June 27, 2016
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Nalfon

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Nalfon




CLINICAL PHARMACOLOGY

Mechanism Of Action

Fenoprofen has analgesic, anti-inflammatory, and antipyretic properties.

The mechanism of action of NALFON, like that of other NSAIDs, is not completely understood but involves inhibition of cyclooxygenase (COX-1 and COX-2).

Fenoprofen is a potent inhibitor of prostaglandin synthesis in vitro. Fenoprofen concentrations reached during therapy have produced in vivo effects. Prostaglandins sensitize afferent nerves and potentiate the action of bradykinin in inducing pain in animal models. Prostaglandins are mediators of inflammation. Because fenoprofen is an inhibitor of prostaglandin synthesis, its mode of action may be due to a decrease of prostaglandins in peripheral tissues.

Pharmacokinetics

Absorption

Under fasting conditions, fenoprofen is rapidly absorbed, and peak plasma levels of 50 mcg/L are achieved within 2 hours after oral administration of 600 mg doses. Good dose proportionality was observed between 200 and 600 mg doses in fasting male volunteers.

Distribution

Fenoprofen is highly bound (99%) to albumin.

Elimination

Metabolism

The plasma half-life is approximately 3 hours.

Excretion

About 90% of a single oral dose is eliminated within 24 hours as fenoprofen glucuronide and 4'-hydroxyfenoprofen glucuronide, the major urinary metabolites of fenoprofen.

Specific Populations

Geriatrics

Peak plasma levels of fenoprofen in normal elderly volunteers were similar to those observed in normal young volunteers. Elderly volunteers had a mean plasma clearance of 2.2 L/hour while plasma clearance of fenoprofen in normal young volunteers ranged from 3 to 3.5 L/hour. The overall elimination rate constant, plasma half-life and ratio of renal to nonrenal clearance of fenoprofen was the same in elderly and young volunteers. The 30 to 60% decrease in plasma clearance is due to a decrease in the volume of distribution in the body.

Drug Interaction Studies

Aspirin: When NSAIDs were administered with aspirin, the protein binding of NSAIDs were reduced, although the clearance of free NSAID was not altered. The clinical significance of this interaction is not known. See Table 1 for clinically significant drug interactions of NSAIDs with aspirin [see DRUG INTERACTIONS].

Antacid: The concomitant administration of antacid (containing both aluminum and magnesium hydroxide) does not interfere with absorption of fenoprofen.

Clinical Studies

NALFON is a nonsteroidal, anti-inflammatory, antiarthritic drug that also possesses analgesic and antipyretic activities. Its exact mode of action is unknown, but it is thought that prostaglandin synthetase inhibition is involved.

Results in humans demonstrate that fenoprofen has both anti-inflammatory and analgesic actions. The emergence and degree of erythemic response were measured in adult male volunteers exposed to ultraviolet irradiation. The effects of NALFON, aspirin, and indomethacin were each compared with those of a placebo. All 3 drugs demonstrated antierythemic activity.

In all patients with rheumatoid arthritis, the anti-inflammatory action of NALFON has been evidenced by relief of pain, increase in grip strength, and reductions in joint swelling, duration of morning stiffness, and disease activity (as assessed by both the investigator and the patient). The anti-inflammatory action of NALFON has also been evidenced by increased mobility (i.e., a decrease in the number of joints having limited motion).

The use of NALFON in combination with gold salts or corticosteroids has been studied in patients with rheumatoid arthritis. The studies, however, were inadequate in demonstrating whether further improvement is obtained by adding NALFON to maintenance therapy with gold salts or steroids. Whether or not NALFON used in conjunction with partially effective doses of a corticosteroid has a “steroid-sparing” effect is unknown.

In patients with osteoarthritis, the anti-inflammatory and analgesic effects of NALFON have been demonstrated by reduction in tenderness as a response to pressure and reductions in night pain, stiffness, swelling, and overall disease activity (as assessed by both the patient and the investigator). These effects have also been demonstrated by relief of pain with motion and at rest and increased range of motion in involved joints.

In patients with rheumatoid arthritis and osteoarthritis, clinical studies have shown NALFON to be comparable to aspirin in controlling the aforementioned measures of disease activity, but mild gastrointestinal reactions (nausea, dyspepsia) and tinnitus occurred less frequently in patients treated with NALFON than in aspirin-treated patients. It is not known whether NALFON causes less peptic ulceration than does aspirin.

In patients with pain, the analgesic action of Nalfon has produced a reduction in pain intensity, an increase in pain relief, improvement in total analgesia scores, and a sustained analgesic effect.

Last reviewed on RxList: 5/19/2016
This monograph has been modified to include the generic and brand name in many instances.

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