CLINICAL PHARMACOLOGY
Mechanism of Action
ConZip™ contains tramadol, 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.
Pharmacodynamics
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 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. ConZip™ is administered as a racemate and both
tramadol and M1 are detected in the circulation. The Cmax and AUC of ConZip™
capsules have been observed to be dose-proportional over an oral dose range of
100 to 300 mg in healthy subjects.
Absorption
After a single dose administration of ConZip™, Tmax occurs
around 10-12 hours.
The mean Cmax and AUC of ConZip™ capsules after a 300 mg
single dose was 308 ng/Ml and 6777 ng*hr/mL, respectively under fasting
conditions. ConZip™ is bioequivalent to a reference extended-release tramadol
product following a single 300 mg dose under fasting conditions.
At steady-state, ConZip™ at 200 mg has been observed to
be bioequivalent to a reference extended-release tramadol product at 200 mg
under fasting conditions (Table 2). Following administration of ConZip™ 200 mg
capsules, steady-state plasma concentrations of both tramadol and M1 are
achieved within four days of once daily dosing.
Figure 2 : Mean (%CV) Steady-State Pharmacokinetic
Parameter Values (N=38)
Parameter |
Tramadol |
O-Desmethyl-Tramadol |
(M1 Metabolite) |
Tramadol hydrochloride Extended Release Capsules 200 mg |
A Reference Extended-Release Tramadol Product 200 mg |
Tramadol hydrochloride Extended Release Capsules 200 mg |
A Reference Extended-Release Tramadol Product 200 mg |
AUC0-24 (ng.h/mL) |
5678 (27%) |
5563 (32%) |
1319 (34%) |
1302 (40%) |
C umax (ng/mL) |
332 (25%) |
350 (31%) |
70 (34%) |
74 (41%) |
Cmin (ng/mL) |
128 (39%) |
125 (45%) |
35 (34%) |
33 (42%) |
Tmax |
5.9 (66%) |
10 (30%) |
11 (37%) |
13 (29%) |
% Fluctuation |
88 (19%) |
101 (30%) |
64 (22%) |
76 (30%) |
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 |
Food Effects
The rate and extent of absorption of ConZip™ capsules
(300 mg) are similar following oral administration with or without food.
Therefore, ConZip™ capsules can be administered without regard to meals.
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 tramadol 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 and
polymorphism, which may affect the therapeutic response [see 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 plasma elimination
half-lives of racemic tramadol and racemic M1 after administration of ConZip™ capsules
are approximately 10 and 11 hours, respectively.
Special Populations
Renal Impairment
Impaired renal function results in a decreased rate and
extent of excretion of tramadol and its active metabolite, M1. The
pharmacokinetics of tramadol was studied in patients with mild or moderate
renal impairment after receiving multiple doses of an extendedrelease tramadol
product at 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 (CLcr > 80 mL/min). However, exposure of M1 increased
20-40% with increased severity of the renal impairment (from normal to mild and
moderate). The pharmacokinetics of tramadol has not been studied in patients
with severe renal impairment (CLcr < 30 mL/min). The limited availability of
dose strengths of ConZip™ does not permit the dosing flexibility required for
safe use in patients with severe renal impairment. Therefore, ConZip™ should
not be used in patients with severe renal impairment [see DOSAGE AND
ADMINISTRATION, WARNINGS AND PRECAUTIONS and Use In Specific
Populations]. The total amount of tramadol and M1 removed during a 4-hour
dialysis period is less than 7% of the administered dose.
Hepatic Impairment
Pharmacokinetics of tramadol was studied in patients with
mild or moderate hepatic impairment after receiving multiple doses of an
extended-release tramadol product at 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 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 ConZip™ does not permit
the dosing flexibility required for safe use in patients with severe hepatic
impairment. Therefore, ConZip™ should not be used in patients with severe
hepatic impairment [see DOSAGE AND ADMINISTRATION, WARNINGS AND
PRECAUTIONS, and Use In Specific Populations].
Gender
Based on pooled multiple-dose pharmacokinetics studies
for an extended-release tramadol product 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.
Age
The effect of age on pharmacokinetics of ConZip™ has not
been studied. Healthy elderly subjects aged 65 to 75 years administered an
immediate-release formulation of tramadol, have plasma concentrations and
elimination half-lives comparable to those observed in healthy subjects less
than 65 years of age. In subjects over 75 years, mean maximum plasma
concentrations are elevated (208 vs. 162 ng/mL) and the mean elimination
halflife is prolonged (7 vs. 6 hours) compared to subjects 65 to 75 years of
age. Adjustment of the daily dose is recommended for patients older than 75
years [see DOSAGE AND ADMINISTRATION].
Drug Interactions
Poor / Extensive Metabolizers, CYP2D6
The formation of the active metabolite, M1, is mediated
by CYP2D6, a polymorphic enzyme. Approximately 7% of the population has reduced
activity of the CYP2D6 isoenzyme of cytochrome P-450 metabolizing enzyme
system. These individuals are “poor metabolizers” of debrisoquine,
dextromethorphan and tricyclic antidepressants, among other drugs. Based on a
population PK analysis of Phase 1 studies with IR tablets in healthy subjects,
concentrations of tramadol were approximately 20% higher in “poor metabolizers”
versus “extensive metabolizers,” while M1 concentrations were 40% lower.
CYP2D6 Inhibitors
In vitro drug interaction studies in human liver
microsomes indicate that concomitant administration with inhibitors of CYP2D6
such as fluoxetine, paroxetine, and amitriptyline could result in some
inhibition of the metabolism of tramadol.
Quinidine
Tramadol is metabolized to active metabolite M1 by
CYP2D6. Coadministration of quinidine, a selective inhibitor of CYP2D6, with
tramadol ER resulted in a 50-60% increase in tramadol exposure and a 50-60%
decrease in M1 exposure. The clinical consequences of these findings are
unknown.
To evaluate the effect of tramadol, a CYP2D6 substrate on
quinidine, an in vitro drug interaction study in human liver microsomes was
conducted. The results from this study indicate that tramadol has no effect on
quinidine metabolism. [see WARNINGS AND PRECAUTIONS and DRUG
INTERACTIONS].
CYP3A4 Inhibitors and Inducers
Since tramadol is also metabolized by CYP3A4,
administration of CYP3A4 inhibitors, such as ketoconazole and erythromycin, or
CYP3A4 inducers, such as rifampin and St. John's Wort, with ConZip™ may affect
the metabolism of tramadol leading to altered tramadol exposure [see WARNINGS
AND PRECAUTIONS and DRUG INTERACTIONS].
Cimetidine
Concomitant administration of tramadol immediate-release
tablets with cimetidine, a weak CPY3A4 inhibitor, does not result in clinically
significant changes in tramadol pharmacokinetics. No alteration of the ConZip™
dosage regimen with cimetidine is recommended.
Carbamazepine
Carbamazepine, a CYP3A4 inducer, increases tramadol
metabolism. Patients taking carbamazepine may have a significantly reduced
analgesic effect of tramadol. Concomitant administration of ConZip™ and
carbamazepine is not recommended.
Non-Clinical Toxicology
Carcinogenesis, Mutagenesis, Impairment of Fertility
Carcinogenicity assessment has been conducted in mice,
rats and p53(+/-)- heterozygous mice. A slight, but statistically significant,
increase in two common murine tumors, pulmonary and hepatic, was observed in a
mouse carcinogenicity study, particularly in aged mice. Mice were dosed orally
up to 30 mg/kg (90 mg/m² or 0.5 times the maximum daily human dosage of 185
mg/m²) for approximately two years, although the study was not done with the
Maximum Tolerated Dose. This finding is not believed to suggest risk in humans.
No treatment-related tumors were noted in a rat
carcinogenicity study (dosing orally up to 30 mg/kg, 180 mg/m², or equivalent
to the maximum daily human dosage) or in a second study where rats were treated
with up to 75 mg/kg/day for males and 100 mg/kg/day for females (approximately
2.4 and 3.2-fold MDHD, respectively) for two years. However, the excessive
decrease in body weight gain observed in the rat study might have reduced their
sensitivity to any potential carcinogenic effect of the drug.
No carcinogenic effect of tramadol was observed in
p53(+/–) – heterozygous mice at oral doses up to 150 mg/kg/day (approximately
2.4-fold maximum daily human dose [MDHD] of 300 mg/day for a 60 kg adult based
on body surface conversion) for 26 weeks.
Tramadol was not mutagenic in the following assays: a
bacterial reverse mutation assay using Salmonella and E. coli, a mouse lymphoma
assay (in the absence of metabolic activation), chromosomal aberration test in
Chinese hamsters, a bone marrow micronucleus test in mice and Chinese hamsters,
and a dominant lethal mutation test in mice. Mutagenic results occurred in the
presence of metabolic activation in the mouse lymphoma assay and micronucleus
test in rats. Overall, the weight of evidence from these tests indicates that
tramadol does not pose a genotoxic risk to humans.
No effects on fertility were observed for tramadol at
oral dose levels up to 50 mg/kg/day in male and female rats (1.6-fold the
MDHD).
Clinical Studies
ConZip™ is bioequivalent under fasting conditions to
another extended-release tramadol product [see CLINICAL PHARMACOLOGY]
which did demonstrate efficacy in two of four clinical trials of patients with
chronic pain. 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).
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 with the extended-release tramadol product was
initiated at 100 mg once daily 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 active 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 extended-release tramadol product 200 mg, 300 mg and
400 mg treatment groups (20%, 27%, and 30% of discontinuations, respectively) compared
to 14% of the patients treated with the extended-release tramadol product 100
mg and 10% 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 2).
Figure 2: Tramadol ER Tablets Study 023 WOMAC Pain
Responder Analysis Patients Achieving Various Levels of Response Threshould
 |
In one 12-week randomized, double-blind,
placebo-controlled flexible-dosing trial of the extended-release tramadol
product in patients with osteoarthritis of the knee, patients titrated to an
average daily dose of approximately 270 mg/day. Forty-nine percent of patients
randomized to the active treatment group completed the study, while 52% of patients
randomized to placebo completed the study. Most of the early discontinuations
in the active 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. Thirtyseven percent of the placebo-treated patients discontinued
the study due to lack of efficacy compared to 15% of active-treated patients.
The active treatment group demonstrated a statistically significant decrease in
the mean Visual Analog Scale (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
the extended-release tramadol product and placebo (see Figure 3).
Figure 3: Tramadol ER Tablets Study 015 Arthritis Pain
VAS Responder Analysis Patients Achieving Various Levels of Response Threshould
Four randomized, placebo-controlled clinical trials of
ConZip™ were conducted, none of which demonstrated efficacy but which differed
in design from the preceding clinical studies described. Two trials were
12-week randomized placebo-controlled trials of ConZip™ 100 mg/day, 200 mg/day,
and 300 mg/day versus placebo in patients with moderate to moderately severe
osteoarthritis pain of the hip and knee. The other two 12 week trials were
similar in design, but only studied ConZip™ 300 mg/day. In this fixed-dose design,
subjects were required to titrate to a fixed dose, even if their pain responded
to a lower titration dose.