Adrenaline absorption: effect of pH in mepivacaine and bupivacaine solutions. A clinical study during halothane anesthesia

The effect of the pH of the solution on the rate of absorption into the blood stream of locally-injected adrenaline using an adrenaline solution mixed with either mepivacaine or bupivacaine was investigated. Forty patients undergoing elective craniotomy received one of the following five solutions for subcutaneous and subgaleaic injection in the dose 0.5 ml/kg: 1) mepivacaine-adrenaline (pH = 6.1), 2) mepivacaine-adrenaline (pH = 7.5), 3) bupivacaine-adrenaline (pH = 6.1), 4) bupivacaine-adrenaline (pH = 7.4), or 5) adrenaline (pH = 6.1). Both mepivacaine and bupivacaine added to the adrenaline solution increased the plasma concentration of adrenaline. Alkalinization attenuated the peak concentration of adrenaline in the case of a mepivacaine-adrenaline solution, but not in the case of a bupivacaine-adrenaline solution.