Metabolism of etidocaine in man

Characterization of methemoglobinemia induced by 3,5-xylidine in rats

The objective of this study was to characterize the dose effect and kinetics of methemoglobinemia in rats following oral or intravenous administration of 3,5-xylidine (XYL). The first set of experiments involved the intravenous administration of 0.06, 0.12, 0.24, 0.48, or 0.60 mmol XYL/kg to groups of 3 rats each and the serial sampling of blood from the tail vein of individual animals for the determination of methemoglobin levels. An additional series of experiments involved the oral administration of 0.24, 0.48, 0.72, 0.96, 1.2, 1.8, 2.4, or 4.8 mmol XYL/kg and the serial sampling of blood for the determination of methemoglobin levels. The results showed a dose-dependent induction of methemoglobinemia by XYL in the rat, for both routes of administration. The maximal percent methemoglobin observed in the treated animals was 28.90 +/- 0.34% and 32.67 +/- 2.14% for the intravenous (0.6 mmol/kg) and oral (4.8 mmol/kg) routes, respectively. The dose levels of 0.06 mmol/kg (iv) and 0.96 mmol/kg (po) were the no-observable-adverse-effect levels with respect to XYL-induced methemoglobinemia in the rat. The dose-effect information on XYL-induced methemoglobinemia obtained in this study may be useful for the characterization of noncarcinogenic risks of acute human exposure to this chemical.

Splanchnic turn-over of some energy metabolites and acid-base balance during intravenous infusion of lidocaine, bupivacaine or etidocaine

The splanchnic turn-over of energy metabolites in circulating blood has been studied in four groups of young, healthy volunteers, receiving intravenous infusions of physiological saline (n = 5), lidocaine 4 mg/min (n = 7), bupivacaine 2 mg/min (n = 7) and etidocaine 2 mg/min (n = 8). The results showed that the local anaesthetic agents increased the splanchnic blood flow and oxygen consumption, the uptake of glycerol and lactate, and the release of 3-hydroxybutyrate. These effects are adrenaline-like but cannot be explained by one single mechanism involving increased activity of the sympathetic nervous system. Only a minor part of the increased oxygen uptake could be attributed to the energy cost of drug metabolism.

The identification of eight hydroxylated metabolites of etidocaine by chemical ionization mass spectrometry

1. Eight hydroxylated metabolites of etidocaine have been identified in urine of man by g.l.c.-chemical ionization mass spectrometry, using methane and a mixture of methane and deuterium oxide as reactant gases. 2. The metabolites identified were N-(2,6-dimethyl-3- and 4-hydroxyphenyl-)-2-(N,N-ethylpropylamino)butyramides, N-(2,6-dimethyl-3- and 4-hydroxyphenyl)-2-aminobutyramides, N-(2,6-dimethyl-3- and 4-hydroxyphenyl)-2-(N-ethylamino)butyramides, and N-(2,6-dimethyl-3- and 4-hydroxyphenyl)-2-(N-propylamino)butyramides. 3. The eight metabolites represent about 10% of the oral dose of etidocaine.

The pharmacokinetics and metabolism of the anilide local anaesthetics in neonates. I. Lignocaine

The pharmacokinetics and metabolism of lignocaine in premature neonates was studied after subcutaneous administration. The collection of serial urine together with a limited number of blood samples from neonates enabled simultaneous computer fitting of data to a pharmacokinetic model. The disposition kinetics of lignocaine in four neonates were compared with similar data reported for adults. Neonates had prolonged t1/2 (neonate mean: 3.16 h; adult mean: 1.80 h), and an increased total volume of distribution (neonate mean: 2.75 l/kg; adult mean: 1.11 l/kg) compared with adults. Total plasma clearance (Cltp) normalised on body weight showed no significant difference between neonates (mean: 0.610 l/h/kg) and adults (mean: 0.550 l/h/kg). The urinary excretion of lignocaine and several of its metabolites was studied in 8 neonates and 11 adults. Neonates were shown to excrete much more unchanged lignocaine (mean: 19.67%) compared with adults (mean: 4.27%) and the proportion of the dose excreted as 4-hydroxyxylidine is considerably reduced in neonates (neonate mean: 8.89%; adult mean: 63.78%). The use of the two pharmacokinetic parameters, t1/2 and Cltp, as indices of drug elimination ability are discussed.

Splanchnic elimination and systemic toxicity of bupivacaine and etidocaine in man

Fifteen healthy young volunteers were studied in connection with an intravenous infusion of a local anaesthetic agent. Seven received bupivacaine and eight etidocaine in a dose rate of 2 mg.min-1 over a period of 150 min. The hepatic blood flow and arterial-hepatic venous differences of the two drugs were measured. The estimated hepatic blood flow increased during the infusion of both drugs. While the splanchnic extraction ratio decreased during infusion of bupivacaine to 0.41 +/- 0.13, the same variable did not change (0.76 +/- 0.07) when etidocaine was infused. After 150 min infusion, the splanchnic clearance of bupivacaine and etidocaine was 0.76 +/- 0.27 and 1.32 +/- 0.21 1.min-1, respectively. Slight symptoms of central nervous toxicity were noted towards the end of the bupivacaine infusion, while no such symptoms appeared with etidocaine. A comparison between earlier published data on the blocking properties and the disposition pharmacokinetics of the two drugs shows that etidocaine is likely to confer a clinical advantage over bupivacaine as regards toxicity.

Lignocaine kinetics in cardiac patients and aged subjects

1 The pharmacokinetics following long term intravenous infusion of lignocaine to cardiac patients have been examined. 2 Plasma levels and half-lives of lignocaine and monoethylglycinexylidide (MEGX) showed wide inter-patient variability. 3 Toxicity reactions to therapy were associated with elevated lignocaine and/or MEGX plasma levels. 4 In a separate study the effect of age on the pharmacokinetics of lignocaine was examined using bolus doses (50 mg) of the drug to young and aged subjects. 5 Elderly subjects had significantly longer half-lives for lignocaine compared to younger individuals although no change in plasma clearance occurred. 6 The drug appeared to distribute differently in the aged as reflected by significantly increased apparent volumes of distribution. 7 The 24 h urinary recovery of the major metabolite (total 4-hydroxyxylidine) showed a significant reduction in the elderly when compared to the young. 8 The clinical significance of these studies with respect to lignocaine therapy has been discussed.

Cyclic metabolites of etidocaine in humans

1. Three cyclic metabolites of etidocaine excreted in urine of man have been investigated by g.l.c.-mass spectrometry. 2. These metabolites have been identified as 3-(2,6-dimethylphenyl)-5-ethyl-2,4-imidazolidinedione, 1-(2,6-dimethylphenyl)-2-methyl-4-ethyl-2-imidazolin-5-one and 1-(2,6-dimethylphenyl)-2,4-diethyl-2-imidazoline-5-one. 3. Formation in vivo of two of the metabolites is proposed to proceed via carbinolamine intermediates.