Copyright © 2001 by Institute of Pharmacology Polish Journal of Pharmacology Polish Academy of Sciences Pol. J. Pharmacol., 2001, 53, 253261 ISSN 1230-6002 INFLUENCE OF DOXEPIN USED IN PREEMPTIVE ANALGESIA ON THE NOCICEPTION IN THE PERIOPERATIVE PERIOD. EXPERIMENTAL AND CLINICAL STUDY Jerzy Wordliczek, Marcin Banach, Magdalena Dorazil, Barbara Przew³ocka*,# Department of Anaesthesiology and Intensive Care, 1st Chair of General Surgery of Collegium Medicum, Jagiellonian University, Kopernika 17, PL 31-501 Kraków, Poland, *Department of Molecular Neuropharmacology, Institute of Pharmacology, Polish Academy of Sciences, Smêtna 12, PL 31-343 Kraków, Poland Influence of doxepin used in preemptive analgesia on the nociception in the perioperative period. Experimental and clinical study. J. WORDLI- CZEK, M. BANACH, M. DORAZIL, B. PRZEW£OCKA. Pol. J. Pharma- col., 2001, 53, 253–261. The aim of the present research was to assess in experimental and clini- cal study the influence of doxepin administered intraperitoneally (ip) as pre- emptive analgesia on the nociception in the perioperative period. The pain thresholds for mechanical stimuli were measured in rats. The objective of clinical investigation was to assess the influence of preemptive administra- tion of doxepin on postoperative pain intensity, analgesic requirement in the early postoperative period as well as an assessment of the quality of postope- rative analgesia by the patient. Doxepin injected ip (3–30 mg/kg) dose-dependently increased the pain threshold for mechanical stimuli measured in paw pressure test in rats. Do- xepin injected 30 min before formalin significantly increased the nociceptive threshold in the paw pressure test. In contrast, doxepin injected 240 min before formalin or 10 min after formalin did not change the nociceptive threshold. Morphine administered subcutaneously (sc) at a dose of 1 mg/kg increased the pain threshold measured in the paw pressure test 55 min after formalin treatment. Injection of 10 mg/kg of doxepin 30 min before formalin further enhanced the response after morphine administration. The results of the clinical study demonstrated that the patients who were administered doxepin preemptively showed significantly lower pethidine requirement in order to achieve a similar level of postoperative analgesia. The results of the research under discussion confirm the theoretical as- sumptions that there is a possibility to modify the nociception process in the perioperative period through preemptive analgesia using a drug that modi- fies the activity of the descending antinociceptive system. Key words: doxepin, nociceptive threshold, formalin test, rat, pethidine requirement, VAS, PCA system, patients correspondence J. Wordliczek, M. Banach, M. Dorazil, B. Przew³ocka Abbreviations: CGRP – calcitonin gene related layer of the dorsal horns [6]. Serotoninergic neu- peptide, EAA – excitatory amino acids, NMDA – rons, projecting into the dorsal horns, inhibit post- N-methyl-D-aspartate, PCA – patient-controlled synaptically the neurons from the spino-thalamic analgesia, PP test – paw pressure test, SP – sub- tract [nociceptive and wide dynamic range cells stance P, TCA – tricyclic antidepressant, VA S – (WDR)], probably inhibit the presynaptic release of visual-analogue pain assessment scale, WDR – substance P (SP) and calcitonin gene related pep- wide dynamic range cells tide (CGRP) from the central primary afferents and through the 5-HT3, activate GABA interneurons in dorsal horns of the spinal cord [5, 8]. INTRODUCTION Among antinociceptive drugs that activate the descending antinociceptive system are, among Pain stimulation related to operative trauma re- others, tricyclic antidepressants (TCA) [18]. They sults in a modified response of the nervous system, act through both raising the level of noradrenaline which causes hypersensitivity to pain stimuli both and/or 5-HT in noradrenergic and serotoninergic in the operative lesion (primary hyperalgesia) and structures of the descending antinociceptive system in surrounding lesion-free tissues (secondary hy- (through inhibiting secondary uptake of those neu- peralgesia). In order to avoid such changes, a stra- rotransmitters), and potentiating opioid analgesia tegy has been developed to prevent hyperalgesia [15, 20, 25, 28]. TCA are also important as modu- from developing in the postoperative period [29, lators of some effects mediated by NMDA recep- 33]. Such a mechanism is known as preemptive an- tors. It is well known that MMDA receptors activa- algesia and involves the modification of the noci- tion is one of the primary factors conditioning the ceptive process starting in the pre-operative period. development of the nociception process [30]. In the In the perioperative period this process consists of presented experiments doxepin, which belongs to two phases [32]. Phase one is directly related to no- the class of TCA was used in order to induce the ciceptive stimulation accompanying tissue injuries preemptive analgesia. Doxepin also demonstrates inflicted during the operation, whereas phase two strong anxiolytic action, which makes it especially appearing after the operation, is the result of in- useful in the perioperative period. flammatory response of injured tissues and changes The aim of the experimental research was to as- in the nociceptive structures of the dorsal horn sess the influence of doxepin administered intrape- caused by phase one. ritoneally (ip) on pain thresholds for mechanical Special possibilities of preemptive analgesia for stimuli in rats (assessment of specific antinocicep- modifying the nociceptive process are offered by tive action of the drug under investigation). Also modulating the activation of the descending antino- we assessed the influence of the drug on morphine ciceptive system, especially the adrenergic and se- activity and on the development of pain-related be- rotoninergic pathways. havior in the formalin model of inflammatory re- Noradrenergic neurons are found in diencepha- sponse following prior administration of doxepin. lon, pons and medulla projecting into the cerebral The objective of clinical investigation was to assess cortex, into the I, II, IV–V layer of the dorsal horn the influence of preemptive administration of do- as well as into the front horn of the spinal cord. Ad- xepin on postoperative pain intensity, analgesic re- renergic 2 receptors are located in the spinal dor- quirement in the early postoperative period, fre- sal horns. Presumably, their activation is essential quency of side effects as well as an assessment of in order to affect opioid analgesia [11]. Moreover, the quality of postoperative analgesia in a patient. the activation of the presynaptic receptors by nor- adrenaline inhibits the release of pronociceptive neurotransmitters, while the stimulation of post- MATERIALS and METHODS synaptic receptors directly inhibits the activity of Animal study neurons in dorsal horns [7, 19]. Serotoninergic neurons are present mainly in Male Wistar rats, weighing 250–320 g, were the nucleus raphe and project both into the peri- housed in groups of eight to a cage under a constant aqueductal grey substance (PAG), hippocampus light-dark cycle (light on between 08.00 and 20.00 h), and into the cerebral cortex, as well as I, II and V with free access to food and water. The experiments 254 Pol. J. Pharmacol., 2001, 53, 253–261 DOXEPIN AND PREEMPTIVE ANALGESIA were carried out according to the protocol appro- animal for 60 min. The number of pain-induced ved by the Ethical Commission of the Institute of behaviors was scored for two characteristic time Pharmacology. points: 0–5 (first phase) and 20–40 min (second phase) after formalin administration. In the third Nociceptive threshold type of experiment, the antinociceptive effect of Nociceptive threshold was evaluated using a paw morphine was measured in the PP test 55 min after pressure (PP) test (Randall-Selitto test, Ugo Ba- formalin injection. sile). An animal was gently restrained and an incre- The effect of doxepin on nociceptive threshold mental pressure was applied via a piston onto the after formalin treatment was measured. Before the dorsal surface of the hind paw. The cut-off pressure experiment nociceptive threshold (baseline) was was 480 g. The measurements were taken 3 times evaluated for every rat and doxepin at a dose of at 15-second intervals, and their mean was used for 10 mg/kg ip was injected 5 min later; 30 (n = 10) or calculations. Before the experiment nociceptive 240 (n = 6) min after doxepin administration, the threshold (baseline) was evaluated for every rat and rats were lightly anesthetized with halothane and doxepin was injected 5 min later at doses of 3, 10 100 l of 10% formalin solution was injected sc and 30 mg/kg ip (n = 27; 9 rats for each dose). The into the dorsal surface of the left hind paw. In one PP test was conducted 30 and 55 min after doxepin group of rats (n = 6) doxepin was injected 10 min administration. after formalin. The nociceptive threshold was measured 55 min after formalin administration. The Formalin model effect of doxepin on formalin-induced pain-related In order to mimic clinical surgical procedures in behavior was measured according to criteria de- which nociceptive stimulation takes place, in our scribed above. experiments the formalin model in rats was used The effect of doxepin injected at a dose of [10, 14, 27]. The rats were lightly anesthetized with 10 mg/kg ip (n = 6) 30 min before formalin injec- halothane (halothane, 2–3 vol