Intravenous Lidocaine for Controlling Pain and Inflammation

Intravenous (IV) lidocaine is one systemic way to manage pain and inflammation, and it also has been used to improve intestinal motility in colic cases. Its use has been a fairly hot topic of late, so Margaret Mudge, VMD, Dipl. ACVS, ACVECC, assistant professor of equine emergency and critical care at The Ohio State University, reviewed its properties and usage at the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla.

Lidocaine is classified as an antiarrhythmic agent (counteracting or preventing cardiac arrhythmia, or an abnormal irregularity of the heartbeat), and its anti-inflammatory effects offer potential value in treating inflammatory conditions such as laminitis and some colics. Lastly, it's often prescribed to combat postoperative ileus (lack of intestinal motility).

Mudge described lidocaine's usage for analgesia (pain relief), ileus, and sepsis (infection) during her presentation, noting that the medication has a fairly narrow therapeutic dosage window (normal doses result in plasma concentrations of 1-2 µg/mL, while toxicity occurs at 2-5 micrograms (µg/mL). Adverse effects can include depression, ataxia, muscle tremors, and at higher dosages hypotension (low blood pressure), bradycardia (slow heart rate), and seizures. These effects are usually dose-dependent and disappear when the medication is stopped.

Analgesia She explained that veterinarians believe lidocaine relieves pain via blockage of sodium channels and/or potassium currents. When used intravenously, it blocks pain signals at the level of the spinal cord for somatic pain (which originates in locations other than the internal organs). It can also be used locally.

Mudge reported that lidocaine is sometimes used as part of a multimodal analgesic approach (one employing multiple analgesics with different modes of action). It can also be used along with general anesthesia, but since it can induce muscle tremors, it's often withdrawn shortly before the end of surgery to improve recovery from anesthesia.

Ileus Lidocaine has been shown to improve analgesia and return of gastrointestinal function in humans after some surgeries. It has been proposed to work the same way in horses; however, research support of this concept has been mixed. Several studies have suggested that lidocaine might hasten return of normal gastrointestinal function and decrease ileus after surgery, but one study on normal horses found it actually decreased gut motility. And there's always the possibility that too much analgesia could mask signs of complications.

Mudge suggested that lidocaine might be most beneficial in ileus cases caused by pain, inflammation, and/or neuroendocrine (nerve/hormone) effects.

Sepsis Studies have shown anti-inflammatory and anti-endotoxic (combating endotoxemia, or release of endotoxins in the blood) properties of lidocaine in several animal species, and equine studies have found that the drug minimizes mucosal damage in ischemia-reperfusion injury (sustained when blood returns to tissue after a lack of blood flow) to the intestine in some colic cases. Lidocaine dampens white blood cell activity, potentially reducing the ability to combat infections. However, Mudge noted that it does not appear to increase infection rates postoperatively.

"Further work is needed to determine which horses may respond best to lidocaine and which doses of lidocaine may be most useful for various applications," noted Mudge. "In summary, IV lidocaine may be a useful adjunct to the treatment of gastrointestinal and surgical pain, ileus, and ischemia, although the infusion must be monitored closely to help avoid toxic effects."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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