The effect of concurrent aspirin upon plasma concentrations of tenoxicam.
1. The effect of chronic, high-dose aspirin therapy upon the disposition of a single dose and multiple doses of tenoxicam was examined in normal volunteers. 2. Aspirin caused a 24% drop in the t1/2 (P less than 0.005), a 49% rise in the volume of distribution (P less than 0.0003) and a 98% increase in the clearance (P less than 0.0001) of tenoxicam after a single dose of the tenoxicam. 3. Steady-state concentrations of tenoxicam decreased significantly from 10.4 +/- 1.5 to 4.5 +/- 1.6 micrograms ml-1 in the presence of chronic, high-dose aspirin treatment. 4. Tenoxicam percentage free measured in plasma from a normal volunteer was 0.56 +/- 0.05% over the tenoxicam concentration range 1-20 micrograms ml-1 and rose to 1.24 +/- 0.07% in the presence of aspirin 150 micrograms ml-1. 5. The effect of aspirin upon the disposition of tenoxicam was consistent with a competitive protein binding interaction.
Day
R O
RO
Department of Clinical Pharmacology, St Vincent's Hospital, Sydney, N.S.W., Australia.
Paull
P D
PD
Lam
S
S
Swanson
B R
BR
Williams
K M
KM
Wade
D N
DN
D000328:Adult; D001241:Aspirin / Q000008:administration & dosage / Q000494:pharmacology*; D004347:Drug Interactions; D005260:Female; D006801:Humans; D008297:Male; D010894:Piroxicam / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics; D011485:Protein Binding; D012459:Salicylates / Q000097:blood; D020156:Salicylic Acid
D012459:Salicylates; D010894:Piroxicam; D020156:Salicylic Acid; D001241:Aspirin; C032801:tenoxicam