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PubMed2004

A new look at the hemolytic effect of local anesthetics, considering their real membrane/water partitioning at pH 7.4.

The interaction of local anesthetics (LA) with biological and phospholipid bilayers was investigated regarding the contribution of their structure and physicochemical properties to membrane partition and to erythrocyte solubilization. We measured the partition into phospholipid vesicles-at pH 5.0 and 10.5-and the biphasic hemolytic effect on rat erythrocytes of: benzocaine, chloroprocaine, procaine, tetracaine, bupivacaine, mepivacaine, lidocaine, prilocaine, and dibucaine. At pH 7.4, the binding of uncharged and charged LA to the membranes was considered, since it results in an ionization constant (pK(app)) different from that observed for the anesthetic in the aqueous phase (pK(w)). Even though it occurred at a pH at which there is a predominance of the charged species, hemolysis was greatly influenced by the uncharged species, revealing that the disrupting effect of LA on these membranes is mainly a consequence of hydrophobic interactions. The correlation between the hemolytic activity and the LA potency shows that hemolytic experiments could be used for the prediction of activity in the development of new LA molecules.

Amides↗
PubMedDate not supplied

Bupivacaine and other amide local anesthetics inhibit the hydrolysis of chloroprocaine by human serum.

The rate of hydrolysis of chloroprocaine by human serum was studied in the presence and absence of a number of aminde local anesthetics and their metabolites. Bupivacaine (2.4 microgram/ml) and etidocaine (2.3 microgram/ml) caused 38% and 21% inhibition respectively of the rate of chloroprocaine hydrolysis. Circulating concentrations of these drugs have been reported in this range by several investigators following epidural doses of 150 to 400 mg of either drug. Mepivacaine, lidocaine, and two lidocaine metabolites (glycine xylidide and monoethylglycine xylidide) were only inhibitory at levels much greater than those seen in blood following the usual local anesthetic doses of the parent compounds. Since serum is an important site of chloroprocaine metabolism in man, the probability of chloroprocaine intoxication may be increased when it is administered with local anesthetics such as bupivacaine and etidocaine.

Anesthetics, Local↗
PubMed1995

Chloroprocaine for epidural anesthesia in infants and children.

The authors discuss their experience with chloroprocaine for epidural anesthesia in five pediatric patients. While bupivacaine remains the most commonly used local anesthetic in children, recent reports of toxicity document the risks of this agent. The major advantage of chloroprocaine is its rapid metabolism, which thereby minimizes the risks of toxicity, especially in patients with preexisting problems such as young age or underlying hepatic dysfunction, which may limit the metabolism of local anesthetics of the amide class. In three cases, the epidural infusion was combined with the general anesthetic. The cases included hepatic resection, repair of bladder exstrophy, and correction of duodenal atresia. In two other cases, epidural anesthesia was used instead of general anesthesia in a former preterm infant who was undergoing inguinal herniorrhaphy and for lower extremity orthopedic procedures in a child with myotonic dystrophy. In all cases, chloroprocaine was chosen because of preexisting or associated conditions that might increase the risk of bupivacaine toxicity, such as hepatic resection, repeated dosing in a neonate, or the need for higher concentrations of local anesthetic to achieve adequate surgical conditions. Adequate intraoperative conditions were achieved in all five patients. No complications related to chloroprocaine epidural anesthesia were noted. This initial experience suggests that chloroprocaine offers an acceptable alternative to bupivacaine for epidural anesthesia in the pediatric population.

Anesthesia, Epidural↗
PubMedDate not supplied

An in vivo method for the quantitative evaluation of local anesthetics.

We describe a mouse model for evaluation of skin anesthesia after infiltration of local anesthetic. The method involves subcutaneous injection of the anesthetic over the abdomen, and monitoring the vocalization response to electrical stimulus as a measure of analgesia. Prior to drug injection, the vocalization threshold was determined. Mice that vocalized at < or = 8 mA were included in the study. The model was tested using representative agents of the two classes of local anesthetics, bupivacaine, an amide, and chloroprocaine, an ester. The time course and dose response were assessed after injection. The median analgesic time was 15, 40, and 55 min for 0.015%, 0.0625%, and 0.25% bupivacaine and 30, 50, and 55 min for 0.125%, 0.25%, and 2.0% chloroprocaine, respectively. Statistical analysis of the data showed that this method is sufficiently sensitive to detect differences between the dose and duration of local anesthesia (p<0.05, by log rank test of the survival curves). To further validate the model, we compared the duration of anesthesia between the 0.5% bupivacaine and a new long-acting liposomal formulation of 2% bupivacaine. The results showed that the new formulation significantly prolonged the duration of anesthesia (p<0.05). This simple and reliable method may facilitate research on the pharmacology of infiltration anesthesia and the development of new local anesthetics and/or formulations.

Abdomen↗
PubMed1983

Intrapartum paracervical block anesthesia with 2-chloroprocaine.

Most of the reports of fetal bradycardia and acidosis following paracervical block anesthesia have involved the use of amide-linked anesthetics, such as lidocaine and mepivacaine. The purposes of this study were (1) to determine placental transfer of an ester-linked local anesthetic, 2-chloroprocaine, and its inactive metabolite, 2-chloroaminobenzoic acid (CABA) following paracervical block and (2) to evaluate the clinical use of 2-chloroprocaine for paracervical block anesthesia. Accordingly, 2-chloroprocaine was administered to 16 normal pregnant women in labor at term. Following injection, the levels of 2-chloroprocaine or CABA in maternal and neonatal plasma or urine were quantitated. Multiple clinical parameters, including the presence or absence of fetal bradycardia, were monitored before and after the paracervical block. The pharmacologic data indicated that 2-chloroprocaine is rapidly hydrolyzed. At delivery only trace levels of 2-chloroprocaine were present in 6.3% of the maternal samples and 25% of the cord vein samples. Furthermore, only 0.24% of the total dose of 2-chloroprocaine administered was recovered in neonatal urine as CABA. The clinical data showed no adverse effects on the parturient or neonate. Therefore, the data suggest that paracervical block anesthesia with 2-chloroprocaine may offer safe analgesia during the first stage of labor. Larger clinical studies appear warranted.

Adolescent↗
PubMed1983

Comparison of lidocaine and 2-chloroprocaine in paracervical block: clinical effects and drug concentrations in mother and child.

2-Chloroprocaine (CP) has recently been recommended as a less toxic alternative to amide-type local anesthetics due to its rapid metabolism. A double-blind, randomized study comparing CP to lidocaine when used for paracervical block was carried out. Twenty-nine patients received CP, while 31 received lidocaine. None of the 60 mothers developed adverse side effects. Adequate pain relief was achieved in 28 cases in each group, with a mean duration of 40 min regardless of the anesthetic. No change in uterine activity was observed. In the CP group one fetus had mild bradycardia, while two in the lidocaine group had severe, and three mild bradycardia within 5-7 min after the block. Low concentrations of CP were detected in the venous blood of 2 of 29 mothers and in the umbilical venous blood of their babies. Measurable amounts of its metabolite, 2-chloro-4-aminobenzoic acid (CABA), were found in all 13 samples of maternal blood 5 min after PCB and in 6 of 27 maternal samples at birth. Traces of CABA were found in umbilical venous blood in three neonates; in a fourth, a level of 1,000 ng/ml was found. In contrast, unmetabolized lidocaine was found in all maternal samples and in all but one of the cord samples at birth. Concentration of lidocaine in cord blood at delivery ranged from less than 100 to 4,000 ng/ml and were similar for both arterial and venous samples. No correlation could be demonstrated between levels of local anesthetics in the cord samples and the frequency or severity of fetal bradycardia regardless of the anesthetic.

Adolescent↗
PubMed1985

Fetal acidosis, 2-chloroprocaine, and epidural anesthesia for cesarean section.

Amide-linked local anesthetic agents, such as lidocaine and bupivacaine, can become "trapped" in their ionized forms on the fetal side of the placenta, and therefore their net transfer across the placenta is increased. An ester-linked local anesthetic agent, 2-chloroprocaine, is rapidly metabolized, and placental transfer is limited. Since the metabolism of 2-chloroprocaine by fetal plasma is slower than in maternal plasma, the potential for ion trapping exists. The purpose of this study was to determine the disposition of 2-chloroprocaine and its metabolite, chloroaminobenzoic acid, in relation to the umbilical cord vein pH at delivery, and specifically, to determine whether ion trapping exists. Epidural anesthesia with 2-chloroprocaine was administered to 44 women at term prior to cesarean section. At delivery the levels of 2-chloroprocaine and chloroaminobenzoic acid in maternal plasma and umbilical cord vein were quantitated. Neonates were divided into two groups based on the umbilical cord vein pH at delivery. Ten of the 44 patients delivered neonates with a pH less than or equal to 7.25 (acidotic group) while 34 delivered neonates with a pH greater than 7.25 (nonacidotic group). The mean umbilical cord vein pH in the acidotic and nonacidotic groups was 7.22 +/- 0.03 and 7.32 +/- 0.03, respectively (p less than 0.001). There were also no differences between the groups in maternal and neonatal clinical characteristics or in the total dose of 2-chloroprocaine administered or the drug-to-delivery interval. The pharmacologic results did not demonstrate a statistical difference in the concentration of 2-chloroprocaine or chloroaminobenzoic acid in the maternal vein or umbilical cord vein at delivery between the two groups. Thus the results of this study demonstrate that placental transfer of 2-chloroprocaine is not influenced by fetal acidosis. Therefore these data suggest that 2-chloroprocaine may be the drug of choice when fetal acidosis or distress is anticipated.

Acidosis↗