- Email: [email protected]
Action of naloxone on gender-dependent analgesic and antianalgesic effects of nalbuphine in humans
Action of Naloxone on Gender-Dependent Analgesic and Antianalgesic Effects of Nalbuphine in Humans Robert W. Gear, Christine Miaskowski, Newton C. Gordon, Steven M. Paul, Philip H. Helter, and Jon D. Levine Abstract:
Previously, we have shown that the Ic-opioid analgesic nalbuphine, when administered at a low dose to treat postoperative pain after extraction of impacted third molar teeth, produced a marked increase in pain in men, whereas in women the effect of this dose was similar to placebo. In the current study, employing the same postoperative model, we found that coadministration of naloxone, which had no analgesic action administered alone, not only reversed the expected pain-enhancing effect of nalbuphine in men, but produced a similar degree of long-lasting analgesia in both sexes. This result further suggests that, at the dose employed, although naloxone antagonizes the pain-enhancing effect, it does not antagonize the analgesic effect of nalbuphine. Although observed only in men, this antianalgesic action also might be present in women but offset by a similar degree of analgesia, thus explaining the lack of analgesia in women produced by this dose of nalbuphine alone. Such action would suggest that the previously reported gender differences in K-mediated analgesia might, in fact, be explained by a gender difference in Kmediated antianalgesia. By avoiding side effects associated with p-opioid analgesics, this drug combination might become an important new pharmacological therapy for pain relief. Key words: K-opioid, hyperalgesia, males, females, pain, gender.
hiI
albuphine, pentazocine, and butorphanol are opioid analgesics that are thought to induce analgesia predominantly by action at K-opioid receptors.’ Recently, we showed that all 3 of these drugs produce greater analgesia in women than in men, suggesting that the pain modulation mechanism activated by K-opioids is sexually dimorphic.2-4 Furthermore, in a placebocontrolled dose-response study, a low dose of nalbuphine (5 mg), which produced effects similar to placebo in women, unexpectedly resulted in markedly increased pain in men.5 Animal studies have shown that receptor-selective K-opioid agonists, in addition to producing antinociception, can induce effects on dorsal root ganglion neurons and on dorsal horn neuro-
Received November 11, 1999; Revised January 6, 2000; Accepted January 18, 2000 From the Department of Oral and Maxillofacial Surgery, the Department of Physiological Nursing, the Department of Epidemiology and Riostatistics, the Department of Medicine, the Department of Anatomy, and the Graduate Program in Neuroscience, the Center for Orofacial Pain, University of California, San Francisco; and the Kaiser Foundation Hospital, Hayward, CA. Supported in part by NIH grant NR03923 and the Kaiser Community Services Program. Address reprint requests to Jon D. Levine, MD, PhD, NIH Pain Center, Levine Research Unit, Box 0440, 521 Parnassus Avenue, Room C-522, University of California San Francisco, CA 94143-0440. E-mail: [email protected] 0 2000 by the American Pain Society 1526-5900/00/01 OZ-0008$8.00/0 doi:l0.1054/xb.2000.6063
122
transmission that would be expected to be pronociceptive.6,7 Whereas such pronociceptive effects have been shown to be sensitive to administration of an opioid antagonist, there is also evidence suggesting that pronociceptive effects of the K-opioid receptor agonists might be mediated by nonopioid mechanisms.8-12 Therefore, to understand the basis of the potent pain-enhancing effect of nalbuphine that we observed in men,5 it was of considerable importance to determine whether opioid mechanisms are involved. It was also of interest to investigate whether the lack of analgesia in women to a similar dose of nalbuphine5 was caused by the presence of some antianalgesia. To answer these questions, in the present study, we investigated whether the prototypic narcotic antagonist naloxone would prevent the pain enhancing effect of low-dose nalbuphine in men and/or uncover the presence of analgesia in women.
Materials and Methods In this clinical trial, 88 patients underwent standardized surgery by the same oral surgeon for removal of third molar teeth, including at least 1 bony, impacted mandibular third molar.13,14 Before surgery, patients received intravenous diazepam, nitrous oxide, and a local anesthetic
The Journal of Pain, Vol 1, No. 2 (Summer),
2000; DD 122-127
ORIGINAL
Table
REPORT/Gear
I.
123
et al
Study ParticipantSampleCharacteristics NALS (5 MG)
PARTKPANT~
(#)
MEN (15) MEAN
Age (Y) Weight Diazepam l!mg/kg) Surgical Time to adm Baseline
(kg)*
VAS*
MEAN
(78) SEM
MEN (72) MEAN
MG) WOMEN
SEM
MEAN
NALS (5 MG) + NLX (0.4 (15) SEM
MEN MEAN
(14)
WOMEN
SEM
MEAN
MC) (14) SEM
22.8
1.6
23.5
1.1
22.2
0.7
23.1
0.9
25.0
1.1
22.6
0.6
72.5
4.7
58.9
2.4
71.8
4.9
55.9
2.1
72.4
1.8
60.9
2.9
0.40
severity drug
SEM
WOMEN
NLX (0.4
0.02
0.41
0.03
0.40
0.04
0.39
0.02
0.39
0.02
0.43
0.03
4.3
0.2
3.8
0.2
4.3
0.2
4.0
0.3
4.0
0.2
4.0
02
98.0
13.4
83.3
6.5
91.7
7.6
88.7
10.4
77.1
4.5
80.0
7.2
3.7
0.3
0.5
4.6
0.6
0.5
5.8
0.7
5.0
5.5
0.5
5.4
Note. The data for the participants who received 5 mg of nalbuphine alone, “Nalb (5mg),” are from a previous study.5 Surgical seventy scores I5 were awgned as follows: upper third molar extrablons. uncomplicated or tissue impacted teeth, 0.25; partial or full bony impacted teeth, 0.50. Lower third molar extractIons: urlcompllcated or tissue Impacted teeth, 1; partial or full bony impacted teeth, 2. The surgical severity score for each patient IS the sum of the assigned values for each extracted tooth. Differences between the groups for each demographic characteristic were considered slgnlficant If a two-way ANOVA showed P < 05 and are ln&cated with an asterisk (*) Abbrevlatlons Nix, naloxone; Nalb, nalbuphlne; VAS, visual analog scale *See note.
(mepivacaine without vasoconstrictor to obtain a nerve block of short duration). After surgery, each patient was randomly assigned to receive an injection of either naloxone (0.4 mg) or a mixture of this dose of naloxone and nalbuphine (5 mg) (Abbott Laboratories, Abbott Park, IL) in an open-injection, double-blinded fashion, through an intravenous line. Because our earlier study showed that the pain-enhancing effect of 5 mg of nalbuphine in men was so striking (P c .0001),5 ethical concerns rendered replication of the protocol problematic. Therefore, data from the previous study5 for 33 of the 88 patients (ie, those who received nalbuphine alone) were included in the current study to avoid replication of an experimental protocol that results in moderately severe pain. Although differences in study design and execution between the 2 studies could potentially confound the results, the previous and current studies were performed sequentially in the same facility, under identical conditions with the same surgical and experimental protocols and the same oral surgeon and research personnel, who were blinded to the experimental treatments in all cases. Most of the data from both studies were collected within a single 8-month period. Therefore, the observed differences between the groups is probably not explained by the use of the “historical” data. Criteria for administration of the test drug were an elapse of a period of at least 80 minutes after the onset of the local anesthetic and a pain rating that was greater than one quarter (2.5 cm) of the maximum possible visual analog scale (VAS) rating (10 cm). Baseline pain intensity was defined as the last VAS pain rating before administration of the test drug. VAS pain ratings were recorded at 20-
minute intervals, beginning 10 minutes after administration of the test drug. The duration of the experiment, measured from the time of administration of the test drug, was 3 hours. For each patient, the magnitude of the analgesic response was defined as the difference between the pain rating at each time point after test drug administration and the baseline VAS pain rating.
Data analysis The demographic characteristics of the patient groups are provided in Table 1. Differences in demographic characteristics were determined using a 2-way analysis of variance (ANOVA) with 2 between-subjects factors (ie, gender with 2 levels and treatment with 3 levels). Because the men weighed more than the women, weight was included as a covariate in subsequent analyses that included both genders. Differences between men and women in baseline intensity scores were accounted for by calculating patient responses as changes from baseline pain intensity. A 3-way repeated-measure ANOVA with 2 between-subjects factors (ie, gender with 2 levels and treatment with 3 levels) and 1 within-subjects factor (ie, time with 9 levels) was used to determine if there were significant (P 2 .05) differences in analgesic responses among the 6 gender/drug groups. Because this 3-way ANOVA showed a significant gender x treatment x time interaction (see later in this article), a separate 2repeated-measures ANOVA with 1 way, between-subjects factor (ie, treatment group with 3 levels) and 1 within-subjects factor (ie, time with 9 levels) was performed for each gender to determine if there were significant differ-
Gender Dependence
124
Men
of NaloxonelNalnuphine
Analgew
Women
+ t + 1 I
nalbuphine (5 mg) naloxone (0.4 mg) nalbuphine/naloxone , 1 I I I / 0 I
Time after drug (min) Figure 1. The effect on postoperative pain of nalbuphine (5 mg), naloxone (0.4 mg), and a combination of nalbuphine (5 mg) and naloxone (0.4 mg) plotted as changes in postoperative pain level over the 3 hours after administration. “Change in VA5 pain score” (ordinate), recorded on a IO-cm VAS, represents changes from baseline level (represented by the horizontal dashed lines) after various times. Decreased oain scores (ie, analaesia) are above the baseline. See Table 1 for number of study participants in each group. Data are plotted as mean * S.E.M: (standard error of the mean).
ences in analgesic effects among the 3 treatment groups (ie, nalbuphine, naloxone, or the nalbuphine/naloxone combination) for either men or women. For each ANOVA, the Mauchley criterion was used to determine if the assumption of sphericity for the within-subjects effects was met; if the Mauchley criterion was not satisfied, Greenhouse-Geisser-adjusted P values are presented. If there was a significant treatment x time interaction, the simple main effects of each treatment group were examined over time to help explain the significant interaction. If there was a significant between-subjects main effect of treatment group, post-hoc contrasts, using the Tukey test, were performed to determine the basis of the significant difference. This study conformed to the ethical guidelines of the 1975 Declaration of Helsinki and was approved by the Committee on Human Research at the University of California, San Francisco. Informed consent was obtained from each person who participated in the research.
Results Overall Comparisons of the Effects of Naibqhine, Naloxone, and the ComMnation of Nalbuphine and Naloxone The 3-way repeated-measures a significant gender x treatment
ANOVA showed x time interac-
tion (F [16,656] = 2.35; P = .050), a significant treatment x time interaction (F [16,656] = 5.37; P = .0003), a significant gender x treatment interaction (F [2,81] = 3.14; P= .0487) and a significant main effect of treatment (F [2,81] = 15.84; P < .OOOl). The 3-way interaction could be interpreted to mean that either the treatment time interaction depended on the participant’s gender or that the gender x time interaction depended on the treatment administered. To determine if the responses to the different treatments differed significantly in women, a 2way repeated-measures ANOVA with 1 betweensubjects (ie, treatment group with 3 levels) and 1 within-subjects factor (ie, time with 9 levels) was performed. A similar analysis was done for men. These analyses were undertaken to determine how the treatment x time interaction depended on gender.
Men The responses of men who received nalbuphine, naloxone, or nalbuphine combined with naloxone are depicted in Fig 1. The ANOVA showed a significant treatment x time interaction (F [16,304] = 6.03; P = .0003) and a significant main effect of treatment (F [2,38] + 12.30, P = .OOOl) indicating that the pattern of change over time depended on the treatment administered. Examination of the simple main effects indicated no significant changes in analgesic
ORIGINAL REPORT/Gear et al
effects over time for naloxone alone or for the nalbuphine/naloxone combination. However, a significant increase in pain was showed for nalbuphine alone (F [8,304] = 12.74; P c .OOOl). Posthoc contrasts, using the Tukey criterion, showed that the analgesic effect of the nalbuphine/ naloxone combination was significantly different from changes in pain level associated with nalbuphine alone (P = .0002).
Women The responses of women who received nalbuphine, naloxone, or nalbuphine combined with naloxone are depicted in Fig 1. The ANOVA showed only a significant main effect of treatment (F v[2,44] = 4.87; P < .0123), indicating significant differences in analgesia produced by the treatments. Post-hoc pairwise contrasts, using the Tukey criterion, indicated that the analgesic effect of nalbuphine alone and naloxone alone were not significantly different from each other. However, the analgesic effect produced by the nalbuphine/naloxone combination was significantly different from both nalbuphine alone (P = .0236) and naloxone alone (P = .0239).
Gender Differences in Responses to Naloxone and to the Combination of Nalbuphine and Naloxone To determine if there were gender differences in response to the different treatments, separate 2way repeated-measures ANOVAs, with 1 betweensubjects factor (ie, gender with 2 levels) and 1 within-subjects factor (ie, time with 9 levels) were performed for each treatment. These analyses were undertaken to determine how the gender x time interaction was dependent on treatment. These analyses failed to show either significant main effects or interaction effects for either naloxone alone or the nalbuphine/naloxone combination indicating a lack of gender differences in response to either treatment. However, a significant gender x treatment interaction was found with nalbuphine alone as reported previously.5
Discussion In a previous study, we observed that, in men, low-dose nalbuphine, compared with placebo, induced a marked pain-enhancing effect.5 Because nalbuphine can act as an antagonist at u-receptors,15 the enhanced pain with low-dose nalbuphine in men could hypothetically result from block of an analgesic effect of endogenously released u-opioids. However, such an explanation is incompatible with the present finding that naloxone, which itself potently
125
antagonizes p-opioid receptors, blocks the painenhancing effect of nalbuphine. Our results show a similar marked analgesia in both men and women when naloxone was added to the administration of low-dose nalbuphine. The ability of the opioid antagonist naloxone to eliminate the previously observed gender differences in response to nalbuphine4f5 suggests the existence of a naloxone-sensitive antianalgesic action of nalbuphine in addition to an analgesic effect that is less sensitive to naloxone. Consistent with such a dual action, we have observed a shortlived analgesia followed by increasing pain (antianalgesia) in men receiving k-opioid receptor agonists in previous studies.2,4,5 The induction of opposing effects, such as analgesia and pain enhancement, by K-opioid receptor agonists might be explained by actions at different k-receptor subtypes.16,17 The conversion of a potent pain enhancement to a potent analgesia in men through the addition of naloxone very strongly suggests that the painenhancing effect of nalbuphine is mediated through action at an opioid receptor. This finding is consistent with previous evidence that antianalgesia can result from action at k-opioid receptors.18-21 If it is an opioid effect that mediates the analgesia, it must be mediated by a receptor subtype that is relatively insensitive to naloxone. Although there are thought to be several subtypes of the K-opioid receptor,16,22,23 their relative sensitivities to naloxone are unknown. Our previous observation that the effect of 5 mg of nalbuphine in women was not significantly different from placebo could be interpreted to indicate that this dose of nalbuphine is not sufficient to produce analgesia. However, our current finding that naloxone, which can antagonize antianalgesia in men, significantly enhances the analgesic effect of this dose of nalbuphine in women suggests that the effect of nalbuphine alone in women might represent the sum of an antianalgesic response and an approximately equal analgesic response. That is, the addition of naloxone to nalbuphine in either gender similarly unmasks the analgesic by selectively antagonizing the response antianalgesic response. If so, the gender differences in k-mediated analgesia that we have previously observed would, in fact, result from gender differences in K-mediated antianalgesia. Alternatively, naloxone might exert agonism at therefore, these findings K-opioid receptors; could theoretically be interpreted as resulting from synergy of 2 K-opioid receptor agonists, although there is little evidence that this is the case. However, this explanation is very unlikely in men because the magnitude of the antianalgesic effect was so large that, unless antago-
Gender
126
Dependence
of Naioxone/Ndlbtiphtne
Analyesi
nized, it would have continued to mask analgesia. The findings in women are more amenable to interpretation as being caused by the synergy of 2 K--agonists, but for men the observed analgesia similar to that in women for nalbuphine plus naloxone would require postulation of different a mechanism. Gender differences in K-opioid receptor antinociception have been observed in animals, but these differences do not seem to parallel our findings in humans. For example, it has been found in male and female rats that administration of a rc-opioid receptor agonist, U69,593, induces a similar degree of antinociception that is differentially sensitive to an N-methyl-D-aspartate receptor (NMDA) antagonist but similarly decreased by naloxone. 25 Also, a series of studies by Gintzler et al 26-28 have shown that the antinociceptive effects of female sex hormones in pregnant rats are k-receptor mediated, a finding that suggests the possibility that women might respond differently to a K-opioid receptor agonist during different phases of their menstrual cycle. Unfortunately, the number of women in our study who could be evaluated in this way (ie, those not taking hormonal contraceptives who were clearly either in the luteal or the follicular phase of their cycle) was too small to analyze. In addition, our findings that naloxone not only
eliminates the gender differences but enhances k-mediated analgesia in both genders argues against a simple hormone-related mechanism. Although it is possible that one or more of the drugs given as part of the surgical protocol (ie, diazepam, nitrous oxide, or mepivacaine) could have influenced these results, these or similar drugs are commonly given for surgical procedures. Therefore, these results should generally apply for postoperative pain. In conclusion, our findings provide important insights into the mechanisms of opioid analgesia produced by k-receptor opioid agonists, including the influence of gender in humans. These findings are of considerable clinical significance, because the combination of naloxone and a low dose of a k-opioid receptor agonist would be expected to produce potent and prolonged analgesia with minimal or no side effects, including none of the significant side effects such as dysphoria that have severely limited the use of this class of opioids as first-line analgesics.
References
7. Suarez-Rota H, Maixner W: Activation receptors by U50488H and morphine release of substance P from rat trigeminal J Pharmacot Exp Ther 264:648-653,1993
1. Jaffee JH, Martin WR: Opioid analgesics and antagonists, in Gilman AG, Rail TW, Nies AS, Taylor P (eds): Goodman and Gilman’s The Pharmacological Basis of Therapeutics, New York, NY, Pergamon, 1990, pp 485-521 2. Gordon NC, Gear RW, Levine JD: Enhancement GABA, agonist baclofen.
Heller PH, Paul S, Miaskowski C, of morphine analgesia by the Neuroscience 69:345-349,1995
3. Gear RW, Gordon NC, Heller PH, Paul Levine JD: Gender difference in analgesic kappa-opioid pentazocine. Neurosci 209,1996 4. Gear RW, Miaskowski Levine JD: Significantly pared to males after 1250,1996
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Acknowledgments The authors thank Ai-Shan Shih, RN, and Barbara Russell, RN, for excellent technical assistance and David Reichling, PhD, for many helpful discussions during the writing of the manuscript.
8. Kest B, Mogli JS, Shamgar BE, Kao Marek P: The NMDA receptor antagonist against the development of morphine intrathecal administration. Proc Western 36:307-3 lo,1993
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10. Laughlin TM, Vanderah TW, Lashbrook J, Nichols ML, Ossipov M, Porreca F, Wilcox GL: Spinally administered dynorphin A produces long-lasting allodynia: Involvement of NMDA but not opioid receptors. Pain 72:253-260,1997
5. Gear RW, Miaskowski C, Gordon NC, Paul SM, Heller PH, Levine JD: The kappa opioid nalbuphine produces gender and dose dependent analgesia and antianalgesia in patients with postoperative pain. Pain 83:339-345,1999
11. Arcaya JL, Cano G, Gomez G, Maixner W, Suarex-Rota H: Dynorphin A increases substance P release from trigeminal primary afferent C-fibers. Eur J Pharmacol 366:27-
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KF, Crain SM: Dynorphin prolongs the action potential of mouse sensory ganglion neurons by decreasing a potassium conductance whereas another specific kappa opioid does so by increasing a calcium conductance. Neuropharmacology 29:343-349,199O
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20. Apfel SC, Newel M, Dormia C, Kessler JA: Kappa opioid receptors participate in nerve growth factor-induced hyperalgesia. Neuroscience 68:1199-1206,1995
14. Levine JD, Gordon NC, Taiwo YO, and Coderre TJ: Potentiation of pentazocine analgesia by low-dose naloxone, J Clin Invest, 82 1988 1574-l 577.
21. Pan ZZ, Tershner SA, Fields HL: Cellular mechanism for antianalgesic action of agonists of the kappa-opioid receptor. Nature 389:382-385,1997
15. Loomis CW, Penning J, Milne 8: A study of the analgesic interaction between intrathecal morphine and subcutaneous nalbuphine in the rat. Anesthesiology 71:704710,1989
22. Rothman RB: A review of the role of antiopioid peptides in morphine tolerance and dependence. Synapse 12:129-138,1992
16. Ni Q, Xu H, Partilla JS, de Costa BR, Rice KC, Kayakiri H, Rothman RB: Opioid peptide receptor studies. 3. Interaction of opioid peptides and other drugs with four subtypes of the kappa 2 receptor in guinea pig brain. Peptides 16:1083-1095.1995 17. Butelman ER, Ko MC, Sobczyk-Kojiro K, Mosberg HI, Van Bemmel B, Zernig G, Woods JH: kappa-Opioid receptor binding populations in rhesus monkey brain: Relationship to an assay of thermal antinociception. J Pharmacol Exp Ther 285:595-601 ,I 998 18. Fujimoto JM, Rady JJ: lntracerebroventricular physostigmine-induced analgesia: Enhancement by naloxone, beta-funaltrexamine and nor-binaltorphimine and antagonism by dynorphin A 1-17. J Pharmacol Exp Ther 251:1045-1052,1989 19. Fujimoto JM, Arts KS, Rady JJ, Tseng LF: Spinal dynorphin A 1-17: Possible mediator of antianalgesic action. Neuropharmacol 29:609-617,199O
23. Pesce GO, Cruciani RA, Munson PJ, Rodbard D: Computer modeling of subtypes of kappa opioid receptors in adrenal medulla. Eur J Pharmacol 182:429-439,199O 24. Kavaliers M, Choleris E: Sex differences in N-methyl-Daspar-tate involvement in kappa opioid and nonopioid predator-induced analgesia in mice. Brain Res 768:30-36,1997 25. Sander HW, Gintzler AR: Spinal cord mediation of the opioid analgesia of pregnancy. Brain Res 408:389-393,1987 26. Sander HW, Portoghese PS, Gintzler AR: Spinal kappaopiate receptor involvement in the analgesia of pregnancy: Effects of intrathecal norbinaltorphimine, a kappa-selective antagonist. Brain Res 474:343-347,1988 27. Dawson-Basoa ME, Gintzler AR: Estrogen and progesterone activate spinal kappa-opiate receptor analgesic mechanisms. Pain 64:607-615,1996 28. Faucett J, Gordon N, Levine J: Differences in postoperative pain severity among four ethnic groups. J Pain Symptom Manage 9:383-389,1994
Previously, we have shown that the Ic-opioid analgesic nalbuphine, when administered at a low dose to treat postoperative pain after extraction of impacted third molar teeth, produced a marked increase in pain in men, whereas in women the effect of this dose was similar to placebo. In the current study, employing the same postoperative model, we found that coadministration of naloxone, which had no analgesic action administered alone, not only reversed the expected pain-enhancing effect of nalbuphine in men, but produced a similar degree of long-lasting analgesia in both sexes. This result further suggests that, at the dose employed, although naloxone antagonizes the pain-enhancing effect, it does not antagonize the analgesic effect of nalbuphine. Although observed only in men, this antianalgesic action also might be present in women but offset by a similar degree of analgesia, thus explaining the lack of analgesia in women produced by this dose of nalbuphine alone. Such action would suggest that the previously reported gender differences in K-mediated analgesia might, in fact, be explained by a gender difference in Kmediated antianalgesia. By avoiding side effects associated with p-opioid analgesics, this drug combination might become an important new pharmacological therapy for pain relief. Key words: K-opioid, hyperalgesia, males, females, pain, gender.
hiI
albuphine, pentazocine, and butorphanol are opioid analgesics that are thought to induce analgesia predominantly by action at K-opioid receptors.’ Recently, we showed that all 3 of these drugs produce greater analgesia in women than in men, suggesting that the pain modulation mechanism activated by K-opioids is sexually dimorphic.2-4 Furthermore, in a placebocontrolled dose-response study, a low dose of nalbuphine (5 mg), which produced effects similar to placebo in women, unexpectedly resulted in markedly increased pain in men.5 Animal studies have shown that receptor-selective K-opioid agonists, in addition to producing antinociception, can induce effects on dorsal root ganglion neurons and on dorsal horn neuro-
Received November 11, 1999; Revised January 6, 2000; Accepted January 18, 2000 From the Department of Oral and Maxillofacial Surgery, the Department of Physiological Nursing, the Department of Epidemiology and Riostatistics, the Department of Medicine, the Department of Anatomy, and the Graduate Program in Neuroscience, the Center for Orofacial Pain, University of California, San Francisco; and the Kaiser Foundation Hospital, Hayward, CA. Supported in part by NIH grant NR03923 and the Kaiser Community Services Program. Address reprint requests to Jon D. Levine, MD, PhD, NIH Pain Center, Levine Research Unit, Box 0440, 521 Parnassus Avenue, Room C-522, University of California San Francisco, CA 94143-0440. E-mail: [email protected] 0 2000 by the American Pain Society 1526-5900/00/01 OZ-0008$8.00/0 doi:l0.1054/xb.2000.6063
122
transmission that would be expected to be pronociceptive.6,7 Whereas such pronociceptive effects have been shown to be sensitive to administration of an opioid antagonist, there is also evidence suggesting that pronociceptive effects of the K-opioid receptor agonists might be mediated by nonopioid mechanisms.8-12 Therefore, to understand the basis of the potent pain-enhancing effect of nalbuphine that we observed in men,5 it was of considerable importance to determine whether opioid mechanisms are involved. It was also of interest to investigate whether the lack of analgesia in women to a similar dose of nalbuphine5 was caused by the presence of some antianalgesia. To answer these questions, in the present study, we investigated whether the prototypic narcotic antagonist naloxone would prevent the pain enhancing effect of low-dose nalbuphine in men and/or uncover the presence of analgesia in women.
Materials and Methods In this clinical trial, 88 patients underwent standardized surgery by the same oral surgeon for removal of third molar teeth, including at least 1 bony, impacted mandibular third molar.13,14 Before surgery, patients received intravenous diazepam, nitrous oxide, and a local anesthetic
The Journal of Pain, Vol 1, No. 2 (Summer),
2000; DD 122-127
ORIGINAL
Table
REPORT/Gear
I.
123
et al
Study ParticipantSampleCharacteristics NALS (5 MG)
PARTKPANT~
(#)
MEN (15) MEAN
Age (Y) Weight Diazepam l!mg/kg) Surgical Time to adm Baseline
(kg)*
VAS*
MEAN
(78) SEM
MEN (72) MEAN
MG) WOMEN
SEM
MEAN
NALS (5 MG) + NLX (0.4 (15) SEM
MEN MEAN
(14)
WOMEN
SEM
MEAN
MC) (14) SEM
22.8
1.6
23.5
1.1
22.2
0.7
23.1
0.9
25.0
1.1
22.6
0.6
72.5
4.7
58.9
2.4
71.8
4.9
55.9
2.1
72.4
1.8
60.9
2.9
0.40
severity drug
SEM
WOMEN
NLX (0.4
0.02
0.41
0.03
0.40
0.04
0.39
0.02
0.39
0.02
0.43
0.03
4.3
0.2
3.8
0.2
4.3
0.2
4.0
0.3
4.0
0.2
4.0
02
98.0
13.4
83.3
6.5
91.7
7.6
88.7
10.4
77.1
4.5
80.0
7.2
3.7
0.3
0.5
4.6
0.6
0.5
5.8
0.7
5.0
5.5
0.5
5.4
Note. The data for the participants who received 5 mg of nalbuphine alone, “Nalb (5mg),” are from a previous study.5 Surgical seventy scores I5 were awgned as follows: upper third molar extrablons. uncomplicated or tissue impacted teeth, 0.25; partial or full bony impacted teeth, 0.50. Lower third molar extractIons: urlcompllcated or tissue Impacted teeth, 1; partial or full bony impacted teeth, 2. The surgical severity score for each patient IS the sum of the assigned values for each extracted tooth. Differences between the groups for each demographic characteristic were considered slgnlficant If a two-way ANOVA showed P < 05 and are ln&cated with an asterisk (*) Abbrevlatlons Nix, naloxone; Nalb, nalbuphlne; VAS, visual analog scale *See note.
(mepivacaine without vasoconstrictor to obtain a nerve block of short duration). After surgery, each patient was randomly assigned to receive an injection of either naloxone (0.4 mg) or a mixture of this dose of naloxone and nalbuphine (5 mg) (Abbott Laboratories, Abbott Park, IL) in an open-injection, double-blinded fashion, through an intravenous line. Because our earlier study showed that the pain-enhancing effect of 5 mg of nalbuphine in men was so striking (P c .0001),5 ethical concerns rendered replication of the protocol problematic. Therefore, data from the previous study5 for 33 of the 88 patients (ie, those who received nalbuphine alone) were included in the current study to avoid replication of an experimental protocol that results in moderately severe pain. Although differences in study design and execution between the 2 studies could potentially confound the results, the previous and current studies were performed sequentially in the same facility, under identical conditions with the same surgical and experimental protocols and the same oral surgeon and research personnel, who were blinded to the experimental treatments in all cases. Most of the data from both studies were collected within a single 8-month period. Therefore, the observed differences between the groups is probably not explained by the use of the “historical” data. Criteria for administration of the test drug were an elapse of a period of at least 80 minutes after the onset of the local anesthetic and a pain rating that was greater than one quarter (2.5 cm) of the maximum possible visual analog scale (VAS) rating (10 cm). Baseline pain intensity was defined as the last VAS pain rating before administration of the test drug. VAS pain ratings were recorded at 20-
minute intervals, beginning 10 minutes after administration of the test drug. The duration of the experiment, measured from the time of administration of the test drug, was 3 hours. For each patient, the magnitude of the analgesic response was defined as the difference between the pain rating at each time point after test drug administration and the baseline VAS pain rating.
Data analysis The demographic characteristics of the patient groups are provided in Table 1. Differences in demographic characteristics were determined using a 2-way analysis of variance (ANOVA) with 2 between-subjects factors (ie, gender with 2 levels and treatment with 3 levels). Because the men weighed more than the women, weight was included as a covariate in subsequent analyses that included both genders. Differences between men and women in baseline intensity scores were accounted for by calculating patient responses as changes from baseline pain intensity. A 3-way repeated-measure ANOVA with 2 between-subjects factors (ie, gender with 2 levels and treatment with 3 levels) and 1 within-subjects factor (ie, time with 9 levels) was used to determine if there were significant (P 2 .05) differences in analgesic responses among the 6 gender/drug groups. Because this 3-way ANOVA showed a significant gender x treatment x time interaction (see later in this article), a separate 2repeated-measures ANOVA with 1 way, between-subjects factor (ie, treatment group with 3 levels) and 1 within-subjects factor (ie, time with 9 levels) was performed for each gender to determine if there were significant differ-
Gender Dependence
124
Men
of NaloxonelNalnuphine
Analgew
Women
+ t + 1 I
nalbuphine (5 mg) naloxone (0.4 mg) nalbuphine/naloxone , 1 I I I / 0 I
Time after drug (min) Figure 1. The effect on postoperative pain of nalbuphine (5 mg), naloxone (0.4 mg), and a combination of nalbuphine (5 mg) and naloxone (0.4 mg) plotted as changes in postoperative pain level over the 3 hours after administration. “Change in VA5 pain score” (ordinate), recorded on a IO-cm VAS, represents changes from baseline level (represented by the horizontal dashed lines) after various times. Decreased oain scores (ie, analaesia) are above the baseline. See Table 1 for number of study participants in each group. Data are plotted as mean * S.E.M: (standard error of the mean).
ences in analgesic effects among the 3 treatment groups (ie, nalbuphine, naloxone, or the nalbuphine/naloxone combination) for either men or women. For each ANOVA, the Mauchley criterion was used to determine if the assumption of sphericity for the within-subjects effects was met; if the Mauchley criterion was not satisfied, Greenhouse-Geisser-adjusted P values are presented. If there was a significant treatment x time interaction, the simple main effects of each treatment group were examined over time to help explain the significant interaction. If there was a significant between-subjects main effect of treatment group, post-hoc contrasts, using the Tukey test, were performed to determine the basis of the significant difference. This study conformed to the ethical guidelines of the 1975 Declaration of Helsinki and was approved by the Committee on Human Research at the University of California, San Francisco. Informed consent was obtained from each person who participated in the research.
Results Overall Comparisons of the Effects of Naibqhine, Naloxone, and the ComMnation of Nalbuphine and Naloxone The 3-way repeated-measures a significant gender x treatment
ANOVA showed x time interac-
tion (F [16,656] = 2.35; P = .050), a significant treatment x time interaction (F [16,656] = 5.37; P = .0003), a significant gender x treatment interaction (F [2,81] = 3.14; P= .0487) and a significant main effect of treatment (F [2,81] = 15.84; P < .OOOl). The 3-way interaction could be interpreted to mean that either the treatment time interaction depended on the participant’s gender or that the gender x time interaction depended on the treatment administered. To determine if the responses to the different treatments differed significantly in women, a 2way repeated-measures ANOVA with 1 betweensubjects (ie, treatment group with 3 levels) and 1 within-subjects factor (ie, time with 9 levels) was performed. A similar analysis was done for men. These analyses were undertaken to determine how the treatment x time interaction depended on gender.
Men The responses of men who received nalbuphine, naloxone, or nalbuphine combined with naloxone are depicted in Fig 1. The ANOVA showed a significant treatment x time interaction (F [16,304] = 6.03; P = .0003) and a significant main effect of treatment (F [2,38] + 12.30, P = .OOOl) indicating that the pattern of change over time depended on the treatment administered. Examination of the simple main effects indicated no significant changes in analgesic
ORIGINAL REPORT/Gear et al
effects over time for naloxone alone or for the nalbuphine/naloxone combination. However, a significant increase in pain was showed for nalbuphine alone (F [8,304] = 12.74; P c .OOOl). Posthoc contrasts, using the Tukey criterion, showed that the analgesic effect of the nalbuphine/ naloxone combination was significantly different from changes in pain level associated with nalbuphine alone (P = .0002).
Women The responses of women who received nalbuphine, naloxone, or nalbuphine combined with naloxone are depicted in Fig 1. The ANOVA showed only a significant main effect of treatment (F v[2,44] = 4.87; P < .0123), indicating significant differences in analgesia produced by the treatments. Post-hoc pairwise contrasts, using the Tukey criterion, indicated that the analgesic effect of nalbuphine alone and naloxone alone were not significantly different from each other. However, the analgesic effect produced by the nalbuphine/naloxone combination was significantly different from both nalbuphine alone (P = .0236) and naloxone alone (P = .0239).
Gender Differences in Responses to Naloxone and to the Combination of Nalbuphine and Naloxone To determine if there were gender differences in response to the different treatments, separate 2way repeated-measures ANOVAs, with 1 betweensubjects factor (ie, gender with 2 levels) and 1 within-subjects factor (ie, time with 9 levels) were performed for each treatment. These analyses were undertaken to determine how the gender x time interaction was dependent on treatment. These analyses failed to show either significant main effects or interaction effects for either naloxone alone or the nalbuphine/naloxone combination indicating a lack of gender differences in response to either treatment. However, a significant gender x treatment interaction was found with nalbuphine alone as reported previously.5
Discussion In a previous study, we observed that, in men, low-dose nalbuphine, compared with placebo, induced a marked pain-enhancing effect.5 Because nalbuphine can act as an antagonist at u-receptors,15 the enhanced pain with low-dose nalbuphine in men could hypothetically result from block of an analgesic effect of endogenously released u-opioids. However, such an explanation is incompatible with the present finding that naloxone, which itself potently
125
antagonizes p-opioid receptors, blocks the painenhancing effect of nalbuphine. Our results show a similar marked analgesia in both men and women when naloxone was added to the administration of low-dose nalbuphine. The ability of the opioid antagonist naloxone to eliminate the previously observed gender differences in response to nalbuphine4f5 suggests the existence of a naloxone-sensitive antianalgesic action of nalbuphine in addition to an analgesic effect that is less sensitive to naloxone. Consistent with such a dual action, we have observed a shortlived analgesia followed by increasing pain (antianalgesia) in men receiving k-opioid receptor agonists in previous studies.2,4,5 The induction of opposing effects, such as analgesia and pain enhancement, by K-opioid receptor agonists might be explained by actions at different k-receptor subtypes.16,17 The conversion of a potent pain enhancement to a potent analgesia in men through the addition of naloxone very strongly suggests that the painenhancing effect of nalbuphine is mediated through action at an opioid receptor. This finding is consistent with previous evidence that antianalgesia can result from action at k-opioid receptors.18-21 If it is an opioid effect that mediates the analgesia, it must be mediated by a receptor subtype that is relatively insensitive to naloxone. Although there are thought to be several subtypes of the K-opioid receptor,16,22,23 their relative sensitivities to naloxone are unknown. Our previous observation that the effect of 5 mg of nalbuphine in women was not significantly different from placebo could be interpreted to indicate that this dose of nalbuphine is not sufficient to produce analgesia. However, our current finding that naloxone, which can antagonize antianalgesia in men, significantly enhances the analgesic effect of this dose of nalbuphine in women suggests that the effect of nalbuphine alone in women might represent the sum of an antianalgesic response and an approximately equal analgesic response. That is, the addition of naloxone to nalbuphine in either gender similarly unmasks the analgesic by selectively antagonizing the response antianalgesic response. If so, the gender differences in k-mediated analgesia that we have previously observed would, in fact, result from gender differences in K-mediated antianalgesia. Alternatively, naloxone might exert agonism at therefore, these findings K-opioid receptors; could theoretically be interpreted as resulting from synergy of 2 K-opioid receptor agonists, although there is little evidence that this is the case. However, this explanation is very unlikely in men because the magnitude of the antianalgesic effect was so large that, unless antago-
Gender
126
Dependence
of Naioxone/Ndlbtiphtne
Analyesi
nized, it would have continued to mask analgesia. The findings in women are more amenable to interpretation as being caused by the synergy of 2 K--agonists, but for men the observed analgesia similar to that in women for nalbuphine plus naloxone would require postulation of different a mechanism. Gender differences in K-opioid receptor antinociception have been observed in animals, but these differences do not seem to parallel our findings in humans. For example, it has been found in male and female rats that administration of a rc-opioid receptor agonist, U69,593, induces a similar degree of antinociception that is differentially sensitive to an N-methyl-D-aspartate receptor (NMDA) antagonist but similarly decreased by naloxone. 25 Also, a series of studies by Gintzler et al 26-28 have shown that the antinociceptive effects of female sex hormones in pregnant rats are k-receptor mediated, a finding that suggests the possibility that women might respond differently to a K-opioid receptor agonist during different phases of their menstrual cycle. Unfortunately, the number of women in our study who could be evaluated in this way (ie, those not taking hormonal contraceptives who were clearly either in the luteal or the follicular phase of their cycle) was too small to analyze. In addition, our findings that naloxone not only
eliminates the gender differences but enhances k-mediated analgesia in both genders argues against a simple hormone-related mechanism. Although it is possible that one or more of the drugs given as part of the surgical protocol (ie, diazepam, nitrous oxide, or mepivacaine) could have influenced these results, these or similar drugs are commonly given for surgical procedures. Therefore, these results should generally apply for postoperative pain. In conclusion, our findings provide important insights into the mechanisms of opioid analgesia produced by k-receptor opioid agonists, including the influence of gender in humans. These findings are of considerable clinical significance, because the combination of naloxone and a low dose of a k-opioid receptor agonist would be expected to produce potent and prolonged analgesia with minimal or no side effects, including none of the significant side effects such as dysphoria that have severely limited the use of this class of opioids as first-line analgesics.
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