Topical use of local anesthetics in neonates

Introduction: Various local anesthetics as in lidocaine ointment, amethocai ne cream and EMLA (R) cream are used topically for minor invasive intervent ions, such as venipuncture, both in children and adults. Since neonates hav e a nervous system that, albeit immature, enables them to feel pain, analge sia for these procedures is also indicated. Several studies in neonates hav e been carried out to establish effectiveness and safety of topically appli ed local anesthetics. These studies are reviewed in order to assess effecti veness and safety. Methods: A Medline search was made in order to review all studies on effect iveness and safety of topical use of local anesthetics in neonates. Effecti vity or safety studies using local anesthetics for circumcision were reject ed. Results: Seven studies on effectiveness were found: Three studies examined lidocaine ointment and four examined EMLA (R) cream. Effectiveness of lidoc aine ointment was questionable in two studies and negative in one. Effectiv eness of EMLA (R) cream was positive in two studies and negative in the oth er two. Four studies were found on safety of EMLA (R) cream. All studies in dicated that use of EMLA (R) cream was safe. Discussion: The poor effectiveness found in the reviewed studies is possibl y due to too long an application time, a lipophilic carrier used and diffic ulties in assessing pain. The time of application is often based upon studi es in children. Since the skin of neonates acts more as a mucosa than as ma ture skin the local anesthetics are able to cross this barrier more rapidly . Also a high bloodflow in the heel enhances the uptake of the drug. The ap plication time in neonates should therefore be reduced compared to children . The use of a lipophilic carrier should be avoided since a lipophilic carr ier impedes the local anesthetic to be absorbed, leading to reduced effect. Various methods of pain assessment were being used. Since not all methods used are validated it is difficult to obtain an objective end point. Conclusion and recommendation: The articles reviewed are non conclusive in their results of effective analgesia. Due to a lipophilic base form and a h ydrophilic matrix EMLA (R) cream is most effective. An application time of 30 minutes is recommended. In spite of the present precautions due to fear of methemoglobinemia, use of EMLA (R) cream proved to be safe when used onc e a day. Since the clinical situation often requires more than one applicat ion a day, more research is needed to establish a safe and effective local anesthetic which can be applied topically several times a day in the neonat e.