New Delivery Systems for Local Anaesthetics—Part 2

Anesthesiology Research and Practice, Dec 2011

Part 2 of this paper deals with the techniques for drug delivery of topical and injectable local anaesthetics. The various routes of local anaesthetic delivery (epidural, peripheral, wound catheters, intra-nasal, intra-vesical, intra-articular, intra-osseous) are explored. To enhance transdermal local anaesthetic permeation, additional methods to the use of an eutectic mixture of local anaesthetics and the use of controlled heat can be used. These methods include iontophoresis, electroporation, sonophoresis, and magnetophoresis. The potential clinical uses of topical local anaesthetics are elucidated. Iontophoresis, the active transportation of a drug into the skin using a constant low-voltage direct current is discussed. It is desirable to prolong local anaesthetic blockade by extending its sensory component only. The optimal release and safety of the encapsulated local anaesthetic agents still need to be determined. The use of different delivery systems should provide the clinician with both an extended range and choice in the degree of prolongation of action of each agent.

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New Delivery Systems for Local Anaesthetics—Part 2

New Delivery Systems for Local Anaesthetics—Part 2 Edward A. Shipton Department of Anaesthesia, University of Otago, Christchurch 8042, New Zealand Received 28 September 2011; Accepted 28 September 2011 Academic Editor: James B. Eisenkraft Copyright © 2012 Edward A. Shipton. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Part 2 of this paper deals with the techniques for drug delivery of topical and injectable local anaesthetics. The various routes of local anaesthetic delivery (epidural, peripheral, wound catheters, intra-nasal, intra-vesical, intra-articular, intra-osseous) are explored. To enhance transdermal local anaesthetic permeation, additional methods to the use of an eutectic mixture of local anaesthetics and the use of controlled heat can be used. These methods include iontophoresis, electroporation, sonophoresis, and magnetophoresis. The potential clinical uses of topical local anaesthetics are elucidated. Iontophoresis, the active transportation of a drug into the skin using a constant low-voltage direct current is discussed. It is desirable to prolong local anaesthetic blockade by extending its sensory component only. The optimal release and safety of the encapsulated local anaesthetic agents still need to be determined. The use of different delivery systems should provide the clinician with both an extended range and choice in the degree of prolongation of action of each agent. 1. Introduction A drug delivery system should have minimal tissue reaction, a reliable drug release profile, and well-defined degradation rate for biodegradable carrier until all nontoxic products are excreted [1]. For local anaesthetics (LAs), the development of new effective delivery systems intends to suitably modulate the release rate of these drugs, extend their anaesthetic effect, and enhance their localisation; this reduces problems of systemic toxicity. Part 2 of this paper deals with the innovations pertaining to formulations, and techniques for drug delivery of topical and injectable local anaesthetics. 2. Routes of Local Anaesthetic Delivery2.1. Epidural Patient controlled epidural analgesia (PCEA) allows patients to self-administer drug doses according to their analgesic needs. This route relies on a staff-programmed pump and skilled and qualified members of the hospital staff for administration. Both local anaesthetics and opioids are agents for epidural analgesia. The use of epidural local anaesthetics is associated with a higher incidence of hypotension, motor block, and urinary retention, compared with use of opioids [2]. However, in a recent meta-analysis, only a continuous infusion of epidural local anaesthetics was superior to intravenous opioids in improving pain control and reducing adverse effects [3]. 2.2. Peripheral Patient-controlled regional analgesia (PCRA) encompasses a variety of techniques that provide effective postoperative pain relief without systemic exposure to opioids. Using PCRA, patients initiate the delivery of small doses of local anaesthetics (ropivacaine, bupivacaine) via an indwelling catheter that can be placed in different regions of the body depending upon the type of surgery. In some cases, a combination of local anaesthetic and opioid is administered. Infusions are controlled either by a staff-programmed electronic pump (Figure 1) or by a disposable elastomeric pump [3]. An elastomeric pump is a device that has a distensible bulb inside a protective bulb with a built-in filling port, delivery tube, and an antibacterial filter. Antibacterial filters are recommended with blocks involving a nerve plexus (and in neuraxial blocks). Analgesia can be delivered directly into a surgical incision (incisional PCRA), the intra-articular tissue (IA PCRA), or the perineural site (perineural PCRA) (Figure 2) [2]. Figure 1: Pharmacia Deltec CADD Ambulatory Infusion Pump. Figure 2: Patient-controlled perineural analgesia via infraclavicular brachial plexus catheter. 2.3. Wound Catheters The insertion of wound catheters allows for continuous infusions of local anaesthetics into the surgical wound at the end of the procedure (Figure 3). Continuous wound catheters can confer several benefits, including improved analgesia, reduced opioid use and adverse effects, increased patient satisfaction, and reduced hospital stay [4]. Figure 3: Elastomeric pump for a wound catheter. The use of continuous wound catheters consistently reduces the need for opioids (both rescue and total dose). Patients have consistently rated postoperative nausea and vomiting (PONV) as a primary concern after surgery [5, 6]. The reduced need for opioids (though an infrequently measured result in Randomised Controlled Trials) might contribute to increased patient satisfaction [4]. Reduced length of hospital stay has been assoc (...truncated)


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Edward A. Shipton. New Delivery Systems for Local Anaesthetics—Part 2, Anesthesiology Research and Practice, 2011, 2012, DOI: 10.1155/2012/289373