Pharmacokinetics: After oral administration, approximately 80% of a radiolabeled dose of nabumetone is found in the urine, indicating that nabumetone is well absorbed from the gastrointestinal tract. Nabumetone itself is not detected in the plasma because, after absorption, it undergoes rapid biotransformation to the principal active metabolite, 6- methoxy-2-naphthylacetic acid (6MNA). Approximately 35% of a 1,000 mg oral dose of nabumetone is converted to 6MNA and 50% is converted into unidentified metabolites which are subsequently excreted in the urine. Following oral administration of nabumetone, 6MNA exhibits pharmacokinetic characteristics that generally follow a one-compartment model with first order input and first order elimination.

6MNA is more than 99% bound to plasma proteins. The free fraction is dependent on total concentration of 6MNA and is proportional to dose over the range of 1,000 mg to 2,000 mg. It is 0.2% to 0.3% at concentrations typically achieved following administration of 1,000 mg of nabumetone and is approximately 0.6% to 0.8% of the total concentrations at steady state following daily administration of 2,000 mg.

Steady-state plasma concentrations of 6MNA are slightly lower than predicted from single-dose data. This may result from higher fraction of unbound 6MNA which undergoes greater hepatic clearance.

Coadministration of food increases the rate of absorption and subsequent appearance of 6MNA in the plasma but does not affect the extent of conversion of nabumetone into 6MNA. Peak plasma concentrations of 6MNA are increased by approximately one third.

Coadministration with an aluminum-containing antacid had no significant effect on the bioavailability of 6MNA.

The simulated curves in the graph below illustrate the range of active metabolite plasma concentrations that would be expected from 95% of patients following 1,000-mg to 2,000-mg doses to steady state. The cross-hatched area represents the expected overlap in plasma concentrations due to intersubject variation following oral administration of 1,000 mg to 2,000 mg of nabumetone.

6MNA undergoes biotransformation in the liver, producing inactive metabolites that are eliminated as both free metabolites and conjugates. None of the known metabolites of 6MNA has been detected in plasma. Preliminary in vivo and in vitro studies suggest that unlike other NSAIDs, there is no evidence of enterohepatic recirculation of the active metabolite. Approximately 75% of a radiolabeled dose was recovered in urine in 48 hours.
Approximately 80% was recovered in 168 hours. A further 9% appeared in the feces. In the first 48 hours, metabolites consisted of:

Following oral administration of dosages of 1,000 mg to 2,000 mg to steady state, the mean plasma clearance of 6MNA is 20 to 30 mL/min and the elimination half-life is approximately 24 hours.

Osteoarthritis: The use of nabumetone in relieving the signs and symptoms of osteoarthritis (OA) was assessed in double-blind, controlled trials in which 1,047 patients were treated for 6 weeks to 6 months. In these trials, nabumetone in a dose of 1,000 mg/day administered at night was comparable to naproxen 500 mg/day and to aspirin 3,600 mg/day.

Rheumatoid Arthritis: The use of nabumetone in relieving the signs and symptoms of rheumatoid arthritis (RA) was assessed in double-blind, randomized, controlled trials in which 770 patients were treated for 3 weeks to 6 months. Nabumetone, in a dose of 1,000 mg/day administered at night, was comparable to naproxen 500 mg/day and to aspirin 3,600 mg/day.

In controlled clinical trials of rheumatoid arthritis patients, nabumetone has been used in combination with gold, d-penicillamine, and corticosteroids.

Patient Exposure in Clinical Trials of Osteoarthritis and Rheumatoid Arthritis:

In clinical trials with osteoarthritis and rheumatoid arthritis patients, most patients responded to nabumetone in doses of 1,000 mg/day administered nightly; total daily dosages up to 2,000 mg were used. In open-labeled studies, 1,490 patients were permitted dosage increases and were followed for approximately 1 year (mode). Twenty percent of patients (n = 294) were withdrawn for lack of effectiveness during the first year of these open-labeled studies. The following table provides patient exposure to doses used in the US clinical trials:

As with other NSAIDs, the lowest dose should be sought for each patient. Patients weighing under 50 kg may be less likely to require dosages beyond 1,000 mg; therefore, after observing the response to initial therapy, the dose should be adjusted to meet individual patients' requirements.

CARDIOVASCULAR EFFECTS

Gastrointestinal Effects, Risk of Ulceration, Bleeding, and Perforation:

NSAIDs, including nabumetone tablets, can cause serious gastrointestinal (GI) adverse events including inflammation, bleeding, ulceration, and perforation of the stomach, small intestine, or large intestine, which can be fatal. These serious adverse events can occur at any time, with or without warning symptoms, in patients treated with NSAIDs. Only 1 in 5 patients, who develop a serious upper GI adverse event on NSAID therapy, is symptomatic. Upper GI ulcers, gross bleeding, or perforation caused by NSAIDs occur in approximately 1% of patients treated for 3 to 6 months, and in about 2 to 4% of patients treated for 1 year. These trends continue with longer duration of use, increasing the likelihood of developing a serious GI event at some time during the course of therapy. However, even short-term therapy is not without risk.

In controlled clinical trials involving 1,677 patients treated with nabumetone (1,140 followed for 1 year and 927 for 2 years), the cumulative incidence of peptic ulcers was 0.3% (95% CI; 0%, 0.6%) at 3 to 6 months, 0.5% (95% CI; 0.1%, 0.9%) at 1 year and 0.8% (95% CI; 0.3%, 1.3%) at 2 years. In patients with active peptic ulcer, physicians must weigh the benefits of therapy with nabumetone against possible hazards, institute an appropriate ulcer treatment regimen and monitor the patients' progress carefully. NSAIDs should be prescribed with extreme caution in those with a prior history of ulcer disease or gastrointestinal bleeding. Patients with a prior history of peptic ulcer disease and/or gastrointestinal bleeding who use NSAIDs have a greater than 10 fold increased risk for developing a GI bleed compared to patients with neither of these risk factors. Other factors that increase the risk for GI bleeding in patients treated with NSAIDs include concomitant use of oral corticosteroids or anticoagulants, longer duration of NSAID therapy, smoking, use of alcohol, older age, and poor general health status. Most spontaneous reports of fatal GI events are in elderly or debilitated patients and therefore, special care should be taken in treating this population.

To minimize the potential risk for an adverse GI event in patients treated with an NSAID, the lowest effective dose should be used for the shortest possible duration. Patients and physicians should remain alert for signs and symptoms of GI ulceration and bleeding during NSAID therapy and promptly initiate additional evaluation and treatment if a serious GI adverse event is suspected. This should include discontinuation of the NSAID until a serious GI adverse event is ruled out. For high risk patients, alternate therapies that do not involve NSAIDs should be considered.

Renal Effects:Long-term administration of NSAIDs has resulted in renal papillary necrosis and other renal injury. Renal toxicity has also been seen in patients in whom renal prostaglandins have a compensatory role in the maintenance of renal perfusion. In these patients, administration of an NSAID results in a dose-dependent decrease in prostaglandin synthesis and, secondarily, in a reduction of renal blood flow, which may precipitate overt renal decompensation. Patients at greatest risk of this reaction are those with impaired renal function, heart failure, liver dysfunction, those taking diuretics, and the elderly. Discontinuation of NSAID therapy is typically followed by recovery to the pretreatment state.

Advanced Renal Disease:No information is available from controlled clinical studies regarding the use of nabumetone tablets in patients with advanced renal disease. Therefore, treatment with nabumetone tablets is not recommended in these patients with advanced renal disease. If nabumetone tablets therapy must be initiated, close monitoring of the patient's renal function is advisable.

Because nabumetone undergoes extensive hepatic metabolism, no adjustment of the dosage of nabumetone is generally necessary in patients with mild renal insufficiency; however, as with all NSAIDs, patients with impaired renal function should be monitored more closely than patients with normal renal function (see CLINICAL PHARMACOLOGY, Pharmacokinetics, Renal Insufficiency). In subjects with moderate renal impairment (creatinine clearance 30 to 49 mL/min) there is a 50% increase in unbound plasma 6MNA and dose adjustment may be warranted. The oxidized and conjugated metabolites of 6MNA are eliminated primarily by the kidneys.

Anaphylactoid Reactions:As with other NSAIDs, anaphylactoid reactions may occur in patients without known prior exposure to nabumetone tablets. Nabumetone tablets should not be given to patients with the aspirin triad. This symptom complex typically occurs in asthmatic patients who experience rhinitis with or without nasal polyps, or who exhibit severe, potentially fatal bronchospasm after taking aspirin or other NSAIDs (see CONTRAINDICATIONS and PRECAUTIONS,General, Preexisting Asthma). Emergency help should be sought in cases where an anaphylactoid reaction occurs.

Skin Reactions:NSAIDs, including nabumetone tablets, can cause serious skin adverse events such as exfoliative dermatitis, Stevens-Johnson Syndrome (SJS), and toxic epidermal necrolysis (TEN), which can be fatal. These serious events may occur without warning. Patients should be informed about the signs and symptoms of serious skin manifestations and use of the drug should be discontinued at the first appearance of skin rash or any other sign of hypersensitivity.

Pregnancy:In late pregnancy, as with other NSAIDs, nabumetone tablets should be avoided because it may cause premature closure of the ductus arteriosus.

General:Nabumetone tablets cannot be expected to substitute for corticosteroids or to treat corticosteroid insufficiency. Abrupt discontinuation of corticosteroids may lead to disease exacerbation. Patients on prolonged corticosteroid therapy should have their therapy tapered slowly if a decision is made to discontinue corticosteroids.

The pharmacological activity of nabumetone tablets in reducing fever and inflammation may diminish the utility of these diagnostic signs in detecting complications of presumed noninfectious, painful conditions.

Information for Patients:Patients should be informed of the following information before initiating therapy with an NSAID and periodically during the course of ongoing therapy. Patients should also be encouraged to read the NSAID Medication Guide that accompanies each prescription dispensed.

1. Nabumetone tablets, like other NSAIDs, may cause serious CV side effects, such as MI or stroke, which may result in hospitalization and even death. Although serious CV events can occur without warning symptoms, patients should be alert for the signs and symptoms of chest pain, shortness of breath, weakness, slurring of speech, and should ask for medical advice when observing any indicative signs or symptoms. Patients should be apprised of the importance of this follow-up (see WARNINGS,CARDIOVASCULAR EFFECTS).
2. Nabumetone tablets, like other NSAIDs, can cause GI discomfort and, rarely, serious GI side effects, such as ulcers and bleeding, which may result in hospitalization and even death. Although serious GI tract ulcerations and bleeding can occur without warning symptoms, patients should be alert for the signs and symptoms of ulcerations and bleeding, and should ask for medical advice when observing any indicative sign or symptoms including epigastric pain, dyspepsia, melena, and hematemesis. Patients should be apprised of the importance of this follow-up (see WARNINGS, Gastrointestinal Effects,Risk of Ulceration, Bleeding, and Perforation).
3. Nabumetone tablets, like other NSAIDs, can cause serious skin side effects such as exfoliative dermatitis, SJS, and TEN, which may result in hospitalization and even death. Although serious skin reactions may occur without warning, patients should be alert for the signs and symptoms of skin rash and blisters, fever, or other signs of hypersensitivity such as itching, and should ask for medical advice when observing any indicative signs or symptoms. Patients should be advised to stop the drug immediately if they develop any type of rash and contact their physicians as soon as possible.
4. Patients should promptly report signs or symptoms of unexplained weight gain or edema to their physicians.
5. Patients should be informed of the warning signs and symptoms of hepatotoxicity (e.g., nausea, fatigue, lethargy, pruritus, jaundice, right upper quadrant tenderness, and "flu-like" symptoms). If these occur, patients should be instructed to stop therapy and seek immediate medical therapy.
6. Patients should be informed of the signs of an anaphylactoid reaction (e.g., difficulty breathing, swelling of the face or throat). If these occur, patients should be instructed to seek immediate emergency help (see WARNINGS).
7. In late pregnancy, as with other NSAIDs, nabumetone tablets should be avoided because they may cause premature closure of the ductus arteriosus.

Laboratory Tests :Because serious G.I.tract ulcerations and bleeding can occur without warning symptoms, physicians should monitor for signs and symptoms of GI bleeding. Patients on long-term treatment with NSAIDs, should have their CBC and a chemistry profile checked periodically. If clinical signs and symptoms consistent with liver or renal disease develop, systemic manifestations occur (e.g., eosinophilia, rash, etc.) or if abnormal liver tests persist or worsen, nabumetone tablets should be discontinued.

Drug Interactions:

Carcinogenesis, Mutagenesis: In 2 year studies conducted in mice and rats, nabumetone had no statistically significant tumorigenic effect. Nabumetone did not show mutagenic potential in the Ames test and mouse micronucleus test in vivo; however, nabumetone- and 6MNA-treated lymphocytes in culture showed chromosomal aberrations at 80 mcg/mL and higher concentrations (equal to the average human exposure to nabumetone at the maximum recommended dose).

Impairment of Fertility: Nabumetone did not impair fertility of male or female rats treated orally at doses of 320 mg/kg/day (1,888 mg/m2) before mating.

Pregnancy: Teratogenic Effects: Pregnancy Category C. Reproductive studies conducted in rats and rabbits have not demonstrated evidence of developmental abnormalities. However, animal reproduction studies are not always predictive of human response. There are no adequate, well-controlled studies in pregnant women. Nabumetone should be used in pregnancy only if the potential benefit justifies the potential risk to the fetus..

Nonteratogenic Effects: Because of the known effects of non-steroidal anti-inflammatory drugs on the fetal cardiovascular system (closure of ductus arteriosus), use during pregnancy (particularly late pregnancy) should be avoided.

Labor and Delivery: In rat studies with NSAIDs, as with other drugs known to inhibit prostaglandin synthesis, an increased incidence of dystocia, delayed parturition, and decreased pup survival occurred. The effects of nabumetone tablets on labor and delivery in pregnant women are unknown.

Nursing Mothers: It is not known whether this drug is excreted in human milk, however 6MNA is excreted in the milk of lactating rats. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from nabumetone, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use : Safety and effectiveness in pediatric patients have not been established.

Geriatric Use: As with any NSAIDs, caution should be exercised in treating the elderly (65 years and older). Of the 1,677 patients in US clinical studies who were treated with nabumetone, 411 patients (24%) were 65 years or older; 22 patients (1%) were 75 years or older. No overall differences in efficacy or safety were observed between these older patients and younger ones. Similar results were observed in a 1 year, non-US postmarketing surveillance study of 10,800 patients treated with nabumetone, of whom 4,577 patients (42%) were 65 years or older.

Incidence ≥ 1% - Probably Causally Related

Gastrointestinal: Diarrhea (14%), dyspepsia (13%), abdominal pain (12%), constipation*, flatulence*, nausea*, positive stool guaiac*, dry mouth, gastritis, stomatitis, vomiting.

Central Nervous System:Dizziness*, headache*, fatigue, increased sweating, insomnia, nervousness, somnolence.

Dermatologic:Pruritus*, rash*.

Special Senses:Tinnitus*.

Miscellaneous: Edema*

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*Incidence of reported reaction between 3% and 9%. Reactions occurring in 1% to 3% of the patients are unmarked.

Incidence < 1% - Probably Causally Related†

Gastrointestinal: Anorexia, jaundice, duodenal ulcer, dysphagia, gastric ulcer, gastroenteritis, gastrointestinal bleeding, increased appetite, liver function abnormalities, melena, hepatic failure.

Central Nervous System: Asthenia, agitation, anxiety, confusion, depression, malaise, paresthesia, tremor, vertigo.

Dermatologic: Bullous eruptions, photosensitivity, urticaria, pseudoporphyria cutanea tarda, toxic epidermal necrolysis, erythema multiforme, Stevens-Johnson syndrome.

Cardiovascular:V asculitis.

Metabolic: Weight gain.

Respiratory:Dyspnea, eosinophilic pneumonia, hypersensitivity pneumonitis, idiopathic interstitial pneumonitis.

Genitourinary:Albuminuria, azotemia, hyperuricemia, interstitial nephritis, nephrotic syndrome, vaginal bleeding, renal failure.

Special Senses: Abnormal vision.

Hematologic/Lymphatic: Thrombocytopenia.

Hypersensitivity: Anaphylactoid reaction, anaphylaxis, angioneurotic edema

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† Adverse reactions reported only in worldwide postmarketing experience or in the literature, not seen in clinical trials, are considered rarer and are italicized.

Incidence < 1% - Causal Relationship Unknown

Gastrointestinal: Bilirubinuria, duodenitis, eructation, gallstones, gingivitis, glossitis, pancreatitis, rectal bleeding.

Central Nervous System: Nightmares.

Dermatologic: Acne, alopecia.

Cardiovascular: Angina, arrhythmia, hypertension, myocardial infarction, palpitations, syncope, thrombophlebitis.

Respiratory: Asthma, cough.

Genitourinary: Dysuria, hematuria, impotence, renal stones.

Special Senses: Taste disorder.

Body as a Whole: Fever, chills.

Hematologic/Lymphatic: Anemia, leukopenia, granulocytopenia.

Metabolic/Nutritional: Hyperglycemia, hypokalemia, weight loss.

Osteoarthritis and Rheumatoid Arthritis: The recommended starting dose is 1,000 mg taken as a single dose with or without food. Some patients may obtain more symptomatic relief from 1,500 mg to 2,000 mg per day. Nabumetone tablets can be given in either a single or twice-daily dose. Dosages greater than 2,000 mg per day have not been studied. The lowest effective dose should be used for chronic treatment (see WARNINGS, Renal Effects). Patients weighing under 50 kg may be less likely to require dosages beyond 1,000 mg; therefore, after observing the response to initial therapy, the dose should be adjusted to meet individual patients' requirements.