Pharmacodynamics: DAYPRO ALTA, the potassium salt of oxaprozin, is a nonsteroidal anti-inflammatory drug (NSAID), which dissociates into the active moiety oxaprozin in vivo. Oxaprozin has been shown to have anti-inflammatory, analgesic, and antipyretic properties in animal models. The mechanism of action of DAYPRO ALTA, like that of other NSAIDs, is not completely understood but may be related to prostaglandin synthetase inhibition.

Pharmacokinetics: (see Table 1)

Absorption: After oral administration, DAYPRO ALTA dissociates into free oxaprozin which is 95% absorbed. Peak plasma concentration occurs at about 1 hour and 45 minutes after single dose administration (see Table 1). When DAYPRO ALTA is administered with food, the peak concentration of oxaprozin is delayed by about 45 minutes, but the extent of absorption is unchanged. Antacids do not significantly affect the extent and rate of oxaprozin absorption.

Table 1 Oxaprozin Pharmacokinetic Parameters with DAYPRO AL (1200mg); Mean (%CV) Healthy Adults (18-42 years; N= 12-24)

Distribution: In dose proportionality studies utilizing 600, 1200 and 1800 mg doses, the pharmacokinetics of oxaprozin in healthy subjects has 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. Concentration dependent changes in the protein binding also resulted in changes in the oxaprozin volume of distribution, which increased for the total drug but decreased for the unbound drug. The apparent volume of distribution (Vd/F) of total oxaprozin is approximately 10-16 L/70 kg. Oxaprozin potassium 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 repetitive 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 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.

Metabolism: Several oxaprozin metabolites excreted in human urine or feces are considered not to have significant pharmacologic activity. Oxaprozin is primarily metabolized by the liver, by both microsomal oxidation (65%) and glucuronic acid conjugation (35%). Ester and ether glucuronides are the major conjugated metabolites of oxaprozin. A small amount ( < 5%) of active phenolic metabolites is produced, but the contribution to overall activity is limited.

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