Preparation and stability testing of a hydrogel for topical analgesia.

With the commercial availability of a cream (EMLA) containing a eutectic mixture of local anaesthetics, 2.5% (w/w) lidocaine and 2.5% (w/w) prilocaine, effective topical anaesthesia of the intact skin is possible without the need for subcutaneous injections or exposure to high concentrations of local anaesthetics. In our hospital a topical anaesthetic product was designed for the same purpose. The home-made product contains a eutectic mixture of a local anaesthetic (5% w/w) and l-menthol (1% w/w). Prilocaine was used as the local anaesthetic because it is known for its safety and its well investigated analgesic effects. The eutectic mixture of prilocaine and l-menthol was mixed with a carbopol hydrogel (1% w/w). Preliminary testing of this anaesthetic hydrogel in our hospital has yielded satisfactory results. The anaesthetic hydrogel was found to be stable after at least 3 months' storage at ambient temperature.