Nonfatty acid-modulated variations in drug binding due to heparin.

Changes in free fatty acids (FFAs) do not always correlate with variations in drug binding. To dissociate heparin effects on FFAs and drug binding, six healthy fasting subjects received 50 units (USP) IV heparin (Harris L932) with and without protamine (3.2 mg IV). Protamine completely suppressed heparin-induced rises in FFAs and warfarin free fraction (W alpha), but diazepam free fraction (D alpha) increased (P less than 0.005). In vitro, increasing concentrations of heparin added to serum increased D alpha (P less than 0.0005) and W alpha (P less than 0.005) without changing FFAs. In eight subjects given 50 units IV heparin (Harris L014), FFAs (P less than 0.001) and propranolol free fraction (P alpha) rose (P less than 0.01), but variations in FFAs and P alpha did not correlate (r = 0.18). When two different heparin lots (Harris L014 and Organon LA39) were tested in vivo. Harris L014 heparin increased FFAs (P less than 0.005) and P alpha (P less than 0.0005), but variations in FFAs and P alpha correlated poorly (r = 0.43, P less than 0.05). In contrast, the Organon LA39 heparin did not change FFAs, but did increase P alpha (P less than 0.0005); variations in FFAs and P alpha did not correlate (r = 0.22). These results indicate that heparin-induced variations in drug binding are not exclusively related to changes in FFAs.

Effect of short- and long-term alcohol use on phenytoin kinetics in chronic alcoholics.

Phenytoin kinetics during long-term alcohol use and withdrawal were studied in 11 male alcoholics with a history of withdrawal seizures and no evidence of chronic liver disease. Ethanol, 20% v/v, was given for 6 days after admission to maintain the blood alcohol level between 500 and 800 mg/l and phenytoin suspension, 150 mg, was given orally or intravenously (on three occasions) every 12 hr for 20 days. The mean (+/- SD) total phenytoin clearance in 9 of 11 subjects was 0.023 +/- 0.006 l/kg/hr during the alcohol ingestion period. Clearance rose to 0.033 +/- 0.013 l/kg/hr (P less than 0.05) during alcohol withdrawal. Total steady-state concentration after 3 wk ranged from 3.4 to 29.9 mg/l, while the weight-corrected dose range was only 3.7 to 5.5 mg/kg/day. Inter- and intra-subject variation in bioavailability was small (0.93 to 1.03). Phenytoin free fractions ranged from 9.09% to 17.75% and changes in total and free phenytoin concentration correlated (r2 = 0.92, P less than 0.001). The data are compatible with the hypothesis that increased phenytoin clearance during alcohol withdrawal is due to the increased metabolic rate of the drug secondary to enzyme induction by ethanol, which becomes unmasked on cessation of drinking. In most alcoholics standard-dose phenytoin (300 mg/l) will induce lower than usual plasma concentrations.

Plasma protein binding of phencyclidine.

In healthy male subjects (n = 12) phencyclidine (PCP) free fraction was 22.0 +/- 2.8 % (mean +/- SD). In male patients with mild to moderate alcoholic liver disease (n = 16) free fraction (23.0 +/- 3.4%) was of the same order as in healthy subjects although age and the concentrations of albumin, bilirubin, and high-density lipoproteins were different (P less than 0.05). Free fraction (76.2 /+- 0.06%) in fatty acid free human serum albumin (HSA, 4.4 gm/dl) was far greater than in plasma. Both the increased binding of PCP in plasma over HSA and the lack of a difference in PCP binding between normals and patients was associated with alpha 1-acid glycoprotein (alpha 1-AGP). This protein is an acute-phase reactant that binds cationic drugs and rises nonspecifically in a variety of diseases. Free fraction of PCP in alpha 1-AGP (75 mg/dl) was 36.4 +/- 1.7%. Half of the variance in PCP binding can be accounted for (r = 0.67, P less than 0.01) from percentage of free PCP = 39.24 - 2.18 (albumin) - 0.094 (alpha 1-AGP). Male rats (n = 14, weight = 251 +/- 7 gm) were alternatively assigned to pretreatment with either saline or alpha 1-AGP (11.6 mg) by cardiac puncture. PCP brain concentrations were reduced (11%, P less than 0.05) in the protein-treated group 5 min after cardiac 3H-PCP (0.17 mg) administration, demonstrating that increased plasma protein binding can reduce free drug concentration during the distribution phase and, thereby, the rate and extent of drug distribution.

Variability in heparin effect on serum drug binding.

Heparinized saline was given to seven men and one woman, aged 21 to 42 yr, after a 14-hr fasting period and 2 hr after breakfast; blood was collected in nonoheparinized tubes. Diazepam (D alpha) and warfarin (W alpha) free fractions were determined in serum by equilibrium dialysis to which radiolabeled drug was added. After 50 U heparin (Harris LO14) intravenously, the maximum effect on D alpha, W alpha, and free fatty acids (FFA) developed in 5 min and lasted 20 to 30 min. D alpha rose and W alpha fell (p < 0.01) at 5 min. Cumulative doses of heparin increased FFAs (F4,16 = 18.29, p < 0.0005). D alpha rises (r = 0.73, p < 0.001) and W alpha falls (r = -0.74, p < 0.001) correlated with changes in FFAs. D alpha rises and W alpha falls were greater postprandially than in the fasted state (p < 0.01). Five subjects were randomly assigned up to 400 U intravenously of each of two different heparin lots (Harris LO14, and Organon LA39.) The FFA rises (reflecting heparin lipolytic activity, F1,32 = 179.62, p < 0.0005), D alpha rises (F1,32 = 34.22, p < 0.0005), and the W alpha falls (F1,32 = 33.20, p < 0.0005) by heparin Harris LO14 were greater than those by heparin Organon LA39. Although small doses of heparin, such as those in heparin locks, can affect drug binding, the extent and variability of the effect depends on the biologic activity of the heparin, and varies with manufacturer and lot, exact time of sampling, and eating.

Methadone binding to orosomucoid (alpha 1-acid glycoprotein): determinant of free fraction in plasma.

The distribution of basic drugs in blood differs qualitatively from that of acidic drugs. The binding of racemic, d-methadone, and l-methadone to human plasma and isolated protein fractions was studied by equilibrium dialysis at 37 degrees. In plasma samples from 29 healthy subjects free fraction of dl-methadone was (mean% +/- SD) 10.62 +/- 1.43. There were significant variations among subjects (p less than 0.001). The free fraction of the d-isomer was 9.24 +/- 1.61% and of the l-isomer, 12.44 +/- 1.53%. Plasma albumin concentration and degree of binding do not correlate, but in normal hypoalbuminemic subjects the free fraction of dl-methadone correlates negatively with the concentration of alpha 1-acid glycoprotein (alpha 1-AGP), an acute-phase reactant protein. Percentage dl-methadone bound to purified human serum albumin (HSA) (4.1 mg/dl) was 36.60% (mean +/- SD). Isolated alpha 1-AGP bound dl-methadone more avidly. As the alpha 1-AGP increased from 0.05 to 2.0 gm/l, free fraction fell from 92.40% to 8.80%. Addition of alpha 1-AGP (0.05 to 2.0 gm/l) to a physiologic concentration of purified HSA or to whole plasma progressively increased methadone binding. In eight monozygotic twin pairs, within-pair differences in binding of dl-methadone were less than in eight dizygotic twin pairs. Less than 20% of naloxone, codeine, morphine, heroin, pentazocine, and diphenoxylate bound to alpha 1-AGP. Elevations of alpha 1-AGP that occur in a variety of diseases may alter the kinetic and pharmacologic activity of methadone.

Acute kinetic and dynamic interactions of zimelidine with ethanol.

The acute interaction of zimelidine (Z) with ethanol (E) was examined in six healthy men aged 20 to 37 yr who randomly received each of four treatments 1 wk apart: Z, 200 mg by mouth, preceded by 1 hr and followed for 7 hr of oral E in juice dosed to maintain blood alcohol concentrations between 800 and 1000 mg/l; placebo Z and E; Z and juice; and placebo Z and juice. E decreased the rate of biotransformation of Z to norzimelidine (NZ) by 46%, but the AUCs of Z, NZ, and their total concentration over 8 hr were not altered by E. Acetaldehyde concentrations did not change and no aversive alcohol-sensitizing reaction was detected. E-induced impairments in memory, body sway, and a manual tracking task were further enhanced by Z, as was the E-induced decrease in friendliness. Data suggest Z and E interact kinetically and dynamically and suggest a mechanism whereby Z may decrease E intake in man.

Binding of drugs to ion-exchange resins in simulated gastric fluid.

The binding of 13 frequently abused drugs to two ion-exchange resins was studied in simulated gastric fluid. The results were compared with those previously obtained with activated charcoal as the adsorbent. The ion-exchange resins adsorbed the drugs more slowly than activated charcoal, and the binding capacities of the resins were inferior. These ion-exchange resins are unlikely to be very useful in removing drugs from the stomach.

Comparative drug adsorption by activated charcoal.

Comparative in vitro studies were carried out to determine the adsorption characteristics of 12 drugs on activated charcoal. At pH 1.3 and 37 degrees, the adsorption capacity of activated charcoal (milligrams per gram of charcoal) was: aspirin, 262; glutethimide, 252; methaqualone, 179; chlordiazepoxide, 157; propoxyphene napsylate, 137; diazepam, 136; amitriptyline, 133; propoxyphene hydrochloride, 127; secobarbital, 124, pentobarbital, 103; phenobarbital, 70; and amobarbital, 51. The adsorption of the weak acids was most markedly decreased at pH 10.8. In patients, actual drug adsorption probably is lower than these maxima because of the presence of mucus, bile salts, and other drugs. In patients investing large amounts of poorly adsorbed drugs, activated charcoal would not be helpful.

The misuse of 'less-hazardous' cigarettes and its detection: hole-blocking of ventilated filters.

Smokers of low-yield, ventilated-filter cigarettes sometimes defeat the purpose of the smoke-dilution holes by occluding them with fingers, lips, or tape. Blocking the holes is shown to have large effects on the delivery by these cigarettes of toxic products (nicotine, tar, and carbon monoxide). Techniques for detecting this misuse of "less hazardous" cigarettes are discussed, with particular emphasis on the distinctive signs of hole-blocking which are left in the spent filters.

Variations in drug free fraction during alcohol withdrawal.

1 Free fractions of diazepam, propranolol and warfarin were determined in 15 male chronic alcoholics in alcohol withdrawal. 2 On admission the mean free fraction of diazepam was 25% above and propranolol 44% below the limits of normal range, while the mean warfarin free fraction was in high normal range. One week later mean free fraction of diazepam declined by 20% while propranolol and warfarin increased by 24% and 19% respectively (P less than 0.05). 3 Propranolol free fraction and alpha 1-AGP concentrations were highly correlated (linear r = -0.83, P less than 0.001). In contrast the sources of variation in diazepam and warfarin free fraction were more complex and less certain. 4 Statistically significant changes of drug free fractions in serum of chronic alcoholics were observed during alcohol withdrawal. The extent and direction of these changes differed for various classes of drugs and their potential causes appear to be quite different. 5 Clinically important changes in drug effect may be present acutely, within the dosing interval, as a result of altered drug binding. These are more likely when the clinical response is closely related to drug concentration and will occur within the dosing interval due to larger fluctuations in free drug concentration, even though the average free drug concentration will remain unchanged. 6 Total drug level changes will be observed during alcohol withdrawal even in absence of detectable changes of drug metabolism.

Ethanol-induced inhibition of hepatic uptake of propranolol in perfused rat liver and in man.

Studies were conducted to determine the mechanism whereby ethanol alters the hepatic disposition of propranolol. In eight isolated perfused rat livers, ethanol (mean = 40.1 mmol/l diminished the clearance of dl-propranolol (1.93 +/- 0.43 to 1.24 +/- 0.22 ml/min/g liver, p less than 0.05); increased its t1/2 (12.8 +/- 1.5 to 20.7 +/- 3.25 min, p less than 0.01); and decreased the proportion metabolized (68.7 +/- 4.7% to 34.3 +/- 10.3%, p less than 0.01). These results suggest that ethanol could substantially increase the oral bioavailability of propranolol in humans. However, in normal human volunteers administered 80 mg of propranolol orally, alone, or preceded and followed by ethanol to maintain breath ethanol concentrations of 800-1000 mg/l, increases in propranolol AUC were smaller than anticipated. Seven subjects had increases in free propranolol AUC0-8h (32%, range: 12-61%) (p less than 0.05), while total propranolol AUC0-8h increased by a mean 22% (range: -4-+49%). Propranolol free fraction varied with time and was higher after ethanol (mean = 0.090 vs 0.084) (p less than 0.077). The extent of the propranolol-induced slowing of heart rate was not influenced by ethanol (mean decrease from baseline of 13 bpm at peak propranolol effect vs 9 bpm without ethanol); mean heart rates following propranolol with ethanol were higher at all times (mean of 7.5 bpm) (p less than 0.001) than after propranolol alone. Ethanol inhibits the hepatic oxidative metabolism of propranolol in vitro; however, any effect on heart rate of higher concentrations of propranolol induced by ethanol in humans is offset by the cardio-acceleratory effect of ethanol.