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Mechanism Of Action
Oxycodone HCl is an opioid agonist and is relatively selective for the mu receptor, although it can interact with other opioid receptors at higher doses. The principal therapeutic action of oxycodone is analgesia. Like all opioid agonists, there is no ceiling effect to analgesia.
Acetaminophen is a non-opioid, non-salicylate analgesic, and antipyretic. The site and mechanism for the analgesic effect of acetaminophen has not been determined. The antipyretic effect of acetaminophen is accomplished through the inhibition of endogenous pyrogen action on the hypothalamic heat-regulating centers.
Effects on Central Nervous System
Oxycodone produces respiratory depression by direct action on brainstem respiratory centers. The respiratory depression involves both a reduction in the responsiveness of the brain stem respiratory centers to increases in carbon dioxide tension and to electrical stimulation.
Oxycodone depresses the cough reflex by direct effect on the cough center in the medulla. Oxycodone causes miosis, even in total darkness. Pinpoint pupils are a sign of opioid overdose but are not pathognomonic (e.g., pontine lesions of hemorrhagic or ischemic origins may produce similar findings). Marked mydriasis rather than miosis may be seen due to hypoxia in overdose situations.
Effects on Gastrointestinal Tract and Other Smooth Muscle
Gastric, biliary, and pancreatic secretions are decreased by oxycodone HCl. Oxycodone, like other opioid analgesics, produces some degree of nausea and vomiting which is caused by direct stimulation of the chemoreceptor trigger zone located in the medulla. The frequency and severity of emesis gradually diminishes with time.
Oxycodone may cause a decrease in the secretion of hydrochloric acid in the stomach that reduces motility while increasing the tone of the antrum of the stomach, and duodenum. Digestion of food in the small intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon are decreased, while tone may be increased to the point of spasm resulting in constipation. Other opioid-induced effects may include a reduction in biliary and pancreatic secretions, spasm of Sphincter of Oddi, and transient elevations in serum amylase.
Effects on Cardiovascular System
Oxycodone, in therapeutic doses, produces peripheral vasodilation (arterial and venous), decreased peripheral resistance, and inhibits baroreceptor reflexes. Manifestations of histamine release and/or peripheral vasodilation may include pruritus, flushing, red eyes, sweating, and/or orthostatic hypotension.
Caution must be used in hypovolemic patients, such as those suffering acute myocardial infarction, because oxycodone may cause or further aggravate their hypotension. Caution must also be used in patients with cor pulmonale who have received therapeutic doses of opioids.
Opioid agonists have been shown to have a variety of effects on the secretion of hormones. Opioids inhibit the secretion of ACTH, cortisol, and luteinizing hormone (LH) in humans. They also stimulate prolactin, growth hormone (GH) secretion, and pancreatic secretion of insulin and glucagon in humans and other species, rats, and dogs. Thyroid stimulating hormone (TSH) has been shown to be both inhibited and stimulated by opioids.
Opioids have been shown to have a variety of effects on components of the immune system in in vitro and animal models. The clinical significance of these findings is unknown.
XARTEMIS XR is an extended-release bilayer formulation of oxycodone and acetaminophen (immediate-and extended-release layers) which is not interchangeable with other oxycodone/acetaminophen products because of differing pharmacokinetic profiles that affect the frequency of administration. The activity of oxycodone hydrochloride is primarily due to the parent drug oxycodone.
The oral bioavailability of oxycodone is 60 to 87%. Bioavailability (dose-normalized AUC and Cmax) of oxycodone and acetaminophen following single- and multiple-doses of XARTEMIS XR tablets is comparable to immediate-release products containing oxycodone or acetaminophen.
Oxycodone plasma concentrations from this bilayer product are detectable within 30 minutes and reach a maximum concentration (Cmax) in 3 to 4 hours after XARTEMIS XR administration. Maximum plasma concentrations of acetaminophen occur in 0.75 to 1 hour after XARTEMIS XR administration.
Steady-state plasma concentrations of oxycodone and acetaminophen are achieved within 24 hours of initiation of dosing of XARTEMIS XR (prior to the third dose of two XARTEMIS XR tablets administered every 12 hours). XARTEMIS XR produces steady-state maximum plasma concentrations of oxycodone that are greater than those following the first dose, while concentrations of acetaminophen are comparable to the first dose (Table 2).
Table 2: Mean (SD) Pharmacokinetics of XARTEMIS XR
(two 7.5 mg oxycodone and 325 mg acetaminophen extended-release tablets; after
a single dose and multiple doses every 12 hours for 4.5 days)
|AUC0-12h (ng•h/mL)||136 (24)||208 (45)||24924 (5667)||28160 (5807)|
|Cmax (ng/mL)||16.0 (3.6)||24.0 (5.4)||4858 (1066)||4793 (1132)|
|Cmin (ng/mL)||6.9 (2.0)||9.3 (2.4)||738 (227)||853 (273)|
|Fluctuation (%)†||NA||83.9 (17.6)||NA||169.1 (39.8)|
|Tmax (h) ‡||3||3||1||1|
|t½ (h)||NA||5.4 (0.9)||NA||6.9 (1.8)|
|* Steady-state results on Day 5 (0-12 hours); † Fluctuation = 100•(Cmax-Cmin)/Cavg; ‡ Median reported for Tmax; NA = not applicable|
When administered with a high- or low-fat meal, median Tmax values of oxycodone were delayed by 2 hours and 1 hour, respectively. Mean AUC values are increased by 15 to 16% and peak concentrations are 12 to 25% higher for oxycodone. Food delayed median acetaminophen Tmax by 1.5 hours. There is no change in mean acetaminophen AUC values and peak concentrations are 23 to 24% lower with food. XARTEMIS XR may be administered with or without food.
Following intravenous administration, the volume of distribution (Vss) for oxycodone was 2.6 L/kg. Oxycodone was approximately 45% bound to plasma protein at 37°C and a pH of 7.4. Oxycodone has been found in breast milk [see Use In Specific Populations].
Acetaminophen appears to be widely distributed throughout most body tissues except fat. Its apparent volume of distribution is about 0.9 L/kg. A relative small portion (~20%) of acetaminophen is bound to plasma protein.
Oxycodone hydrochloride is extensively metabolized to noroxycodone, oxymorphone, and their glucuronides. The major circulating metabolite is noroxycodone with an AUC ratio of 0.6 relative to that of oxycodone. Oxymorphone is present in the plasma only in low concentrations. The analgesic activity profile of other metabolites is not known at present.
The formation of oxymorphone, but not noroxycodone, is mediated by CYP2D6 and as such its formation can, in theory, be affected by other drugs [see WARNINGS AND PRECAUTIONS].
Acetaminophen is primarily metabolized in the liver by first-order kinetics and involves three principal separate pathways:
- conjugation with glucuronide;
- conjugation with sulfate; and
- oxidation via the cytochrome, P450-dependent, mixed-function oxidase enzyme pathway to form a reactive intermediate metabolite, which conjugates with glutathione and is then further metabolized to form cysteine and mercapturic acid conjugates.
The principal cytochrome P450 isoenzyme involved appears to be CYP2E1, with CYP1A2 and CYP3A4 as additional pathways.
In adults, the majority of acetaminophen is conjugated with glucuronic acid and, to a lesser extent, with sulfate. These glucuronide-, sulfate-, and glutathione-derived metabolites lack biologic activity. In premature infants, newborns, and young infants, the sulfate conjugate predominates.
Oxycodone and its metabolites are eliminated primarily via the kidney. The amounts measured in the urine have been reported as follows: free oxycodone up to 19%; conjugated oxycodone up to 50%; free oxymorphone 0%; and conjugated oxymorphone ≤ 14%. Both free and conjugated noroxycodone have been found in urine but not quantified. The total plasma clearance was 0.8 L/min for adults. Apparent elimination half-life (mean ± SD) of oxycodone following administration of XARTEMIS XR was 4.5 ± 0.6 hours as compared to 3.9 ± 0.3 hours for immediate-release oxycodone.
Acetaminophen is eliminated from the body primarily by formation of glucuronide and sulfate conjugates in a dose-dependent manner Less than 9% of acetaminophen is excreted unchanged in urine. Following administration of XARTEMIS XR, the apparent elimination half-life is 5.8 ± 2.1 hours as compared to 4.1 ± 1.1 hours for immediate-release acetaminophen.
Elderly: Population pharmacokinetic studies indicate that the plasma concentrations of oxycodone did not appear to be increased in patients over the age of 65. A population pharmacokinetic analysis of data obtained from a clinical trial in patients with chronic pain which included 55 patients between 65 and 75 years of age and 19 patients over 75 years of age, showed no significant changes in the pharmacokinetics of acetaminophen in elderly patients with normal renal and hepatic function.
Gender: Population pharmacokinetic analyses performed in a clinical study support the lack of gender effect on the pharmacokinetics of oxycodone.
Hepatic Impairment: The pharmacokinetics of XARTEMIS XR in patients with impaired hepatic function has not been studied. Oxycodone and acetaminophen are extensively metabolized, resulting in decreased clearance in patients with hepatic impairment [see Use in Specific Populations].
Renal Impairment: The pharmacokinetics of XARTEMIS XR in patients with renal impairment has not been studied. Patients with renal impairment (defined as creatinine clearance < 60 mL/min) have higher plasma concentrations of oxycodone than subjects with normal renal function [see Use in Specific Populations].
Post-Operative Bunionectomy Pain Study
Efficacy was demonstrated in one multicenter, randomized, double-blind, placebo-controlled, parallel-arm, multiple-dose clinical trial comparing XARTEMIS XR and placebo in patients with acute pain following a unilateral first metatarsal bunionectomy. A total of 303 patients with a mean age of 43 (range 18 to 73) years, meeting criteria for randomization (pain intensity ≥ 4 on a 0 to 10 numerical pain rating scale) and receiving a fixed-dose of 2 tablets of XARTEMIS XR 7.5 mg oxycodone hydrochloride and 325 mg acetaminophen tablets or placebo every 12 hours over 48 hours were randomized. There were 36 early discontinuations (9% from XARTEMIS XR, 13% from placebo). Ibuprofen 400 mg every 4 hours as needed was allowed as rescue medication.
Mean baseline pain intensity scores were 6.2 in the XARTEMIS XR group (range: 4 to 10) and 6.0 in the placebo group (range: 1 to 10). Approximately 85% of the 150 subjects treated with XARTEMIS XR and 98% of the 153 subjects treated with placebo took rescue medication at least once for pain management during the 48 hours after the first dose. Median rescue medication use was 2 doses for XARTEMIS XR-treated subjects and 4 doses for placebo-treated subjects over the 48 hours; rescue medication was used by less than 50% of the XARTEMIS XR-treated patients after the first dose interval. Pain intensity was recorded at 2, 4, 8, and 12 hours after each dose, with additional recordings at 15, 30, 45, 60, and 90 minutes after the first dose. The median time to onset of pain relief was less than one hour for XARTEMIS XR. The primary endpoint was the summed pain intensity difference (change in pain from baseline) over 48 hours (SPID48), which demonstrated improvement in pain from baseline for the XARTEMIS XR treatment group compared to placebo.
Last reviewed on RxList: 3/28/2014
This monograph has been modified to include the generic and brand name in many instances.
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