Absorption
The absolute oral bioavailability of oxymorphone is approximately 10%.
Steady-state levels are achieved after three days of multiple dose administration. Under both single-dose and steady-state conditions, dose proportionality has been established for the 5 mg, 10 mg, 20 mg, and 40 mg doses of oxymorphone hydrochloride extended-release tablets, for both peak plasma levels (Cmax) and extent of absorption (AUC) (see Table 4).
Table 4: Mean (± SD) Oxymorphone Hydrochloride Extended-Release Tablets Pharmacokinetic Parameters |
Regimen | Dosage | Cmax (ng/mL) | AUC (ng•hr/mL) | T1/2 (hr) |
Single Dose | 5 mg | 0.27 ± 0.13 | 4.54 ± 2.04 | 11.30 ± 10.81 |
10 mg | 0.65 ± 0.29 | 8.94 ± 4.16 | 9.83 ± 5.68 |
20 mg | 1.21 ± 0.77 | 17.81 ± 7.22 | 9.89 ± 3.21 |
40 mg | 2.59 ± 1.65 | 37.90 ± 16.20 | 9.35 ± 2.94 |
Multiple Dosea | 5 mg | 0.70 ± 0.55 | 5.60 ± 3.87 | NA |
10 mg | 1.24 ± 0.56 | 9.77 ± 3.52 | NA |
20 mg | 2.54 ± 1.35 | 19.28 ± 8.32 | NA |
40 mg | 4.47 ± 1.91 | 36.98 ± 13.53 | NA |
NA = not applicable a Results after 5 days of q12h dosing. |
Food Effect
Two studies examined the effect of food on the bioavailability of single doses of 20 and 40 mg of oxymorphone hydrochloride extended-release tablets in healthy volunteers. In both studies, after the administration of oxymorphone hydrochloride extended-release tablets, the Cmax was increased by approximately 50% in fed subjects compared to fasted subjects. A similar increase in Cmax was also observed with oxymorphone solution.
The AUC was unchanged in one study and increased by approximately 18% in the other study in fed subjects following the administration of oxymorphone hydrochloride extended-release tablets. Examination of the AUC suggests that most of the difference between fed and fasting conditions occurs in the first four hours after dose administration. After oral dosing with a single dose of 40 mg, a peak oxymorphone plasma level of 2.8 ng/mL is achieved at 1 hour in fasted subjects and a peak of 4.25 ng/mL is achieved at 2 hours in fed subjects and that beyond the 12 hour time point, there is very little difference in the curves. As a result, oxymorphone hydrochloride extended-release tablets should be dosed at least one hour prior to or two hours after eating [see Dosage and Administration (2.1, 2.2)].
Distribution
Formal studies on the distribution of oxymorphone in various tissues have not been conducted. Oxymorphone is not extensively bound to human plasma proteins; binding is in the range of 10% to 12%.
Metabolism
Oxymorphone is highly metabolized, principally in the liver, and undergoes reduction or conjugation with glucuronic acid to form both active and inactive metabolites. The two major metabolites of oxymorphone are oxymorphone-3-glucuronide and 6-OH-oxymorphone. The mean plasma AUC for oxymorphone-3-glucuronide is approximately 90-fold higher than the parent compound. The pharmacologic activity of the glucuronide metabolite has not been evaluated. 6-OH-oxymorphone has been shown in animal studies to have analgesic bioactivity. The mean plasma 6-OH-oxymorphone AUC is approximately 70% of the oxymorphone AUC following single oral doses, but is essentially equivalent to the parent compound at steady-state.
Excretion
Because oxymorphone is extensively metabolized, < 1% of the administered dose is excreted unchanged in the urine. On average, 33% to 38% of the administered dose is excreted in the urine as oxymorphone-3-glucuronide and less than 1% excreted as 6-OH-oxymorphone in subjects with normal hepatic and renal function. In animals given radiolabeled oxymorphone, approximately 90% of the administered radioactivity was recovered within 5 days of dosing. The majority of oxymorphone-derived radioactivity was found in the urine and feces.
Specific Populations
Geriatric Patients
The steady-state plasma concentrations of oxymorphone, 6-OH-oxymorphone, and oxymorphone-3-glucuronide are approximately 40% higher in elderly subjects (≥ 65 years of age) than in young subjects (18 to 40 years of age). On average, age greater than 65 years was associated with a 1.4-fold increase in oxymorphone AUC and a 1.5-fold increase in Cmax. This observation does not appear related to a difference in body weight, metabolism, or excretion of oxymorphone [see Use in Specific Populations (8.5)].
Gender
The effect of gender was evaluated following single- and multiple-doses of oxymorphone hydrochloride extended-release tablets in male and female adult volunteers. There was a consistent tendency for female subjects to have slightly higher AUCss and Cmax values than male subjects; however, gender differences were not observed when AUCss and Cmax were adjusted by body weight.
Hepatic Impairment
The bioavailability of orally administered oxymorphone is markedly increased in patients with moderate to severe liver disease. The disposition of oxymorphone was compared in six patients with mild, five patients with moderate, and one patient with severe hepatic impairment and 12 subjects with normal hepatic function. The bioavailability of oxymorphone was increased by 1.6-fold in patients with mild hepatic impairment and by 3.7-fold in patients with moderate hepatic impairment. In one patient with severe hepatic impairment, the bioavailability was increased by 12.2-fold. The half-life of oxymorphone was not significantly affected by hepatic impairment.
Renal Impairment
Data from a pharmacokinetic study involving 24 patients with renal dysfunction show an increase of 26%, 57%, and 65% in oxymorphone bioavailability in mild (creatinine clearance 51 to 80 mL/min; n = 8), moderate (creatinine clearance 30 to 50 mL/min; n = 8), and severe (creatinine clearance < 30 mL/min; n = 8) patients, respectively, compared to healthy controls.
Drug Interaction/Alcohol Interaction
An in vivo study of the effect of alcohol (40%, 20%, 4% and 0%) on the bioavailability of a single dose of 40 mg of oxymorphone hydrochloride extended-release tablets in healthy, fasted volunteers demonstrated a highly variable effect on Cmax with concomitant administration of alcohol and oxymorphone hydrochloride extended-release tablets. The change in Cmax ranged from a decrease of 50% to an increase of 270% across all conditions studied. Following administration of 240 mL of 40% ethanol, the Cmax increased on average by 70% and up to 270% in individual subjects. Following the concomitant administration of 240 mL of 20% ethanol, the Cmax increased on average by 31% and up to 260% in individual subjects. Following the concomitant administration of 240 mL of 4% ethanol, the Cmax increased 7% on average and by as much as 110% for individual subjects. After oral dosing with a single dose of 40 mg in fasted subjects, the mean peak oxymorphone plasma level is 2.4 ng/mL and the median Tmax is 2 hours. Following co-administration of oxymorphone hydrochloride extended-release tablets and alcohol (240 mL of 40% ethanol) in fasted subjects, the mean peak oxymorphone level is 3.9 ng/mL and the median Tmax is 1.5 hours (range 0.75 to 6 hours). The oxymorphone mean AUC was 13% higher after co-administration of 240 mL of 40% alcohol. The AUC was essentially unaffected in subjects following the co-administration of oxymorphone hydrochloride extended-release tablets and ethanol (240 mL of 20% or 4% ethanol).
In vitro studies have demonstrated that oxymorphone hydrochloride extended-release tablets do not release oxymorphone more rapidly in 500 mL of 0.1N HCl solutions containing ethanol (4%, 20%, and 40%),
Instruct patients to avoid use of alcohol when taking oxymorphone hydrochloride extended-release tablets.
In vitro studies revealed little to no biotransformation of oxymorphone to 6-OH-oxymorphone by any of the major cytochrome P450 (CYP P450) isoforms at therapeutically relevant oxymorphone plasma concentrations.
No inhibition of any of the major CYP P450 isoforms was observed when oxymorphone was incubated with human liver microsomes at concentrations of ≤ 15.1 mcg/mL. An inhibition of CYP3A4 activity occurred at oxymorphone concentrations ≥ 45.3 mcg/mL. Therefore, it is not expected that oxymorphone, or its metabolites will act as inhibitors of any of the major CYP P450 enzymes in vivo.
Increases in the activity of the CYP 2C9 and CYP 3A4 isoforms occurred when oxymorphone was incubated with human hepatocytes. However, clinical drug interaction studies with oxymorphone hydrochloride extended-release tablets showed no induction of CYP450 3A4 or 2C9 enzyme activity, indicating that no dose adjustment for CYP 3A4- or 2C9-mediated drug-drug interactions is required.