In the present study, we demonstrated that repeated treatment with fentanyl, but not morphine or oxycodone, causes a rapid desensitization to its ability to block the hyperalgesia associated with the attenuation of mu-opioid receptor resensitization in mice in a chronic pain-like state. In contrast, no such effect was noted in beta-endorphin knockout mice under the chronic pain-like conditions. On the assumption that beta-endorphin might be released within the spinal cord under pain-like conditions, we further examined whether beta-endorphin could be responsible for a desensitization and resensitization of fentanyl under the chronic pain. In cultured cells, unlike morphine, fentanyl and oxycodone induced a robust mu-opioid receptor internalization and, in turn, its resensitization. In the presence of beta-endorphin, the internalized mu-opioid receptor induced by fentanyl, but not oxycodone, remained within the cytosolic component even after washing out. The findings suggest that beta-endorphin could attenuate the resensitization of mu-opioid receptors. This phenomenon may explain the high degree of tolerance to fentanyl that develops with hyperalgesia caused by a chronic pain-like state.

OBJECTIVE: Although opioid analgesics are used in the management of neuropathic pain syndromes, evidence of their efficacy remains to be established. We evaluated the clinical efficacy and safety of oxycodone in neuropathic pain using postherpetic neuralgia as a model. METHODS: Patients with postherpetic neuralgia of at least moderate intensity were randomized to controlled-release oxycodone 10 mg or placebo every 12 hours, each for 4 weeks, using a double-blind, crossover design. The dose was increased weekly up to a possible maximum of 30 mg every 12 hours. Pain intensity and pain relief were assessed daily, and steady (ongoing) pain, brief (paroxysmal) pain, skin pain (allodynia), and pain relief were recorded at weekly visits. Clinical effectiveness, disability, and treatment preference were also assessed. RESULTS: Fifty patients were enrolled and 38 completed the study (16 men, 22 women, age 70+/-11 years, onset of postherpetic neuralgia 31+/-29 months, duration of pain 18+/-5 hours per day). The oxycodone dose during the final week was 45+/-17 mg per day. Compared with placebo, oxycodone resulted in pain relief (2.9+/-1.2 versus 1.8+/-1.1, p=0.0001) and reductions in steady pain (34+/-26 versus 55+/-27 mm, p=0.0001), allodynia (32+/-26 versus 50+/-30 mm, p=0.0004), and paroxysmal spontaneous pain (22+/-24 versus 42+/-32 mm, p=0.0001). Global effectiveness, disability, and masked patient preference all showed superior scores with oxycodone relative to placebo (1.8+/-1.1 versus 0.7+/-1.0, p=0.0001; 0.3+/-0.8 versus 0.7+/-1.0, p=0.041; 67% versus 11%, p=0.001, respectively). CONCLUSIONS: Controlled-release oxycodone is an effective analgesic for the management of steady pain, paroxysmal spontaneous pain, and allodynia, which frequently characterize postherpetic neuralgia.

BACKGROUND: Painful neuropathy is one of the most common long-term complications of diabetes mellitus and often proves difficult to relieve.METHODS: Patients with diabetic neuropathy with moderate or greater pain for at least 3 months, were evaluated for efficacy, safety and health-related quality of life (QOL) while receiving controlled-release (CR) oxycodone (OxyContin) or active placebo. Patients underwent washout from all opioids 2-7 days before randomization to 10 mg CR oxycodone or active placebo (0.25 mg benztropine) q12h. The dose was increased, approximately weekly, to a maximum of 40 mg q12h CR oxycodone or 1 mg q12h benztropine, with crossover to the alternate treatment after a maximum of 4 weeks. Acetaminophen, 325-650 mg q4-6h prn was provided as rescue.RESULTS: Thirty-six patients were evaluable for efficacy (21 men, 15 women, mean age 63.0+/-9.4 years). CR oxycodone resulted in significantly lower (P=0.0001) mean daily pain (21.8+/-20.7 vs. 48.6+/-26.6 mm VAS), steady pain (23.5+/-23.0 vs. 47.6+/-30.7 mm VAS), brief pain (21.8+/-23.5 vs. 46.7+/-30.8 mm VAS), skin pain (14.3+/-20.4 vs. 43.2+/-31.3 mm VAS), and total pain and disability (16.8+/-15.6 vs. 25.2+/-16.7; P=0.004). Scores from 6 of the 8 SF-36 domains and both summary scales, Standardized Physical Component (P=0.0002) and Standardized Mental Component (P=0.0338) were significantly better during CR oxycodone treatment. The number needed to treat to obtain one patient with at least 50% pain relief is 2.6 and clinical effectiveness scores favoured treatment with CR oxycodone over placebo (P=0.0001).CONCLUSION: CR oxycodone is effective and safe for the management of painful diabetic neuropathy and improves QOL.

In a double-blind crossover study, morphine and oxycodone hydrochloride were administered to 20 patients who were experiencing severe cancer pain. The peroral doses were determined on the basis of patient-controlled intravenous titration. The assumed oral bioavailability ratios were 44%(group 1, first 10 patients) and 33%(group 2, last 10 patients) for morphine and 66%(group 1) and 50%(group 2) for oxycodone hydrochloride, respectively. However, the patients were able to readjust their oral dosings. Equal analgesia was achieved with both drugs, but the intravenous dose of oxycodone hydrochloride needed was 30% higher than that of morphine. The median calculated oral/intravenous ratios giving comparable analgesia were 0.31 for morphine and 0.70 for oxycodone hydrochloride. Morphine caused more nausea than oxycodone hydrochloride and hallucinations occurred only during morphine treatment. Otherwise, there were no major differences in the side effects between these two opioids.

BACKGROUND: Oxycodone is metabolized in the liver by means of O-demethylation to form oxymorphone in a reaction catalyzed by the enzyme cytochrome P450 2D6 (CYP2D6). This enzyme is expressed as 2 phenotypes (extensive and poor metabolizers). Several drugs are metabolized by CYP2D6, and clinically relevant drug interactions may occur. The aim of this study was to evaluate the role of oxymorphone in mediating the opioid effects of oxycodone by means of blocking CYP2D6 with quinidine. METHODS: Ten healthy extensive metabolizers were administered 20 mg controlled-release oxycodone after premedication with placebo or 200 mg quinidine in this randomized, double-blind crossover study. A dose of 100 mg quinidine was administered 6 hours later. Plasma opioid concentrations, subjective pharmacodynamic ratings, and psychomotor function were assessed for 24 hours after drug administration. RESULTS: No oxymorphone was detected at any time after quinidine premedication in 8 of 10 subjects. Plasma oxycodone (difference not significant) and noroxycodone (P <.01) concentrations were greater after quinidine pretreatment. Prevention of the production of oxymorphone by quinidine did not affect the psychomotor or subjective drug effects of oxycodone. No difference in number of adverse effects was observed after the 2 pretreatments. CONCLUSIONS: A significant reduction in plasma oxymorphone levels did not substantially alter the pharmacodynamic effects of oxycodone. Analgesia was not evaluated because pain was not present.

PURPOSE: Use of oxycodone for chronic cancer pain has been hampered by its short elimination half-life. This study was designed to compare the efficacy and safety of controlled-release formulations of oxycodone and morphine for cancer pain. PATIENTS AND METHODS: Thirty-two adult patients with cancer pain and a > or = 3-day history of stable analgesia with oral opioids provided written informed consent and were randomized to controlled-release oxycodone or controlled-release morphine for 7 days. To blind the study using available tablet strengths, the dose ratio of oxycodone to morphine was set at 1:1.5. On day 8, patients were crossed over to the alternate drug for 7 days. Pain intensity was assessed using a visual analog scale (VAS 0 to 100 mm) and a categorical scale (CAT 0 to 4). Side effects were assessed using a checklist (four-point categorical severity) and a nondirected questionnaire. Patients and investigators made blinded global ratings of efficacy and treatment preference. RESULTS: Twenty-three patients completed the study (10 men, 13 women). The VAS and CAT scores were (mean+/-SD) 23+/-21 and 1.2+/-0.8 on controlled-release oxycodone, and 24+/-20 (P=.43) and 1.3+/-0.7 (P=.36) on controlled-release morphine. No period or carryover effect was detected. There were no significant differences in adverse effects (P=.40) or ratings of efficacy and preference. The median oxycodone/morphine dose ratio was 1.5 and the maximum was 2.3. CONCLUSION: Controlled-release oxycodone is as safe and effective as controlled-release morphine in the treatment of cancer pain.

1. The pharmacokinetics and metabolism of oxycodone were studied in nine healthy young volunteers in a cross-over study. Each subject received oxycodone chloride once intramuscularly (0.14 mg kg-1) and twice orally (0.28 mg kg-1) at intervals of 2 weeks. A double-blind randomized pretreatment with amitriptyline (10-50 mg a day) or placebo was given prior to oral oxycodone. 2. The concentrations of oxycodone, noroxycodone and oxymorphone in plasma and the 24 h urine recoveries of their conjugated and unconjugated forms were measured by gas chromatography. 3. No differences were found between treatments in mean Cmax and AUC values of oxycodone which varied from 34 to 38 ng ml-1 and from 208 to 245 ng ml-1 h, respectively. The median tmax of oxycodone was 1 h in all groups. The bioavailability of oral relative to i.m. oxycodone was 60%. The mean renal clearance of oxycodone was 0.07-0.08 l min-1. The kinetics of oxycodone were unaffected by amitriptyline. 4. The mean ratio of the AUC(0.24 h) values of unconjugated noroxycodone to oxycodone was 0.45 after i.m. oxycodone and 0.6-0.8 after oral oxycodone. Plasma oxymorphone concentrations were below the limit of the assay. Eight to 14% of the dose of oxycodone was excreted in the urine as unconjugated and conjugated oxycodone over 24 h. Oxymorphone was excreted mainly as a conjugate whereas noroxycodone was recovered mostly in an unconjugated form.

Plasma concentrations of oxycodone, oxymorphone, and noroxycodone were determined after administration of 20 mg oral controlled-release oxycodone tablets to four subject groups: young (aged 21 to 45 years) men, elderly (aged 65 to 79 years) men, young women, and elderly women. Area under the oxycodone and noroxycodone concentration-time curve (AUC) values were comparable among the four groups. Compared with oxycodone, the oxymorphone AUC values were small, with significant differences between subject groups. AUC values were also calculated for the pharmacodynamic variable "drug effect," scored on a 100 mm visual analog scale. The two groups with the highest oxycodone AUC values (young and elderly women) had the lowest oxymorphone AUC values and the greatest drug effect AUC values. The two groups with the lowest oxycodone AUC values (young and elderly men) had the highest oxymorphone AUC values and the lowest drug effect AUC values. These results support oxycodone, and not oxymorphone, as being primarily responsible for pharmacodynamic and analgesic effects.

BACKGROUND: The authors conducted two studies to compare the analgesic efficacy and safety of the cyclooxygenase, or COX,-2-specific inhibitor, valdecoxib, with oxycodone/ acetaminophen in patients who have undergone oral surgery. METHODS: In total, 205 eligible subjects in Study A and 201 in Study B were randomized to receive a single oral dose of valdecoxib (20 or 40 milligrams), a combination of oxycodone 10 mg/acetaminophen 1,000 mg or placebo. Eligible subjects experienced moderate-to-severe pain within six hours of surgery during which two or more impacted third molars were extracted. Analgesic efficacy was assessed over 24 hours or until the patient required rescue analgesia. RESULTS: In both studies, subjects receiving either dose of valdecoxib experienced a rapid onset of analgesia and (among those who received valdecoxib 40 mg) a level of pain relief comparable with that of those who received oxycodone/ acetaminophen. Both valdecoxib doses had a significantly longer duration of analgesic effect than did oxycodone/acetaminophen. Pooled safety data demonstrated that each valdecoxib dose had a tolerability profile superior to that of oxycodone/ acetaminophen and similar to that of placebo. CONCLUSIONS: Orally administered valdecoxib is as rapidly acting and effective as oxycodone/acetaminophen, and it has a superior duration of analgesic effect in patients after oral surgery. Valdecoxib has a tolerability profile superior to that of oxycodone/acetaminophen. CLINICAL IMPLICATIONS: The current standard of care for alleviating acute pain after oral surgery has rested largely on conventional nonsteroidal anti-inflammatory drugs or opioid/analgesic combination products. The studies reported here suggest that the COX-2-specific inhibitor valdecoxib offers an efficacious and safe alternative to other analgesics used to treat pain after oral surgery.

Reconstruction of the anterior cruciate ligament (ACL) of the knee is associated with a considerable degree of postoperative pain. Although immediate-release oral opioids are usually effective in relieving moderate to severe pain, they must be given every 4-6 h. A controlled-release (CR) formulation of oxycodone maintains therapeutic opioid concentrations for a more prolonged period, thus providing sustained pain relief. We designed this study to determine whether CR oxycodone is more effective and clinically acceptable than immediate-release oxycodone for managing pain after ambulatory ACL repair surgery. All patients received a standard general anesthetic and postoperative analgesic regimen with one of three oxycodone dosing regimens: oxycodone 10 mg every 4 h as needed, oxycodone 10 mg every 4 h, and CR oxycodone 20 mg every 12 h. Rescue analgesic consisted of oxycodone 5 mg every 6 h as needed. At 24, 36, 48, 60, and 72 h, there was a difference in pain scores among the groups (P < 0.0001); there was less pain in the CR oxycodone group. At most times, the fixed-dose group had lower pain scores than the as-needed group. The sedation scores were significantly different at 12 h (P < 0.02) and at 24, 36, 48, 60, and 72 h (P < 0.0001); the patients were more alert in the CR oxycodone group. The 72-h consumption of oxycodone was less in the CR oxycodone group (P < 0.0001). The patients had less sleep disturbance (P < 0.0001), were more satisfied (P < 0.0001), and experienced less vomiting (P < 0.02) in the CR oxycodone group compared with the other two groups. In conclusion, using CR oxycodone in the immediate 72 h after ambulatory ACL surgery provides more effective analgesia with less sedation, sleep disturbance, and postoperative vomiting compared with oxycodone prescribed on either a fixed dose or as-needed schedule. IMPLICATIONS: A controlled-release formulation of oxycodone in patients undergoing anterior cruciate ligament repair on an ambulatory basis provides significant analgesic benefit and a lowering of side effects compared with either fixed-dose or as-needed oxycodone regimens.

OBJECTIVE: To compare the efficacy and safety of controlled-release oxycodone given every 12 hours with immediate-release oxycodone given four times daily in patients with persistent back pain. DESIGN: Randomized, double-blind, active-controlled, two-period crossover trial. PATIENTS: Fifty-seven adult outpatients with stable, chronic, moderate-to-severe low back pain despite analgesic therapy were enrolled; 47 were randomized; 11 discontinued for side effects, most commonly nausea and vomiting. INTERVENTIONS: Controlled-release oxycodone tablets given every 12 hours; immediate-release oxycodone tablets given four times daily; dose titration with controlled-release or immediate-release for up to 10 days; double-blind treatment for 4-7 days each. OUTCOME MEASURES: Patients' pain scores (0 = none, 1 = slight, 2 = moderate, 3 = severe). RESULTS: Pain intensity decreased from moderate to severe at baseline to slight at the end of titration with both oxycodone formulations. The daily oxycodone dose was 40 mg or less in 68% of patients. During double-blind treatment, mean pain intensity was maintained at 1.2 (0.1 SE) with controlled-release and at 1.1 (0.1 SE) with immediate-release oxycodone. The most common adverse events were constipation, nausea, pruritus, somnolence, and dizziness. CONCLUSIONS: Controlled-release oxycodone given every 12 hours was comparable with immediate-release oxycodone given four times daily in efficacy and safety, and it provides convenient, twice-daily, around-the-clock treatment for selected patients with persistent back pain that is inadequately controlled by nonopioids or as-needed opioid therapy.