The risks associated with short-term placebo-controlled antihypertensive clinical trials: a descriptive meta-analysis.

Short-term (4-8 weeks) placebo-controlled trials are used to evaluate new antihypertensive drug treatment. To evaluate the consequences of such practice, a descriptive meta-analysis was conducted, consisting of blinded review of original case report forms for all patients who died or left a study before its completion for all short-term, placebo-controlled hypertension trials submitted to the Food and Drug Administration from 1973 through 2001. There were 93 marketing applications or supplements involving 590 individual trials that involved 86137 randomized patients (64438 randomized to experimental drug and 21 699 randomized to placebo) with 12658 patient years of observation. There were 9636 dropouts (mean time to dropout was 28 days) and relative risk (RR (placebo/drug))= 1.33 (95% confidence limits, 1.28, 1.39; P < 10(-16)). As expected, lack of blood pressure (BP) control was far more common in patients randomized to placebo; therapeutic failure, RR = 2.53 (2.35, 2.73; P < 10(s15)) and hypertensive emergency, RR = 2.75 (2.19, 3.57; P < 10(-15)). When administrative dropouts and dropouts resulting from inadequate BP control were excluded, the remaining 38% of dropouts were disproportionately more from drug (2810 drug, 816 placebo), RR = 0.80 (0.74, 0.86; P < 10(-8)). There were 43 deaths, RR=0.72 (0.33, 1.45; P=0.37); 40 strokes, RR = 1.43 (0.68, 2.81; P=0.33) and 77 myocardial infarctions, RR=1.06 (0.62, 1.75; P= 0.82). Irreversible harm (a combination of death, stroke and myocardial infarction, 160 total events) was equally distributed between the drug and placebo groups, RR=1.03 (0.71, 1.47; P=0.86).

Distribution of radioactivity and anthracycline-fluorescence in tissues of mice one hour after [14C]-labeled AD 32 administration. Evidence for tissue aglycone formation.

Levels of radioactivity and total anthracycline fluorescence in tissues of A/JAX mice were compared 1 h after IV administration of unlabeled or [14C]-labeled AD 32 (50 mg/kg). Highest levels of both fluorescence and radioactivity were found in the small intestine (including contents) and liver, a result consistent with the known hepatobiliary excretion of AD 32 and metabolites. Significant accumulations of radioactivity and fluorescence were found in kidney, spleen, large intestine (including contents), lung, and heart. Lesser levels were found in muscle and fat. Little radioactivity and fluorescence were found in brain. Liquid chromatographic analysis of extracts of small intestine and liver homogenates showed N-trifluoroacetyladriamycin (AD 41) as the major fluorescent species, and also revealed N-trifluoroacetyladriamycinol (AD 92) and occasional low levels of AD 32. In addition, there was a major peak of nonfluorescent radioactive material and two fluorescent nonradioactive signals (unknowns 1 and 2), indicative of cleavage of the radiolabel from the chromophore.

Pharmacologic studies with radiolabeled N-trifluoroacetyladriamycin-14-valerate (AD 32). Comparison of total anthracycline fluorescence and radioactivity in mouse serum and urine.

In connection with pharmacologic studies with AD 32, isotopically-labeled drug prepared from 1-[14C]-trifluoroacetic anhydride and adriamycin-14-valerate was used to determine murine serum and urine levels of radioactivity. Other studies, performed in parallel, measured serum and urinary total fluorescence. Serum fluorescence disappeared in a biphasic pattern, with an initial rapid rate of disappearance followed by a somewhat slower phase. For the first hour, serum radioactivity levels were not significantly different than those measured by fluorescence. After this, however, serum radioactivity decayed at a much slower rate than did fluorescence. Furthermore, a large fraction of the injected radioactivity was found excreted in the urine, whereas urine accounted for only a small fraction of the fluorescence. These results suggest the formation, in part, of a hitherto unrecognized nonfluorescent metabolite, most probably N-trifluoracetyldaunosamine.

Kinetic studies of sheep kidney gamma-glutamyl transpeptidase.

The kinetics of sheep kidney gamma-glutamyl transpeptidase was studied using a novel substrate L-alpha-methyl-gamma-glutamyl-L-alpha-aminobutyrate. When the substrate was incubated with the enzyme in the presence of an amino acid or peptide acceptor, the corresponding L-alpha-methyl-gamma-glutamyl derivatives of the acceptors were formed. In the absence of acceptor only hydrolysis occurred, and no transpeptidation products were detected. The presence of the methyl group on the alpha-carbon apparently prevents enzymatic transfer of the L-alpha-methyl-gamma-glutamyl residue to the amino group of the substrate itself (autotranspeptidation). When the enzyme was incubated with conventional substrates, such as glutathione or gamma-glutamyl-p-nitroanilide and an amino acid acceptor, hydrolysis, autotranspeptidation, and transpeptidation to the acceptor occurred concurrently. Initial velocity measurements in which the concentration of L-alpha-methyl-gamma-glutamyl-L-alpha-aminobutyrate was varied at several fixed acceptor concentrations, and either the release of alpha-aminobutyrate or the formation of the transpeptidation products was determined, yielded results which are consistent with a ping-pong mechanism modified by a hydrolytic shunt. A scheme of such a mechanism is presented. This mechanism predicts the formation of an alpha-methyl-gamma-glutamyl-enzyme intermediate, which can react with an amino acid to form the transpeptidation product; or in the absence of, or in the presence of low concentrations of amino acids, can react with water to form the hydrolytic products. Kinetic derivations for the reaction of the enzyme with the conventional substrate gamma-glutamyl-p-nitroanilide predict either linear or nonlinear double-reciprocal plots, depending on the prevalence of the hydrolytic, autotranspeptidation, or transpeptidation reactions. The results of kinetic experiments confirmed these predictions.