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Biomedical subjects

D A Willard

Publications and source records attributed to D A Willard.

At least 19 recordsLinked to original sources
PubMed1993

Automatic spring-loaded biopsy gun with ultrasonic control for renal transplant biopsy.

The automatic spring-loaded biopsy gun with 18-gauge needle was used to perform 20 renal transplant biopsies. A total of 35 needle passes were used during the 20 biopsies to obtain 31 cores of renal tissue (ratio of successful cores to passes 0.88). Nineteen of 20 biopsies (95%) resulted in renal tissue sufficient for diagnosis. One patient experienced gross hematuria that required blood transfusion and resulted in temporary ureteral clot obstruction. We believe the automatic spring-loaded biopsy gun with ultrasonic control allows rapid, accurate, and safe histologic assessment of the renal allograft, and we recommend this system for routine use.

Biopsy↗
PubMed1993

Effect of food on pravastatin pharmacokinetics and pharmacodynamics.

The pharmacokinetics and pharmacodynamics of pravastatin 20 mg administered twice daily when taken with or one hour before meals were evaluated in 24 hypercholesterolemic men in an 8-week, open-label, randomized, two-way crossover study. The bioavailability of pravastatin was reduced significantly (p < or = 0.001) when it was taken with meals (AUC dropped 31% and Cmax dropped 49%), and mean Tmax increased 50% (p < or = 0.01). The mean elimination t1/2 was unaffected by taking pravastatin with food. However, reductions in mean total cholesterol and low density lipoprotein cholesterol were identical whether pravastatin was given with or before meals. In both treatment groups, total cholesterol and low-density lipoprotein cholesterol were significantly reduced from baseline (p < 0.001). These results indicate that although the bioavailability of pravastatin is reduced when taken with meals, the lipid-lowering efficacy of pravastatin is not altered. It can be concluded that pravastatin can be ingested without regard to meal time.

Cholesterol↗
PubMed1991

Pharmacokinetics, safety, and pharmacologic effects of fosinopril sodium, an angiotensin-converting enzyme inhibitor in healthy subjects.

The pharmacokinetics, pharmacodynamics, and safety of fosinopril sodium (SQ 28,555), a new orally active angiotensin-converting enzyme (ACE) inhibitor, was evaluated in 73 healthy men in two separate studies. In study I, doses ranging from 10 to 640 mg were administered once daily for 3 days to seven groups of five subjects each. Serum aldosterone levels, ACE activity, and sitting blood pressure were determined, as were pharmacokinetic parameters of fosinoprilat, the active diacid of fosinopril. In a dose-tolerance study (study II), 80 and 160 mg of the drug were administered in doses of 40 mg bid and 80 mg bid for 2 weeks. Pharmacokinetics were determined on days 1 and 14, and blood pressure and ACE activity were measured daily. One hour after all doses of fosinopril, serum ACE activity was undetectable. Peak blood levels of fosinoprilat occurred at about 3 hours after dosing, and linear kinetics of the diacid were observed. ACE activity remained undetectable for more than 24 hours after the treatment was stopped in study II. Serum aldosterone levels were decreased by 50% of baseline values in both studies. In study I, maximal reductions in mean blood pressure occurred approximately 6 hours postdose; once-daily doses of 20 mg or greater achieved reductions of 11.3 to 21.6% (P less than or equal to .05, compared with placebo reductions). Fosinopril was well tolerated. Subjects reported only mild gastrointestinal complications at doses of 80 mg/day or higher. These data show that fosinopril is a safe and effective inhibitor of ACE with a long duration of action on serum ACE activity.

Adolescent↗
PubMed1991

Pharmacokinetic interaction between propranolol and the HMG-CoA reductase inhibitors pravastatin and lovastatin.

1. Single oral 20 mg doses of the HMG-CoA reductase inhibitors pravastatin and lovastatin, with and without concomitant propranolol (40 mg twice daily), were administered to 16 healthy male subjects participating in a randomized, four-way crossover study. 2. Serum concentrations of total and active inhibitors were measured by bioassay and concentrations of pravastatin, two pravastatin metabolites and lovastatin acid were measured by gas chromatography/mass spectrometry. 3. Coadministration of propranolol with pravastatin reduced the mean area under the serum concentration-time curve (AUC) of total inhibitors by 23%, of active inhibitors by 20% and of pravastatin by 16%. 4. Coadministration of propranolol with lovastatin also resulted in decreases in the mean serum AUC of total inhibitors by 18%, of active inhibitors by 12% and of lovastatin acid by 13%. 5. These decreases in systemic drug concentrations may reflect enhanced drug first-pass hepatic clearance in the presence of propranolol. 6. The clinical significance of these changes is likely to be small.

Adult↗
PubMed1990

Disposition of zofenopril calcium in healthy subjects.

Zofenopril calcium (1) is a prodrug that is hydrolyzed in vivo to the active angiotensin-converting enzyme (ACE) inhibitor SQ 26,333 (2). In a two-way crossover study, six healthy male subjects (age range 25-36 years) each received an iv 11.2-mg dose of [14C]SQ 26,703 (14C-3; the L-arginine salt of 2) and an oral 10-mg (equimolar) dose of 14C-1. After the iv dose of 14C-3, the 0-96-h recovery of radioactivity averaged 76 and 16% of the dose in urine and feces, respectively, indicating substantial biliary secretion. After the oral dose of 14C-1, excretion of radioactivity averaged 70% (urine) and 26% (feces). Negligible amounts of 1 were present in urine, indicating complete hydrolysis of the orally administered prodrug. The oral absorption of 1 was almost complete and the oral bioavailability of 2 averaged approximately 70%. The terminal elimination half-life for 2 after the iv dose averaged 5.5 h. Whole body clearance, renal clearance, nonrenal clearance, and Vdss averaged 11.4, 3.1, and 8.3 mL/min/kg and 1.3 L/kg, respectively. These data indicated that 2 is eliminated by the kidney as well as the liver, is extensively metabolized, and is distributed extensively into extravascular sites.

Administration, Oral↗
PubMed1990

Pharmacokinetics and pharmacodynamics of pravastatin alone and with cholestyramine in hypercholesterolemia.

The pharmacokinetics, pharmacodynamics, and safety of pravastatin, a new selective 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, were evaluated during monotherapy and with subsequent concomitant cholestyramine therapy in 33 patients with primary hypercholesterolemia in this randomized study. After 4 weeks, pravastatin monotherapy (5 mg, 10 mg, and 20 mg twice daily) significantly decreased total cholesterol by 17% to 24% (p less than 0.001 versus baseline) and low-density lipoprotein cholesterol by 23% to 35% (p less than 0.001). High-density lipoprotein cholesterol increased by 8% to 9%, and triglycerides decreased by 6% to 9%. The area under the serum concentration-time curve and maximum serum concentration of pravastatin showed dose-proportionality; time to maximum serum concentration and serum elimination half-life were independent of dose. When added to pravastatin therapy, cholestyramine enhanced the lipid-lowering effects of pravastatin. After 4 weeks of combination therapy, total cholesterol was reduced by 32% to 38% (p less than 0.001 versus baseline), and low-density lipoprotein cholesterol was reduced by 47% to 56% (p less than 0.001). High-density lipoprotein cholesterol increased by 11% to 18% (p less than 0.05). Pravastatin was well tolerated; no clinical adverse events directly attributable to the drug were reported.

Adult↗
PubMed1990

Disposition of pravastatin sodium, a tissue-selective HMG-CoA reductase inhibitor, in healthy subjects.

Pravastatin sodium, a competitive inhibitor of HMG-CoA reductase, is a new orally effective hypocholesterolaemic agent. In a two-way crossover study, eight healthy male subjects each received an intravenous and an oral dose of [14C]-pravastatin sodium. The oral absorption of [14C] activity from pravastatin sodium was about 34% and the oral bioavailability was about 18%, suggesting first-pass metabolism of pravastatin. After the intravenous dose, the recovery of radioactivity averaged 60% and 34% in urine and faeces, respectively. Corresponding values were 20% (urine) and 71% (faeces) for the oral dose. The estimated average plasma elimination half-life of pravastatin was 0.8 and 1.8 h for the intravenous and oral routes, respectively. The average values for total and renal clearances were 13.5 and 6.3 ml min-1 kg-1, respectively, and the steady-state volume of distribution averaged 0.51 kg-1. These results suggest that both kidney and liver are important sites of elimination for pravastatin.

Administration, Oral↗
PubMed1988

Dose proportionality of nadolol pharmacokinetics after intravenous administration to healthy subjects.

To support the increasing use of intravenous beta-blockers during cardiovascular emergency and surgery, dose proportionality of pharmacokinetics of nadolol was evaluated after intravenous administration of 14C-nadolol at doses of 1, 2 and 4 mg to nine healthy volunteers. There were no observed differences in the excretion or the pharmacokinetics of nadolol with respect to the dose administered. Over a 72-h period after drug administration, an average of about 60% of the dose was excreted in the urine and about 15% was excreted in the feces. The range of values for total body clearance (219 to 250 ml.min-1), renal clearance (131 to 150 ml.min-1), mean residence time (10.5 to 11.3 h), half-life (8.8 to 9.4 h), and steady-state volume of distribution (Vss) (147 to 157 l) indicated that nadolol was extensively distributed and slowly cleared from the body. There was a linear correlation (r2 = 0.97) between the area under the plasma concentration of nadolol versus time curve (AUC) and the dose. All pharmacokinetics parameters, except Vss, were slightly, but significantly, different at the 4 mg dose. Superposition of the dose-normalized average concentrations indicated that despite these minor differences in parameters, the pharmacokinetic behavior of nadolol was linear with respect to dose. Urinary excretion of nadolol was dose independent.

Adult↗
PubMed1988

Pharmacokinetics of intravenous captopril in healthy men.

The pharmacokinetic characteristics of intravenously-administered captopril were investigated in 7 healthy men 20 to 33 years old. Capropril, labeled with 14C, was given by injection over a 1 min period at mean doses of 2.78 mg (13.8 microCi), 5.67 mg (28.2 microCi) and 11.4 mg (56.8 microCi). Concentrations of unchanged captopril, captopril disulfide, and other metabolites (collectively) were determined in body fluids. Pharmacokinetic parameters were calculated for unchanged captopril, and it was shown that the disposition of intravenously-administered drug was linear with respect to dose over the dosage range studied.

Adult↗
PubMed1988

Disposition of fosinopril sodium in healthy subjects.

1 Fosinopril sodium is the first phosphorus-containing angiotensin-converting enzyme (ACE) inhibitor to be studied clinically as an antihypertensive agent. It is an ester prodrug that is hydrolysed in vivo to the active diacid ACE inhibitor, SQ 27, 519. 2 In a three-way crossover study, nine healthy male subjects (age range 20-34 years) each received an intravenous 7.5 mg dose of SQ 27, 519-[14C] and two oral 10 mg doses of [14C]-fosinopril sodium, administered as a capsule and in solution. 3 After the intravenous dose of SQ 27, 519, the 0 to 96 h recovery of radioactivity averaged 44 and 46% of the dose in urine and faeces, respectively, indicating substantial biliary secretion. Only intact SQ 27, 519 was detected in the plasma, urine, and faeces following the intravenous dose of SQ 27, 519. 4 After oral doses of fosinopril sodium, about 75% of the radioactivity in plasma and urine was present as SQ 27, 519; the remainder corresponded mainly to a beta-glucuronide conjugate of SQ 27, 519 (15-20%), and a monohydroxylated analogue of SQ 27, 519 (about 5%). Negligible amounts of fosinopril sodium were present, indicating complete hydrolysis of the prodrug. 5 For the solution and capsule doses, respectively, the oral absorption of fosinopril sodium averaged 32% and 36% and the oral bioavailability of SQ 27, 519 averaged 25% and 29%. 6 The average values for clearance (39 ml min-1), renal clearance (17 ml min-1), Vss (10 1), and plasma protein binding (approximately 95%), indicated that SQ 27, 519 was slowly cleared from the body and not distributed extensively into extravascular sites.

Administration, Oral↗
PubMed1986

Quantitation of drug levels and platelet receptor blockade caused by a thromboxane antagonist.

SQ 28,668 is a structural analog of thromboxane A2. It inhibits the effects of thromboxane in vitro. Fifty-six healthy male subjects were given either placebo or three equal daily doses of SQ 28,668 ranging from 25 to 1200 mg. Plasma drug concentrations increased in a dose-dependent manner. The shape of the plasma drug concentration-time curve was consistent with enterohepatic recirculation. The effects of SQ 28,668 on ex vivo platelet aggregation suggested that SQ 28,668 is a specific competitive antagonist of thromboxane A2 with a platelet receptor dissociation constant (estimated by Schild analysis) of about 19 nmol/L. Approximately 94% occupation of thromboxane receptors by SQ 28,668 was required to produce a small but measurable increase of the template bleeding time. Dose-ranging studies of antithrombotic drugs are difficult and expensive. For this reason, a method was developed that allows estimation of the dose of a thromboxane receptor antagonist that would be expected to be therapeutically equivalent to a given dose of aspirin.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1984

Comparison of kinetic interactions of nadolol and propranolol with cimetidine.

Plasma levels of nadolol and propranolol following a single 80 mg dose of each beta blocker in the presence and absence of cimetidine were determined in 12 healthy male subjects. Cimetidine increased (p less than 0.01) the area under the plasma concentration-time curve and peak plasma levels of propranolol by 46% and 35%, respectively. Nadolol kinetics were not altered significantly by cimetidine, except for a reduction in time to reach peak concentrations. The higher blood levels of propranolol during administration of cimetidine were not associated with any changes in resting blood pressure or heart rate compared with propranolol alone. Cimetidine had no effect on elimination half-lives or apparent mean residence times for either beta blocker.

Adolescent↗
PubMed1982

Renal handling of captopril: effect of probenecid.

14C-Captopril was given intravenously to four normal subjects in a 4-mg priming dose followed by constant intravenous infusion of 1.7 mg/hr for 3.5 hr with and without concomitant probenecid. Steady-state levels of unchanged captopril were obtained between 1.5 and 3.5 hr. In the presence of probenecid, the average steady-state blood levels of total radioactivity were higher (36%) than on captopril alone. Unchanged captopril levels were slightly higher (14%) in the presence of probenecid. Kinetic evaluations were carried out exclusively on data for unchanged captopril. The average total body clearance (ClT) and renal clearance (ClR) of captopril in the absence of probenecid were 775 and 388 ml/kg/hr. The corresponding values for captopril with probenecid (631 and 217 ml/kg/hr) were lower. The average ratio of ClR to ClT for captopril alone was 0.50 and fell to 0.35 in the presence of probenecid. When captopril alone was given, a minimum of 78% of the renal excretion of captopril during steady-state could be attributed to net tubular secretion, but when captopril was given with probenecid, net tubular secretion was only 56%. The volume of distribution of captopril during steady state was not altered by probenecid. For the first 3.5 hr, cumulative renal excretion of total radioactivity with and without probenecid was 55% and 60%, but cumulative excretion of unchanged captopril was higher after captopril alone (36% of dose) than after the combination (21% of dose).

Adult↗
PubMed1982

Captopril kinetics.

Captopril, an angiotensin-converting enzyme inhibitor with antihypertensive properties, was given by mouth and intravenously in 10-mg doses to five healthy subjects. After intravenous dosing, semilogarithmic plots of captopril blood levels : time showed a triexponential decay. Data were analyzed using an open three-compartment model. The average volume of distribution (Vd) was 0.2 l/kg for the central compartment and 2 l/kg for the elimination (beta) phase. The Vd at steady-state was 0.7 l/kg. The total body clearance of captopril averaged 0.8 l/kg/hr and the mean blood half-life during the beta phase was 1.9 hr. In the 0- to 96-hr urine, after intravenous and oral drug, excretion of radioactivity accounted for 87% and 61% of dose. In the 0- to 24-hr urine, averages of 38% (intravenous) and 24% (oral) of the doses were excreted as unchanged captopril. Absolute absorption of the radioactive oral dose was 71% and the absolute oral bioavailability of captopril was 62%.

Absorption↗