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Biomedical subjects

S Hvidt

Publications and source records attributed to S Hvidt.

At least 37 records · Page 2Linked to original sources
PubMed1983

Effects of physical activity and immobilization on plasma digoxin concentration and renal digoxin clearance.

Plasma digoxin concentration and renal digoxin clearance were determined during 2 hr of normal physical activity and during 2 hr of complete immobilization in eight healthy subjects on steady-state digoxin dosing. Mean plasma digoxin concentration rose from 0.64 +/- 0.13 ng/ml during physical activity to 1.04 +/- 0.19 ng/ml (63%) after 2 hr of rest. Resumption of physical activity resulted in gradual decline of plasma digoxin, and subsequent strenuous exercise reduced the value to preimmobilization level. Mean renal digoxin clearance was reduced from 168.4 +/- 18.7 ml/min during physical activity to 137.2 +/- 32.7 ml/min during rest whereas creatinine clearance was unchanged. The rise in plasma digoxin during rest is presumed to be due to changes in the binding of the drug to tissues such as skeletal muscles. Our findings indicate that attention should be given to the state of physical activity when kinetic studies are performed or when digoxin therapy is monitored by means of plasma digoxin analysis.

Adult↗
PubMed1983

The diagnostic value of determination of intraerythrocytic sodium and potassium concentrations versus plasma digoxin concentration in digoxin intoxication.

Plasma digoxin measurements have proved unserviceable as a means of differentiating between toxic and non-toxic patients. In order to assess the value of a biological effect of digoxin in this discrimination, intraerythrocytic sodium and potassium concentrations were determined in 55 chronically digitalized patients of whom 10 were digoxin-intoxicated according to ECG criteria. Digitoxicity was associated with elevated intraerythrocytic sodium concentration (mean +/- SEM 19.3 +/- 1.2 versus 11.3 +/- 0.3 mmol/l, p less than 0.001) and reduced intraerythrocytic potassium concentration (94.6 +/- 2.3 versus 100.0 +/- 0.6 mmol/l, p less than 0.001) compared to non-toxic patients. Mean (+/- SEM) plasma digoxin concentrations in the two groups were 3.14 +/- 0.41 and 1.57 +/- 0.09 nmol/l, respectively (p less than 0.001). When diagnosing toxicity in chronically digitalized patients, plasma digoxin and intraerythrocytic sodium determinations showed sensitivities of 60 and 100%, respectively. The predictive values of a positive test were 75% for plasma digoxin and 83% for intraerythrocytic sodium.

Aged↗
PubMed1982

Flexibility of myosin rod determined from dilute solution viscoelastic measurements.

The frequency dependencies of the storage and loss shear moduli, G' and G", of myosin rod solutions at 1.0 and 7.0 degrees C were measured by use of the Birnboim-Schrag multiple lumped resonator apparatus in solvents with and without glycerol. The infinite dilution moduli were determined and compared with theoretical models for a rigid rod and a freely jointed trinodular rod and with an empirical model for a semiflexible rod. Only the latter could fit the data. A rotational relaxation time of 25 mus and a slowest bending time of 3.1 mus, both reduced to water at 20 degrees C, were determined from the fit. A persistence length of about 130 nm was obtained from either the bending time, the rotational relaxation time, or the intrinsic viscosity. The average thermal excursion of the end of subfragment 2 was estimated to be 26 nm, more than sufficient to span the gap between the thick and thin filaments in muscles at all sarcomere lengths. Thus, a hinge between heavy meromyosin and light meromyosin does not appear necessary for myosin-actin contact. Young's modulus of about 1 x 10(9) N/m2 also makes it unlikely that subfragment 2 can be the elastic element in the Huxley-Simmons model of muscle contraction.

Animals↗
PubMed1982

The long-term effect of verapamil on plasma digoxin concentration and renal digoxin clearance in healthy subjects.

Single-dose investigations in healthy subjects have demonstrated substantial impairment of renal and extrarenal clearance of digoxin during coadministration of verapamil. A longitudinal study has been performed to assess the changes in digoxin disposition during long-term verapamil therapy. After one week of verapamil 240 mg/d mean plasma digoxin had risen from 0.21 +/- 0.01 ng/ml (SE) to 0.34 +/- 0.01 ng/ml(p less than 0.01), and renal digoxin clearance had fallen from 197.57 +/- 17.37 ml/min to 128.20 +/- 10.33 ml/min (p less than 0.001). These changes gradually subsided, and after six weeks, renal digoxin clearance had normalized and plasma digoxin had declined to 0.27 +/0 0.02 ng/ml (NS). The 24-h urinary recovery of digoxin increased from 46.46 +/- 3.23% before to 69.78 +/- 3.69% (p less than 0.001) after six weeks of verapamil co-administration, and this elevation persisted throughout the study. The verapamil-induced suppression of renal digoxin elimination disappears over a few weeks of drug exposure, whereas the inhibition of the extrarenal clearance of digoxin seems to persist.

Adult↗
PubMed1982

Effect of nifedipine on digoxin kinetics in healthy subjects.

Verapamil has been shown to reduce total-body digoxin clearance by 35% due to impairments of both renal and extrarenal clearances. Our study was undertaken to evaluate the influence of the related calcium antagonist nifedipine on single-dose kinetics. Nifedipine increased extrarenal clearance of digoxin from 1.09 +/- 0.30(SD) to 1.45 +/- 0.23 ml/min/kg (P less than 0.05) and reduced the total urinary recovery of the drug from 69.2% +/- 5.9(SD) to 64.3% +/- 5.2 (P less than 0.05). There were no significant changes in renal digoxin clearance, distribution, or biological half-life or in digoxin distribution volumes during nifedipine coadministration.

Adult↗
PubMed1982

Intraerythrocytic sodium and potassium concentrations during acute and chronic digitalization.

To assess the cellular effects of digoxin, intraerythrocytic sodium and potassium concentrations were measured in 17 patients during the early phase of digitalization, in 45 patients on long-term therapy and in 64 non-digitalized control patients. Acute digitalization raised intraerythrocytic sodium from 11.6 +/- 0.4 to 16.7 +/- 1.0 mmol/l (mean +/- SEM) (p less than 0.01) and reduced intraerythrocytic potassium from 100.1 +/- 1.3 to 95.9 +/- 1.8 mmol/l (p less than 0.01). These changes were strongly correlated with the steady-state plasma digoxin concentration. During a few weeks of digoxin therapy, the intraerythrocytic cation composition normalized gradually. In patients on chronic treatment, neither intraerythrocytic sodium (11.3 +/- 0.3 mmol/l) nor potassium concentrations (100.0 +/- 0.6 mmol/l) differed significantly from the values of the control group (11.4 +/- 0.2 and 99.9 +/- 0.5 mmol/l, respectively). The changes in intraerythrocytic cation concentrations, induced by acute digitalization, seem to disappear during chronic administration of the drug.

Aged↗
PubMed1981

Digoxin-verapamil interaction.

To explore a possible interaction between digoxin and verapamil, a single-dose kinetic study of digoxin was performed and then repeated after 10 days of verapamil treatment in eight healthy subjects. Verapamil diminished the apparent central distribution volume of digoxin from 0.83 +/- 0.25 to 0.64 +2- 0.17 l/kg (P less than 0.05) and reduced total body clearance of digoxin from 3.28 +/- 0.58 to 2.15 +/- 0.66 ml/min/kg (P less than 0.001) by impairing both renal and extrarenal clearance. Biological digoxin half-life rose from 38.6 +/- 8.5 to 50.5 +/- 8.3 hr (P less than 0.005). Reduction of renal clearance of digoxin may be due to inhibition of tubular secretion. The underlying mechanisms of extrarenal interaction are not known, but impaired hepatic degradation of digoxin induced by verapamil should be considered.

Adult↗
PubMed1980

The effect of quinidine on digoxin kinetics in cardiac patients.

The pharmacokinetics of digoxin was studied in 11 subjects before and during quinidine treatment. Renal clearances of digoxin and creatinine were calculated from plasma concentrations and urinary excretions of digoxin and creatinine in subjects on long-term digoxin treatment. The investigations were repeated in the same subjects during administration of quinidine. Renal clearance of digoxin decreased, while plasma concentration of digoxin and renal excretion of digoxin increased in the presence of quididine, indicating substantial changes of digoxin kinetics, induced by quinidine. The reduction in renal clearance of digoxin may be due to a specific inhibition of tubular secretion of digoxin. The considerable rise of the plasma digoxin level and the increased excretion of digoxin support the assumption of a major extrarenal mechanism of interaction.

Aged↗
PubMed1975

Alprenolol in angina pectoris. A comparative study of the tablet form and slow-release formulation.

In a double-blind crossover trial in angina pectoris patients, alprenolol in a slow-release formulation (Aptin Durules) was compared with ordinary Aptin tablets. Four hundred mg per day in tablets given four times a day produced the same increase in exercise tolerance five hours after last intake as did an equivalent dose of slow-release formulation given twice per day nine hours after intake. Aptin Durules in double the dosage had a considerably greater effect. An optimal, sustained and antianginal effect of alprenolol is best achieved by giving 400 to 800 mg per day of slow-release formulation with 10 to 12 hours' dosage interval.

Aged↗
PubMed1974

Effect of prolonged thiazide treatment on renal lithium clearance.

Renal lithium clearances were determined after the administration of a small test dose of lithium carbonate in 22 patients when they were on long-term treatment with thiazides and when they were not on such treatment. Thiazide administration led to a 24% reduction in the lithium clearance. Diuretic drugs should be used with caution in patients given lithium treatment, and lithium should be used with caution in patients receiving diuretic treatment.

Bendroflumethiazide↗