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Biomedical subjects

J R Powell

Publications and source records attributed to J R Powell.

At least 163 records · Page 9Linked to original sources
PubMed1982

Digoxin-quinidine interaction in patients with chronic renal failure.

We evaluated the effect of quinidine on digoxin pharmacokinetic in six patients with severe renal failure. Quinidine reduced the total body clearance of digoxin from 1.87 to 1.06 l/hour (p less than 0.001), and prolonged the digoxin half-life of elimination from 5.20 to 9.61 days (p less than 0.01). The digoxin volume of distribution was unchanged. Renal clearance of digoxin was negligible; thus, the decrease in total body clearance was due to a decrease in the nonrenal clearance of digoxin. The mean trough serum concentrations of quinidine ranged from 1.0 to 3.0 micrograms/ml. We conclude that in patients with chronic renal failure, the dose of digoxin should be decreased by 50% if quinidine therapy is initiated.

Adult↗
PubMed1981

Human plasminogen.

Explore the source record for details and available documents.

Amino Acid Sequence↗
PubMed1981

Effect of tunicamycin on appearance of carbohydrate variants of plasminogen in rat and rabbit plasma.

The in vivo incorporation of [4,5-3H]leucine and [2-3H]mannose into the lysine-Sepharose affinity chromatography-resolvable carbohydrate variants of rat and rabbit plasminogen has been studied in the absence and presence of tunicamycin (TM). When rabbits and rats were exposed to 0.5 mg of TM per kg of body weight for 30 min and 2 hr, respectively, followed by a single pulse of [4,5-3H]leucine for 2 hr, no radiolabel was found in rat or rabbit variant 1 plasminogen, whereas [4,5-3H]leucine was incorporated into variant 2 plasminogen. In similar experiments utilizing [2-3H]mannose in place of [4,5-3H]leucine, very little [2-3H]mannose was incorporated into either plasminogen variant in the presence of TM. The trichloroacetic acid-precipitable protein of rabbit plasma incorporated virtually identical quantities of [4,5-3H]leucine in the absence or presence of TM, under the above dosage regimens, while, at the same time, a large decrease in the incorporation of [2-3H]mannose was observed in the plasma proteins of rabbits treated with TM. This indicates that many of the plasma proteins may be secreted into plasma divested of asparagine-linked carbohydrate side chains. Further, we conclude that the functional difference (antifibrinolytic amino acid binding capacity) between the two plasma variants of plasminogen more than likely results from additional glycosylation of asparagine in variant 1 plasminogen that normally does not occur in variant 2 plasminogen.

Animals↗
PubMed1981

Poor rectal absorption of trimethoprim/sulphamethoxazole in treating Pneumocystis carinii pneumonia.

A 24-year-old female with Hodgkin's disease and Pneumocystis carinii pneumonia was tested with trimethoprim/sulphamethoxazole (TMP/SMX) tablets. Because treatment failure was feared owing to chronic emesis potentially resulting in incomplete drug absorption, the same TMP/SMX dose was administered by rectal suppositories after the 5th day of oral dosing. The relative fractions (rectal/oral) or the suppository dose absorbed for TMP and SMX were 3.0% and 19.5% respectively. When TMP/SMX treatment is required and the oral route is not practical, the investigational i.v. preparation should be obtained.

Administration, Oral↗
PubMed1981

Cimetidine decreases theophylline clearance.

This study tested the hypothesis that cimetidine decreases theophylline clearance. Aminophylline (6 mg/kg) was administered intravenously both before and after cimetidine treatment in 5 healthy adults. Cimetidine (300 mg) was administered orally every 6 h for 2 days before and 18 h after the aminophylline dose. Plasma samples were collected before and for 24 h after each aminophylline dose, and theophylline concentrations were determined by an enzyme-mediated immunoassay technique. Cimetidine significantly decreased theophylline clearance, mean decrease, 39% (3.85 +/- 0.27 L/h control versus 2.34 +/- 0.23 L/h with cimetidine treatment, p less than 0.002). The apparent volume of distribution was unchanged (p greater than 0.5), whereas the elimination rate constant was significantly decreased by a mean of 42% (control, 0.091 +/- 0.013 h-1 versus 0.053 +/- 0.007 h-1 with cimetidine treatment, p less than 0.005). This corresponded to an average increase in elimination half-life of 73% (range, 50 to 97%). Cimetidine probably slowed theophylline elimination by relatively nonspecific inhibition of the hepatic microsomal mono-oxygenase system. This effect may produce clinically significant changes in serum theophylline concentrations.

Administration, Oral↗
PubMed1980

Genetics and the origin of a vector population: Aedes aegypti, a case study.

Thirty-four population samples representing the worldwide distribution of the mosquito Aedes aegypti were analyzed for variation at 19 to 22 enzyme-coding genes. A multivariate discriminant analysis revealed that the genetic differences among populations in six geographic regions and between two subspecies enable one to determine the regional origin of a population. Such studies of population genetics may have quite general applicability in studying vector-borne diseases.

Aedes↗
PubMed1980

The objective evaluation of dysmenorrhea therapy.

Past attempts to obtain objective evaluation of dysmenorrhea therapy have been severly limited by the lack of accurate, reliable intrauterine pressure data. The development of the catheter-tip microtransducer has made accurate, error- and artifact-free intrauterine pressure recording a reality. This information has made assessment of uterine effects of drug therapy feasible. The combination of this type of information with the use of mathematical processing of data has finally made truly objective assessment attainable. A description of the current technique and the findings made possible by its use are presented.

Clinical Trials as Topic↗
PubMed1980

Evaluation of the absorption from 15 commercial theophylline products indicating deficiencies in currently applied bioavailability criteria.

The bioavailability of theophylline from alcoholic and aqueous oral solutions was compared to that from an intravenous dose in 12 normal adults. The alcoholic elixir surprisingly gave rise to a significantly greater (114 +/- 14%, mean +/- SD) amount absorbed than did the intravenous dose. The aqueous solution (99 +/- 8%) and intravenous dose were statisticlly indistinguishable in this respect, and, furthermore, the extent of absorption from a 300-mg dose of the aqueous solution was 99 +/- 10% of that from a 500-mg dose, and not statistically different. The aqueous solution was thus employed in three subsequent studies as a standard with which to compare 13 different types of theophylline tablets, all marketed in the United States. Of the 13 tablets, eight showed bioavailability statistically distinguishable from that of the standard. Nevertheless, for only two tablets could it be claimed with 95% confidence level that the bioavailability was less than 95%. For none can it be stated at this confidence level that the bioavailability is less than 90%. Bioavailability studies should include criteria of clinical significance in addition to criteria of statistical significance. Contrary to the usual rationale behind choice of a bioavailability standard, nine of the 12 uncoated tablets appeared to allow more rapid absorption of theophylline than did the standard oral solution, an aqueous syrup. Increasing the dose of syrup decreased the rate of theophylline absorption. Orally administered drug solutions may have properties more absorption rate limiting than the disintegration of many brands of tablet.

Absorption↗
PubMed1980

Evaluation of the absorption from some commercial sustained-release theophylline products.

Absorption of theophylline from three commerical products labeled as sustained release was compared to the absorption from a standard uncoated tablet (Searle 200-mg aminophylline tablet) in a single-dose study. Aminodur tablets (Cooper) and Slophyllin Gyrocap capsules (Dooner) had bioavailability (100.2% +/- 19.8% and 98.5% +/- 13.8%) statistically indistinguishable from that of the standard but showed significantly slower absorption (peak times of 10.4 +/- 2.8 and 4.36 +/- 1.35 hr) and lower peak plasma concentrations (13.9 +/- 4.5 and 22.6 +/- 3.5 micrograms/ml/g dose) than the standard (tpeak, 1.52 +/- 0.45 hr; Cpeak, 28.1 +/- 6.2 micrograms/ml/g dose). The time of the plasma concentration peak (2.47 +/- 1.38 hr) after a dose of Tedral S.A. (Warner/Chilcott) was not statistically different from that after the standard, but both the peak concentration (16.0 +/- 3.9 micrograms/ml/g dose) and availability (76.0 +/- 18.4%) were. Multiple-dose projections from single-dose data indicate that of the three test products only Aminodur maintains reasonably constant interdose plasma levels during 12 hoursly dosing. With an 8 hourly dosing schedule Gyrocaps also might be satisfactory. Reasonable predictions of the plasma concentrations arising from Aminodur doses have been made using a single-compartment body model and assuming input from an outer followed by an inner layer of the tablet.

Biological Availability↗