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Mechanism of Action
ULTRAM ER (tramadol hcl extended-release) is a centrally acting synthetic opioid analgesic. Although its mode of action is not completely understood, from animal tests, at least two complementary mechanisms appear applicable: binding of parent and M1 metabolite to μ-opioid receptors and weak inhibition of reuptake of norepinephrine and serotonin.
Opioid activity is due to both low affinity binding of the parent compound and higher affinity binding of the O-demethylated metabolite M1 to μ-opioid receptors. In animal models, M1 is up to 6 times more potent than tramadol in producing analgesia and 200 times more potent in μ-opioid binding. Tramadol-induced analgesia is only partially antagonized by the opiate antagonist naloxone in several animal tests. The relative contribution of both tramadol and M1 to human analgesia is dependent upon the plasma concentrations of each compound.
Tramadol has been shown to inhibit reuptake of norepinephrine and serotonin in vitro , as have some other opioid analgesics. These mechanisms may contribute independently to the overall analgesic profile of tramadol. The relationship between exposure of tramadol and M1 and efficacy has not been evaluated in the ULTRAM ER (tramadol hcl extended-release) clinical studies.
Apart from analgesia, tramadol administration may produce a constellation of symptoms (including dizziness, somnolence, nausea, constipation, sweating and pruritus) similar to that of other opioids. In contrast to morphine, tramadol has not been shown to cause histamine release. At therapeutic doses, tramadol has no effect on heart rate, left-ventricular function or cardiac index. Orthostatic hypotension has been observed.
The analgesic activity of tramadol is due to both parent drug and the M1 metabolite. ULTRAM ER (tramadol hcl extended-release) is administered as a racemate and both the [-] and [+] forms of both tramadol and M1 are detected in the circulation.
The pharmacokinetics of ULTRAM ER (tramadol hcl extended-release) are approximately dose-proportional over a 100-400 mg dose range in healthy subjects. The observed tramadol AUC values for the 400-mg dose were 26% higher than predicted based on the AUC values for the 200-mg dose. The clinical significance of this finding has not been studied and is not known.
In healthy subjects, the bioavailability of a ULTRAM ER (tramadol hcl extended-release) 200 mg tablet relative to a 50 mg every six hours dosing regimen of the immediate-release dosage form (ULTRAM) was approximately 85-90%. Consistent with the extendedrelease nature of the formulation, there is a lag time in drug absorption following ULTRAM ER administration. The mean peak plasma concentrations of tramadol and M1 after administration of ULTRAM ER (tramadol hcl extended-release) tablets to healthy volunteers are attained at about 12 h and 15 h, respectively, after dosing (see Table 1 and Figure 2). Following administration of the ULTRAM ER (tramadol hcl extended-release) , steady-state plasma concentrations of both tramadol and M1 are achieved within four days with once daily dosing.
The mean (%CV) pharmacokinetic parameter values for ULTRAM ER (tramadol hcl extended-release) 200 mg administered once daily and tramadol HCl immediate-release (ULTRAM) 50 mg administered every six hours are provided in Table 1.
Table 1: Mean (%CV) Steady-State Pharmacokinetic Parameter
|Pharma-cokinetic Parameter||Tramadol||M1 Metabolite|
|ULTRAM ER (tramadol hcl extended-release)
|ULTRAM ER (tramadol hcl extended-release)
|AUC0-24(ng•h/mL)||5975 (34)||6613 (27)||1890 (25)||2095 (26)|
|Cmax (ng/mL)||335 (35)||383 (21)||95 (24)||104 (24)|
|Cmin (ng/mL)||187 (37)||228 (32)||69 (30)||82 (27)|
|Tmax (h)||12 (27)||1.5 (42)||15 (27)||1.9 (57)|
|% Fluctuation||61 (57)||59 (35)||34 (72)||26 (47)|
|AUC0-24: Area Under the Curve in a 24-hour dosing interval; Cmax: Peak Concentration in a 24-hour dosing interval; Cmin: Trough Concentration in a 24-hour dosing interval; Tmax: Time to Peak Concentration|
Figure 2: Mean Steady-State Tramadol (a) and M1 (b) Plasma
Concentrations on Day 8 Post Dose after Administration of 200 mg ULTRAM ER (tramadol hcl extended-release) Once-Daily
and 50 mg ULTRAM Every 6 Hours.
After a single dose administration of 200 mg ULTRAM ER (tramadol hcl extended-release) tablet with a high fat meal, the Cmax and AUC0-∞ of tramadol decreased 28% and 16%, respectively, compared to fasting conditions. Mean Tmax was increased by 3 hr (from 14 hr under fasting conditions to 17 hr under fed conditions). While ULTRAM ER (tramadol hcl extended-release) may be taken without regard to food, it is recommended that it be taken in a consistent manner.
The volume of distribution of tramadol was 2.6 and 2.9 liters/kg in male and female subjects, respectively, following a 100-mg intravenous dose. The binding of tramadol to human plasma proteins is approximately 20% and binding also appears to be independent of concentration up to 10 μg/mL. Saturation of plasma protein binding occurs only at concentrations outside the clinically relevant range.
Tramadol is extensively metabolized after oral administration. The major metabolic pathways appear to be N – (mediated by CYP3A4 and CYP2B6) and O – (mediated by CYP2D6) demethylation and glucuronidation or sulfation in the liver. One metabolite (O-desmethyl tramadol, denoted M1) is pharmacologically active in animal models. Formation of M1 is dependent on CYP2D6 and as such is subject to inhibition, which may affect the therapeutic response (see PRECAUTIONS: DRUG INTERACTIONS).
Tramadol is eliminated primarily through metabolism by the liver and the metabolites are eliminated primarily by the kidneys. Approximately 30% of the dose is excreted in the urine as unchanged drug, whereas 60% of the dose is excreted as metabolites. The remainder is excreted either as unidentified or as unextractable metabolites. The mean terminal plasma elimination half-lives of racemic tramadol and racemic M1 after administration of ULTRAM ER (tramadol hcl extended-release) are approximately 7.9 and 8.8 hours, respectively.
Impaired renal function results in a decreased rate and extent of excretion of tramadol and its active metabolite, M1. The pharmacokinetics of tramadol were studied in patients with mild or moderate renal impairment after receiving multiple doses of ULTRAM ER (tramadol hcl extended-release) 100 mg. There is no consistent trend observed for tramadol exposure related to renal function in patients with mild (CLcr: 50-80 mL/min) or moderate (CLcr: 30-50 mL/min) renal impairment in comparison to patients with normal renal function. However, exposure of M1 increased 20-40% with increased severity of the renal impairment (from normal to mild and moderate). ULTRAM ER has not been studied in patients with severe renal impairment (CLcr < 30 mL/min). The limited availability of dose strengths of ULTRAM ER (tramadol hcl extended-release) does not permit the dosing flexibility required for safe use in patients with severe renal impairment. Therefore, ULTRAM ER (tramadol hcl extended-release) should not be used in patients with severe renal impairment (see PRECAUTIONS, Use in Renal and Hepatic Disease and DOSAGE AND ADMINISTRATION). The total amount of tramadol and M1 removed during a 4-hour dialysis period is less than 7% of the administered dose.
Pharmacokinetics of tramadol was studied in patients with mild or moderate hepatic impairment after receiving multiple doses of ULTRAM ER (tramadol hcl extended-release) 100 mg. The exposure of (+)- and (-)-tramadol was similar in mild and moderate hepatic impairment patients in comparison to patients with normal hepatic function. However, exposure of (+)- and (-)-M1 decreased ~50% with increased severity of the hepatic impairment (from normal to mild and moderate). The pharmacokinetics of tramadol after the administration of ULTRAM ER (tramadol hcl extended-release) has not been studied in patients with severe hepatic impairment. After the administration of tramadol immediate-release tablets to patients with advanced cirrhosis of the liver, tramadol area under the plasma concentration time curve was larger and the tramadol and M1 half-lives were longer than subjects with normal hepatic function. The limited availability of dose strengths of ULTRAM ER (tramadol hcl extended-release) does not permit the dosing flexibility required for safe use in patients with severe hepatic impairment. Therefore, ULTRAM ER (tramadol hcl extended-release) should not be used in patients with severe hepatic impairment (see PRECAUTIONS, Use in Renal and Hepatic Disease and DOSAGE AND ADMINISTRATION).
The effect of age on the absorption of tramadol from ULTRAM ER (tramadol hcl extended-release) in patients over the age of 65 years has not been studied and is unknown (see PRECAUTIONS and DOSAGE AND ADMINISTRATION).
Based on pooled multiple-dose pharmacokinetics studies for ULTRAM ER (tramadol hcl extended-release) in 166 healthy subjects (111 males and 55 females), the dose-normalized AUC values for tramadol were somewhat higher in females than in males. There was a considerable degree of overlap in values between male and female groups. Dosage adjustment based on gender is not recommended.
The formation of the active metabolite, M1, is mediated by CYP2D6. Approximately 7% of the population has reduced activity of the CYP2D6 isoenzyme of cytochrome P-450. Based on a population PK analysis of Phase I studies with immediate-release tablets in healthy subjects, concentrations of tramadol were approximately 20% higher in “poor metabolizers” versus “extensive metabolizers,” while M1 concentrations were 40% lower. In vitro drug interaction studies in human liver microsomes indicate that inhibitors of CYP2D6 (fluoxetine, norfluoxetine, amitriptyline, and quinidine) inhibit the metabolism of tramadol to various degrees, suggesting that concomitant administration of these compounds could result in increases in tramadol concentrations and decreased concentrations of M1. The full pharmacological impact of these alterations in terms of either efficacy or safety is unknown.
Tramadol is also metabolized by CYP3A4. Administration of CYP3A4 inhibitors, such as ketoconazole and erythromycin, or inducers, such as rifampin and St. John's Wort, with ULTRAM ER (tramadol hcl extended-release) may affect the metabolism of tramadol leading to altered tramadol exposure (see PRECAUTIONS: DRUG INTERACTIONS).
Tramadol is metabolized to M1 by CYP2D6. A study was conducted to examine the effect of quinidine, a selective inhibitor of CYP2D6, on the pharmacokinetics of tramadol by administering 200 mg quinidine two hours before the administration of ULTRAM ER (tramadol hcl extended-release) 100 mg. The results demonstrated that the exposure of tramadol increased 50-60% and the exposure of M1 decreased 50-60% (see PRECAUTIONS: DRUG INTERACTIONS). In vitro drug interaction studies in human liver microsomes indicate that tramadol has no effect on quinidine metabolism.
Carbamazepine, a CYP3A4 inducer, increases tramadol metabolism. Patients taking carbamazepine may have a significantly reduced analgesic effect of tramadol. Because of the seizure risk associated with tramadol, concomitant administration of ULTRAM ER (tramadol hcl extended-release) and carbamazepine is not recommended (see PRECAUTIONS: DRUG INTERACTIONS).
Concomitant administration of tramadol immediate-release tablets with cimetidine does not result in clinically significant changes in tramadol pharmacokinetics. No alteration of the ULTRAM ER (tramadol hcl extended-release) dosage regimen with cimetidine is recommended.
ULTRAM ER (tramadol hcl extended-release) was studied in patients with chronic, moderate to moderately severe pain due to osteoarthritis and/or low back pain in four 12-week, randomized, double-blind, placebo-controlled trials. To qualify for inclusion into these studies, patients were required to have moderate to moderately severe pain as defined by a pain intensity score of ≤ 40 mm, off previous medications, on a 0 – 100 mm visual analog scale (VAS). Adequate evidence of efficacy was demonstrated in the following two studies:
In one 12-week randomized, double-blind, placebo-controlled study, patients with moderate to moderately severe pain due to osteoarthritis of the knee and/or hip were administered doses from 100 mg to 400 mg daily. Treatment was initiated at 100 mg QD for four days then increased by 100 mg per day increments every five days to the randomized fixed dose. Between 51% and 59% of patients in the ULTRAM ER (tramadol hcl extended-release) treatment groups completed the study and 56% of patients in the placebo group completed the study. Discontinuations due to adverse events were more common in the ULTRAM ER (tramadol hcl extended-release) 200 mg, 300 mg and 400 mg treatment groups (20%, 27%, and 30% of discontinuations, respectively) compared to 14% of the patients treated with ULTRAM ER (tramadol hcl extended-release) 100 mg and 20% of patients treated with placebo.
Pain, as assessed by the WOMAC Pain subscale, was measured at 1, 2, 3, 6, 9, and 12 weeks and change from baseline assessed. A responder analysis based on the percent change in WOMAC Pain subscale demonstrated a statistically significant improvement in pain for the 100 mg and 200 mg treatment groups compared to placebo (see Figure 3).
In one 12-week randomized, double-blind, placebo-controlled flexible-dosing trial of ULTRAM ER (tramadol hcl extended-release) in patients with osteoarthritis of the knee, patients titrated to an average daily ULTRAM ER (tramadol hcl extended-release) dose of approximately 270 mg/day. Fortynine percent of patients randomized to ULTRAM ER (tramadol hcl extended-release) completed the study, while 52% of patients randomized to placebo completed the study. Most of the early discontinuations in the ULTRAM ER (tramadol hcl extended-release) treatment group were due to adverse events, accounting for 27% of the early discontinuations in contrast to 7% of the discontinuations from the placebo group. Thirty-four percent of the placebo-treated patients discontinued the study due to lack of efficacy compared to 15% of ULTRAM ER (tramadol hcl extended-release) -treated patients. The ULTRAM ER (tramadol hcl extended-release) group demonstrated a statistically significant decrease in the mean VAS score, and a statistically significant difference in the responder rate, based on the percent change from baseline in the VAS score, measured at 1, 2, 4, 8, and 12 weeks, between patients receiving ULTRAM ER (tramadol hcl extended-release) and placebo (see Figure 4).
Last reviewed on RxList: 5/18/2010
This monograph has been modified to include the generic and brand name in many instances.
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