Oxaprozin (Page 5 of 7)

8.5 Geriatric Use

Elderly patients, compared to younger patients, are at greater risk for NSAID-associated serious cardiovascular, gastrointestinal, and/or renal adverse reactions. If the anticipated benefit for the elderly patient outweighs these potential risks, start dosing at the low end of the dosing range, and monitor patients for adverse effects [see Warnings and Precautions (5.1, 5.2, 5.3, 5.6, 5.14)].

No adjustment of the dose of OXAPROZIN CAPSULES is necessary in the elderly, although many elderly may need to receive a reduced dose because of low body weight or disorders associated with aging [see Clinical Pharmacology (12.3) ].

Of the total number of subjects evaluated in four placebo controlled clinical studies of oxaprozin, 39% were 65 and over, and 11% were 75 and over. No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out. Although selected elderly patients in controlled clinical trials tolerated oxaprozin as well as younger patients, caution should be exercised in treating the elderly.

OXAPROZIN CAPSULES is substantially excreted by the kidney, and the risk of toxic reactions to OXAPROZIN CAPSULES may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function [see Warnings and Precautions (5.6) ].

10 OVERDOSAGE

Symptoms following acute NSAID overdosages have been typically limited to lethargy, drowsiness, nausea, vomiting, and epigastric pain, which have been generally reversible with supportive care. Gastrointestinal bleeding has occurred. Hypertension, acute renal failure, respiratory depression, and coma have occurred, but were rare [see Warnings and Precautions (5.1, 5.2, 5.4, 5.6)].

Manage patients with symptomatic and supportive care following an NSAID overdosage. There are no specific antidotes. Consider emesis and/or activated charcoal (60 grams to 100 grams in adults, 1 gram to 2 grams per kg of body weight in pediatric patients) and/or osmotic cathartic in symptomatic patients seen within four hours of ingestion or in patients with a large overdosage (5 to 10 times the recommended dosage). Forced diuresis, alkalinization of urine, hemodialysis, or hemoperfusion may not be useful due to high protein binding.For additional information about overdosage treatment contact a poison control center (1-800-222-1222).

11 DESCRIPTION

OXAPROZIN CAPSULES (oxaprozin) is a nonsteroidal anti-inflammatory drug, available as capsules of 300 mg for oral administration. The chemical name is 4,5-diphenyl-2-oxazole-propionic acid. The molecular weight is 293.32 g/mol. Its molecular formula is C18 H15 NO3 , and it has the following chemical structure.

Chemical Structure
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Oxaprozin is a white to off-white powder with a slight odor and a melting point of 162°C to 163°C. It is slightly soluble in alcohol and insoluble in water, with an octanol/water partition coefficient of 4.8 at physiologic pH (7.4). The pKa in water is 4.3.

The inactive ingredients in OXAPROZIN CAPSULES include: microcrystalline cellulose, pregelatinized corn starch, hypromellose 2910, sodium starch glycolate, stearic acid, and silicon dioxide. OXAPROZIN CAPSULES 300 mg capsules are white opaque capsules imprinted “403” on the cap in black ink.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

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

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

Oxaprozin is a potent inhibitor of prostaglandin synthesis in vitro. Oxaprozin 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 oxaprozin is an inhibitor of prostaglandin synthesis, its mode of action may be due to a decrease of prostaglandins in peripheral tissues.

12.3 Pharmacokinetics

General Pharmacokinetic Characteristics

In dose proportionality studies utilizing 600 mg, 1,200 mg, and 1,800 mg doses, the pharmacokinetics of oxaprozin in healthy subjects demonstrated nonlinear kinetics of both the total and unbound drug in opposite directions, i.e., dose exposure related increase in the clearance of total drug and decrease in the clearance of the unbound drug. Decreased clearance of the unbound drug was related predominantly to a decrease in the volume of distribution of the unbound drug and not an increase inthe elimination half-life. This phenomenon is considered to have minimal impact on drug accumulation upon multiple dosing. The pharmacokinetic parameters of oxaprozin in healthy subjects receiving a single dose of 600 mg (two 300 mg capsules) are presented in Table 3.

image description
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Absorption

OXAPROZIN CAPSULES is 95% absorbed after oral administration. Food may reduce the rate of absorption of oxaprozin, but the extent of absorption is unchanged.

Distribution

The apparent volume of distribution (Vd/F) of total oxaprozin is approximately 11 to 17 L/70 kg. Oxaprozin is 99% bound to plasma proteins, primarily to albumin. At therapeutic drug concentrations, the plasma protein binding of oxaprozin is saturable, resulting in a higher proportion of the free drug as the total drug concentration is increased. With increases in single doses or following multiple once-daily dosing, the apparent volume of distribution and clearance of total drug increased, while that of unbound drug decreased due to the effects of nonlinear protein binding.

Oxaprozin penetrates into synovial tissues of rheumatoid arthritis patients with oxaprozin concentrations 2-fold and 3-fold greater than in plasma and synovial fluid, respectively. Oxaprozin is expected to be excreted in human milk based on its physical-chemical properties; however, the amount of oxaprozin excreted in breast milk has not been evaluated.

Elimination

Metabolism

Several oxaprozin metabolites have been identified in human urine or feces.

Oxaprozin is primarily metabolized in the liver, by both microsomal oxidation (65%) and glucuronic acid conjugation (35%). Ester and ether glucuronide are the major conjugated metabolites of oxaprozin. On chronic dosing, metabolites do not accumulate in the plasma of patients with normal renal function. Concentrations of the metabolites in plasma are very low.

Oxaprozin’s metabolites do not have significant pharmacologic activity. The major ester and ether glucuronide conjugated metabolites have been evaluated along with oxaprozin in receptor binding studies and in vivo animal models and have demonstrated no activity. A small amount (<5%) of active phenolic metabolites are produced, but the contribution to overall activity is limited.

Excretion

Approximately 5% of the oxaprozin dose is excreted unchanged in the urine. Sixty-five percent (65%) of the dose is excreted in the urine and 35% in the feces as metabolites. Biliary excretion of unchanged oxaprozin is a minor pathway, and enterohepatic recycling of oxaprozin is insignificant. Upon chronic dosing, the accumulation half-life is approximately 22 hours. The elimination half-life is approximately twice the accumulation half-life due to increased binding and decreased clearance at lower concentrations.

Specific Populations

Geriatric: A multiple dose study comparing the pharmacokinetics of oxaprozin (1,200 mg once daily) in 20 young (21 to 44 years) adults and 20 elderly (64 to 83 years) adults did not show any statistically significant differences between age groups.

Pediatric: A population pharmacokinetic study indicated no clinically important age dependent changes in the apparent clearance of unbound oxaprozin between adult rheumatoid arthritis patients (N=40) and juvenile rheumatoid arthritis (JRA) patients (≥6 years, N=44) when adjustments were made for differences in body weight between these patient groups. The extent of protein binding of oxaprozin at various therapeutic total plasma concentrations was also similar between the adult and pediatric patient groups. Pharmacokinetic model-based estimates of daily exposure (AUC0–24 ) to unbound oxaprozin in JRA patients relative to adult rheumatoid arthritis patients suggest dose to body weight range relationships, as shown in Table 4.

Table 4. Dose to Body Weight Range to Achieve Similar Steady-State Exposure (AUC0–24hr ) to Unbound Oxaprozin in JRA Patients Relative to 70 kg Adult Rheumatoid Arthritis Patients Administered Oxaprozin 1,200 mg Once Daily *
Dose (mg) Body Weight Range (kg)
*
Model-based nomogram derived from unbound oxaprozin steady-state plasma concentrations in JRA patients weighing 22.1 – 42.7 kg or ≥45.0 kg administered oxaprozin 600 mg or 1,200 mg once daily for 14 days, respectively.
600 22 –31
900 32 –54
1,200 ≥ 55

Race: Pharmacokinetic Differences due to race have not been identified.

Hepatic Impairment: Approximately 95% of oxaprozin is metabolized by the liver. However, patients with well-compensated cirrhosis do not require reduced doses of oxaprozin as compared to patients with normal hepatic function. Nevertheless, monitor patients with severe hepatic dysfunction for adverse reactions.

Renal Impairment: Oxaprozin’s renal clearance decreased proportionally with creatinine clearance (CrCL), but since only approximately 5% of oxaprozin dose is excreted unchanged in the urine, the decrease in total body clearance becomes clinically important only in those subjects with highly decreased CrCL. Oxaprozin is not significantly removed from the blood in patients undergoing hemodialysis or continuous ambulatory peritoneal dialysis (CAPD) due to its high protein binding. Oxaprozin plasma protein binding may decrease in patients with severe renal deficiency. Dosage adjustment may be necessary in patients with renal insufficiency [see Warnings and Precautions (5.6) ].

Cardiac Failure: Well-compensated cardiac failure does not affect the plasma protein binding or the pharmacokinetics of oxaprozin.

Drug Interaction Studies

ACE inhibitors (enalapril): Oxaprozin has been shown to alter the pharmacokinetics of enalapril (significant decrease in dose-adjusted AUC0-24and Cmax ) and its active metabolite enalaprilat (significant increase in dose-adjusted AUC0-24) [see Drug Interactions (7) ].

Aspirin: When oxaprozin was administered with aspirin, the protein binding of oxaprozin was reduced, although the clearance of free oxaprozin was not altered. The clinical significance of this interaction is not known. An in vitro study showed that oxaprozin significantly interfered with the anti-platelet activity of aspirin [see Drug Interactions (7) ].

Beta-blockers (metoprolol): Subjects receiving 1,200 mg oxaprozin once daily with 100 mg metoprolol twice daily exhibited statistically significant but transient increases in sitting and standing blood pressures after 14 days [see Drug Interactions (7) ].

Glyburide: Oxaprozin altered the pharmacokinetics of glyburide; however, coadministration of oxaprozin to type II non-insulin dependent diabetic patients did not affect the area under the glucose concentration curve nor the magnitude or duration of control [see Drug Interactions (7) ].

H2 -receptor antagonists (cimetidine, ranitidine): The total clearance of oxaprozin was reduced by 20% in subjects who concurrently received therapeutic doses of cimetidine or ranitidine; no other pharmacokinetic parameter was affected. A change of clearance of this magnitude lies within the range of normal variation and is unlikely to produce a clinically detectable difference in the outcome of therapy.

Lithium: Oxaprozin has produced an elevation in plasma lithium levels and a reduction in renal lithium clearance. The mean minimum lithium concentration increased 15%, and the renal clearance decreased by approximately 20% [see Drug Interactions (7) ].

Methotrexate: Coadministration of oxaprozin with methotrexate resulted in approximately 36% reduction in apparent oral clearance of methotrexate [see Drug Interactions (7) ].

Other drugs: The coadministration of oxaprozin and acetaminophen, or conjugated estrogens resulted in no statistically significant changes in pharmacokinetic parameters in single- and/or multiple-dose studies. The interaction of oxaprozin with cardiac glycosides has not been studied.

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