| JOURNAL HOME | CME HOME | THIS MONTH | PAST ISSUES | ETOC | COLLECTIONS |
| AUTHORS | REVIEWERS | EDITORIAL BOARD | FEEDBACK | RSS | HELP |
 
|
|
|
||
|
|
© 2001 International Anesthesia Research Society
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
We sought to analyze the mode of interaction of spinal morphine with systemic morphine or buprenorphine, administered in a wide range of antinociceptive doses. The study was performed on Sprague-Dawley rats by using a plantar stimulation test and isobolographic and fractional analyses of drug interaction. The isobolographic and fractional analyses demonstrated that intrathecal morphine interacted with subcutaneous morphine in a synergistic manner while producing a 50% or 75% antinociceptive effect. The sum of D75 fractions was more than that for 50% antinociception, suggesting a less dramatic interaction. The combination with a maximal relative dose of systemic morphine (0.66:1) showed a maximal degree of supraadditivity. The interaction between spinal morphine and systemic buprenorphine was similar to that of morphine/morphine, although the supra-additivity was not as pronounced. For the doses that produced a 50% antinociceptive effect, a synergistic interaction was observed only for the combination with a morphine/buprenorphine ratio of 1.33:1. When the relative amount of intrathecal morphine was decreased or increased, the effect became additive. At the doses that produced 75% antinociception, both combinations of morphine and buprenorphine demonstrated supraadditive interaction.
Implications: Spinal morphine interacts with systemic morphine or buprenorphine in asupraadditive manner. This mode of interaction most probably results from thesimultaneous activation of spinal and supraspinal antinociceptive systems.Supraspinal structures played a more important role in the antinociceptiveeffect of experimental combinations than structures of the spinal cord.
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
It has been demonstrated that the concurrent administration of µ-opioid agonists directly to the brain and spinal cord produces a supraadditive antinociceptive effect (1,2). This effect was attributed to the simultaneous activation of spinal and supraspinal antinociceptive mechanisms. We have shown that the combined administration of spinal morphine and systemic morphine (3) or buprenorphine (4), at doses that alone produce marginal antinociception, result in a supraadditive antinociceptive effect. We also believe that this effect is a result of an interaction between spinal and supraspinal antinociceptive mechanisms, because the antinociceptive effect of systemic opioids is mediated predominantly by supraspinal systems (5).
The results of our studies suggest that it is possible to obtain a potent antinociceptive effect with relatively small doses of opioids. Decreasing the total doses of opioids might minimize the incidence of side effects while the desired effect is maintained or even improved because of a synergistic interaction.
Our experiments had been performed using a single pair of spinal and systemic doses of opioids. However, the interaction of pharmacologic substances often may vary depending on the doses of these substances and their ratio (6). Therefore, the aim of this study was to analyze the mode of interaction of spinal morphine with systemic morphine or buprenorphine, administered in a wide range of antinociceptive doses, using isobolographic and fractional analyses.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Experiments were approved by the Animal Care and Use Committee of the University of Southern California, Los Angeles. Male Sprague-Dawley rats (Harlan Industries, Indianapolis, IN) weighing 300–350 g at the time of surgery were used in these experiments. They were housed individually in a room maintained at 23°C ± 1°C with a 12-h light/dark cycle. Food and water were available ad libitum. Tests were performed during the light-on phase.
For the intrathecal (IT) injections, we used a modified method of chronic catheterization of the lumbar subarachnoid space (7). Under the general anesthesia (oxygen, N2O, and halothane), the animals were placed on the operating table. After depilating the skin of the neck and cutting it over the spinous processes of the cervical vertebrae, a small incision was made in the atlantooccipital membrane. A PE 10 catheter was introduced to a length of 10 cm caudal with its internal tip located at the level of the lumbar enlargement. The external tip of the catheter was secured to the muscles at the back of the neck, the muscles and the skin were sutured, and anesthesia was discontinued. The rats were allowed to recover for 1 wk before testing. Animals exhibiting any signs of neurologic deficit were excluded from the experiment.
The following drugs were used in the study: morphine sulfate (Sigma Chemical, St. Louis, MO, and Steris Laboratories, Inc., Phoenix, AZ) and buprenorphine hydrochloride (Sigma Chemical). IT injection was performed with a 10-µL syringe attached to a segment of PE 10 tubing. First, 10 µL of a drug was administered, and this was flushed by an additional 10 µL of saline. For systemic administration, morphine or buprenorphine was dissolved in saline and injected subcutaneously (SC) in a volume of 1 mL/kg.
Nociception was evaluated by the plantar stimulation test (8). In our experiments, we used a Paw Thermal Stimulator System developed at the Anesthesia Research Laboratory, University of California, San Diego. Briefly, the animal was placed in a clear plastic cage on an elevated glass surface with a radiant heat source (halogen projector lamp) located beneath the surface. The temperature of the surface was maintained at 30°C throughout the experiment. After 30 min of adaptation, the under-surface heat source was positioned in such a way that it focused on the plantar surface of one of the hind paws that was in contact with the glass. The light was activated, and the time between the application of the stimulus and the hind paw withdrawal response of the animal was measured. The intensity of the stimulus was chosen in such a way that the average latency of nociceptive response in control animals was approximately 5 s. Changes in nociception were determined as changes in response latencies. To minimize tissue injury caused by the exposure to the heat stimulus, a cutoff time of 15 s was imposed.
To assess baseline paw withdrawal latencies of operated animals, three determinations were performed at 5-min intervals before drug administration. Animals with baseline values that differed significantly from those of not-operated controls were not included in the study. After drug administration, paw withdrawal latencies were measured at 5, 10, 15, 20, 30, 45, and 60 min after injection, and then at 30-min intervals until response latencies returned to the baseline. The latency to peak drug effect and duration of antinociceptive effects were established with these data. In experiments in which the combination of drugs was studied, injections were timed so that the peak effect of IT morphine and SC morphine or buprenorphine coincided.
During the first series of experiments, dose-response curves were plotted for IT morphine (1–10 µg), SC morphine (3–8 mg/kg), and SC buprenorphine (0.05–0.5 mg/kg). By using the dose-response curves of each drug, the D50s and D75s of IT morphine and SC morphine or buprenorphine were determined.
During the second series of experiments, IT morphine was administered concurrently with SC morphine or buprenorphine. The doses of IT morphine in these combinations were equal to various fractions of its D50. Each pair of drugs was administered in three different dose ratios of 1.33:1, 2.66:1, or 0.66:1 (fraction of D50 of morphine IT/fraction of D50 of morphine SC or buprenorphine SC). A separate dose-response curve was plotted for each dose ratio of each pair of drugs. After dose-response curves for all combinations were plotted, the fractional dose combinations that produced 50% and 75% effects were determined. Isobolographic and fractional methods were used to analyze the mode of interaction between IT morphine and SC morphine or buprenorphine.
The dose-response curves were obtained from the peak effects of the particular opioid plotted against its dose. The peak effect was calculated as a percentage of maximal possible effect (%MPE) according to the following formula:
|
|
where postdrug response = the longest latency observed after drug administration, predrug response = the mean of the three latencies observed before drug administration, and cutoff time = 15 s.
Each rat was used in only one experiment. At the end of the experiment, all rats with catheters were injected with 10 µL of 2% lidocaine. Data from rats that did not develop motor paralysis within 3 min were excluded.
Isobolographic analysis for drug-drug interaction was conducted according to the procedure of Tallarida et al. (9). The isobologram is constructed for a certain level of effect (for instance, D50) by plotting single drug points on the dose coordinates and combined points in the dose field. It is expected that, if the drugs do not interact, the isobole connecting the points representing the combinations with those on the axes representing single drug doses, isoeffective with the combination, will be a straight line. This line is termed the additive line. All points that fall on the theoretical additive line are consistent with zero interaction (additive effect). Points to the left or to the right would indicate a supraadditive or a subadditive interaction, respectively.
To analyze the mode of interaction between IT morphine and SC morphine or buprenorphine, the isobolograms for 50% and 75% effects were constructed. Single-drug D50 or D75 points were plotted on the dose coordinates. Experimental combined D50 or D75 points were plotted in the field of the isobologram, and the difference between the experimental and the theoretical additive points was calculated for statistical significance with Student’s t-test. The SDs for each point were calculated from the variances of each component alone. A P value <0.05 was considered significant.
Fractional analysis is based on the assumption that if the drugs in the combination do not interact, then any amount of one drug can be replaced by the equieffective amount of the second without any changes in the resultant effect. The following is an equation for zero interaction (additive effect).
|
|
where Da and Db are the doses of drugs a and b producing a certain level of effect given alone and da and db are the doses of drugs a and b producing the same level of effect given in combination.
When the drugs in combination are more effective than expected from individual dose-response curves, smaller amounts are needed to produce a certain effect (supraadditive interaction):
|
|
On the contrary, when the drugs in combination are less effective than expected, da, db, or both must be increased to produce the required effect (subadditive interaction):
|
|
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The IT (1–10 µg) and SC (3–8 mg/kg) morphine, as well as SC buprenorphine (0.05–0.5 mg/kg), increased the latencies of nociceptive responses and the %MPE in a dose-dependent manner (Fig. 1). The combined administration of IT morphine with SC morphine or buprenorphine (Fig. 2) also produced a dose-dependent increase in the latencies of nociceptive responses and %MPE for all combinations used in the study. The antinociceptive effect of all combinations was more potent than that of individual drugs, as indicated by the leftward shift of the dose-response curves of all combinations (Fig. 2).
|
|
The leftward shift by itself, however, does not reflect the mode of interaction between the drugs in the combinations. Therefore, the fractional and isobolographic analyses (as presented in Methods) were performed to analyze the mode of interaction.
The experimentally-determined D50s for the combination of IT with SC morphine are presented in Table 1. The points A, B, and C on Figure 3A represent experimental D50s for combinations of IT and SC morphine used in fixed-dose ratios of 1.33:1, 0.66:1, and 2.66:1, respectively. The theoretical additive D50s for the point A1 were calculated to be 2.31 ± 0.31 µg (IT morphine) and 2.4 ± 0.1 mg/kg (SC morphine) for the point B1 = 1.52 ± 0.18 µg (IT morphine) and 3.43 ± 0.13 mg/kg (SC morphine), and for the point C1 = 2.92 ± 0.29 µg (IT morphine) and 1.53 ± 0.06 mg/kg (SC morphine). Statistical analysis demonstrated that the doses of IT and SC morphine determined experimentally were significantly smaller than respective theoretical additive doses (Fig. 3A).
|
|
The fractional analysis confirmed the synergistic mode of interaction. The sum of fractions of D50s was smaller than 1 in all combinations (Table 1).
Isobolographic and fractional analyses were also performed for D75s of nociceptive response inhibition. The experimental D75 values (points A, B, and C in Fig. 3B) are presented in Table 2. The theoretical additive D75s (points A1, B1, and C1 in Fig. 3B) were calculated to be 3.22 ± 0.08 µg (IT morphine) and 2.8 ± 0.08 mg/kg (SC morphine) for the 1.33:1 combination; 2.25 ± 0.07 µg (IT morphine) and 3.91 ± 0.11 mg/kg (SC morphine) for the 0.66:1 combination; and 4.11 ± 0.11 µg (IT morphine) and 1.78 ± 0.06 mg/kg (SC morphine) for the 2.66:1 combination. Statistical analyses demonstrated that the doses of IT and SC morphine determined experimentally were significantly smaller than the respective theoretical additive doses (Fig. 3B).
|
In the next series of experiments, we evaluated the antinociceptive effect of the combinations of IT morphine and SC buprenorphine. The D50 values for both drugs alone and in combinations are presented in Table 1. The points A, B, and C in Figure 4A represent the experimental D50s for combinations of IT morphine and SC buprenorphine used in fixed-dose ratios of 1.33:1, 0.66:1, or 2.66:1, respectively. The theoretical additive D50s for the point A1 were 2.35 ± 0.29 µg (IT morphine) and 46.5 ± 3.5 µg/kg (SC buprenorphine); for the point B1 = 1.64 ± 0.2 µg (IT morphine) and 65 ± 12.5 µg/kg (SC buprenorphine); and for the point C1 = 3.0 ± 0.36 µg (IT morphine) and 29.5 ± 5.6 µg/kg (SC buprenorphine). Statistical analysis demonstrated that the doses of IT morphine determined experimentally were not significantly different from the respective theoretical additive doses. An experimental dose of SC buprenorphine in 1.33:1 combination was significantly different from the theoretical additive dose. In the other two combinations, the experimental doses of SC buprenorphine were not significantly different from the respective theoretical doses. Although the sum of D50 fractions was close to 1 in all combinations (Table 1), the statistical analysis of the isobologram demonstrated a synergistic interaction in one of them (1.33:1).
|
The experimental D75 values for morphine IT and buprenorphine SC alone and in combinations are presented in Table 2. The points A and B in Figure 4B represent experimental D75s for combinations of IT morphine and SC buprenorphine used in fixed-dose ratios of 1.33:1 or 0.66:1, respectively. The theoretical additive D75s for the 1.33:1 combination (point A1) were 3.22 ± 0.07 µg (IT morphine) and 77.1 ± 3.9 µg/kg (SC buprenorphine), and for the 0.66:1 combination (point B1) they were 2.25 ± 0.05 µg (IT morphine) and 108.5 ± 4.5 µg/kg (SC buprenorphine). We were not able to determine D75 values for the 2.66:1 combination because the maximal effect of this combination did not reach 75%. Statistical analysis demonstrated that the doses of IT morphine and SC buprenorphine determined experimentally for the 1.33:1 combination were significantly different from the respective theoretical additive doses; this indicates the supraadditive mode of interaction. An experimental dose of IT morphine in a 0.66:1 combination was not different, whereas the dose of SC buprenorphine was significantly different from the respective theoretical additive dose. The fractional analysis demonstrated that the sum of D75 fractions was close to 1 in the 0.66:1 combination (Table 2); however, because the experimental dose of buprenorphine was significantly different from the theoretical one, we can consider this combination to be supraadditive as well.
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
In previous studies, we demonstrated that the combination of morphine administered IT with morphine or buprenorphine administered systemically produced a profound and prolonged antinociceptive effect (3,4). The effect was more pronounced than that expected from individual dose-response curves. This was achieved by combining single pairs of doses that produced a moderate antinociceptive effect when administered separately. The analysis of interaction showed that the observed effect was a result of a supra-additive mode of interaction between spinal morphine and systemic morphine or buprenorphine.
No systematic attempt was made in the previous studies to determine the ratios between systemic and spinal opioids in producing antinociceptive effects, nor did we study the dose range within which synergism between these two routes of administration occurred.
In this study we decided to analyze the mode of interaction of spinal morphine with systemic morphine or buprenorphine, administered in a wide range of doses in three different spinal/systemic ratios. A fractional analysis and an isobolographic method, which is considered a gold standard for analyzing drug interactions, were used in the study.
The isobolographic analysis demonstrated that IT morphine interacted with SC morphine in a synergistic manner while producing a 50% antinociceptive effect. The fractional analysis showed that the sum of D50 fractions able to produce a 50% effect was 0.54, 0.52, or 0.69 for the combinations with 1.33:1, 0.66:1, or 2.66:1 spinal/systemic ratios, respectively. This analysis suggested that the supraspinal structures play a more important role in the antinociceptive effect of morphine than the structures of the spinal cord. A relative decrease in the dose of spinal morphine in the combination (spinal/systemic ratio equal to 0.66:1 vs 1.33:1) did not result in changes in the sum of D50 fractions able to produce 50% antinociception (0.52 vs 0.54). However, a relative decrease in the dose of systemic morphine (spinal/systemic ratio equal to 2.66:1 vs 1.33:1) resulted in an increase in the sum of D50 fractions (0.69 vs 0.54) (Table 1).
IT morphine interacted with SC morphine also in a supraadditive manner when administered in the doses producing a 75% antinociceptive effect. The sum of D75 fractions, although different from 1, was more than that for 50% antinociception, suggesting less dramatic interaction. The synergistic interaction was observed for all spinal/systemic ratios, although the combination with maximal relative dose of systemic morphine (0.66:1) showed the minimal sum of D75 fractions (0.58 vs 0.69 or 0.73), suggesting a maximal degree of supraadditivity (Table 2).
In the second part of this study, we analyzed the mode of interaction between spinal morphine and systemic buprenorphine. The results were similar, although the supraadditivity was not as pronounced as for morphine-morphine interaction. For the doses that produced a 50% antinociceptive effect, a synergistic interaction was observed only for the combination with a morphine/buprenorphine ratio equal to 1.33:1. In this combination, the amount of spinal as well as systemic agonism was probably sufficient to result in supraadditive interaction (the sum of D50 fractions was equal to 79) (Table 1). When the relative amount of IT morphine was decreased (0.66:1), the effect became additive, probably because the amount of systemic agonism produced by SC buprenorphine was not sufficient to maintain supraadditivity. We believe that the lack of systemic agonism was a result of a low intrinsic activity of buprenorphine (10) compared with that of morphine. When the relative dose of IT morphine was increased, the effect was also additive (the sum of D50 fractions was equal to 0.92). The most likely explanation is that the spinal cord level has less significant weight in the antinociceptive effects of µ-opioids (see the above discussion), and the reduced amount of SC buprenorphine at the same time did not provide sufficient systemic agonism.
At the doses that produced 75% antinociception, both combinations of morphine and buprenorphine demonstrated supraadditive interaction. The degree of supraadditivity was more for 1.33:1 than for 0.66:1 morphine/buprenorphine combination (the sum of D75 fraction was 0.68 vs 0.82). This probably resulted from a small amount of systemic agonism provided by SC buprenorphine in the second combination, which was not sufficient to maintain the same degree of supraadditivity as was observed in the first combination, in which the lack of systemic agonism was compensated by a larger dose of IT morphine.
In animal studies, systemic morphine and other opioids do not show substantial spinal effects, even in doses that produce profound antinociception (5,11–13). It has been also proposed that buprenorphine acts at the supraspinal level to produce its antinociceptive effect (14), and even spinal administration of buprenorphine has been suggested to result in a supraspinal effect (15) because of the high lipid solubility of this compound. Therefore, we can assume that systemically-injected morphine or buprenorphine exert their antinociceptive effect predominantly at the supraspinal level. Subsequently, the antinociceptive effect of the combination of IT morphine and SC morphine or buprenorphine must be a result of a concurrent activation of spinal and supraspinal antinociceptive mechanisms.
|
Acknowledgments |
|---|
Supported in part by Departments of Anesthesiology and Cell & Neurobiology, University of Southern California, and the Health Research Association, University of Southern California, Los Angeles Campus.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
-
Yeung JC, Rudy TA. Multiplicative interaction between narcotic agonisms expressed at spinal and supraspinal sites of antinociceptive action as revealed by concurrent intrathecal and intracerebroventricular injections of morphine. J Pharmacol Exp Ther 1980; 215: 633–42.
[Abstract/Free Full Text] -
Roerig SC, Fujimoto JM. Multiplicative interaction between intrathecally and intracerebroventricularly administered mu opioid agonists but limited interactions between delta and kappa agonists for antinociception in mice. J Pharmacol Exp Ther 1989; 249: 762–8.
[Abstract/Free Full Text] - Niv D, Nemirovsky A, Rudick V, et al. Antinociception induced by simultaneous intrathecal and intraperitoneal administration of low doses of morphine. Anesth Analg 1995; 80: 886–9.[Abstract]
-
Niv D, Nemirovsky A, Metzner J, et al. Antinociceptive effect induced by the combined administration of spinal morphine and systemic buprenorphine. Anesth Analg 1998; 87: 583–6.
[Abstract/Free Full Text] - Pasternak GW. Pharmacological mechanisms of opioid analgesics. Clin Neuropharmacol 1993; 16: 1–19.[Web of Science][Medline]
- Berenbaum MC. What is synergy? Pharmacol Rev 1989; 41: 93–141.[Web of Science][Medline]
- Yaksh TL, Rudy TA. Chronic catheterization of the spinal subarachnoid space. Physiol Behav 1976; 17: 1031–6.[Medline]
- Hargreaves K, Dubner R, Brown F, et al. A new method for measuring thermal nociception in cutaneous hyperalgesia. Pain 1988; 32: 77–88.[Web of Science][Medline]
- Tallarida RJ, Porreca F, Cowan A. Statistical analysis of drug-drug and site-site interactions with isobolograms. Life Sci 1989; 45: 947–61.[Web of Science][Medline]
- Abram SE, Mampilly GA, Milosavljevic D. Assessment of the potency and intrinsic activity systemic versus intrathecal opioids in rats. Anesthesiology 1997; 87: 127–34.[Web of Science][Medline]
- Bolander H, Kortopoulos H, Lundberg S, Persson SA. Morphine concentrations in serum, brain and cerebrospinal fluid after intravenous administration of a single dose. J Pharm Pharmacol 1983; 35: 656–9.[Web of Science][Medline]
- Gustafsson LL, Post C, Edvardsen B, Ramsay CH. Distribution of morphine and meperidine after intrathecal administration in rat and mouse. Anesthesiology 1985; 63: 483–9.[Web of Science][Medline]
- Advokat C, Burton P. Antinociceptive effect of systemic and intrathecal morphine in spinally transected rats. Eur J Pharmacol 1987; 139: 335–43.[Web of Science][Medline]
- Bryant RM, Olley JE, Tyers MB. Antinociception actions of morphine and buprenorphine given intrathecally in the conscious rat. Br J Pharmacol 1983; 78: 659–63.[Web of Science][Medline]
-
Guirimand F, Chauvin M, Willer J-C, Le Bars D. Effects of intrathecal and intracerebroventricular buprenorphine on a C-fiber reflex in the rat. J Pharmacol Exp Ther 1995; 275: 629–37.
[Abstract/Free Full Text]
This article has been cited by other articles:
|
|
 |
|
  P. J. Borgdorff, T. I. Ionescu, P. L. Houweling, and J. T. A. Knape Large-Dose Intrathecal Sufentanil Prevents the Hormonal Stress Response During Major Abdominal Surgery: A Comparison with Intravenous Sufentanil in a Prospective Randomized Trial Anesth. Analg., October 1, 2004; 99(4): 1114 - 1120. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
