Pharmacokinetics and pharmacodynamics of NTBC (2-(2-nitro-4-fluoromethylbenzoyl)-1,3-cyclohexanedione) and mesotrione, inhibitors of 4-hydroxyphenyl pyruvate dioxygenase (HPPD) following a single dose to healthy male volunteers.

AIMS: NTBC (2-(2-nitro-4-fluoromethylbenzoyl)-1,3-cyclohexanedione) and mesotrione (2-(4-methylsulphonyl-2-nitrobenzoyl)-1,3-cyclohexanedione) are inhibitors of 4-hydroxyphenyl pyruvate dioxygenase (HPPD). NTBC has been successfully used as a treatment for hereditary tyrosinaemia type 1 (HT-1), while mesotrione has been developed as an herbicide. The pharmacokinetics of the two compounds were investigated in healthy male volunteers following single oral administration. The aim of the NTBC study was to assess the bioequivalence of two different formulations and to determine the extent of the induced tyrosinaemia. The mesotrione study was performed to determine the magnitude and duration of the effect on tyrosine catabolism. Additionally, the urinary excretion of unchanged mesotrione was measured to assess the importance of this route of clearance and to help develop a strategy for monitoring occupational exposure. METHODS: A total of 28 volunteers participated in two separate studies with the compounds. In the first study, the relative bioavailability of NTBC from liquid and capsule formulations was compared and the effect on plasma tyrosine concentrations measured. In the second study the pharmacokinetics of mesotrione were determined at three doses. Plasma tyrosine concentrations were monitored and the urinary excretion of mesotrione and tyrosine metabolites was measured. RESULTS: Both compounds were well tolerated at the dose levels studied. Peak plasma concentrations of NTBC were rapidly attained following a single oral dose of 1 mg x kg(-1) body weight of either formulation and the half-life in plasma was approximately 54 h. There were no statistical differences in mean (+/- s.d.) AUC(0,infinity) (capsule 602 +/- 154 vs solution 602 +/- 146 microg x ml(-1) h) or t1/2 (capsule 55 +/- 13 vs solution 54 +/- 8 h) and these parameters supported the bioequivalence of the two formulations. Mesotrione was also rapidly absorbed, with a significant proportion of the dose eliminated unchanged in urine. The plasma half-life was approximately 1 h and was independent of dose and AUC(0,infinity) and Cmax increased linearly with dose. Following administration of 1 mg NTBC x kg(-1) in either formulation, the concentrations of tyrosine in plasma increased to approximately 1100 nmol x ml(-1). Concentrations were still approximately 8 times those of background at 14 days after dosing, but had returned to background levels within 2 months of the second dose. Administration of mesotrione resulted in an increase in tyrosine concentrations which reached a maximum of approximately 300 nmol x ml(-1) following a dose of 4 mg x kg(-1) body weight. Concentrations returned to those of background within 2 days of dosing. Urinary excretion of tyrosine metabolites was increased during the 24 h immediately following a dose of 4 mg mesotrione x kg(-1), but returned to background levels during the following 24 h period. CONCLUSIONS: NTBC and mesotrione are both inhibitors of HPPD, although the magnitude and duration of their effect on tyrosine concentrations are very different. When normalized for dose, the extent of the induced tyrosinaemia after administration of NTBC and over the duration of these studies, was approximately 400 fold greater than that following administration of mesotrione. The persistent and significant effect on HPPD following administration of NTBC make it suitable for the treatment of patients with hereditary tyrosinaemia type 1 (HT-1), whilst the minimal and transient effects of mesotrione minimize the likelihood of a clinical effect in the event of systemic exposure occurring during occupational use.

Effect of amitriptyline on the thyrotropin response to thyrotropin-releasing hormone in endogenous depression.

Patients with endogenous depression whose depressive episodes were clinically resolved after electroconvulsive therapy were divided into two groups: one in which patients remained well (n = 16) and another in which patients relapsed within 6 months (n = 11). Treatment with amitriptyline for 3 weeks did not affect the median thyrotropin (thyroid-stimulating hormone; TSH) response to thyrotropin-releasing hormone (TRH) in recovered patients, whereas that in relapsed patients was significantly enhanced. The data suggest that amitriptyline affects the TSH response to TRH differently in stably recovered and relapsed patients. If this effect is maintained beyond the 3-week period studied, treatment with amitriptyline will invalidate the predictive value of the TRH test.

Prediction of relapse with the TRH test and prophylactic amitriptyline in 39 patients with endogenous depression.

The authors conducted a double-blind prospective study of 39 patients with unipolar endogenous depression who recovered after ECT. Thyrotropin (TSH)-releasing hormone (TRH) tests were performed before and after ECT. Patients were divided into three groups on the basis of their altered TSH response: Persistent remission was predicted for patients in group 1 (N = 15) and relapse was predicted for groups 2A (N = 13) and 2B (N = 11). Patients in groups 1 and 2A received placebo and those in group 2B received amitriptyline for 6 months. Fewer relapses occurred in groups 1 and 2B than in group 2A (p less than .05), showing that relapse can be predicted by the TRH test and prevented by amitriptyline.

Ampicillin and propylthiouracil pharmacokinetics in intestinal bypass patients followed up to a year after operation.

The pharmacokinetics of ampicillin and prophylthiouracil were studied in 6 and 9 patients, respectively, before and several times up to a year after a shunt operation for extreme obesity. The drugs were given intravenously and orally making it possible to estimate the absolute bioavailability. The bioavailability of propylthiouracil (about 80%) was unchanged by the surgical procedure but the fraction of ampicillin (given as pivampicillin) absorbed decreased from a preoperative value of 109 +/- 44% to 44 +/- 30% 12 months after the bypass operation. Volumes of distribution transiently decreased in the postoperative period for ampicillin. Clearance was initially reduced for both ampicillin and propylthiouracil after operation but returned to normal values a year later. Half-lives of both drugs were unchanged. These results are compared with previous data on pharmacokinetics in intestinal shunt patients and a tabular review is presented. Although no general rules presently emerge from the data available, it seems prudent to closely monitor intestinal shunt patients on drug therapy by both laboratory and clinical methods.

Acute effects of parathyroid hormone on vitamin D metabolism in patients with the bone loss of aging.

This study was carried out to evaluate the effects of an iv injection of parathyroid extract on serum levels of 1,25-dihydroxyvitamin D [1,25-(OH)2D3] in elderly osteopenic patients and age-matched nonosteopenic controls. Serum concentrations of 1,25-(OH)2D were reduced in elderly osteopenic subjects (mean +/- SEM, 20 +/- 3 pg/ml) compared with values in age-matched nonosteopenic controls (35 +/- 3 pg/ml), whereas no differences were found in serum 24,25-dihydroxyvitamin D levels (1.5 +/- 0.3 and 2.2 +/- 0.5 ng/ml, respectively). An iv injection of parathyroid extract was followed by a significant increase in serum 1,25-(OH)2D levels in both osteopenic patients (16 +/- 6 pg/ml) and controls (15 +/- 5 pg/ml). The mean 4-h increases in serum 1,25-(OH)2D of 11-18 pg/ml were not significantly different in the two groups. The results indicate that the reduced 1,25-(OH)2D concentrations in the osteopenic patients are secondary to changes in factors that normally stimulate this enzyme system.

Unaltered metabolism of phenytoin in thyroid disorders.

The metabolism of phenytoin was studied in 9 hyperthyroid and 7 hypothyroid patients before and after treatment with either antithyroid drugs or 1-thyroxine. No difference in the half-life, volume of distribution and metabolic clearance rate was found between untreated hyper- and hypothyroid subjects. Furthermore, normalisation of thyroid function test did not change the kinetic parameters of phenytoin. The results indicate that the well-known correlation between thyroid function and antipyrine kinetics cannot be extrapolated uncritically to other drugs. It is concluded that no general rules are valid in the kinetics among different drugs in thyroid pathological conditions. Each drug must be evaluated by itself in different pathological conditions.

Extrathyroidal effects of propylthiouracil and carbimazole on serum T4, T3, reverse T3 and TRH-induced TSH-release in man.

A possible extrathyroidal effect of propylthiouracil (PTU) and carbimazole on serum levels of thyroxine (T4), triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3) and on thyrotrophin-releasing hormone (TRH) induced thyrotrophin (TSH) release was estimated in 19 patients with severe hypothyroidism treated with T4. During PTU medication a significant decrease in serum T3 from 90 +/- 16 (SD) to 79 +/- 23 ng/100 ml (P less than 0.01) and a reciprocal increase in serum reverse T3 from 51 +/- 14 (SD) to 58 +/- 20 ng/100 ml (P less than 0.025) were found. No significant changes in serum T4, basal serum TSH or response to TRH could be demonstrated. Carbimazole did not change any of the parameters studied.

HLA antigens in Graves' disease.

HLA typing of 86 patients with Graves' disease was performed for the A, B, C and D series antigens. An increased frequency of HLA-B8 (47 per cent) and Dw3 (51 per cent) compared with controls (23.7 and 21 per cent, respectively) was observed. The increase of B8 and Dw3 was almost exclusively found in a group of 48 patients with relapse of disease, whereas the frequency of B8 and Dw3 in patients without relapse did not differ significantly from that of the control group. No association with the presence of exophthalmos, thyroid antibodies, or antibodies to Yersinia enterocolitica serotype 3 could be found.

Sulfamethizole-induced inhibition of diphenlhydantoin, tolbutamide, and warfarin metabolism.

The influence of sulfamethizole on the metabolism of diphenylhydatoin (DPH) tolbutamide, and warefarian is examined. In 8 patients DPH means half-life (T/2) increased from 11.8 plus or minus 3.6 hr to 19.6 plus or minus 5.2 hr and mean metabolic clearance rate (MCR) decreased from 43.7 plus or minus 16,8 to 28.1 plus or minus 9.1 ml/min durus or minus 1.2 to 9.2 plus or minus 1.2 hr MCR decrease from 17.0 plus or minus 5.4 to 10.5 plus or minus 1.2 ml/min. In 2 patients warfarin T/2 increased fron an average of 64.7 to 92.7 hr and MCR decreased from 1.65 ml/min to 1.05 ml/min. In 4 patients on long-term DPH treatment after 1 wk on sulfamethizole inhibits hepatic metabolism of DPH, tolbutamide, and warfarin.