Kinetics of drug action in disease states. XXV. Effect of experimental hypovolemia on the pharmacodynamics and pharmacokinetics of desmethyldiazepam

It has been reported that hypovolemia secondary to extensive blood loss alters the functionality of the central nervous system and is associated with changes in the dose requirements or intensity of action of various central nervous system depressants, including a benzodiazepine. To investigate the mechanism(s) of this effect, the influence of experimental hypovolemia on the pharmacodynamics, receptor binding and pharmacokinetics of a benzodiazepine drug was determined. Adult male Sprague-Dawley rats were made hypovolemic by removal of about 30% of their blood over 30 min. An i.v. infusion of desmethyldiazepam (DDZP) was started 30 min later and continued until the animals lost their righting reflex. Compared to results obtained with normal controls, the hypovolemic rats required about one-half the dose of DDZP to produce loss of righting reflex and had significantly lower DDZP concentrations in serum and cerebrospinal fluid at that time. This effect of substantial blood removal could not be reversed by prompt return of the removed blood to the animals. Experimental hypovolemia had no apparent effect on the in vitro binding of tritiated diazepam to benzodiazepine receptor sites in the cerebral cortex of rats. The plasma clearance of DDZP was decreased significantly and the biological half-life was increased in hypovolemic rats compared to normal animals when both received a 30-mg/kg dose by i.v. infusion over 10 min. It is concluded that acute hemorrhagic hypovolemia increases the sensitivity of the central nervous system to the depressant effect of DDZP and decreases the body clearance of that drug in rats. Thus, the pharmacodynamics as well as the pharmacokinetics of a benzodiazepine are altered by hypovolemia.

Kinetics of drug action in disease states. XXIV. Pharmacodynamics of diazepam and its active metabolites in rats

The purpose of this investigation was to determine the relative contribution of diazepam and its active metabolites (desmethyldiazepam, oxazepam and temazepam) to the hypnotic activity of this benzodiazepine drug and to assess the role of rate of drug administration as a determinant of the relative concentrations of diazepam and its active metabolites in serum and in the central nervous system at the onset of a predefined pharmacologic endpoint. Rats were given i.v. infusions of diazepam to onset of loss of righting reflex. Samples of cerebrospinal fluid (CSF), blood (for serum) and brain were obtained at that time and were analyzed for diazepam and its active metabolites. Based on the results of six experiments on groups of 6 to 14 rats performed at the same time of day over 11 months, the pharmacologic response of the animals was found to be relatively consistent, with little variation between rats and between experiments in body weight-normalized effective dose and in diazepam serum and CSF concentrations. All three active metabolites of diazepam were found in serum, CSF and brain; they were relatively more prominent in CSF than in serum. Variation of the diazepam infusion rate (four rates between 0.10 and 0.34 mg/min per approximately 200-g rat) was associated with changes in average onset time (50 to 10 min) and dose (26 to 17 mg/kg) required to produce the pharmacologic effect. The drug and metabolite concentrations in CSF determined in these experiments, together with corresponding concentrations obtained by infusion of each active metabolite individually, yielded estimates of their relative hypnotic potency that were unaffected by differences in serum protein binding and tissue distribution.(ABSTRACT TRUNCATED AT 250 WORDS)

[Simultaneous intrauterine and extrauterine pregnancies]

The frequency of such combinations is currently equal or inferior to one for 10,000 pregnancies. The use of ovulation-inducers as well as the increased frequency of ectopic pregnancies are, for a large part, responsible for this increased frequency. Five of the six cases that we did observe in seven years follow a clomiphen citrate-induced ovulation. The clinical diagnosis remains difficult. It is greatly facilitated by echography and laparoscopy. Adjusting the treatment of induction of ovulation in case of sterility should decrease the incidence of these pregnancies.

[Biological diagnosis of myocardial infarction]

The biochemical diagnosis of myocardial infarction is mainly based on assays of serum enzymes. The most commonly used markers are creatine kinase, lactic dehydrogenase and aspartate amino-transferase. They are useful to diagnose the infarction, determine its time of onset and evaluate its importance. Changes in concentration of these enzymes are measured during their release from cells, their diffusion and their elimination in order to establish their characteristic profile in the acute phase of the disease. The diagnostic value and contribution to the prognosis of these tests are detailed. Heart diseases other than myocardial infarction, and other diseases in which serum levels are raised are described. The other laboratory abnormalities associated with myocardial infarction are listed.

Immune responses in small intestinal transplantation in the rat: correlation of histopathology and monocyte procoagulant activity

No predictive serologic marker exists for rejection or graft versus host disease (GVHD) reactions in small intestinal transplantation (SIT). SIT was performed in Lewis (Lew) and Lew X Brown Norway Fl hybrid (LBN) rats in the following combinations: group 1, Lew X Lew; group 2 (isolated rejection), LBN X Lew, and group 3 (isolated GVHD), Lew X LBN. Procoagulant activity (PCA), an index of monocyte immune activation, was measured in the peripheral blood mononuclear cells of graft recipients to assess its value as an immunologic monitor. Histologic findings and PCA were evaluated on days 1, 2, and 3 and every 2 to 3 days after SIT. No pathologic findings of graft or host tissue developed in group 1 (n = 14). Histologic rejection (blunted villi and mononuclear cell infiltration) was seen beginning on day 5 in group 2 (n = 19); early GVHD (loss of nodal and splenic architecture) was first noted on days 5 and 6 in group 3 (n = 17). PCA elevation in SIT was seen to precede histologic evidence of rejection or graft versus host disease in this model and may constitute an important marker for these immunologic events.

Kinetics of drug action in disease states. XXI. Relationship between drug infusion rate and dose required to produce a pharmacologic effect

Computer simulations were performed to determine if the threshold dose of an infused drug (rather than the drug concentration in the biophase at onset of action) can be a suitable index for pharmacodynamic investigations as proposed by others. A two-compartment pharmacokinetic model with drug elimination from the central compartment was used for the simulations. Drug was administered into the central compartment by a constant-rate infusion, and concentrations in the central and peripheral compartments were calculated as a function of time. The pharmacologic effect was assumed to be reversible and to occur at a defined concentration (the effective concentration) in one or the other compartment. The dose required to produce an effective concentration (threshold dose) was determined as a function of infusion rate. The relationship between infusion rate and the dose required to produce an effective concentration in the peripheral compartment was found to be affected by drug distribution and elimination kinetics and by the effective concentration. The infusion rate-dose relationship showed a dose minimum at an infusion rate which others have designated as the "optimal dose rate" and have used for pharmacodynamic studies. No such minimum occurred for pharmacologic effects associated directly with drug concentrations in the central compartment. Since optimum dose rate and threshold dose are affected by both pharmacokinetic and pharmacodynamic alterations, it is concluded that this method (which avoids determination of drug concentrations) is not generally suitable for quantitative pharmacodynamic investigations.

Effect of age on the pharmacodynamics of phenobarbital and ethanol in rats

The purpose of this investigation was to determine the effect of age on the sensitivity of the central nervous system (CNS) to the depressant action of phenobarbital and ethanol. For this purpose, one or the other of these drugs was administered by slow iv infusion to male rats of various ages until the animals lost their righting reflex. The drug concentrations at that time in serum, brain, and cerebrospinal fluid were determined. The results obtained in studies on 1, 9, and 18-month-old Sprague-Dawley rats and on 7, 16, and 24-month-old Fischer-344 rats showed that phenobarbital concentrations at the pharmacologic end-point decreased with increasing age, indicative of an increased sensitivity of older animals to the CNS depressant effect of the barbiturate. Similar studies with ethanol on Sprague-Dawley rats (only) showed substantially higher drug concentrations at all sampling sites in 5-week-old animals than in 9- and 12-month-old animals at the onset of loss of righting reflex, but no significant differences between the 9- and 12-month-old groups. This investigation, which was designed to exclude or account for pharmacokinetic variables and to avoid confounding secondary effects, such as hypothermia and development of acute functional tolerance, showed a substantial increase in CNS sensitivity to phenobarbital and ethanol with increasing age in rats between the age of 1 and 9 months, and a less pronounced increase (phenobarbital) or no significant change (ethanol) in rats between 9 and 18 months of age.

Kinetics of drug action in disease states. XX. Effects of acute starvation on the pharmacodynamics of phenobarbital, ethanol and pentylenetetrazol in rats and effects of refeeding and diet composition

Severely ill patients often do not eat or cannot retain ingested food. Malnutrition occurs frequently in hospitalized individuals and is known to be associated with substantial changes in the pharmacokinetics of certain drugs. On the other hand, little is known about the effect of acute starvation or malnutrition on the pharmacodynamics (concentration-effect relationship) of drugs. To explore the effects of acute starvation on the pharmacodynamics of drugs that depress or stimulate the central nervous system, adult male Sprague-Dawley rats were deprived of food (but not water) for 3 days, whereas control animals had free access to food and water. Slow i.v. infusion of phenobarbital to onset of loss of righting reflex showed that the starved animals required a larger body weight normalized dose and that they had higher phenobarbital concentrations in serum, serum water, brain and cerebrospinal fluid at the pharmacologic endpoint. Refeeding of the rats for 2 or 7 days did not normalize the decreased body weight and serum total protein concentration. The starvation-associated decrease in the sensitivity of the central nervous system to the hypnotic effect of phenobarbital was only reversed slightly by refeeding for 2 days and persisted even after 7 days of refeeding. Acute starvation had no apparent effect on the dose of i.v. infused ethanol required to cause loss of righting reflex and on ethanol concentrations in serum, brain and cerebrospinal fluid at that time. The infused dose and the concentrations of pentylenetetrazol in serum, brain and cerebrospinal fluid at onset of maximal seizures did not differ significantly between starved and control (fed) rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of drug action in disease states. XXII. Effects of contraceptive steroids on the pharmacodynamics of ethanol in rats

This investigation was designed to determine the effect of treatment with contraceptive steroids on the central nervous system depressant activity of ethanol. Adult female rats received oral doses of ethynyl estradiol (0.1 mg kg-1 day-1), ethynyl estradiol and norethindrone (0.1 and 10 mg kg-1 day-1), or vehicle only for 14 days. Ethanol was then infused slowly iv until the animals lost their righting reflex. The concentrations of ethanol at that time in serum and cerebrospinal fluid were statistically significantly higher in rats treated with the estrogen-progestin combination than in control animals. Ethanol concentrations in rats treated only with the estrogen were intermediate and did not differ significantly from control values. These results indicate that treatment with an estrogen-progestin combination is associated with a decreased sensitivity of the central nervous system to the hypnotic activity of ethanol. This evidence of a pharmacodynamic interaction between contraceptive steroids and ethanol in rats is consistent with a recent clinical report of significant contraceptive steroid-related improvement in tolerance to ethanol with no apparent effect on the pharmacokinetics of ethanol.

Kinetics of drug action in disease states. XIX. Effect of experimental liver disease on the neurotoxicity of theophylline in rats

There are pronounced interindividual differences in the neurotoxicity of theophylline in humans as reflected by the wide range of plasma theophylline concentrations associated with the occurrence of life-threatening, generalized seizures in patients treated with this widely used bronchodilator. The variability indicates that there may be a number of as yet unrecognized risk factors for theophylline neurotoxicity. After the development of an animal model of theophylline-induced seizures, renal failure was identified as one such risk factor. This investigation was designed to determine if experimental liver disease will alter the neurotoxic effect of theophylline. Studies were performed on rats with extrahepatic cholestasis produced by bile duct ligation and with hepatic necrosis induced by carbon tetrachloride administration and on respective controls. Theophylline was infused i.v. at 1.03 mg/min until the onset of maximal seizures. Theophylline and theophylline metabolite concentrations at that time were determined in serum (unbound and total drug), brain and cerebrospinal fluid. Extrahepatic cholestasis was associated with small increases in unbound theophylline concentration in serum, theophylline concentration in brain and serum free fraction in serum at onset of seizures. The concentrations of theophylline metabolites were negligible. There were no apparent effects of extrahepatic cholestasis or hepatic necrosis on theophylline concentrations at onset of seizures in cerebrospinal fluid, the fluid that was shown in a preceding study to be the best indicator of the theophylline concentration at the site of the neurotoxic effect. It is concluded that experimental liver disease had no apparent effect on the neurotoxicity of theophylline under the conditions of this investigation.

Kinetics of drug action in disease states. XVIII. Effect of experimental renal failure on the pharmacodynamics of theophylline-induced seizures in rats

Theophylline, the bronchodilating agent, can cause life-threatening, generalized seizures when plasma concentrations exceed the usual therapeutic concentration range. However, the plasma concentrations of theophylline associated with this neurotoxic effect vary widely between patients. To determine the reasons for the wide variation, and thereby to facilitate prevention or early treatment of theophylline-induced neurotoxicity, an animal model of theophylline-induced seizures was developed and has now been used to determine the effect of experimental renal failure on the concentrations of theophylline that cause convulsions. Adult female rats were subjected to bilateral ureteral ligation or injected with uranyl nitrate to produce renal failure or dysfunction. Sham-operated and saline-injected rats, respectively, served as controls. Theophylline was infused i.v. at either 1.03 or 2.06 mg/min until the onset of maximal seizures. Renal failure due to ureter ligation was associated with a substantial reduction of the dose of drug required to produce seizures, the concentrations of total and free (unbound) theophylline in serum and the concentrations of theophylline in the brain and cerebrospinal fluid at onset of seizures. The concentrations of theophylline metabolites were very low and did not account for the enhanced neurotoxicity. No apparent change in the neurotoxicity of theophylline was observed in rats with uranyl nitrate-induced renal dysfunction. The results of the investigation on ureter-ligated rats are consistent with recent clinical findings of a higher incidence of theophylline-induced neurotoxicity in azotemic patients. The experimental methodology may therefore be suitable for the prospective identification of other potential clinical risk factors for theophylline neurotoxicity.