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Effects of pH and buffer capacity modulation on the analgesic efficacy of lignocaine and pethidine solutions
Author(s) -
Dyhre H.,
Wallin R.,
Renck H.
Publication year - 1996
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1996.tb04392.x
Subject(s) - medicine , pethidine , analgesic , anesthesia , analgesic agents
Background. Objectives were to study the effects of variations in the pH and the buffer capacity of solutions of lignocaine or pethidine on their analgesic efficacy in peripheral nerve block. Methods. Infraorbital nerve blocks (IONB) were induced in rats during light pentobarbitone anaesthesia employing 0.2 ml of test solutions containing 10 mg · ml ‐1 of lignocaine or pethidine dissolved in normal saline, 50 mmol and 150 mmol tris‐hydroxymethylaminomethane (THAM) hydrochloride (THAM · HCI) of pH 4.8 and 4.5, respectively, or 100 mmol THAM‐THAM · HCI of pH 7.4. The pH of solutions in saline was varied from 3.0 to 9.3 by adding HCI or NaHCO 3 . The analgesic efficacy is expressed as the interval from injection to elicitation of a minimal response to electric stimulation at various intensities (threshold intensities) within the blocked area (IONB 3 to 10), and in terms of the area under the curve (AUC, threshold intensities vs. time). Results. When dissolved in saline, pH 7.4, pethidine exerted more pronounced effects than lignocaine [AUC by 3.5 times (P<0.001), IONB 3 to 10 by 2.7 (P<0.05) to 3.6 (P< 0.001) times]. Variations of the pH of solutions did not affect their analgesic efficacy. Lignocaine exerted more pronounced local analgesic effects when mixed with 150 mmol THAM · HCI than when mixed with saline (pH 7.4), but manifested even more pronounced effects when dissolved in THAM+THAM · HCI [AUC by 3.7 times (P<0.001), IONB 3 to 10 by 2.7 (P0.01) to 3.8 (P<0.001) times]. When dissolved in THAM+THAM · HCI, the analgesic efficacy of pethidine increased by 2.0 to 2.8 times (P<0.001), as compared to a solution in saline at the same pH. Conclusions. It is concluded that variations in the pH of solutions of lignocaine or pethidine in saline does not affect the analgesic efficacy of the drugs, presumably due to the low buffer capacity of the medium, whereas when dissolved in THAM+THAM · HCI · their effect is enhanced.