Mechanism of Action
ULTRAM ER 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 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.
Pharmacokinetics
The analgesic activity of tramadol is due to both parent drug and the M1 metabolite. ULTRAM ER 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 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.
Absorption
In healthy subjects, the bioavailability of a ULTRAM ER 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 extended-release 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 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, 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 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
Values (n=32)
Pharmacokinetic
Parameter |
Tramadol |
M1 Metabolite |
| ULTRAM ER 200- mg Tablet Once-Daily |
ULTRAM 50-mg
Tablet Every 6
Hours |
ULTRAM ER 200- mg Tablet Once- Daily |
ULTRAM 50-mg Tablet Every 6 Hours |
| 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 Once-Daily and 50
mg ULTRAM Every 6 Hours.
Food Effects
After a single dose administration of 200 mg ULTRAM ER 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 may be taken without regard to food, it is recommended that it be taken in
a consistent manner.
Distribution
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.
Metabolism
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).
Elimination
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 are approximately 7.9 and 8.8 hours, respectively.
Special Populations
Renal
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 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 does not
permit the dosing flexibility required for safe use in patients with severe
renal impairment. Therefore, ULTRAM ER should not be used in patients with severe
renal impairment (see WARNINGS, 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.
Hepatic
Pharmacokinetics of tramadol was studied in patients with mild or moderate
hepatic impairment after receiving multiple doses of ULTRAM ER 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 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 does not permit the dosing flexibility required
for safe use in patients with severe hepatic impairment. Therefore, ULTRAM ER
should not be used in patients with severe hepatic impairment (see WARNINGS,
Use in Renal and Hepatic Disease and DOSAGE AND
ADMINISTRATION).
Geriatric
The effect of age on the absorption of tramadol from ULTRAM ER in patients
over the age of 65 years has not been studied and is unknown (see PRECAUTIONS
and DOSAGE AND ADMINISTRATION).
Gender
Based on pooled multiple-dose pharmacokinetics studies for ULTRAM ER 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.
Drug Interactions
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 may affect the metabolism of tramadol leading to
altered tramadol exposure (see PRECAUTIONS: DRUG
INTERACTIONS).
Quinidine
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 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
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 and carbamazepine is not recommended (see PRECAUTIONS: DRUG
INTERACTIONS).
Cimetidine
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 dosage regimen with cimetidine is recommended.
Clinical Studies
ULTRAM ER 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.
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).
Figure 3
In one 12-week randomized, double-blind, placebo-controlled flexible-dosing trial of ULTRAM ER in patients with osteoarthritis of the knee, an average daily ULTRAM ER dose of approximately 270 mg/day 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 and placebo (see Figure 4).
Figure 4.
ULTRAM ER Study 015 Arthritis Pain Intensity VAS Responder Analysis Patients
Achieving Various Levels of Response Threshold
Last updated on RxList: 1/31/2008