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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.58 no.5 Campinas Sept./Oct. 2008
LETTERS TO THE EDITOR
Comparative study between 0.125% racemic bupivacaine (S50-R50) and 0.125% and 0.25% of 50% enantiomeric excess bupivacaine in epidural block for labor analgesia
The Power of Clinics: a fact
The study by Duarte et al. 1 confirmed the theoretical fundaments by which enantiomeric excess bupivacaine or enantiomeric mixture of bupivacaine was developed.
When we developed this drug, we geared the pre-clinical phase to study whether handling of the isomers regarding their ability to block the nerve would be possible. For such, the mice sciatic nerve was used. Once confirmed the activity as a local anesthetic, the "birth certificate" of enantiomeric excess bupivacaine or enantiomeric mixture of bupivacaine was published in Regional Anesthesia and Pain Medicine in 1999 2, and found "sponsorship" on the study of Trachez et al. in Acta Anaesthesiologica Scandinavica in 2005 3. Both studies used the mixture in a concentration of 0.5%, which was capable of blocking motor fibers and induce analgesia. But it still had to be demonstrated whether cardiotoxicity would be decreased since in theory the right isomer would be responsible for the greater affinity for sodium channels, especially in cardiac cells, and for this reason it would be proportionally reduced in the left isomer. Tranchez and our group found a reduced toxicity of this drug in different mice preparations of hemodynamic and electrophysiological parameters 3,4.
Due to the wide acceptance of this new local anesthetic and since the power relies on clinical grounds, studies in humans replaced basic studies, which, in this case, is scarce. The study of Duarte et al. 1 in which lower concentrations of this drug were used confirmed the local anesthetic activity and, particularly, the stereoselectivity of the isomers of bupivacaine. It is an original work, since concentrations of 0.125% and 0.25% had not been used yet. On those concentrations, the compound showed the results expected, reassuring the trustworthiness of the use of this new anesthetic in labor analgesia.
The 75%-reduction of the right isomer, which is a characteristic of this compound, is a reality because it reduced the intensity of the motor blockade in a way that it did not induce instrumental deliveries and did not hinder ambulation of labor patients.
Keeping in mind the power of Clinical evidence, I congratulate the authors by the complementation provided to preliminary basic studies. The main objective of those studies was whether the interference of enantiomeric excess bupivacaine or enantiomeric mixture of bupivacaine would be as effective as that of racemic bupivacaine, but without the accompanying cardiotoxicity 5.
Quoting Nakamura et al. 6 who demonstrated greater motor blockade of levobupivacaine (homoquiral compound) than racemic bupivacaine (which is in theory not logical), I suggest that the authors should add an additional group to the study using the homoquiral agent. Even though levobupivacaine is not commercially available in Brazil, this comparison could confirm or deny their results. Therefore, this well-conducted study by Duarte et al. 1 would give an invaluable contribution to the stereoisomeric phenomenon and "its mysteries..."
Dra. Maria P. B.
Professora Doutora ICB-USP