Nabumetone

BRAND NAMES

1. Relafen (most widely recognized original brand name) 

2. Relafen DS (double-strength formulation in some markets)

MECHANISM OF ACTION

Nabumetone is a prodrug that is converted in the liver to its active metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA). This active form exerts its effects by inhibiting cyclooxygenase (COX) enzymes, primarily COX-2, with relatively less effect on COX-1 compared to some traditional NSAIDs.

PHARMACOKINETICS

Absorption

Nabumetone is a prodrug that is well absorbed orally from the gastrointestinal tract. After absorption, it undergoes rapid first-pass metabolism in the liver to its active form, 6-methoxy-2-naphthylacetic acid (6-MNA). Food may slightly delay absorption but does not significantly affect overall bioavailability. Peak plasma concentrations of the active metabolite are typically reached within 2 to 4 hours.

Distribution

The active metabolite of nabumetone is highly bound to plasma proteins (>99%), primarily albumin. It has a moderate volume of distribution, allowing it to penetrate inflamed tissues effectively. Due to high protein binding, displacement interactions with other drugs can occur.

Metabolism

Nabumetone undergoes extensive hepatic metabolism, where it is converted to its active metabolite (6-MNA). Further metabolism occurs via hepatic biotransformation, including hydroxylation and demethylation, followed by formation of inactive conjugates.

Elimination

Elimination occurs mainly through the kidneys, with metabolites excreted in urine. A smaller portion is excreted via bile and feces. The elimination half-life of the active metabolite is approximately 20–24 hours, allowing for once- or twice-daily dosing.

PHARMACODYNAMICS

Nabumetone exerts its effects through its active metabolite, which inhibits cyclooxygenase (COX) enzymes, with a relative preference for COX-2 over COX-1. This reduces prostaglandin synthesis, leading to anti-inflammatory, analgesic, and antipyretic effects. Compared with non-selective NSAIDs, it may have a somewhat lower risk of gastrointestinal irritation due to reduced COX-1 inhibition.

ADMINISTRATION

Nabumetone is administered orally in tablet form, usually once or twice daily depending on clinical response. It is commonly prescribed for chronic conditions such as osteoarthritis and rheumatoid arthritis. It should be taken consistently, often with food if gastrointestinal discomfort occurs.

DOSAGE AND STRENGTH

Typical adult dosing ranges from 500 mg to 1000 mg per day, given as a single dose or divided doses. In osteoarthritis, initial dosing often starts at 1000 mg once daily, with adjustments based on response and tolerability.

DRUG INTERACTIONS

Nabumetone may interact with several drug classes, mainly due to its effects on prostaglandin synthesis and renal function. Concomitant use with anticoagulants such as warfarin can increase the risk of bleeding because NSAIDs may enhance anticoagulant effects and cause gastrointestinal mucosal damage.

FOOD INTERACTIONS

Food does not significantly alter absorption, but taking nabumetone with meals may reduce gastrointestinal irritation. Alcohol use should be limited due to increased risk of GI bleeding.

CONTRAINDICATIONS

Nabumetone is contraindicated in patients with known hypersensitivity to nabumetone or other nonsteroidal anti-inflammatory drugs (NSAIDs), including those who experience asthma, urticaria, or allergic-type reactions after aspirin or NSAID use. It should not be used in individuals with active peptic ulcer disease or a history of recurrent gastrointestinal bleeding or perforation related to NSAIDs, due to the increased risk of serious GI complications.

SIDE EFFECTS

• Dyspepsia or abdominal pain

• Nausea

• Dizziness

• Headache

• Fluid retention or mild edema

OVER DOSAGE

Overdose of nabumetone, a nonsteroidal anti-inflammatory drug (NSAID), may lead to dose-dependent toxicity, primarily affecting the gastrointestinal, renal, and central nervous systems. Common symptoms include nausea, vomiting, abdominal pain, drowsiness, dizziness, and headache.

TOXICITY

Overdose may lead to severe gastrointestinal irritation, renal dysfunction, CNS symptoms (drowsiness, dizziness), and metabolic disturbances. Management is primarily supportive, as there is no specific antidote. Monitoring of renal and gastrointestinal status is important in chronic therapy.