The pharmacokinetic profile of pyrazinobutazone in man

The rate of absorption of phenylbutazone from pyrazinobutazone (Ranoroc/Carudol) capsules is distinctly lower than that from phenylbutazone capsules. The capsules are bioequivalent to an equimolar dose of Na-phenylbutazone in solution, as judged by both the area under the plasma level curves (AUC), and the sum of the unchanged phenylbutazone excreted in the urine. A single dose of 300 mg pyrazinobutazone produces maximum plasma levels of 35.2 +/- 1.1 micrograms/ml at 5.5 h after administration (+/- SEM, 70 kg bodyweight, N = 39). Two dosage schedules for long-term therapy were tested (2400 and 1500 mg/week). Both produced accumulation to saturation plasma levels within approximately three days. The concentration of phenylbutazone obtained with the lower dosage was about 110 micrograms/ml plasma. This corresponds with the recommendations for long-term therapy with phenylbutazone. With the higher dosage, the plasma levels were elevated by only 25%, however, the renal elimination of unchanged drug and the number of side-effects were remarkably increased. The recommended dosage scheme is specifically adapted to the pharmacokinetics of pyrazinobutazone.