Search PubMed⌕ Search

Biomedical subjects

K A Conrad

Publications and source records attributed to K A Conrad.

At least 55 records · Page 3Linked to original sources
PubMed1983

The influence of a cooked meat meal on creatinine plasma concentration and creatinine clearance.

1 The influence of a meal containing cooked meat (225 g) on creatinine plasma concentration, creatinine urinary excretion and creatinine clearance was determined in six healthy male subjects. 2 The meat meal produced an average 52% increase in creatinine plasma concentration within 1.5 to 3.5 h after ingestion. The 24 h area under the creatinine plasma concentration-time curve increased by about 19%. Urinary creatinine excretion during 24 h increased by an average of 13%. Creatinine clearance was not altered in response to the meal of cooked meat.

Adult↗
PubMed1982

The effect of vitamin C on the pharmacokinetics of caffeine in elderly men.

The influence of vitamin C on the pharmacokinetics of caffeine was investigated in 10 elderly males, age 66 to 86 yr. Caffeine was administered intravenously on three different occasions over a 7-wk period: before vitamin C restriction, after approximately 4 wk of vitamin C restriction (15 mg dietary intake per day), and after 2 wk of vitamin C supplementation (500 mg orally, twice daily). Blood and urine samples were collected over a 48-h period after each caffeine administration. The plasma half-life, rate constant of elimination, apparent volume of distribution, total body clearance, renal clearance, and metabolic clearance of caffeine were determined. Simultaneous plasma, whole blood and leukocyte vitamin C concentrations were obtained. All of the average vitamin C concentrations monitored (plasma, whole blood, and leukocyte) changed significantly during the study, corresponding to the alterations in dietary vitamin C intake. Conversely, none of the caffeine pharmacokinetic parameters evaluated changed significantly during the study. The average metabolic clearance was approximately 77 (ml hr-1) kg-1 and the average half-life was approximately 4.6 h for all caffeine administrations. These results indicate that the elimination of caffeine in the elderly is not affected significantly by the concentrations of vitamin C achieved during this study.

Aged↗
PubMed1982

Cardiovascular effects of caffeine in elderly men.

Ten healthy elderly male volunteers were given 4 mg/kg of caffeine by intravenous infusion on three separate occasions. This resulted in mean peak plasma concentrations of caffeine of 7.4 +/- 0.7 micrograms/ml. Immediately after each of the three caffeine infusions, the mean systolic blood pressures increased 14, 7, and 16 mm Hg, and the mean diastolic blood pressures increased 7, 4, and 7 mm Hg, respectively. Both the systolic and the diastolic blood pressures returned to preinfusion values within 4 hours. The QS2 index and the left ventricular ejection time (LVET) index increased after caffeine, probably as a result of the caffeine-induced increase in arterial blood pressure. The pre-ejection period (PEP), the PEP/LVET ratio, and the diastolic time remained unchanged. Caffeine, in doses equal to those contained in 2 to 3 cups of coffee, produces an increase in blood pressure but has no demonstrable positive inotropic effect in healthy elderly men.

Aged↗
PubMed1981

Cardiovascular effects of theophylline. Partial attenuation by beta-blockade.

The effects of theophylline upon cardiovascular function were studied in 8 male subjects, aged 22-33 years, before and during concomitant administration of metoprolol (50 mg every 6 h) and propranolol (40 mg every 6 h). Theophylline, as aminophylline (6.7-7.3 mg/kg) was given over 30 min. The theophylline level five minutes after completion of the aminophylline infusion was 15.9 +/- 1.8 micrograms/ml in the absence of beta blockade, 16.1 +/- 1.7 micrograms/ml during metoprolol, and 15.1 +/- 1.6 micrograms/ml during propranolol. Theophylline produced a 7% increase in mean arterial pressure which was not attenuated by either metoprolol or propranolol. Heart rate was not changed by theophylline. The QS2 Index (QS2I), a sensitive indicator of inotropism, was shortened from 488 +/- 16 to 476 +/- 16 msec (p less than 0.01) by theophylline alone. After administration of metoprolol or propranolol, theophylline produced no shortening of the QS2I. Theophylline has a mild inotropic effect in healthy subjects. This effect is prevented by pretreatment with beta-adrenergic antagonists.

Adrenergic beta-Antagonists↗
PubMed1981

Clodronate kinetics and dynamics.

Clodronate disodium (Cl2MDP) was given intravenously in doses of 3, 6 and 10 mg/kg to six men (aged 23 to 30 yr). Volume of distribution was 0.2720 +/- 0.0255 l/kg (mean +/- SD) after 3 mg/kg dose, 0.3037 +/- 0.0445 l/kg after 6 mg/kg, and 0.2528 +/- 0.417 l/kg after 10 mg/kg. The elimination rate constant was 0.3787 +/- 0.0546 hr(-1), 0.3492 +/- 0.0616 hr(-1), adn 0.3962 +/- 0.0358 hr(-1) after 3, 6, and 10 mg/kg. Corresponding total body clearances were 0.1026 /+- 0.0149, 0.1049 +/- 0.0159, and 0.0998 +/- 0.0172 l/kg/hr. Renal clearance accounted for 73% of total body clearance; 73% of the drug was extracted unchanged in the urine in 24 hr. After Cl2MDP serum phosphate decreased approximately 13%; this was associated at the 10 mg/kg dose with a transient fall in fractional phosphate excretion. There was no significant changes in the serum concentration of fractional excretion of calcium, sodium, or uric acid. Creatinine clearance and renal concentrating ability were not altered by Cl2MDP. After short-term administration Cl2MDP is excreted primarily by the kidney but has no significant effects on renal function.

Adult↗
PubMed1981

Effects of atropine on diastolic time.

Atropine was given intravenously to 10 normal volunteers in increments of 0.01 mg/kg to a total dose of 0.04 mg/kg. This produced an increase in heart rate from 65 +/- 11 to 112 +/- 14 beats/min, a decrease in diastolic time from 534 +/- 131 to 180 +/- 65 msec, and a decrease in percent diastole from 55.6 +/- 5.3% to 32.4 +/- 7.2% (p < 0.001). Administration of isoproterenol in doses that increased heart rate from 69 +/- 9 to 99 +/- 12 beats/min produced a decrease in diastolic time from 485 +/- 98 to 312 +/- 47 msec and only a slight decrease in percent diastole, from 54.2 +/- 4.3% to 50.6 +/- 3.9%. Atropine, in doses commonly used clinically, may significantly reduce diastolic time and the percent diastole. Because diastolic time is an important determinant of coronary perfusion, administration of atropine to patients with coronary artery disease may increase myocardial ischemia.

Adult↗
PubMed1980

Effect of quinine on digoxin kinetics.

Six subjects were evaluated for the effect of quinine, the l-isomer of quinidine, on digoxin pharmokinetics. A 1.0-mg intravenous digoxin dose was given before and during quinine administration, followed by the measurement of digoxin serum and urine concentrations for 96 hr after each dose. Quinine reduced digoxin total body clearance by 26% from 2.98 to 2.22 ml/min/kg (p < 0.03). Digoxin elimination half-life (t 1/2) was lengthened from 34.2 to 51.8 hr, reflecting a 32% decrease in digoxin elimination rate constant (p < 0.003). Quinine did not reduce digoxin renal clearance or any volumes of distribution. The amount of digoxin excreted into the urine increased from x = 628. 29 micrograms to x = 772.52 micrograms (p < 0.02). Digoxin nonrenal clearance decreased an average of 55% from 1.2 to 0.55 ml/min/kg (p < 0.05). These results suggest that quinine alters digoxin metabolism or biliary secretion, reducing digoxin total body clearance by a mechanism that is qualitatively similar, but quamtitatively different, from quinidine.

Adult↗
PubMed1980

Effects of metoprolol and propranolol on theophylline elimination.

The effects of beta adrenergic blockade on theophylline elimination were studied in nine nofmal subjects. Oral propranolol, 40 mg every 6 hr, induced a fall in theophylline clearance from 0.0464 +/- 0.0294 +/- 0.0129 l/kg/hr (p < 0.001). Oral metoprolol, 50 mg every 6 hr, did not reduce theophylline clearance in the group as a whole but had reducing effect intermediate to that of propranolol on theophylline clearance in some smokers whose theophylline clearance was high initially. Beta adrenergic blockade may reduce theophylline clearance, particularly in subjects whose theophylline metabolism has been induced by cigarette smoking.

Adult↗
PubMed1980

Digitoxin-quinidine interaction: pharmacokinetic evaluation.

The effect of quinidine on digitoxin single-dose pharmacokinetics was evaluated in five healthy adults. Blood was collected for 3 weeks, and a complete urine collection was obtained for 4 days, after a single intravenous dose of digitoxin. The protocol was conducted once while each subject was taking oral quinidine, for 3 weeks, and then repeated 10 days after discontinuing quinidine treatment. Quinidine induced the following changes in digitoxin pharmacokinetics: Elimination half-life was prolonged from 174 +/- 25 to 261 +/- 58 hours (p less than 0.02); total body clearance decreased from 1.54 +/- 0.40 to 1.09 +/- 0.31 mL/h . kg (p less than 0.05); renal clearance decreased from 0.65 +/- 0.07 to 0.46 +/- 0.17 mL/h . kg (p less than 0.05). Digitoxin volume of distribution and protein binding were unaltered by quinidine. Quinidine caused a rise in serum digitoxin levels. Digitoxin total body clearance was decreased by quinidine to an extent comparable to that reported for digoxin; however, the mechanism of the interaction with the two digitalis glycosides may, in part, be different.

Adult↗
PubMed1980

Improved liquid-chromatographic determination of caffeine in plasma.

We describe a rapid, specific, and sensitive liquid-chromatographic micro-method for caffeine in plasma. Each plasma sample can be assayed within about 15 min of its receipt. Samples are denatured with acetonitrile, centrifuged, and the supernate is chromatographed on a reversed-phase column. Only 100 microL of plasma is required, and concentrations as low as 0.3 mg/L can be measured accurately. Other xanthines and their metabolites do not interfere. The small sample required makes the procedure ideally suited for measuring caffeine in the plasma of infants and small animals as well as adults.

Caffeine↗
PubMed1977

Pharmacokinetic studies of quinidine in patients with arrhythmias.

The absorption and disposition of quinidine were measured in nine patients following single oral and intravenous dosing. A new specific chromatographic method was used to measure the drug in plasma and urine. After intravenous administration, the plasma half-life (t1/2beta) was 7.8+/-0.7 h, the volume of distribution (Vd) was 3.0+/-0.5 liters/kg, and the total body clearance was 4.8+/-0.8 ml/min/kg. After oral administration, 87+/-7% (mean+/-SEM) was available to the systemic circulation. Quinidine was removed primarily by hepatic metabolism, with the renal clearance averaging only 1.0+/-0.2 ml/min/kg. Mean quinidine concentrations were estimated in 42 patients on chronic therapy by averaging blood levels during a dosing interval. In patients without heart failure, these corresponded well to mean drug levels predicted from the pharmacokinetic parameters measured after a single intravenous dose, but in patients with heart failure, the values for mean quinidine concentrations were higher than predicted. This suggests that impaired elimination of the drug or a decreased volume of its distribution, or both, may develop in heart failure.

Administration, Oral↗
PubMedDate not supplied

The influence of vitamin C on antipyrine pharmacokinetics in elderly men.

The influence of vitamin C on the pharmacokinetics of antipyrine was investigated in eleven elderly men aged 65-74. Antipyrine (15 mg kg-1) was administered intravenously on three separate occasions over a 7-week period: (a) before dietary vitamin C restriction, (b) after approximately 5 weeks of dietary vitamin C restriction, and (c) after 2 weeks of vitamin C supplementation (500 mg orally twice daily). The mean plasma and leucocyte vitamin C levels (+/- S.D.) before vitamin C restriction were 1.26 +/- 0.31 mg dl-1 and 26.6 +/- 6.7 micrograms 10(-8) leucocytes, respectively. These values decreased and then increased significantly following vitamin C restriction and supplementation, respectively. The mean plasma half-life of antipyrine was 10.2 h and the mean plasma clearance was 2.561 h-1 1.73 m-2 before vitamin C restriction. No significant changes in the clearance, volume of distribution, or half-life of antipyrine occurred during the study, indicating that short-term alterations in vitamin C intake do not affect the pharmacokinetics of antipyrine in elderly males.

Aged↗