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Biomedical subjects

G Levy

Publications and source records attributed to G Levy.

At least 451 records · Page 25Linked to original sources
PubMed1976

Pharmacokinetics in clinical practice. 2. Applications.

The pharmacokinetic concepts introduced and defined in a preceding article are now applied to the management of drug therapy for the individual patient. The factors that affect the time course of drug concentrations in plasma produced by repetitive administration include the dosing rate, total clearance, biologic half-life, and systemic availability of the drug. A clinical pharmacokinetics service can monitor drug concentrations in biologic fluids, design individualized drug-dosing regimens, and carry out pharmacokinetic diagnostic work-ups to help determine the reasons for a patient's unusual response to drug therapy.

Administration, Oral↗
PubMed1976

Pharmacokinetics in clinical practice. I. Concepts.

Important concepts of pharmacokinetics, such as the biologic half-life, clearance, and bioavailability of drugs, can be utilized to describe and predict the time course of drug concentrations in plasma as a function of dose and frequency of drug administration. In quantitative terms, they can serve to characterize the individuality of the patient, including the effects of disease, with respect to drug absorption, distribution, excretion, and metabolism.

Administration, Oral↗
PubMed1976

Serum protein binding as a determinant of warfarin body clearance and anticoagulant effect.

The serum protein binding and elimination kinetics of warfarin were determined in 31 patients with cardiovascular disease who were taking warfarin regularly. The free fraction of warfarin in the serum ranged from 0.00436 to 0.0189, indicating 98.11% to 99.56% protein binding. There was no apparent relationship between the extent of protein binding of warfarin and the concentration of albumin or total protein in the serum. The estimated total body clearance of warfarin in the patients ranged from 1.16 to 4.35ml/hr/kg of body weight and correlated significantly with the free fraction of warfarin in serum. This correlation has been predicted on theoretical grounds and shows that serum protein binding is a major determinant of the elimination kinetics of warfarin in man and an important cause of interindividual variations in its body clearance. The interindividual variation of free warfarin concentrations in the serum of patients with similar prothrombin times was somewhat smaller than the variations in total serum-warfarin concentrations and in the daily dose of warfarin. There was no correlation between prothrombin time and the concentration of free warfarin in serum, indicating that variables other than protein binding also affect the anticoagulant response of patients.

Adult↗
PubMed1976

Intrasubject variation of warfarin binding to protein in serum of patients with cardiovascular disease.

A study of 31 patients with cardiovascular disease who were taking warfarin regularly had shown pronounced intersubject differences in serum protein binding of warfarin and a highly significant correlation between the body clearance of warfarin and the free fraction of the drug in serum. Similar observations have been made in experimental animals and are consistent with predictions based on theoretical considerations. The purpose of this investigation was to determine the intrasubject variation in the free fraction of warfarin in serum. Samples of serum were obtained from 23 of the 31 patients previously studied. The time interval between the two studies was 3.4 to 5.7 mo. The daily dose of warfarin had been changed by 10.6% on the average. With two exceptions, there was no change in concurrent medications. The ratio of free fraction values of warfarin in serum, second/first study, was 0.948 +/- 0.297 (mean +/- S.D.), and there was a highly significant correlation (P less than 0.001) between the individual free fraction values in the first and second studies.

Adult↗
PubMed1976

Effect of renal transplantation on protein binding of drugs in serum of donor and recipient.

Blood samples were obtained periodically before and for about 3 mo after renal transplantation from a donor (mother) and a recipient (9-yr-old son with bilateral nephrectomy) for determination of serum protein binding of salicylate and sulfisoxazole. Ten days after the transplant, the recipient had an acute rejection episode which was treated successfully. The free fraction values of the drugs in serum of the recipient was considerably above normal before transplantation, decreased to normal within 2 days after transplantation, increased again several days before the rejection episode and remained elevated for about 50 days, and then returned to normal. Serum protein binding of the drugs in the serum of the donor was decreased for only a few days after transplantation and then returned to normal.

Adult↗
PubMed1976

Renal clearance of theophylline in man.

The renal clearance of theophylline was determined in 12 experiments with six healthy human adult volunteers and was found to decrease from 8.50+/-2.20 to 276.+/-1.13 ml/min/m2 during 8 hours after oral administration of a single dose of theophylline, 200 mg/m2. There was a strong and highly statistically significant positive correlation between the renal clearance of theophylline and the urine flow rate for each subject, but there was no consistent correlation between renal clearance and plasma concentrations of theophylline.

Adult↗
PubMed1976

Drug biotransformation interactions in man VI: acetaminophen and ascorbic acid.

Oral administration of 3 g of ascorbic acid 1.5 hr after an oral dose of 1 g of acetaminophen caused a rapid and pronounced decrease in the excretion rate of acetaminophen sulfate in five healthy adult volunteers. There was a statistically significant increase in the fractions of the dose of acetaminophen excreted as such as as acetaminophen glucuronide but a decrease in the fraction excreted as acetaminophen sulfate. The apparent biological half-life of acetaminophen increased from 2.3 +/- 0.2 (mean +/- SD) to 3.1 +/- 0.5 hr. Concomitant administration of sodium sulfate prevented these effects. Ascorbic acid, which itself is metabolized in part to the sulfate, inhibits the conjugation of acetaminophen with sulfate by competing for available sulfate in the body.

Acetaminophen↗
PubMed1976

Pharmacokinetics of acetaminophen elimination by anephric patients.

The pharmacokinetics of acetaminophen elimination were determined in five surgically anephric and five physiologically anephric patients on an interdialysis day, and in three normal adult volunteers. There was no significant difference in the biologic half-life and no apparent difference in the volume of distribution of acetaminophen between the three groups of subjects but the anephrics, unlike the normal subjects, showed pronounced accumulation of acetaminophen glucuronide and sulfate in plasma. The apparent volume of distribution for conjugated acetaminophen is considerably smaller than that for the unmetabolized drug even though neither acetaminophen nor its glucuronide or sulfate is significantly bound to plasma proteins. The results of this study indicate that the kidneys do not contribute significantly to the elimination of acetaminophen in man. Sin ce acetaminophen is eliminated largely by conjugation with glucuronic acid and sulfate, it can be concluded that the kidneys do not contribute significantly to the formation of these metabolites.

Acetaminophen↗
PubMed1976

Relationship between dicumarol distribution and the effect of enzyme induction on dicumarol elimination in rats.

Pronounced intersubject differences in the apparent first-order elimination rate constant (kapp) for dicumarol in rats have been found to be due to corresponding differences in the distribution of dicumarol between the liver (the site of dicumarol biotransformation) and the rest of the body. From theoretical considerations and experimental results in animals given only dicumarol, it has been shown that kapp is linearly related to the fraction of drug in the liver (FL). The proportionality constant (k) for these variables was defined as the intrinsic elimination rate constant for dicumarol which should reflect the activity of the enzyme system(s) involved in the elimination of this drug. The purpose of this investigation was to determine the effect of enzyme induction on dicumarol distribution and on the relationship between kapp and FL in rats. It was found that pretreatment with phenobarbital caused a substantial increase in kapp, but that it had no apparent effect on the serum/liver and serum/kidney concentration ratios of dicumarol. The relative weight of the liver was significantly increased by phenobarbital treatment but the weight of the kidneys was not affected. Linear relationships between kapp and FL were found for both the control and the phenobarbital treated groups, but with a significant difference in the slopes of the regression lines. This study illustrates the application of a pharmacokinetic technique which permits a clear and quantitative distinction between the relative contributions of enzyme activity and body distribution to the in vivo elimination kinetics of a drug.

Animals↗
PubMed1976

Effect of route of administration on competitive drug biotransformation interaction: salicylamide-ascorbic acid interaction in rats.

The effect of route of administration on competitive drug biotransformation interactions was explored with respect to the interaction between salicylamide and ascorbic acid. Previous studies in man have shown that this interaction involves competition for available sulfate and consequent inhibition of drug sulfate formation. Adult rats received salicylamide (100 mg/kg i.v. or 500 mg/kg orally) alone or with ascorbic acid (500 mg/kg i.v. or orally). Plasma concentrations and urinary excretion rates of salicylamide, salicylamide glucuronide and salicylamide sulfate were determined as a function of time. With i.v. salicylamide, i.v. ascorbic acid caused a modest decrease of salicylamide sulfate formation and thereby of salicylamide body clearance. Orally administered vitamin had a somewhat more pronounced effect. The vitamin had no effect on the apparent volume of distribution of salicylamide and on the renal clearances of its conjugates. With orally administered salicylamide, oral ascorbic acid caused a very pronounced decrease of salicylamide sulfate formation and salicylamide body clearance, whereas intravenous vitamin had little or no effect. These observations are consistent with the assumption that the magnitude of competitive drug biotransformation interactions, being a function of concentration, is most pronounced when the interactants are co-administered orally, due to their high concentrations in the intestinal wall and liver during the first pass.

Administration, Oral↗
PubMed1976

Effect of activated charcoal on acetaminophen absorption.

Acetaminophen intoxication can cause hepatic, renal, and myocardial necrosis which is often fatal. These lesions develop very rapidly, perhaps during the first pass of the drug through the liver. In case of acute ingestion of an overdose it is therefore essential to employ measures for reducing the absorption of acetaminophen. The effect of activated charcoal on acetaminophen absorption by normal volunteers was determined as a function of the dose of charcoal, the dosage form of acetaminophen, and the charcoal-to-acetaminophen dose ratio. The results indicate that activated charcoal can be an effective antidote for acute acetaminophen intoxication, if administered promptly and in sufficient quantity.

Acetaminophen↗