The effects of phenylbutazone on thyroid function

It is known that phenylbutazone suppresses the thyroidal uptake of radioactive iodine and the serum level of protein-bound iodine (PBI) during the first week of treatment, with a return to normal values after 2 weeks of continuous treatment. Up till now the initial suppression of thyroid function has been presumed due to inhibition of TSH secretion.

In the present study, total serum thyroxine and percentage dialysable thyroxine have been measured and the serum absolute free thyroxine concentration calculated in 12 patients before starting treatment with phenylbutazone orally, after 4 days of treatment and again after 14 days. Serum TSH was assayed in 10 of these patients before, and on the 4th day of treatment. Sera were assayed for TSH after 14 days on the drug in 6 patients.

On the 4th day of treatment, the levels of total thyroxine had fallen but the levels of free thyroxine remained unchanged. TSH levels were also unaltered.

By the 14th day of treatment, free thyroxine levels had fallen significantly below pre-treatment values but no significant rise in TSH could be demonstrated in the 6 patients studied.

At no time was there a fall in TSH levels and we conclude that suppression of some thyroid function tests during the first week of treatment with phenylbutazone is due to direct inhibition of the gland by the drug.

Delayed manifestation of ultraviolet reaction in the guinea-pig caused by anti-inflammatory drugs

1. Exposure of depilated skin of guinea-pig to ultraviolet (u.v.) light for 20 s produces a prolonged inflammatory response.2. The erythaema becomes evident within 15-30 min after the exposure and progressively increases in intensity reaching its maximum by 4-6 hours. The erythaema persists over 24 hours.3. Increase in vascular permeability is biphasic with an early short-lived rise peaking at 0.5 h and a prolonged secondary response peaking at 9-12 h and lasting over 48 hours.4. In presence of aspirin, phenylbutazone and indomethacin, administered prior to u.v. exposure, the inflammatory reaction is partially suppressed, depending upon the dose. The drugs are ineffective in aborting or minimizing the response when given after the inflammation is established. Corticosteroids fail to influence the u.v. inflammation in this test. The significance of these findings is discussed.