THE USE OF ANTIPYRINE IN THE MEASUREMENT OF TOTAL BODY WATER IN MAN

The use of gas chromatographic-mass spectrometric-computer systems in pharmacokinetic studies

Pharmacokinetic studies involving plasma, urine, breast milk, saliva and liver homogenates have been carried out by selective ion detection with a gas chromatographic-mass spectrometric-computer system operated in the chemical ionization mode. Stable isotope labeled drugs were used as internal standards for quantification. The half-lives, the concentration at zero time, the slope (regression coefficient), the maximum velocity of the reaction and the apparent Michaelis constant of the reaction were determined by regression analysis, and also by graphic means.

The plasma half-life of antipyrine in chromic uraemic and normal subjects

1. Antipyrine was given intravenously in a dose of 18 mg/kg body weight to twelve patients with chronic renal failure (plasma creatinine greater than 4.9 mg/100 ml) who were not taking drugs and twenty normal subjects. 2. Plasma antipyrine levels were measured by a specific method, the plasma half-life of the drug was determined and used as an index of drug oxidation. 3. The mean (+/- s.d) plasma antipyrine half-life in patients with chronic renal failure (7.3 +/- 2.0 h) was significantly shorter than in normal subjects (13.2 +/- 4.3 h: P less than 0.002). There was no difference in the apparent volume of distribution of antipyrine between the two groups (P greater than 0.6). 4. Pretreatment of five patients with chronic renal failure and seven normal subjects with antipyrine or phenobarbitone for weeks significantly shortened the mean plasma antipyrine half-life from 7.4 +/- 2.5 h to 5.0 +/- 1.5 h in uraemics (P less than 0.005) and from 13.2 +/- 4.5 h to 6.9 +/- 1.5 h in normal subjects (P less than 0.0025).5. These results suggest that oxidation of antipyrine by hepatic microsomal enzymes is increased in patients with chronic renal failure, but a state of maximal induction of these enzymes was not observed. The clinical implication of this finding with regard to the association between liver microsomal enzyme induction and vitamin D resistant osteomalacia is discussed.

Total and regional myocardial blood flow measurements with 25 micron, 15 micron, 9 micron, and filtered 1-10 micron diameter microspheres and antipyrine in dogs and sheep

The accuracy of regional myocardial blood flow measurements made with microspheres of different sizes is uncertain. Therefore, we simultaneously injected radioactive microspheres of different sizes into the left atria of dogs and sheep; the microsphere diameters were 25µ, 15µ, 9µ, 1-l0µ, and filtered 1-10µ (most > 7µ). Antipyrine was sometimes simultaneously infused for 15-60 seconds. Myocardial blood flow was altered by hemorrhage, tachycardia, supravalvar aortic constriction, or infusion of methoxamine or adenosine triphosphate; left coronary artery branches were occluded on two occasions. Sometimes the percent of untrapped microspheres was estimated. All sizes of microspheres measured similar total myocardial blood flows when the percent of untrapped microspheres was known. All indicators were distributed identically to the right and left ventricular free walls and septum; ischemic areas had a 1% excess of antipyrine. With any pair of microspheres, the larger had a subendocardial excess except for 25µ microspheres, which were in excess compared with 15µ microspheres in the higher flow layer whether it was subendocardial or subepicardial. The greatest difference for any pair of microspheres was 10.53% of flow in a layer. Antipyrine did not define which size of microspheres measured true regional blood flow, since many previously unemphasized limitations were discovered. Nevertheless, we believe that microspheres 9µ in diameter are probably the best for measuring regional myocardial blood flow.

Immediate decrease by hydrocortisone of the plasma half-life of antipyrine

Infusion of hydrocortisone in man caused an immediate shortening of the plasma half-life of antipyrine. There was no change in the 'apparent' volume of distribution of antipyrine and the plasma concentrations of hydrocortisone during the infusion remained within physiological limits. Similar changes in plasma half-lives of antipyrine were observed in the dog, but in vitro studies of drug oxidation with dog liver failed to show any difference between biopsy samples taken before and during steroid infusion.Many drugs and chemicals are known to stimulate rates of drug oxidation in both man and animals. Administration of these inducing agents results in an increase in the activity of enzymes catalyzing drug oxidation, most of which are located with-in the endoplasmic reticulum of liver cells. In man there is usually a delay of 4-8 days before an appreciable change in rates of drug metabolism is seen when such an agent is administered (Breckenridge, Orme, Thorgeirsson, Davies & Brooks, 1971); in rats, the administration of enzyme-inducing agents causes increased rates of drug metabolism only 24-48 h after their administration.We wish to report in this paper an immediate and hitherto undescribed effect of hydrocortisone on rates of antipyrine elimination in man.

Drug-metabolizing capacity in states of drug dependence and withdrawal

1. Drug-metabolizing capacity was assessed in 8 barbiturate-dependent and in 3 Mandrax-dependent patients using, as indices, plasma antipyrine half-life and in some cases urinary output of 6beta-hydroxycortisol. For comparison, antipyrine half-life was also measured in volunteers before and after a period of taking hypnotic doses of these agents.2. Both indices indicated a very high drug-metabolizing capacity in the dependent subjects on admission, the antipyrine half-life value in the barbiturate patients being the shortest reported to date for any drug-exposed group. The urinary output of 6beta-hydroxycortisol was approximately three times that in a control population.3. This induction of drug-metabolizing capacity presumably contributed to the marked drug tolerance observed in the dependent patients.4. It appeared that drug-metabolizing capacity eventually returned to normal levels after withdrawal of the barbiturate.5. It is concluded that the abnormal drug-metabolizing capacity of dependent patients must be taken into account in assessing dose requirements for other drugs.

Increased antipyrine half-life in women taking oral contraceptives

The plasma half-life of antipyrine has been measured in 18 women taking oral contraceptives and in 19 control subjects. The mean half-life in the oral contraceptive group of 13.2±2.0 hr. was significantly prolonged compared to the control value of 10.5±2.5 hours

Genetic control of drug levels in man: antipyrine

Antipyrine was administered to identical or monozygotic twins and to fraternal or dizygotic twins. Individuals with identical genotypes (monozygotic twins) exhibited significantly less variability in antipyrine halflife than did genetically different individuals (dizygotic twins). Therefore variations in antipyrine metabolism appear to be determined genetically rather than environmentally. In the 36 twins tested, antipyrine half-lives varied between 5.1 and 16.7 hours. No significant correlation occurred between half-lives for phenylbutazone and antipyrine in the 28 twins who received both drugs.

Genetic control of drug levels in man: phenylbutazone

Phenylbutazone was administered to seven pairs of identical (monozygotic) twins and to seven pairs of fraternal (dizygotic) twins. Individual half-lives ranged from 1.2 to 7.3 days. Subjects with identical genotypes (monozygotic twins) exhibited very similar phenylbutazone half-lives; significantly greater differences in half-life occurred in dizygotic twins. The previously established large variations among individuals in phenylbutazone metabolism appear to be genetically, rather than environmentally, determined.