Clinical pharmacology of tramadol

Opioids in pain management of blood-related malignancies

Opioids are basic analgesics used in the treatment of moderate to severe pain in patients affected by blood-related malignancies. They should be sequentially administered according to the World Health Organisation scale for cancer pain. Initial treatment and titration with opioids should be based on immediate-release preparations, to be administered at appropriate intervals in order to relieve pain and to satisfy the individual opioid requirement. Once a relatively good pain control has been achieved, a slow release formulation at equivalent doses can be given. Most patients can be adequately managed using oral formulation opioids. However, a small group, such as those presenting severe mucositis or requiring a rapid pain relief, should be managed by intravenous continuous infusion and/or by a patient-controlled analgesia system; while for patients in the community, there are distinct advantages to using the subcutaneous route. Other available routes of administration for opioids, can be used in selected circumstances, including rectal, transdermal, epidural, intrathecal and intramuscular. The invasive neuraxial route has a very limited role in patients with haematological malignancies, given the high risk of infection and bleeding. Through a close observation and a careful management, opioid-related side effects can be effectively prevented and treated. This article reviews the principles of opioid therapy and how opioids can be adapted for patients with pain due to haematological malignancies.

Use of hydrophilic natural gums in formulation of sustained-release matrix tablets of tramadol hydrochloride

The objective of this work was to develop matrix sustained-release tablets of highly water-soluble tramadol HCl using natural gums (xanthan [X gum] and guar [G gum]) as cost-effective, nontoxic, easily available, and suitable hydrophilic matrix systems compared with the extensively investigated hydrophilic matrices (ie, hydroxypropyl methylcellulose [HPMC]/carboxymethyl cellulose [CMC] with respect to in vitro drug release rate) and hydration rate of the polymers. Matrix tablets of tramadol (dose 100 mg) were produced by direct compression method. Different ratios, of 100∶0, 80∶20, 60∶40, 20∶80, 0∶100 of G gum (or X):HPMC, X gum:G gum, and triple mixture of these polymers (G gum, X gum, HPMC) were applied. After evaluation of physical characteristics of tablets, the dissolution test was, performed in the phosphate buffer media (pH 7.4) up to 8 hours. Tablets with only X had the highest mean dissolution time (MDT), the least dissolution efficiency (DE8%), and released the drug following a zero-order model via swelling, diffusion, and erosion mechanisms. Guar gum alone could not efficiently control the drug release, while X and all combinations of natural gums with HPMC could retard tramadol HCl release. However, according to the similarity factor (f 2), pure HPMC and H8G2 were the most similar formulations to Topalgic-LP as the reference standard.

Safety and efficacy of tramadol in the treatment of premature ejaculation: a double-blind, placebo-controlled, fixed-dose, randomized study

PURPOSE

To evaluate the efficacy and safety of a new serotonergic centrally acting drug tramadol in delaying ejaculation in patients with premature ejaculation.

MATERIALS AND METHODS

Sixty-four potent men with premature ejaculation were randomly assigned to receive 50 mg tramadol (group 1, n = 32) or placebo (group 2, n = 32) approximately 2 hours before planned sexual activity, for 8 weeks. Pretreatment evaluation included history and physical examination, intravaginal ejaculatory latency time, International Index of Erectile Function, and Meares-Stamey test. The efficacy of 2 treatments was assessed using responses to International Index of Erectile Function, intravaginal ejaculatory latency time evaluation, and several general assessment questions.

RESULTS

Fifty-seven (89%) completed the whole treatment schedule. The mean intravaginal ejaculatory latency time after tramadol and placebo increased from 19 and 21 seconds to approximately 243 and 34 seconds, respectively (P < 0.001). The mean weekly intercourse episodes increased from pretreatment values of 1.07 and 1.1 to 2.3 and 1.3, for tramadol and placebo, respectively (P < 0.05). Baseline mean intercourse satisfaction domain values of International Index of Erectile Function 10 and 11 reached to 14 and 10 at 8-week treatment in groups 1 and 2, respectively (P < 0.05). There was no withdrawal caused by adverse effects with tramadol or placebo, but more adverse events were associated with tramadol treatment (P < 0.05).

CONCLUSIONS

Tramadol seems to provide significantly better results in terms of intravaginal ejaculatory latency time and intercourse satisfaction versus placebo. Further studies are required to draw final conclusions on the efficacy of this drug in premature ejaculation.

The use of opioids in the treatment of osteoarthritis: when, why, and how?

As life expectancy increases every decade, the incidence and prevalence of osteoarthritis (OA) also will increase. Despite progress in our knowledge of the pathophysiology of OA, the management of OA-mediated pain continues to challenge physicians. Concern regarding the cardiovascular effects of cyclooxygenase-2 inhibitors and the gastrointestinal and renal side effects of nonsteroidal anti-inflammatory drugs (NSAIDs) in general has limited the use of these medications in the management of chronic non-cancer pain. Appropriately dosed and monitored use of opioids for OA pain, when more conservative methods have failed, has potentially fewer life-threatening complications associated with it than the more commonly and often less successfully employed pharmacotherapeutic approaches to care. When used as part of a multimodal approach to pain control, opioids are a safe and effective treatment for joint pain, including that of OA. Patients for whom NSAIDs are contraindicated, or for whom combined acetaminophen, tramadol, and NSAID therapy is ineffective, may be started on low-dose opioids and titrated as needed and tolerated. Patient education and informed consent, exercise, complementary medicine, and the use of a controlled substance agreement increases the likelihood of patient compliance with treatment guidelines, improving functional capacity and quality of life.

In vitro and in vivo vasodilator activity of racemic tramadol and its enantiomers in Wistar rats

Tramadol ((+/-)-tramadol) is an analgesic agent formulated as a racemic mixture (1:1) of (-)- and (+)-tramadol, which differ in their potency to bind to mu-opioid receptors and to inhibit monoamine-reuptake. We investigated the stereoselectivity of in vitro tramadol-induced vasodilatation of aortic rings and its effect on the arterial blood pressure measured in conscious Wistar rats. (+)-Tramadol, but not (-)-tramadol, produced a concentration-dependent relaxation of aorta precontracted with phenylephrine. The concentration-response curve was significantly altered by the removal of endothelium. Vascular relaxation was also inhibited by pre-incubation of endothelium-intact aorta with naloxone, suggesting the involvement of opioid receptors. The vasodilatation produced by tramadol was stereoselective, and the (+)-tramadol-induced vasodilatation was mediated by mu-opioid receptors and partially dependent on endothelium integrity. The hypotensive response induced by (+)-tramadol was also observed after bolus injection of 5.0 and 10.0 mg/kg. The results indicate that only high doses of tramadol cause cardiac depression and hypotension, indicating that it can be used safely.

O-demethylation of tramadol in the first months of life

OBJECTIVE

Assess in vivo O-demethylation activity in the first months of life.

METHODS

Time-concentration profiles of tramadol (M) and O-demethyl tramadol (M1) in plasma and urine were simultaneously collected in the first 24 h of continuous intravenous tramadol administration in neonates and young infants. M and M1 were determined by high performance liquid chromatography. Correlations between perinatal characteristics [postnatal age (PNA), postmenstrual age (PMA)] and the contribution of metabolites (M, M1) to overall tramadol elimination and to the plasma and urine log M/M1 were calculated.

RESULTS

Plasma samples were available in 20/29 and complete 24-h urine collections were available in 25/29 neonates (25-53 weeks PMA). Mean plasma log M/M1 value (>4 h, n=86) was 0.8 (SD 0.4). A significant correlation between plasma log M/M1 and PMA (r=-0.73, P<0.0001) and PNA (r=-0.58, P<0.005) was observed. In a multiple regression model, only PMA remained an independent variable. Mean urine log M/M1 was 0.94 (SD 0.7). Significant correlations of the urine log M/M1 ratio with PMA (r=-0.73, P<0.0001) and PNA (r=-0.56, P=0.0035) were observed. In a multiple regression model with the urine log M/M1 ratio as dependent variable, only PMA remained an independent variable. The maturational half-life of the log M/M1 ratio in early neonatal life in the age range evaluated is about 12-16 weeks without plateau.

CONCLUSIONS

O-demethylation activity was already observed in early neonatal life. A significant correlation with PMA was documented, but PMA can only partially explain the observed variability in O-demethylation activity. Polymorphism therefore likely already contributes to the interindividual variability observed in neonates.

Profiling the subjective, psychomotor, and physiological effects of tramadol in recreational drug users

Tramadol is a mu opioid agonist that also inhibits the reuptake of norepinephrine and serotonin. Because non-medical use of prescription opioids, including tramadol, has increased in the U.S. over the last several years, we sought to profile its subjective, psychomotor, and physiological effects in recreational drug users. Twenty-two subjects received placebo, 50 or 100 mg tramadol, morphine, or 2 mg lorazepam in a randomized, crossover, double-blind design. The last 12 subjects in the study received 25 mg morphine, a dose that is putatively equianalgesic to 100 mg tramadol. In these subjects, morphine induced miosis and several other mu agonist subjective effects; 100 mg tramadol increased "feel drug effect" and drug liking ratings, and decreased pupil size, but the miotic effect was not statistically significant. Lorazepam, but neither tramadol nor morphine, impaired psychomotor performance. When the placebo, tramadol, and lorazepam data from all 22 subjects were analyzed, 100 mg tramadol induced miosis, and several subjective effects were increased significantly, including ratings of drug liking and "want to take again." The present results indicating that a clinically-prescribed dose of oral tramadol has abuse liability-related effects in recreational drug users suggest the need for further abuse liability testing of the oral formulation in opioid abusers.

Tramadol-induced hyponatraemia following unicompartmental knee replacement surgery

We report a case of postoperative hyponatraemia following routine knee surgery, followed by a subsequent, less severe, episode after identical surgery on the contralateral knee. On each occasion the patient had been given the weak opioid tramadol for postoperative pain relief. Through its effects on serotonergic neurotransmission in the central nervous system, we hypothesise that tramadol may have been directly involved in this patient's biochemical disorder.

Tramadol disposition in the very young: an attempt to assess in vivo cytochrome P-450 2D6 activity

BACKGROUND

Tramadol is potentially a very useful pain relief medication in neonates and infants. It is primarily metabolized into O-demethyl tramadol (M1) by CYP2D6. Data concerning tramadol disposition and CYP2D6 activity in young infants are not available.

METHODS

A population pharmacokinetic analysis of tramadol and M1 time-concentration profiles was undertaken using non-linear mixed-effects models (NONMEM), based on newly collected data on tramadol and M1 time-concentration profiles in neonates and young infants (n=20) and published studies on intravenous tramadol in children and adults. M1 formation served as a surrogate for CYP2D6 activity.

RESULTS

Tramadol clearance was described using a two-compartment linear model with zero-order input and first-order elimination. Clearance increased from 25 weeks post-conception age (PCA) (5.52 litre h(-1) [70 kg](-1)) to reach 84% of the mature value by 44 weeks PCA (standardized to a 70 kg adult using allometric '1/4 power' models). The central volume of distribution decreased from 25 weeks PCA (256 litre [70 kg](-1)) to reach 120% of its mature value by 87 weeks PCA. Formation clearance to M1 contributed 43% of tramadol clearance, but had no relationship with PCA. There was a weak non-linear relationship between PCA and M1 metabolite clearance.

CONCLUSIONS

Maturational clearance of tramadol is almost complete by 44 weeks PCA. A target concentration of 300 microg litre(-1) is achieved after a bolus of tramadol hydrochloride 1 mg kg(-1) and can be maintained by infusion of tramadol hydrochloride 0.09 mg kg(-1) h(-1) at 25 weeks PCA, 0.14 mg kg(-1) h(-1) at 30 weeks PCA, 0.17 mg kg(-1) h(-1) at 35 weeks PCA, 0.18 mg kg(-1) h(-1) at 40 weeks, 0.19 mg kg(-1) h(-1) at 50 weeks PCA to 1 yr, 0.18 mg kg(-1) h(-1) at 3 yr and 0.12 mg kg(-1) h(-1) in adulthood. CYP2D6 activity was observed as early as 25 weeks PCA, but the impact of CYP2D6 polymorphism on the variability in pharmacokinetics, metabolism and pharmacodynamics of tramadol remains to be established.

Economic Evaluation of Tramadol/Paracetamol Combination Tablets for??Osteoarthritis Pain in The Netherlands

OBJECTIVE

To compare the costs of treating osteoarthritis (OA) pain using combination tramadol/paracetamol tablets, NSAIDs alone, NSAIDs plus proton pump inhibitors (PPIs), or NSAIDs plus histamine H(2)-receptor antagonists (H(2)RAs) from the perspective of the Dutch healthcare system.

DESIGN AND METHODS

A decision-analytical model was constructed to model the cost outcomes of the four treatment strategies over 6 months. A cost-minimisation approach was used, which considered data related to resource utilisation, medication costs and costs for the treatment of adverse events. Data, derived mainly from the clinical literature, were supplemented by inputs from a Delphi panel as well as official price and tariff lists. The base-case analysis considered direct medical costs, including those for treating all adverse events with tramadol/paracetamol and gastrointestinal (GI) adverse events with NSAIDs. Separate scenario analyses explored costs of NSAID-based regimens: (i) according to 21 levels of risk for GI adverse events, and (ii) when renal events attributable to NSAIDs were considered. Robustness of the model was tested using univariate sensitivity analysis.

RESULTS

In the base-case analysis, costs for 6 months' treatment of OA pain using tramadol/paracetamol were euro244.45, compared with euro317.32 for NSAIDs + PPIs, euro200.67 for NSAIDs + H(2)RAs, and euro125.86 for NSAIDs alone. This provided a cost saving of euro72.87 per patient over 6 months for tramadol/paracetamol compared with NSAIDs + PPIs. Tramadol/paracetamol became cost saving compared with NSAIDs alone and NSAIDs + H(2)RAs for GI risk levels >13 and >10, respectively. When renal adverse events of NSAIDs were con- sidered, tramadol/paracetamol was cost saving compared with all NSAID-based regimens (saving euro228.40 vs NSAIDs, euro418.42 vs NSAIDs + PPIs, and euro302.69 vs NSAIDs + H(2)RAs [year of costing 2005]). Sensitivity analysis confirmed the model was robust to wide-ranging changes in the value of input parameters.

CONCLUSION

Tramadol/paracetamol is cost saving compared with NSAIDs + PPIs for the treatment of OA pain over a period of 6 months regardless of the risk of GI or renal complications. Tramadol/paracetamol is also cost saving compared with treatment with NSAIDs alone and NSAIDs + H(2)RAs for patients at medium and high risk of GI adverse events and in all cases if considering renal adverse events. Despite not being quantified in monetary terms, the lower incidence of adverse events with tramadol/paracetamol is a clinical benefit.