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Fenoprofen (Fenoprofen Calcium) - Description and Clinical Pharmacology

 
 



DESCRIPTION

Fenoprofen calcium is a non-steroidal, anti-inflammatory, antiarthritic drug. Chemically, fenoprofen calcium is an arylacetic acid derivative. The structural formula is as follows:

Benzeneacetic acid, α-methyl-3-phenoxy-, calcium salt (2:1)-(±)-, dihydrate

Fenoprofen calcium, USP is a white, crystalline powder, soluble in alcohol (95%) to the extent of approximately 15 mg/mL at 25°C, slightly soluble in water, and insoluble in benzene.

The pKa of fenoprofen calcium is 4.5 at 25°C.

Film-coated fenoprofen calcium tablets for oral administration are available containing fenoprofen calcium as the dihydrate equivalent to 600 mg of fenoprofen and the following inactive ingredients: colloidal silicon dioxide, croscarmellose sodium, hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, polysorbate 80, pregelatinized starch, sodium lauryl sulfate, titanium dioxide and FD&C Yellow No. 6 Aluminum Lake.

CLINICAL PHARMACOLOGY

Fenoprofen calcium is a non-steroidal, 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. Fenoprofen has been shown to inhibit prostaglandin synthetase isolated from bovine seminal vesicles. Reproduction studies in rats have shown fenoprofen to be associated with prolonged labor and difficult parturition when given during late pregnancy. Evidence suggests that this may be due to decreased uterine contractility resulting from the inhibition of prostaglandin synthesis. Its action is not mediated through the adrenal gland.

Fenoprofen shows anti-inflammatory effects in rodents by inhibiting the development of redness and edema in acute inflammatory conditions and by reducing soft-tissue swelling and bone damage associated with chronic inflammation. It exhibits analgesic activity in rodents by inhibiting the writhing response caused by the introduction of an irritant into the peritoneal cavities of mice and by elevating pain thresholds that are related to pressure in edematous hindpaws of rats. In rats made febrile by the subcutaneous administration of brewer's yeast, fenoprofen produces antipyretic action. These effects are characteristic of non-steroidal, anti-inflammatory, antipyretic, analgesic drugs.

The results in humans confirmed the anti-inflammatory and analgesic actions found in animals. The emergence and degree of erythemic response were measured in adult male volunteers exposed to ultraviolet irradiation. The effects of fenoprofen, aspirin and indomethacin were each compared with those of a placebo. All three drugs demonstrated antierythemic activity.

In all patients with rheumatoid arthritis, the anti-inflammatory action of fenoprofen 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 fenoprofen has also been evidenced by increased mobility (i.e., a decrease in the number of joints having limited motion).

The use of fenoprofen 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 fenoprofen to maintenance therapy with gold salts or steroids. Whether or not fenoprofen, 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 fenoprofen 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 fenoprofen 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 fenoprofen than in aspirin-treated patients. It is not known whether fenoprofen calcium causes less peptic ulceration than does aspirin.

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

Under fasting conditions, fenoprofen is rapidly absorbed and peak plasma levels of 50 mcg/mL are achieved within 2 hours after oral administration of 600 mg doses. Good dose proportionality was observed between 200 mg and 600 mg doses in fasting male volunteers. The plasma half-life is approximately 3 hours. About 90% of a single oral dose is eliminated within 24 hours as fenoprofen glucuronide and 4'-hydroxy-fenoprofen glucuronide, the major urinary metabolites of fenoprofen. Fenoprofen is highly bound (99%) to albumin.

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

There is less suppression of collagen-induced platelet aggregation with single doses of fenoprofen calcium than there is with aspirin.

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