• Efficacy of FBT treatment compared with oxycodone treatment in alleviating BTP as assessed by the PID, the sum of the pain intensity differences (SPID), and the percentage change in PID (% PID) at specific intervals after study drug administration. [ Time Frame: Up to 6 weeks double-blind administration period ] [ Designated as safety issue: No ]
• Evaluate the efficacy of FBT treatment compared with immediate-release oxycodone treatment in alleviating BTP, through the Patient's assessment of pain relief. [ Time Frame: End of Double-Blind Treatment Period ] [ Designated as safety issue: No ]
• Evaluate the efficacy of FBT treatment compared with oxycodone treatment in alleviating BTP as assessed by the Clinical Global Impression of Change (CGIC) and the Patient Global Impression of Change (PGIC) questionnaires. [ Time Frame: Weeks 4, 8, and 12 of open-label extension ] [ Designated as safety issue: No ]
• Evaluate the effect on patient function as measured by the Patient Assessment of Function (PAF) and Clinician Assessment of Patient Function (CAPF). [ Time Frame: Weeks 4, 8, and 12 of open-label extension ] [ Designated as safety issue: No ]
• Evaluate the safety of FBT treatment as assessed by vital signs measurements, clinical laboratory test results, oral mucosal and physical examination findings, and concomitant medication usage throughout the study [ Time Frame: During the 6 month study, including extension ] [ Designated as safety issue: Yes ]

Evaluate the efficacy of treatment with the fentanyl buccal tablet (FBT) compared with immediate release oxycodone treatment in alleviating breakthrough pain (BTP) in opioid tolerant patients with chronic pain.

Key Inclusion Criteria:

• The patient has chronic pain of at least 3 months duration associated with any of the following conditions: diabetic peripheral neuropathy, postherpetic neuralgia, traumatic injury, complex regional pain syndrome, back pain, neck pain, fibromyalgia, chronic pancreatitis, osteoarthritis, rheumatoid arthritis, or cancer. Other chronic painful conditions may be evaluated for possible inclusion.
• The patient is currently using at least one of the following: at least 60 mg of oral morphine/day, or at least 25 mcg of transdermal fentanyl/hour, or at least 30 mg of oxycodone/day, or at least 8 mg of hydromorphone/day, or an equianalgesic dose of another opioid/day as ATC therapy for at least 7 days before administration of the first dose of study drug.
• The patient is willing to provide written informed consent, including a written opioid agreement form, to participate in this study.
• Women must be surgically sterile, 2 years postmenopausal, or, if of childbearing potential, using a medically accepted method of birth control and agree to continued use of this method for the duration of the study.
• Any patient with cancer should have a life expectancy of at least 3 months.
• The patient reports an average PI score, over the 24 hours prior to screening, of 6 or less (0=no pain through 10=pain as bad as you can imagine) for their chronic pain.
• The patient experiences, on average, at least 1 and less than 5 BTP episodes per day while taking ATC opioid therapy, and on average, the duration of each BTP episode is less than 4 hours during the screening period.
• The patient currently uses opioid therapy for alleviation of BTP episodes, occurring at the location of the chronic pain, and achieves at least partial relief.
• The patient must be willing and able to successfully self administer the study drug, comply with study restrictions, complete the electronic diary, and return to the clinic for scheduled study visits as specified in this protocol.

Key Exclusion Criteria:

• The patient has uncontrolled or rapidly escalating pain as determined by the investigator or has pain uncontrolled by therapy that could adversely impact the safety of the patient or that could be compromised by treatment with study drug.
• The patient has a recent history (within 5 years) or current evidence of alcohol or other substance abuse.
• The patient has known or suspected hypersensitivities, allergies, or other contraindications to any ingredient in either study drug.
• The patient has a diagnosis of chronic headache or migraine as the primary painful condition with associated BTP.
• The patient has cardiopulmonary disease that would, in the opinion of the investigator, significantly increase the risk of treatment with potent synthetic opioids.
• The patient has medical or psychiatric disease that, in the opinion of the investigator, would compromise the patient's safety or collected data.
• The patient has suicidal ideation at screening or has a history of suicidal ideation within 1 year or history of suicide attempt within 2 years before screening, or a diagnosis of bipolar disorder or history of schizophrenia
• The patient is expected to have surgery during the study that will impact the patient's chronic pain and/or BTP.
• The patient has had therapy before study drug treatment that, in the opinion of the investigator, could alter pain or response to pain medication.
• The patient is pregnant or lactating.
• The patient has participated in a previous study with FBT.
• The patient has participated in a study involving an investigational drug in the prior 30 days.
• The patient is currently using FBT or oral transmucosal fentanyl citrate for BTP.
• The patient is currently using immediate-release oxycodone for BTP and is unwilling to undergo re-titration.
• The patient has received a monoamine oxidase inhibitor (MAOI) within 14 days before the first treatment with study drug.
• The patient has any other medical condition or is receiving concomitant medication/therapy (e.g., regional nerve block) that could, in the opinion of the investigator, compromise the patient's safety or compliance with the study protocol, or compromise collected data.
• The patient is involved in active litigation in regard to the chronic pain currently being treated.
• The patient has a positive UDS for an illicit drug or a medication not prescribed for him/her or which is not medically explainable (i.e., active metabolites).
• The investigator feels that the patient is not suitable for the study for any reason (e.g., the patient's social history indicates an increased risk of drug diversion)
• Additional exclusion criteria will apply for patients who decide to participate in the pharmacokinetics assessment to be performed at designated study sites.