Infants who were treated with bupivacaine injected as a DPNB had significantly better post-operative analgesia compared with lidocaine, as judged by their lower requirement of acetaminophen 24 hours after circumcision. Despite the recommendation to use 0.5% bupivacaine for DPNB in the previous edition of a major textbook of regional analgesia , a Medline search failed to identify any reports on the use of bupivacaine in DPNB for neonatal circumcision.
The use of bupivacaine for pediatric analgesia for circumcision was reported in two recently published studies performed on children older than 1 year. A study by Choi et al  compared the use of topical EMLA cream with bupivacaine in a randomized placebo-controlled manner and concluded that, despite no difference in the score obtained using a pain scale between the two groups, bupivacaine DPNB resulted in significantly longer analgesia. A second recently published study by Gauntlett  compared bupivacaine in DPNB with caudal bupivacaine with ketamine in 60 boys and reported no immediate adverse effects.
The use of bupivacaine may be potentially more hazardous than lidocaine in cases of accidental intravenous injection. Cardiac toxic effects of high doses or unintentional intravascular injection may lead to high plasma levels and related depression of the myocardium, decreased cardiac output, heart block, hypotension, bradycardia, ventricular arrhythmias and cardiac arrest . Adverse central nervous system effects include restlessness, anxiety, dizziness, tinnitus, blurred vision or tremors and sometimes convulsions . The safety of DPNB was recently studied in 3,909 pediatric patients undergoing circumcision. The authors did not report the type of medication and dosage that had been used and also failed to note if there had been any patients with accidental intravenous injection of the local anesthetic medication . An additional study of neonatal circumcision with DPNB in 491 patients found that the only complication was bruising at the injection site in 11% of patients . The type of drug used in this study was not specified in this study.
The mechanism of the reduced requirement of acetaminophen after bupivacaine injection is not clear. High protein binding, better lipid solubility and high pKa all contribute to the longer duration of analgesia, reported mean elimination half-life of 8.1 hours versus 3.2 hours of lidocaine . It is possible that, in addition, the longer period of blocked nociception is sufficient to blunt the hypersensitization associated with persistent postoperative pain input. This secondary hyperalgesia is mediated in the spinal cord and contributes to postoperative pain .
Some potential limitations of our study should be mentioned. The data for this study were collected retrospectively and patient allocation was in a sequential fashion. This approach may introduce a potential bias: for example, while it is theoretically possible that the performance of the analgesia improved over time, thereby resulting in a better outcome in the bupivacaine group, the study was performed during a relatively short time frame and this drawback is not very likely. Secondly, the assessment of pain in the infants was done subjectively by the parents. Crying may have been misinterpreted by the parents as pain, but could have stemmed from other reasons, and could have been managed by some of the parents by modalities other than acetaminophen (e.g., feeding, diaper changing, rocking the infant). Since the parents in both groups were instructed in an identical manner (verbal and written instructions) to give acetaminophen if they felt that their son was in pain, this potential bias was probably not significant.