Ninety-three hyperthyroid patients were treated with 1 dose of iodine-131 (131I) during the past 10 years. Thirty-three were pretreated with propylthiouracil (PTU), 22 with methimazole (MMI), and 38 received no antithyroid drugs (ATD). ATD were discontinued 5-55 days before 131I therapy in three fourths of the cases and more than 4 months before therapy in one fourth of the cases. The frequency of cures in the 3 groups, 6-8 months after radioiodine therapy, was retrospectively studied. The cure rate among those who discontinued PTU for 5-55 days before 131I was significantly reduced (24%), compared with those who discontinued MMI for the same duration (61%) or those who received no ATD (66%). When PTU was discontinued for more than 4 months, the cure rate was similar to those who received no ATD. It is concluded that if ATD are used as initial therapy for hyperthyroidism, then PTU (but not MMI) may reduce the therapeutic efficacy of subsequent 131I. The reduction in cure rate was observed even when PTU was discontinued for as long as 55 days before 131I therapy. To our knowledge, this is the first report to compare, in one study, the effects of pretreatment with PTU and MMI on 131I therapy.

We present a technique for measuring the coercivity of magneto-optical and perpendicular recording media on a submicron scale using a magnetic force microscope and an electromagnet. Co–Cr coated silicon tips were used to write and image magnetic bits down to 150 nm in diameter. Bits were written when the sum of the tip stray field and an external field Hext exceeded the local, or ‘‘point’’ coercivity. Media can be characterized by a continuous write probability Pw(Hext) which differs significantly from bulk hysteresis loops. For an intermediate field range, writing was intermittent (0<Pw<1) due to spatial variations in media properties.

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1. Racial differences in propranolol enantiomer kinetics following oral dosing were previously documented in our laboratory. The purpose of this study was to more completely describe propranolol kinetics in black and white subjects with the goal of gaining a better understanding of the mechanism(s) responsible for racial differences in oral propranolol kinetics. 2. Twelve white and 13 black healthy males were included in the study. Poor metabolizers of dextromethorphan and mephenytoin were excluded. Subjects took oral propranolol 80 mg every 8 h for 16 doses and received an intravenous dose of radiolabelled propranolol with the 16th dose. Serum and urine samples were collected for 24 h after the 16th dose. Serum concentrations of R- and S-propranolol and urine concentrations of its three primary metabolites were determined by h.p.l.c. 3. Apparent oral clearances of R- and S-propranolol were higher (P < 0.05) in blacks than whites (R-propranolol: 5036 +/- 4175 ml min-1 vs 2854 +/- 879 ml min-1; S-propranolol 3255 +/- 1723 ml min-1 vs 2125 +/- 510 ml min-1; blacks vs whites). 4. R- and S-propranolol clearances were higher in blacks than whites (R-propranolol 1069 +/- 316 ml min-1 vs 841 +/- 161 ml min-1; S-propranolol 947 +/- 271 ml min-1 vs 771 +/- 142 ml min-1; blacks vs whites, P < 0.05). 5. There were trends (P > 0.05 < 0.10) toward higher side chain oxidation, 4-hydroxylation and R-propranolol glucuronidation in blacks compared with whites. Ethnic differences in the enantiomeric ratios of partial metabolic clearance values were not observed. 6. We conclude the higher propranolol oral clearances in black subjects are explained by blacks having slightly higher hepatic metabolism via all three of its major metabolic pathways. Higher propranolol clearances among black subjects were also observed and we conclude this finding is explained largely by the higher hepatic metabolism, but also by slightly higher liver blood flow among black subjects.

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