Piroxicam kinetics were studied after a single, oral, 20-mg capsule was taken by 12 young (six women, six men) and 13 elderly (seven women, six men) healthy subjects. Plasma samples were drawn for 216 hr after dosing. Plasma protein binding was studied in vitro by equilibrium dialysis and piroxicam concentrations were measured by HPLC with ultraviolet detection. The apparent volume of distribution was smaller in elderly women (7.8 +/- 0.4 l) than in young men (11.3 +/- 0.3 l) and elderly men (10.8 +/- 0.8 l). There were no such differences when the apparent volume of distribution was normalized for total body weight. There was a strong correlation between total body weight and apparent volume of distribution in all subjects (r = 0.83). Plasma protein binding of piroxicam ranged from 98.90% to 99.54% bound and was not affected by age or sex. Piroxicam body clearance in elderly women (0.026 +/- 0.002 ml/min/kg) was approximately 33% lower than in young women (0.039 +/- 0.003 ml/min/kg). This difference was reflected in different t1/2s of 61.7 and 44.9 hr. Predicted steady-state plasma piroxicam concentrations were 5.7 micrograms/ml in young women, 5.4 micrograms/ml in young men, 5.7 micrograms/ml in elderly men, and 9.3 micrograms/ml in elderly women. The high value in elderly women results from the lower piroxicam body clearance and total body weight. Our data suggest that healthy elderly women eliminate piroxicam at a slower rate than healthy young women. The clinical significance of these data needs to be assessed in patients.

Piroxicam (20 mg once daily) was administered orally to six healthy young volunteers for 15 days. Trough steady-state levels of piroxicam and 5'-hydroxypiroxicam were 5.5 and 1.2 micrograms/ml, respectively. Piroxicam's plasma half-life (54.9 h) was significantly shorter than that of 5'-hydroxypiroxicam (70.5 h). Percent unbound piroxicam and 5'-hydroxypiroxicam in plasma at steady-state averaged 1.10 and 8.07 respectively. An average of 25.2% of the dose was recovered in urine as 5'-hydroxypiroxicam; approximately two-thirds (17.2%) in the form of the glucuronide conjugate. Average steady-state plasma levels (Css) of piroxicam (7.0 micrograms/ml) were significantly higher than predicted from a previously reported single dose study (5.3 micrograms/ml).

Serum activity of hexosaminidases A and B has been measured to identify patients with Tay-Sachs and Sandhoff diseases, and may also be influenced by other clinical conditions including neonatal necrotizing enterocolitis. We have characterized the normal developmental pattern of hexosaminidase activity in serum by measuring this enzyme activity in 61 neonates of 27–40 weeks gestation who were followed from birth to age 4–8 weeks. Total serum hexosaminidase activity significantly increased with postnatal and gestational age, and with initiation of enteral feeding. We conclude that serum hexosaminidase activity in infants with clinical conditions that may influence serum activity of this enzyme must be compared to that in normal infants of similar gestational and postnatal ages.

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