Showing papers by "B.K. Park published in 1988"

The relationship between inhibition of vitamin K1 2,3-epoxide reductase and reduction of clotting factor activity with warfarin.

Abstract: 1 The effect of low dose steady state warfarin (0.2 mg and 1 mg daily) on clotting factor activity and vitamin K1 metabolism was studied in seven healthy volunteers. 2 Steady state plasma warfarin concentrations were 41-99 ng ml-1 for the 0.2 mg dose and 157-292 ng ml-1 for the 1 mg dose. 3 There was a significant prolongation of the mean prothrombin time (0.9 s) after 1 mg warfarin daily, but no significant change in prothrombin time after 0.2 mg warfarin daily. There was no significant change in individual clotting factor activity (II, VII, IX or X) with either dose of warfarin. 4 Following the administration of a pharmacological dose of vitamin K1 (10 mg), all seven volunteers had detectable levels of vitamin K1 2,3-epoxide with both doses of warfarin (Cpmax 31-409 ng ml-1). 5 Both the Cpmax and the AUC for vitamin K1 2,3-epoxide were significantly greater on 1 mg of warfarin daily than 0.2 mg daily (P less than 0.01). 6 The apparent dissociation between inhibition of vitamin K1 2,3-epoxide reductase and reduction of clotting factor activity, produced by warfarin, may reflect the insensitivity of functional clotting factor assays to a small reduction in clotting factor concentration.

An in vitro study of the microsomal metabolism and cellular toxicity of phenytoin, sorbinil and mianserin.

Abstract: 1. The cytotoxicity of metabolites generated from phenytoin, sorbinil and mianserin by human and mouse liver microsomes was assessed by co-incubation with human mononuclear leucocytes as target cells. Cytotoxicity was determined by trypan blue dye exclusion. 2. Phenytoin and sorbinil were metabolised by NADPH-dependent murine microsomal enzymes to cytotoxic metabolites. Cytotoxicity produced by both drugs was significantly enhanced by the epoxide hydrolase inhibitor trichloropropane oxide (TCPO). No significant cytotoxicity was observed in the presence of human liver microsomes. 3. Mianserin was metabolised by both human and mouse liver microsomes to a cytotoxin. Cytotoxicity was greater in the presence of human liver microsomes (13.7 +/- 2.2%; mean +/- s.d. for four livers, compared with 6.0 +/- 2.4%, mean +/- s.d., n = 4, with mouse liver microsomes), and was unaffected by pretreatment with TCPO. 4. Stable metabolites were quantified by radiometric high performance liquid chromatography. Phenytoin and sorbinil were metabolised to 5-(p-hydroxyphenyl)-5-phenyl-hydantoin (0.3-0.5% of incubated radioactivity) and 2-hydroxysorbinil (0.4-2.7% of incubated radioactivity), respectively, by both human and mouse liver microsomes. 5. Mianserin was metabolised to 8-hydroxymianserin and desmethylmianserin by both human and mouse liver microsomes. Desmethylmianserin was the major product in incubations with human liver microsomes (32.3 +/- 12%, mean +/- s.d. for four livers), whereas 8-hydroxymianserin was the predominant metabolite generated by mouse liver microsomes (25.9 +/- 1.5%, mean +/- s.d., n = 4). 6. Generation of electrophilic metabolites was assessed by determination of the amount of radiolabelled material which became irreversibly bound to protein. Only mouse liver microsomes activated phenytoin to a chemically reactive metabolite, whereas both mouse and human liver microsomes generated reactive metabolites from sorbinil and mianserin. 7. These studies show that drug cytotoxicity can be mediated by low concentrations (circa microM) of metabolites generated by NADPH-dependent hepatic microsomal enzymes; however demonstration of cytotoxicity in vitro has not been established as a means of predicting in vivo toxicity.

Selective inhibition of drug oxidation after simultaneous administration of two probe drugs, antipyrine and tolbutamide.

Abstract: The effects of sulphaphenazole, cimetidine and primaquine on the disposition of antipyrine and tolbutamide in healthy volunteers have been investigated. The model substrates were administered simultaneously in order more clearly to define any selective effects of the potential inhibitors. Sulphaphenazole produced a significant increase in the half-life of tolbutamide (7.10 to 21.50 h) and a correponding decrease in its clearance (0.260 to 0.084 ml·min−1·kg−1). Clearance to hydroxytolbutamide (OHTOL) and carboxytolbutamide (COOHTOL) was also significantly decreased. In contrast, sulphaphenazole had no effect on the disposition of antipyrine. Administration of cimetidine did not significantly alter the disposition of either model drug. However, a 1.6-times higher dose of cimetidine did increase the half lives both of tolbutamide and antipyrine (6.21 to 9.04 h and 14.2 to 19.2 h, respectively) and decrease their clearance (0.226 to 0.148 and 0.50 to 0.31 ml·min−1 kg−1, respectively). Clearance to OHTOL and hydroxymethylantipyrine (HMA) was reduced. A single dose of primaquine had no demonstrable effect on tolbutamide disposition whereas the half-life of antipyrine was increased (12.1 to 15.0 h) and its clearance decreased (0.63 to 0.38 ml·min−1·kg−1). The partial clearance to HMA, 4-hydroxyantipyrine (OHA) and norantipyrine (NORA) was also significantly reduced. The two main inferences are first, that tolbutamide and antipyrine are metabolished by different forms of cytochrome P-450, and second that a battery of model substrates is needed to investigate the inhibitory effects of a drug in man.

A comparative study of the formation of chemically reactive drug metabolites by human liver microsomes.

Abstract: 1. The metabolism of amodiaquine (A), ethinyloestradiol (E), mianserin (M), phenytoin (Ph), sulphanilamide (S) and paracetamol (Pa) to both stable and chemically reactive, i.e. irreversibly protein bound, metabolites was investigated using microsomes prepared from histologically normal human liver obtained from eight kidney donors. 2. All drugs, except amodiaquine, were metabolized by NADPH-dependent microsomal enzymes to chemically reactive metabolites. The degree of NADPH-dependent binding varied between drugs (E, 11.5 +/- 5.8% incubated drug; M, 3.0 +/- 1.9%; Ph, 0.10 +/- 0.09%; S, 0.57 +/- 0.38%; Pa, 1.2 +/- 1.2%; mean of eight livers +/- s.d.). 3. Inclusion of glutathione (1 mM) or ascorbic acid (1 mM) in the incubation reduced the NADPH-dependent binding for all substrates, indicating the involvement of electrophilic oxidation products. 4. Binding of M and Pa correlated with each other (Spearman's r = 0.86) and with total cytochrome P-450 content (r = 0.76 and 0.78 respectively). E binding also correlated with the binding of M (r = 0.79) and Pa (r = 0.81) but not with cytochrome P-450. Binding of Ph and S did not correlate with any of the other measured metabolic parameters.

A survey of the prevalence of penicillin-specific IgG, IgM and IgE antibodies detected by ELISA and defined by hapten inhibition, in patients with suspected penicillin allergy and in healthy volunteers

Abstract: 1. IgG, IgM and IgE anti-benzylpenicilloyl (BPO) antibody activities were determined by enzyme-linked immunosorbent assay (ELISA) in sera from 100 patients who claimed to be allergic to penicillin, and from 50 healthy volunteers. Continuous frequency distributions for all three classes of anti-BPO antibody, defined as differential binding (delta OD) to BPO-human serum albumin (HSA) and HSA, were obtained for both groups. 2. For IgM and IgE classes the anti-BPO activities were slightly but statistically significantly higher in the patient group compared with the volunteer group. 3. Hapten inhibition ELISAs were performed to confirm specificity for the BPO determinant. On the basis of antibody activities (delta OD values) greater than or equal to 0.3 and 50% inhibition of binding in the presence of 100 micrograms ml-1 BPO-caproate, BPO-specific IgG antibody was identified in 4/100 of the patients' sera and in 1/50 of the volunteers' sera; BPO-specific IgM was identified in 7/100 patients' sera and 1/50 volunteers' sera; and BPO-specific IgE in 5/100 patients' sera and 1/50 volunteers' sera. 4. Not all sera with differential antibody binding to BPO-HSA/HSA were inhibited by the BPO hapten. Hence, hapten inhibition assays are essential for the unambiguous demonstration of drug specific antibodies.

The effects of chronic carbamazepine treatment on haem biosynthesis in man and rat

Abstract: The anticonvulsant drug carbamazepine has been reported to produce a condition clinically and biochemically similar to acute intermittent porphyria (AIP). We have determined the effect of chronic carbamazepine treatment on the activities of the enzymes of haem biosynthesis in circulating blood cells and on the urinary excretion of porphyrins and their precursors in 53 epileptic patients receiving monotherapy and in 42 age- and sex-matched controls. In the patients the mean activity of leucocyte 5-aminolaevulinic acid (ALA) synthase, the rate-limiting enzyme of the pathway, was 218% of control values (p<0.001) and ALA-dehydratase activity was reduced by 37% (p<0.001). Circulating carbamazepine concentrations correlated negatively with ALA dehydratase (r s=−0.45;p<0.01). Porphobilinogen deaminase and uroporphyrinogen decarboxylase appeared unaffected by carbamazepine treatment. Significant quantitative increases in the urinary excretion of porphobilinogen and total porphyrins (bothp<0.05) accompanied the changes in enzyme activity. Similar dose-dependent effects on ALA synthase and ALA dehydratase were shown to occur in rats treated for 5 days with 3 different doses of carbamazepine. These findings further support the porphyrinogenicity of carbamazepine, but the pattern of enzyme alteration differs from that found in AIP.

An investigation of the pharmacological response to vitamin K1 in the rabbit.

Abstract: 1 The relationship between pharmacological response and disposition of a dose of vitamin K1 (10 mgkg-1, iv) in normal rabbits and in rabbits treated with the coumarin anticoagulant brodifacoum, has been studied 2 High performance liquid chromatography (hplc) with electrochemical detection (EC) was used to determine concentrations of vitamin K1 in plasma, whole liver homogenate, and liver microsomes 3 After intravenous administration of vitamin K1, plasma concentrations of the vitamin declined in a tri-exponential fashion There were no differences between the two groups over the first 24 h of the experiment However, between 24 h and the end of the study, plasma concentrations of vitamin K1 in the presence of brodifacoum were significantly (P less than or equal to 005) below those of vehicle-treated rabbits 4 Seventy-two hours after administration of vitamin K1, plasma concentrations of the vitamin were not different from normal 5 Three hours after administration of vitamin K1, the concentrations of the vitamin in whole liver were 466 +/- 43 micrograms g-1 in the presence of brodifacoum, and 328 +/- 64 micrograms g-1 in the absence of brodifacoum; and were significantly (P less than or equal to 005) greater than normal (1277 +/- 443 ng g-1) Likewise, microsomal concentrations of vitamin K1 (400 +/- 238 micrograms mg-1 protein, and 265 +/- 101 micrograms mg-1 protein, in the presence and absence of brodifacoum, respectively) were significantly (P less than or equal to 001) greater than normal (160 +/- 35 ng mg-1 protein) 6 In conclusion, there appears to be no direct effect of coumarins on clearance of vitamin K1 from either plasma or liver; the need for large doses of vitamin K1 during coumarin poisoning is due to a greatly increased requirement for the vitamin