Prescription Drug Information: TRAMADOL HYDROCHLORIDE (Page 9 of 10)

12.3 Pharmacokinetics

The analgesic activity of tramadol is due to both parent drug and the M1 metabolite. Tramadol hydrochloride extended-release tablet is administered as a racemate and both the [-] and [+] forms of both tramadol and M1 are detected in the circulation.

The pharmacokinetics of tramadol hydrochloride extended-release tablets are approximately dose-proportional over a 100 to 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 tramadol hydrochloride extended-release 200 mg tablet administered once daily relative to a 50 mg immediate-release (IR) tablet (tramadol hydrochloride) administered every six hours was approximately 85 to 90%. Consistent with the extended-release nature of the formulation, there is a lag time in drug absorption following tramadol hydrochloride extended-release tablets administration. The mean peak plasma concentrations of tramadol and M1 after administration of tramadol hydrochloride extended-release tablets to healthy volunteers are attained at about 12 h and 15 h, respectively, after dosing (see Table 3 and Figure 1). Following administration of the tramadol hydrochloride extended-release tablets, 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 tramadol hydrochloride extended-release tablets 200 mg administered once daily and tramadol HCl IR (tramadol hydrochloride) 50 mg administered every six hours are provided in Table 3.

Table 3: Mean (%CV) Steady-State Pharmacokinetic Parameter Values (n=32)
Tramadol M1 Metabolite
Pharmacokinetic Parameter Tramadol Hydrochloride Extended Release 200 mg Tablet Once Daily Tramadol Hydrochloride 50 mg Tablet Every 6 Hours Tramadol Hydrochloride Extended Release 200 mg Tablet Once Daily Tramadol Hydrochloride 50 mg Tablet Every 6 Hours
AUC 0 t o 2 4 (ng∙h/mL) 5975 (34) 6613 (27) 1890 (25) 2095 (26)
C m a x (ng/mL) 335 (35) 383 (21) 95 (24) 104 (24)
C m i n (ng/mL) 187 (37) 228 (32) 69 (30) 82 (27)
T m a x (h) 12 (27) 1.5 (42) 15 (27) 1.9 (57)
% Fluctuation 61 (57) 59 (35) 34 (72) 26 (47)

AUC 0 to 24 : Area Under the Curve in a 24-hour dosing interval; C max : Peak Concentration in a 24- hour dosing interval; C min : Trough Concentration in a 24-hour dosing interval; T max : Time to Peak Concentration

Figure 1: Mean Steady-State Tramadol (a) and M1 (b) Plasma Concentrations on Day 8 Post Dose after Administration of 200 mg Tramadol Hydrochloride Extended-Release Tablets Once-Daily and 50 mg Tramadol Hydrochloride Tablets Every 6 Hours.

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Food Effects

After a single dose administration of 200 mg tramadol hydrochloride extended-release tablet with a high fat meal, the C max and AUC 0 to ∞ of tramadol decreased 28% and 16%, respectively, compared to fasting conditions. Mean T max was increased by 3 hr (from 14 hr under fasting conditions to 17 hr under fed conditions). While tramadol hydrochloride extended-release tablets may be taken without regard to food, it is recommended that it be taken in a consistent manner [see Dosage and Administration ( 2.1)] .

Distribution

The volume of distribution of tramadol was 2.6 and 2.9 L/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 mcg/mL. Saturation of plasma protein binding occurs only at concentrations outside the clinically relevant range.

Elimination

Tramadol is eliminated primarily through metabolism by the liver and the metabolites are eliminated primarily by the kidneys. The mean terminal plasma elimination half-lives of racemic tramadol and racemic M1 after administration of tramadol hydrochloride extended-release tablets are approximately 7.9 and 8.8 hours, respectively.

Metabolism

Tramadol is extensively metabolized after oral administration. The metabolic pathways appear to be N – demethylation (mediated by CYP3A4 and CYP2D6), O – demethylation (mediated by CYP2D6) and glucuronidation or sulfation in the liver. The CYP2D6 metabolite, O-desmethyl tramadol, (denoted M1) is observed to be 6 times more potent than tramadol in producing analgesia and 200 times more potent in µ-opioid binding in animal models.

Excretion

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.

Special Populations

Hepatic Impairment

Pharmacokinetics of tramadol was studied in patients with mild or moderate hepatic impairment after receiving multiple doses of tramadol hydrochloride extended-release tablets 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 active metabolite (+)- 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 tramadol hydrochloride extended-release tablets has not been studied in patients with severe hepatic impairment (Child-Pugh Class C). After the administration of tramadol IR tablets to patients with advanced cirrhosis of the liver, tramadol exposure was increased and the tramadol and M1 half-lives were longer than patients with normal hepatic function [see Use in Specific Populations ( 8.6)] .

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 were studied in patients with mild or moderate renal impairment after receiving multiple doses of tramadol hydrochloride extended-release tablets 100 mg. There is no consistent trend observed for tramadol exposure related to renal function in patients with mild (CLcr: 50 to 80 mL/min) or moderate (CLcr: 30 to 50 mL/min) renal impairment in comparison to patients with normal renal function. However, exposure of M1 increased 20 to 40% with increased severity of the renal impairment (from normal to mild and moderate). Tramadol hydrochloride extended-release tablet has not been studied in patients with severe renal impairment (CLcr < 30 mL/min). The total amount of tramadol and M1 removed during a 4-hour dialysis period is less than 7% of the administered dose [see Use in Specific Populations ( 8.7)].

Sex

Based on pooled multiple-dose pharmacokinetics studies for tramadol hydrochloride extended-release tablets 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 sex is not recommended.

Age: Geriatric Population

The effect of age on pharmacokinetics of tramadol hydrochloride extended-release tablet 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 younger 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 half-life 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 ( 2.4].

Drug Interaction Studies

Potential for Tramadol to Affect Other Drugs

In vitro studies indicate that tramadol is unlikely to inhibit the CYP3A4-mediated metabolism of other drugs when tramadol is administered concomitantly at therapeutic doses. Tramadol does not appear to induce its own metabolism in humans, since observed maximal plasma concentrations after multiple oral doses are higher than expected based on single-dose data.

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 P450 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 hydrochloride extended-release tablets resulted in a 50 to 60% increase in tramadol exposure and a 50 to 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 ( 5.6), Drug Interactions ( 7)] .

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 tramadol hydrochloride extended-release tablets may affect the metabolism of tramadol leading to altered tramadol exposure [see Warnings and Precautions ( 5.6), Drug Interactions ( 7)] .

Cimetidine

Concomitant administration of tramadol IR tablets with cimetidine, a weak CYP3A4 inhibitor, does not result in clinically significant changes in tramadol pharmacokinetics. No alteration of the tramadol hydrochloride extended-release tablets 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 tramadol hydrochloride extended-release tablets and carbamazepine is not recommended.

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