Preparation of Local Anesthetic Ointments for Home Care Patients with Post Herpetic Neuralgia. (1). Effects of Lipid Solubility of Local Anesthetics and Ointment Bases on Analgesic Effects.

We prepared ointments containing local anesthetics (LA) with different octanol/water partition coefficient (Pc) (procaine hydrochloride (Pc: 0.02), lidocaine (Pc: 2.9) and bupivacaine hydrochloride (Pc: 27.5)) for home care patients suffering from post herpetic neuralgia. The analgesic effects of these ointments were measured in rats and healthy volunteers. Macrogol ointment (water soluble) or white petrolatum (oil soluble) was used as the ointment base.The analgesic effects of 10% bupivacaine hydrochloride-macrogol ointment in rats were approximately 4 times that of the 2% aspirin ointment (used as a reference ointment) and were almost the same as commercially available indomethacin creams (another reference ointment). Judging from the area under the analgesic effect-time curves by 150 min after the application, the effects of procaine hydrochloride-white petrolatum were approximately 5 times that of the aspirin ointments and 1.2 times that of the indomethacin creams. The results of a test on healthy volunteers with a pain meter were also similar to those in rats. From these findings, it was thus indicated that the ointments in the combinations of LA having a high Pc value and water soluble ointment base, or LA with low Pc and oil soluble ointment base may thus be clinically useful. A good correlation was also observed between the Pc value and the analgesic effect of LA in both rats and in healthy volunteers. Furthermore, the analgesic effects in healthy volunteers also correlated well with those in rats (r=0.796 for macrogol ointment and r=0.953 for white petrolatum).