Plasma concentrations and therapeutic effect of anti-inflammatory and anti-rheumatic drugs

Variability in response to nonsteroidal anti-inflammatory analgesics: evidence from controlled clinical therapeutic trial of flurbiprofen in rheumatoid arthritis

1. A clinical trial was conducted with flurbiprofen 100 mg three times a day by mouth in rheumatoid arthritis to determine variability in response. 2. Forty patients entered the study, but only 32 completed it. Patients were treated with flurbiprofen on two occasions at a month's interval, each being preceded by a 3 day wash out period. Pain relief and a Ritchie articular index of joint tenderness was assessed at the beginning and end of each treatment period. 3. Flurbiprofen produced significant improvement in both pain relief and articular tenderness. No significant differences were observed between the two trial periods in the mean of these outcome measures. 4. No evidence was found to support the concept of responders and non-responders.

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.

A comparison of plasma and synovial fluid profiles of standard and controlled-release formulations of ketoprofen in patients with rheumatoid arthritis

The plasma and synovial fluid profiles of standard and controlled-release formulations of ketoprofen were compared in 8 patients with rheumatoid arthritis. During chronic dosing with both forms of ketoprofen, peak drug concentrations were lower and occurred later in the synovial fluid than in the plasma. These findings were more pronounced in the case of the controlled-release formulation. The apparent elimination half-life of standard ketoprofen in synovial fluid was prolonged compared to its half-life in plasma, a finding which has not been previously documented. This may explain the clinical observation that, despite a very short plasma elimination half-life, standard ketoprofen exerts a satisfactory therapeutic effect when given twice daily. There was no accumulation of ketoprofen from either formulation in synovial fluid after steady state had been achieved. It is suggested that future pharmacological studies with anti-inflammatory agents should include both synovial fluid and plasma concentration data.

Correlation plasma levels, NSAID and therapeutic response

A regular control of nonsteroidal anti-inflammatory drug (NSAID) plasma levels may be useful to avoid undesirable side-effects to monitor therapeutic progress to see if patients are complying with their prescription. Trying to establish a relationship between the plasma concentration of a drug and its clinical effects requires a few prerequisites which may or may not be fulfilled according to the NSAID (e.g. a drug acting by itself, a reversible action, no tolerance to the drug, a highly specific and sensitive enough analytical method of the drug, similar free drug concentrations in the plasma and at the receptor sites,...), the most important of them-which is also probably the most difficult to fulfil in the case of rheumatic diseases-being that the clinical effect of the drug must be easily measured. In fact, the evidence for a good correlation between clinical effects and drug plasma levels are very scarce in the field of NSAID. The best correlation was obtained with salicylates for which ranges of plasma concentrations needed for observing therapeutic effects in rheumatoid arthritis as well as in juvenile rheumatoid arthritis have been established. Similar correlations have been made for side effects such as tinnitus or headaches as well as for toxic manifestations of salicylism. However, many individual variations have been described and there is considerable overlap between therapeutic and toxic concentrations. According to different authors there are or there are no correlations between phenylbutazone plasma levels and either is therapeutic or its side-effects.(ABSTRACT TRUNCATED AT 250 WORDS)