Anesthetic effects of lidocaine hydrochloride gel using low frequency ultrasound of 0.5 MHz.

PURPOSE Low-frequency ultrasound has a significant effect on the transdermal permeation of high molecular weight drugs. However, the rate of permeation in pulsed mode is quite low necessitating considerable time to apply the ultrasound. 0.5 MHz ultrasound, which is a relatively higher frequency in the low-frequency range, can be applied in high intensity in continuous mode. METHODS A transducer was used to administer an anesthetic drug transdermally on healthy volunteers. The anesthetic effect was measured following administration on placebo, lidocaine HCl alone and lidocaine HCl with 0.5 and 1.0 MHz ultrasound (n=8/group). RESULTS In surface anesthesia, the phonophoresis group showed a significantly higher pain threshold than the other groups but there was no significant difference between the phonophoresis groups according to the ultrasound frequency. In conduction anesthesia, the 0.5 MHz phonophoresis group showed a significant change in their pain threshold and amplitude of sensory nerve action potential (SNAP) compared with the other groups. CONCLUSIONS Although there are limitations in applying 0.5 MHz ultrasound in phonophoresis for conduction anesthesia using lidocaine hydrochloride for a nerve block, it is more effective than the 1 Mhz that is widely used in clinical situations. Carbamazepine is a poor water soluble drug and its bioavailability is limited by dissolution rate. Dissolution, serum concentration and anticonvulsive effect of the drug have been evaluated after cogrinding with microcrystalline cellulose. A cogrinding technique was used to increase the dissolution, serum concentrations and anticonvulsive effect of the drug. A novel deconvolution technique of in vitro-in vivo correlation was evaluated.