Local Anaesthetics for Oromucosal Use

Painful conditions of the mouth are uncomfortable and can significantly impair oral intake of fluid and nutrition. Mucositis is often cited as the most debilitating side effect of cancer chemotherapy and radiotherapy. Options recommended by eviQ for the symptomatic management of oral mucositis and stomatitis include systemic analgesics, topical anti-inflammatories, topical steroids, and local anaesthetic mouthwashes.

When it comes to local anaesthetic mouthwashes, there are few proprietary products available. Xylocaine® Viscous, containing 2% lidocaine, is one option. This product is formulated as a thick solution to increase adherence to the oral mucosa. Absorption from the gastrointestinal tract is relatively high, although systemic lidocaine exposure is usually low due to extensive first-pass metabolism. Caution is advised in patients with hepatic impairment as the half-life may be increased up to three-fold. While true allergic reactions to local anaesthetics are rare, Xylocaine® Viscous is contraindicated in patients with a known history of hypersensitivity to lidocaine or any other amide-type local anaesthetic.

Cocaine may be considered for patients who are allergic to amide local anaesthetics. Cocaine belongs to the ester family of local anaesthetics and does not display cross-reactivity with amides. No cocaine products are currently registered with the Therapeutic Goods Administration (TGA). However, cocaine mouthwash is produced by a TGA-licensed manufacturer and is now available in 0.5% (200mL) and 1% (100mL) strengths.

Cocaine is primarily metabolised in the plasma and tissue fluids. Its anaesthetic effect is similar to other local anaesthetics, although it does possess some unique characteristics. It is a vasoconstrictor across all dosing levels and induces platelet activation and thrombus formation. These effects may be useful to prolong the duration of effect, minimise systemic absorption, reduce swelling, and improve haemostasis in patients with mucosal bleeding.

There is a risk of systemic toxicity if used in patients with traumatised mucosa or if the recommended dose is exceeded. The estimated LD₅₀ (lethal dose that is fatal in 50% of cases) for cocaine is 500mg for adults following oral administration. This equates to 50mL of the 1.0% solution. It is, therefore, crucial to stress the importance of adhering to dosing recommendations and to expectorate the solution following use. Caution is advised in patients with hypertension, cardiovascular disease, thyroid disease, severe hepatic impairment, or a history of drug abuse.