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| RESEARCH ARTICLE |
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| Year : 2013 | Volume
: 45
| Issue : 1 | Page : 76-79 |
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Study of interaction of tramadol with amlodipine in mice
Hiral Modi, Bipa Mazumdar, Jagatkumar Bhatt
Department of Pharmacology, Medical College, Baroda, Gujarat, India
| Date of Submission | 08-Nov-2011 |
| Date of Decision | 04-Oct-2012 |
| Date of Acceptance | 29-Oct-2012 |
| Date of Web Publication | 24-Jan-2013 |
Correspondence Address:
Jagatkumar Bhatt
Department of Pharmacology, Medical College, Baroda, Gujarat
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0253-7613.106440
Objective: To study a possible interaction between tramadol, an opioid analgesic and amlodipine, a dihydropyridine calcium channel blocker with proposed antinociceptive property.
Materials and Methods: Albino mice of Haffkine strain were used for the study. The experiment was carried out using tail-flick method. Different doses of tramadol (50 mg/kg, 22.8 mg/kg and 10 mg/kg) were administered intraperitoneally to select the nonanalgesic dose. The animals were treated with different doses of amlodipine (2.5 mg/kg, 3.0 mg/kg, 3.5 mg/kg) to study its antinociceptive action. Combination of different doses of both the drugs were administered to study antinociceptive effect of the combination.
Results: Tramadol, showed dose dependent antinociception which persisted for entire two hours of the study period. Antinociceptive action was seen with amlodipine at a dose of 3.5 mg/kg. Different doses of amlodipine (2.5 mg/kg, 3.0 mg/kg) in combination with the nonanalgesic dose of tramadol (10 mg/kg) produced a significant enhancement of antinociceptive effect of tramadol. Combination of 3.5 mg/kg dose of amlodipine with nonanalgesic dose of tramadol (10 mg/kg) further enhances antinociceptive activity.
Conclusion: It is concluded that combination of amlodipine, a N - type calcium channel blocker, with tramadol produce significant enhancement of antinociceptive activity of tramadol.
Keywords: Amlodipine, tail flick latency, tramadol
How to cite this article:
Modi H, Mazumdar B, Bhatt J. Study of interaction of tramadol with amlodipine in mice. Indian J Pharmacol 2013;45:76-9 |
| » Introduction | |  |
Opioid analgesics are widely used for the control of moderate to severe pain. The prototypical agents, morphine, pethidine etc. are very useful agents but are limited by their adverse effects. Tramadol hydrochloride, a synthetic opioid is an orally active, clinically effective centrally acting analgesic having a lower incidence of respiratory depression, cardiac depression, side effects on smooth muscle and abuse potential as compared to typical opioid agents. [1],[2] Apart from being an opioid agonist, tramadol also activates monoaminergic spinal inhibition of pain by inhibiting serotonin and noradrenaline reuptake. [3] It was initially reported due to lack selectivity for μ, d and k receptors but recent studies show some selectivity for μ-receptors. [3]
Another common group of drugs which occupy an important place in the treatment of various cardiovascular and non-cardiac conditions are the calcium channel blockers.These drugs act by blocking one or more types of calcium channels located in the cells. It has been noted that blockade of the voltage gated calcium channels results in antinociception. [4] Voltage dependent T, N and L type of calcium channels contribute significantly to the excitability of sensory neurons, however, N channels are particularly important as they control release of neuro-transmitters from peripheral and central terminals. N - and L - type channels can be blocked by endogenous chemical transmitters and drugs to prevent nociceptive signalling. [4] Amlodipine a calcium channel blocker is commonly used in treatment of hypertension, angina etc. Amlodipine, cilnidipine, and omega-conotoxin GVIA exert their antinociceptive action by blocking N-type Ca 2+ channels in the primary nociceptive afferent fibers which results in attenuation of synaptic transmission of nociceptive neurons. [5] Amlodipine has been shown to enhance the antinociceptive action of morphine and ketorolac, possibly through a decrease in cellular calcium availability. [6]
Therefore, the present study was done with a hypothesis that a combination of tramadol with amlodipine would enhance the antinociceptive effect of tramadol.
| » Materials and Methods | | |
Albino mice of Haffkine strain of either gender (25-35 gms) were used in the study. All animals were maintained in the departmental animal house at a room temperature of 25-35°C with food and water available ad libitum. The animals were divided into the following groups (n = 6 in each group).
Group I: receiving saline (control).
Group II: receiving dimethylsulfoxide (DMSO; vehicle for amlodipine).
Groups III, IV and V: receiving three doses of tramadol [10 mg/kg (< ED50), 22.8 mg/kg (ED50) and 50 mg/kg (ED90) respectively. [3],[7]
Groups VI, VII and VIII: receiving different doses of amiodipine (2.5 mg/kg, 3.0 mg/kg and 3.5 mg/kg) respectively.
Group IX: receiving a combination of tramadol (10 mg/kg) and amlodipine (2.5 mg/kg).
Group X: receiving a combination of tramadol (10 mg/kg) and amlodipine (3.0 mg/kg)
Group XI: receiving a combination of tramadol (10 mg/kg) and amlodipine (3.5 mg/kg)
Drugs
Amlodipine (Intas Pharmaceuticals, Ahmedabad) and tramadol hydrochloride (Sarabhai Chemicals, Vadodara) were dissolved in dimethylsulfoxide (DMSO) and saline respectively. All the stock solutions dilutions were freshly made on the day of the experiment.
Determination of Analgesic Activity
Analgesic activity (antinociceptive activity) was measured by tail flick method [8] using analgesiometer. [8] Radiant heat from an electric source was used as a stimuli and the time required for the sudden flicking of the tail was considered as the 'reaction time' or 'the tail-flick latency. In order to prevent tissue injury due to repeated exposure to the heat stimulus, the 'cut-off time' was considered as seven seconds.
The baseline reaction time was obtained at the start of experiment (0 hrs) just before the drug administration (control value). In case of the groups in which tramadol and its control (saline) were given (group I, III, IV and V), the test was repeated at 0.25, 0.5, 1 and 2 hrs after the administration of the vehicle or drug. In case of the groups in which amlodipine and its control (DMSO) were given (group II, VI, VII and VIII), the test was repeated at 6, 6.25, 6.5, 7, 7.5 and 8 hrs after administration of vehicle or drug.
In the groups receiving combined treatment (group IX, X and XI), the two drugs were administered at different times. The baseline (0 hour) reaction time was obtained at the start of experiment (just before amlodipine was given) and the test was repeated at 6, 6.25, 6.5, 7, 7.5 and 8 hrs after administration of amlodipine. The dose of tramadol was given 5.75 hrs after the administration of amlodipine i.e. 0.25 hrs before the repeat test done at 6 hrs. In case of animals not responding within the cutoff time, the reaction time was taken as 7 seconds. [9] All the drugs were admistered intraperitoneally.
Statistical Analysis
The results are expressed as mean ± S.E.M. One way ANOVA with post hoc test of significance was performed for comparision amongst different means. P < 0.05 was regarded as statistically significant.
| » Results | | |
Animals treated with either saline (group I) or DMSO (group II) showed no significant change in reaction time (or tail flick latency) as compared to their baseline values at 0 hr (Control: 2.4±0.03 secs vs Saline: 2.4±0.02 secs and DMSO: 2.6±0.8 secs.).
Treatment with tramadol
Tramadol in a dose of 10 mg/kg ( < ED 50 ) showed no significant effect on tail flick latency during the entire test period of two hours as compared to the baseline value at 0 hr [Table 1]. Tramadol in doses of 22.8 mg/kg (ED50) and 50 mg/ kg (ED 90 ) showed antinociceptive activity which started at 0.25 hr after drug administration and was maximum at 0.5 hr and and persisted for the entire test period of 2 hrs. Both doses produced a significant increase (p<0.01) in the reaction time (or tail-flick latency) at all the time intervals, as compared to value at 0 hr [Table 1]. Thus, administration of tramadol in doses of 22.8 and 50 mg/kg produced dose-dependent antinociception.
Treatment with amlodipine
Amlodipine in doses of 2.5 mg/kg and 3.0 mg/kg showed no significant change in the tail flick latency as compared to the baseline values at 0 hr during the entire period of 2 hrs [Table 2]. However, the dose of 3.5 mg/kg showed antinociceptive effect from 6 hrs onwards with the peak effect at 7 hrs, which was significantly higher than the baseline values at 0 hr (p < 0.01) [Table 2]. | Table 2: Effects on tail flick latency after amlodipine treatment in mice
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Effect of combined treatment
Combination of nonanalgesic doses of tramadol (10 mg/kg) and amlodipine (2.5 mg/kg) did not produce any significant increase in the tail flick latency during the entire period of 2 hrs. Tramadol (10 mg/kg) when combined with 3.0 mg/kg amlodipine showed a significant increase in the tail flick latency, at 6.25 hrs onwards as compared to the values at 0 hr and 6 hrs. The peak of the antinociceptive effect was observed at 7 hrs and persisted significantly throughout the entire test duration [Table 3]. Further combination of tramadol (10 mg/kg) with 3.5 mg/kg amiodipine showed antinociceptive effect from 6 hrs onwards, reaching a peak at 6.5 hr after amlodipine treatment and persisted significantly throughout the entire test period as compared to the values at 0 and 6 hrs [Table 3]. | Table 3: Effects on tail flick latency after tramadol treatment in amlodipine pre-treated mice
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Also the combination of tramadol (10 mg/kg) and amlodipine (3.5 mg/kg) produced a significant increase in tail flick latency as compared to their corresponding values obtained in only amlodipine (3.5 mg/kg) treated group at all the time intervals after 6.5 hrs [Table 4]. | Table 4: Comparision between change in tail fl ick latency after treatment with amlodipine and its combination with tramadol
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| » Discussion | | |
The present study aimed to study the possible interaction between tramadol and amlodipine in terms of their antinociceptive action. Three doses of tramadol were selected (10, 22.8 and 50 mg/kg). The dose which did not demonstrate significant analgesic activity (10 mg/kg which was below the ED 50 ) was chosen for combination with amlodipine to study their interaction and whether addition of amlodipine to it would result in significant antinociceptive effect. In non analgesic doses, tramadol, being a μ - agonist, may poorly inhibit N - type calcium channels (which is mainly k mediated) and thus fails to produce antinociceptive effect. However, its antinociceptive action was enhanced when combined with amlodipine in our study. This could probably be due to N - type calcium channel blocking action of amlodipine.
Amlodipine, which acts on both L and N - type voltage dependent calcium channels, showed antinociception at selectively higher doses by increasing the tail-flick latency in mice. Murakami [6] and others have demonstrated that intrathecal injection of amlodipine significantly shortened the licking time in the late phase of a formalin test, while no effect was found with another dihydropyridine derivative, nicardipine. Further, other N - type calcium channel blockers, clinidipine and omega conotoxin also showed marked analgesic effects under similar experimental conditions. Their work suggested that amlodipine, clinidipine and omega-conotoxin exert their antinociceptive effect by blocking N - type calcium channels in the primary afferent fibres. Blocking of calcium channel results in attenuation of synaptic transmission of nociceptive neurons. [10] Furthermore, it is suggested that some N - type calcium channel blockers might have therapeutic potential as analgesics when applied directly into the subarachnoid space. Thus, several studies have demonstrated the role of N - type of calcium channels in antinociceptive action of calcium channel blockers. Since amlodipine also blocks N - channels, it is likely that antinociceptive action could be due to blockade of N-type calcium channels.
In order to study the interaction between amlodipine and tramadol, combination of different doses of both the drugs was studied by tail flick method using radiant heat. Combination of different doses of both the drugs produced significant dose - dependent antinociceptive action. A similar study reported that amlodipine enhances antinociceptive action of morphine and ketorolac, possibly through a decrease in cellular calcium availability. [10] Using acetic acid writhing test in mice, it has been reported that calcium channel blockers (diltiazem, verapamil, flunarazine, nicardipine, cinnarizine) produce antinociception and enhance antinociception of morphine. [11] In agreement of the above studies, the present study demonstrated that amlodipine enhanced the analgesic action of tramadol. Similarly, Omote et al [12],[13] reported dose dependent synergestic antinociceptive action of an N - type voltage dependent calcium channel blocker, omega-conotoxin and morphine. Intrathecal administration of a N - type calcium channel blocker, omega-conotoxin with a delta opioid agonist (DADLE) was shown to be the most effective combination to produce antinociception in the rat tail-flick test. [14]
Thus, from our study, it can be concluded that amlodipine, a N - type calcium channel blocker, when combined with the opioid agonist tramadol, enhances antinociceptive effects of tramadol as well as prolongs the duration of its antinociceptive effect. These results could thus have a potential clinical implication. Patients, who are on amlodipine therapy for cardiovascular problems, would probably need a lower dose of tramadol, for pain relief. This would also minimize development of the side effects due to tramadol therapy. However, further clinical studies are required to substantiate the results from our study.
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[Table 1], [Table 2], [Table 3], [Table 4]
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