was 5 minutes, and the duration was 90 minutes for RWJ 20085 and 30 minutes for bupivacaine or etidocaine while lidocaine was active for only 15 minutes. In the rabbit corneal assay, RWJ 20085 [ED₅₀ = 0.012% (0.0049–0.023%)] was more potent than bupivacaine [ED₅₀ = 1.4% (0.47–3.05%)]. The lowest topical local anesthetic ED₅₀ of each agent was observed within 5 or 15 minutes after administration, and RWJ 20085 was active for 300 minutes, whereas bupivacaine and etidocaine were active for 90 or 45 minutes, respectively. In the guinea pig intradermal assay RWJ 20085 [ED50 = 0.017% (0.0094–0.028%)], bupivacaine [ED₅₀ = 0.016% (0.0078–0.028%)], and etidocaine [ED₅₀ = 0.02% (0.0093–0.042%)] were equipotent while lidocaine [ED₅₀ = 0.072% (0.040–0.12%)] was less potent. The onset of action of each compound was 5 minutes. The duration of action of RWJ 20085 and etidocaine was 60 minutes, whereas bupivacaine and lidocaine were active for 45 and 15 minutes, respectively. In the frog isolated-sciatic nerve preparation, similar concentrations of RWJ 20085 (2.5 × 10^?3M) and lidocaine (5.0 × 10^?3M) produced a 50% reduction of the amplitude of the pretreatment action potential; however, bupivacaine and etidocaine were each effective at a lower concentration (5.0 × 10^?4M). When their intramuscular therapeutic ratios (TR = lethal dose LD₅₀/local anesthetic ED₅₀) were calculated in mice, the therapeutic ratio of RWJ 20085 (82) was less than that of etidocaine (103) but was larger than that of either lidocaine (36) or bupivacaine (29). Calculation of the therapeutic ratios by using the intravenous LD₅₀ values suggests that lidocaine would have the smallest margin of safety if inadvertently administered by the intravenous route. The therapeutic ratios of the other agents were larger than that of lidocaine; however, there was little difference among them. RWJ 20085 has a low potential for dermal irritation as shown in rabbits and has no liability for contact sensitization as shown in guinea pigs. RWJ 20085 may have clinical utility as an injectable and/or topical local anesthetic.     

The effects of opioids, local anesthetics and adjuvants on isolated pregnant rat uterine muscles

Local anaesthetics, opioids and adjuvants are often used for managing labor pain. Some others of these agents are reported to cause alterations on uterine contractility during labor. However, there are controversies and the effects of some others are unknown. In the present study, we aimed to elucidate the effects of opioids such as alfentanyl, meperidine, remifentanyl; local anesthetics such as mepivacaine, ropivacaine, bupivacaine; and adjuvants such as clonidine and midazolam on isolated pregnant rat uterine muscle. Strips of longitudinal uterine smooth muscle obtained from rats pregnant for 18-21 days were suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. The effects of cumulative concentrations of alfentanyl, meperidine, remifentanyl, mepivacaine, ropivacaine, bupivacaine, clonidine and midazolam (10(-8) - 10(-4) M, for all) on contractions induced by oxytocin (1 mU/ml) were studied. Alfentanyl (10(-5) M), meperidine (10(-5) M), remifentanyl (10(-4) M), bupivacaine (10(-4) M), ropivacaine (10(-4) M) and midazolam (3 x 10(-5) M) caused significant decreases in contractile responses of uterine strips to oxytocin. Contrastingly, mepivacaine increased (33.1% +/- 7.2%) oxytocin-induced contractions of uterine strips while clonidine exerted no significant effect. The sensitivity of myometrial preparations to tested local anesthetics or opioids did not differ significantly. The findings of the present study demonstrated that some local anesthetics, opioids and adjuvants caused significant and agent-specific alterations on contractility of the pregnant rat myometrium. Therefore, they seemed to have a potential to influence uterine contractility during clinical management of pain during labor. However, further research is needed to extrapolate these finding to clinical practice.     

Diffusive transport properties of some local anesthetics applicable for iontophoretic formulation of the drugs

As part of a general study to improve the iontophoretic delivery of local anaesthetics of the amide type, the diffusion properties of the hydrochloride salts of bupivacaine, etidocaine, lidocaine, mepivacaine, prilocaine and ropivacaine, were studied in a 1% w/w agarose hydrogel. A source drug solution (25 mM) was placed in contact with the gel and, after an appropriate time, the drug concentration profile in the gel was analyzed to give a diffusion coefficient, D. The values of Dx10(10) expressed in m(2) s(-1) were: (bupi) 6.71, (eti) 6.71, (ropi) 6.39, (mepi) 7.31, (lido) 7.49 and (prilo) 7.76. For comparative reasons, the diffusion coefficient for LidHCl in an aqueous solution according to the Nernst-Hartley relation for the diffusion of ion-pairs was calculated, hereby taking into account ionic activity of LidH+ and Cl-. The diffusion coefficient thus obtained was 7.76x10(-10) m2 s-1 at infinite dilution. The relationship between the molecular weight of the compounds and the diffusion coefficient was investigated.     

Urine drug testing of chronic pain patients. III. Normetabolites as biomarkers of synthetic opioid use

Opioids are important therapeutic agents available to patients with moderate to severe pain. The synthetic opioids, buprenorphine, fentanyl, meperidine, methadone, and propoxyphene have been utilized for decades as analgesics. One of the major biotransformation pathways of these drugs occurs through N-demethylation leading to the formation and excretion of normetabolites. Normetabolites generally exhibit longer half-lives than the parent drug leading to accumulation with prolonged use. As part of continuing research efforts to improve monitoring programs of chronic pain patients undergoing opioid treatment, we evaluated the prevalence and relative abundance of normetabolites of buprenorphine, fentanyl, meperidine, methadone, and propoxyphene in patients? urine specimens. Selected sets of specimens were analyzed without prior immunoassay screening by liquid chromatography-tandem mass spectrometry for buprenorphine, fentanyl, meperidine, methadone, propoxyphene, and their respective normetabolites. Limits of quantitation (LOQ) were as follows: buprenorphine, 1 ng/mL; fentanyl, 0.5 ng/mL; meperidine, 50 ng/mL; methadone, 50 ng/mL; and propoxyphene, 50 ng/mL. LOQs for normetabolites were equal to the parent drug with the exception of norbuprenorphine (2.5 ng/mL). The percentage of positive specimens that contained normetabolite (only) ranged from 8.0% for EDDP (2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine) to 53.1% for norpropoxyphene. Inclusion of the five normetabolites in the test panel produced an increase in detection rates for parent drug use as follows: buprenorphine, 10.0%; fentanyl, 42.1%; meperidine, 98.7%; methadone, 8.7%; and propoxyphene, 113.2%. The authors conclude that testing for synthetic opioid normetabolites enhances the effectiveness of monitoring programs for pain patients.     

Immunological modulation by lidocaine-epinephrine and prilocaine-felypressin on the functions related to natural immunity in neutrophils and macrophages

There is accumulating evidence that local anesthetics have immunological properties in addition to their direct anesthetic activity. Because local anesthetics are often used together with blood vessel contraction drugs, such as epinephrine and felypressin in the clinical setting, we have examined possible abilities of both local anesthetic alone including lidocaine, mepivacaine, procaine, prilocaine and tetracaine, and local anesthetics with blood vessel contraction drugs including lidocaine with epinephrine and prilocaine with felypressin on the functions related to natural immunity in neutrophils and macrophages. In contrast, lidocaine, mepivacaine, procaine, prilocaine and tetracaine all inhibited adhesion, chemotaxis, phagocytosis, and the production of superoxide anion and hydrogen peroxide by neutrophils and macrophages. Lidocaine with epinephrine and prilocaine with felypressin were effective in significantly inhibiting adhesion, chemotaxis, phagocytosis, and the production of hydrogen peroxide by neutrophils and macrophages. Interestingly, lidocaine with epinephrine potentiated the production of superoxide anion, whereas prilocaine with felypressine inhibited the production, irrespective of cells. In addition, epinephrine potentiated the production of superoxide anion, whereas epinephrine inhibited the production of hydrogen peroxide as well as lidocaine with epinephrine. This potentiation by epinephrine was not prevented by adrenergic antagonists. Furthermore, superoxide dismutase potentiated the production of hydrogen peroxide, which was in part prevented by epinephrine. These results suggest that local anesthetics may inhibit the functions related to natural immunity in neutrophils and macrophages. In addition, lidocaine with epinephrine evidently differs from prilocaine with felypressine regarding the molecular mechanisms underlying the modulation of superoxide anion production by neutrophils and macrophages.     

Determination of some local anesthetics in human serum by gas chromatography with solid-phase extraction

A method of analysis based on solid-phase extraction coupled with capillary gas chromatographic system for determination of mepivacaine, bupivacaine and lidocaine from human serum was developed. As extraction sorbents were used Chromosorb 103, Tenax-GC and Chromosorb T. The best extraction sorbent proved to be Chromosorb 103. Their recoveries ranged from 91 to 94% at the target concentrations of approx. 1.5 microgml(-1) in serum. Relative standard deviation of the recoveries ranged from 3.11 to 5.30 at these concentrations. As internal standard was used lidocaine. The chromatographic analysis was performed on a gas chromatograph equipped with a capillary column, HP-Innowax, and flame ionisation detector. Samples were injected in splitless mode. This method was applied in a stomatological clinic to healthy volunteers to whom superior-posterior alveolar nerve block anesthesia with mepivacaine was administered.     

Effects of Four Local Anaesthetics on the Membrane Stability of Isolated Rat Liver Lysosomes

Abstract The effects of the local anaesthetics bupivacaine, lidocaine, mepivacaine and prilocaine on lysosomal membrane stability have been studied on isolated rat liver lysosomes. The lysosomal membranes were stabilized by the local anaesthetics only within a very narrow range of concentration (around 0.001 M). In lower concentrations there was no effect of the substances while in higher concentrations there was a marked labilizing effect on the lysosomal membranes. The phlogistic effect of an injected suspension of lysosomes in the rat paw was increased by mepivacaine in concentrations of 1 % (0.04 M) and higher. The labilizing effects of local anaesthetics on lysosomes were probably due to precipitation of lysosomal membrane proteins by the local anaesthetics.     

Percutaneous penetration kinetics of lidocaine and prilocaine in two local anesthetic formulations assessed by in vivo microdialysis in pigs

The aim of this study was to characterize and compare the percutaneous penetration kinetics of lidocaine (L) and prilocaine (P) in two local anesthetic formulations by in vivo microdialysis coupled with HPLC. The microdialysis system for studying lidocaine and prilocaine was calibrated by a no-net-flux method in vitro and retrodialysis method in vivo, respectively. A dosage of 0.2 g/cm2 of an in-house P-L formulation (2.5% lidocaine and 2.5% prilocaine, methylcellulose-based) and commercially available Eutectic Mixture of Local Anesthesia (EMLA, 2.5% lidocaine and 2.5% prilocaine, carbopol-based) was separately but symmetrically applied in the dorsal region of pigs. Saline (0.9%, w/v) was perfused into the linear microdialysis probe at a flow rate of 1.5 microl/min. Dialysate was collected upon topical application up to 6 h at 20-min intervals and assessed by HPLC. The results demonstrated the area under the concentration-time curve (AUC(0-6 h)) of lidocaine and prilocaine in EMLA was 71.95+/-23.36 microg h/ml and 38.01+/-14.8 microg h/ml, respectively, in comparison to 167.11+/-56.12 microg h/ml and 87.02+/-30.38 microg h/ml in the P-L formulation. The maximal concentrations (Cmax) of lidocaine and prilocaine in the dermis were 29.2+/-9.08 microg/ml and 16.54+/-5.31 microg/ml in EMLA and 80.93+/-17.98 microg/ml and 43.69+/-12.87 microg/ml in the P-L formulation, respectively. This study indicates a well-calibrated microdialysis system can provide vital real-time information on percutaneous drug delivery and specifically a methylcellulose-based P-L formulation can increase percutaneous absorption of both lidocaine and prilocaine in pigs compared to carbopol-based EMLA.     

Use of negatively charged cyclodextrins for the simultaneous enantioseparation of selected anesthetic drugs by capillary electrophoresis-mass spectrometry.

The simultaneous enantioseparation of selected anesthetic drugs was studied by capillary electrophoresis (CE) in presence of three different negatively charged cyclodextrins (CDs). Among the chiral selectors tested, namely carboxymethyl, sulfobutyl ether and sulfated-beta-CD, the latter appeared to be the most effective to achieve the enantiomeric resolution of the investigated compounds. Beside CD type, resolution was greatly influenced by the buffer pH, the molecular structure of the anesthetic compounds, CD concentration and temperature. The optimum electrophoretic conditions for the stereoselective analysis of the studied anesthetics were obtained with a poly(vinyl alcohol) coated capillary (48.5 cm total length x 50 microm I.D.), a 50 mM Tris-phosphate buffer at pH 2.5 containing 6 mg ml(-1) of sulfated-beta-CD, an applied voltage of 30 kV and a temperature of 30 degrees C. Under these optimized conditions, four drugs, namely bupivacaine, mepivacaine, ketamine and prilocaine, were simultaneously enantioresolved in less than 12 min. Furthermore, the method was applied to the stereoselective analysis of mepivacaine in a pharmaceutical preparation. Finally, the method was on-line coupled to electrospray ionization mass spectrometry using the counter current partial-filling technique.     

Immunoassay screening of lysergic acid diethylamide (LSD) and its confirmation by HPLC and fluorescence detection following LSD ImmunElute extraction

In all, 3872 urine specimens were screened for lysergic acid diethylamide (LSD) using the CEDIA DAU LSD assay. Forty-eight samples, mainly from psychiatric patients or drug abusers, were found to be LSD positive, but only 13 (27%) of these could be confirmed by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) following immunoaffinity extraction (IAE). Additional analysis for LSD using the DPC Coat-a-Count RIA was performed to compare the two immunoassay screening methods. Complete agreement between the DPC RIA assay and HPLC-FLD results was observed at concentrations below a cutoff concentration of 500 pg/mL. Samples that were LSD positive in the CEDIA DAU assay but not confirmed by HPLC-FLD were also investigated for interfering compounds using REMEDI HS drug-profiling system. REMEDI HS analysis identified 15 compounds (parent drugs and metabolites) that are believed to cross-react in the CEDIA DAU LSD assay: ambroxol, prilocaine, pipamperone, diphenhydramine, metoclopramide, amitriptyline, doxepine, atracurium, bupivacaine, doxylamine, lidocaine, mepivacaine, promethazine, ranitidine, and tramadole. The IAE/HPLC-FLD combination is rapid, easy to perform and reliable. It can reduce costs when standard, rather than more advanced, HPLC equipment is used, especially for labs that perform analyses for LSD infrequently. The chromatographic analysis of LSD, nor-LSD, and iso-LSD is not influenced by any of the tested cross-reacting compounds even at a concentration of 100 ng/mL.     

Simultaneous determination of mepivacaine,tetracaine, and p-butylaminobenzoic acid by high-performance liquid chromatography

INTRODUCTION: The purpose of the present study was to develop a simple method for the simultaneous determination of mepivacaine, tetracaine, and p-butylaminobenzoic acid (BABA) in human plasma using high-performance liquid chromatography (HPLC) with a multiwavelength detector. METHODS: Human blood samples containing heparin, as an anticoagulant, and physostigmine (100 microg/ml), as an anticholinesterase, or human plasma containing physostigmine were spiked with various concentrations of mepivacaine, tetracaine and, in some cases, BABA. Blood samples were centrifuged and plasma was deproteinized with trifluoroacetic acid (TFA; 7%). After centrifugation, the pH was adjusted to 4.5 and an aliquot of 20, 50 or 100 microl was injected into the HPLC apparatus. The detection was done simultaneously at wavelengths of 214 and 300 nm. Analytical chromatography was done on a Waters microBondapak C(18) reverse-phase column (3.9 x 300 mm; particle size 10 microm) with a 30-min increasing linear gradient of 20-40% acetonitrile+0.05% TFA in H(2)O+0.05% TFA at a flow rate of 1 ml/min. The Waters HPLC system included two pumps, an automatic injector, a column oven, and a M490 multiwavelength detector. Quantification was done using integration of peak areas with peaks of authentic mepivacaine, tetracaine, and BABA standards. RESULTS: Calibration curves for standards of mepivacaine, tetracaine, and BABA were linear in the concentration ranges from 0.1 to 100 microg/ml, and the correlation coefficients exceeded.99 for all compounds. The lower limits of detection were 100 ng/ml for mepivacaine and 50 ng/ml for tetracaine and BABA. The yields for mepivacaine, tetracaine, and BABA were 91+/-2.1%, 82+/-3.3%, and 88+/-2.0% (mean+/-S.E.M., n=6), respectively. Degradation of tetracaine by human plasma at 37 degrees C was inhibited by physostigmine. DISCUSSION: The method is sensitive enough to allow blood concentration determinations of mepivacaine and tetracaine or its metabolite, BABA, following local anesthesia induced by these two drugs, especially when their toxic effect may be present. This method also may be useful in forensic medicine for determination of the cause of death after local anesthesia with mepivacaine and/or tetracaine.     

Physico-chemical modification of lidocaine uptake in rat lung tissue.

The uptake of lidocaine, methyllidocaine, bupivacaine, etidocaine was studied in rat lung slices at different pH-values. The accumulation of the quaternary analogue, methyllidocaine, was not changed in the pH interval 7.0--8.0. The uptake of the three other substances was about 3--4 times lower at pH 7.0 than at pH 8.0. The rank order of distribution at a fixed cation/base ratio was bupivacaine greater than etidocaine greater than lidocaine. Interactions between lidocaine and other substances were studied in lung slices and in isolated perfused lungs. Bupivacaine and nortriptyline counteracted the accumulation of 14C-lidocaine in lung slices in a dose-dependent manner. Nortriptyline was more effective than bupivacaine. In isolated perfused lung, bolus injections of nortriptyline and lidocaine rapidly displaced 14C-lidocaine from the tissue. In this study we suggest that the base form of local anaesthetics accumulate in the lung tissue, while the cationic form binds to accessible binding sites in the cell membranes.