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Biomedical subjects

F Varin

Publications and source records attributed to F Varin.

At least 55 records · Page 3Linked to original sources
PubMed1991

Isolation of 6-mercaptopurine in human plasma by aluminum ion complexation for high-performance liquid chromatographic analysis.

A sample preparation technique and a high-performance liquid chromatographic method for 6-mercaptopurine (6-MP) that is simple, sensitive and without interference from its metabolites is described. 6-Thioguanine (6-TG) is added as an internal standard to the plasma sample, which is then treated with an aqueous solution of aluminum perchlorate to denature the plasma proteins and form complexes with 6-TG, 6-MP and its major metabolite, 6-thiouric acid (6-TUA). These complexes coprecipitate with proteins on centrifugation. 6-MP and its analogues are then extracted from the precipitate with perchloric acid containing sodium hydrosulfite and the extract is chromatographed on an Ultrasphere ODS column eluted with 0.1 M phosphoric acid and 0.001 M dithiothreitol in deionized water. The eluate is monitored at 340 nm. No interfering peak was encountered in over 300 clinical plasma samples. 6-TUA was separated from 6-MP and was found to be present in much higher concentration than 6-MP itself throughout the sampling time (6 h) following oral administration of the drug.

Aluminum↗
PubMed1991

Residual curarization in the neonate after caesarean section.

The transplacental transfer and the neonatal effects of atracurium 0.3 mg.kg-1 (ED95) were compared with those of d-tubocurarine at the usual clinical dose of 0.3 mg.kg-1 (ED90) in 46 patients undergoing elective Caesarean section. The atracurium group (25 patients) was similar to the d-tubocurarine group (21 patients) as far as age, parity and time intervals between precurarization, induction, skin incision, muscle relaxant administration, hysterotomy and birth. The transplacental transfer of atracurium was lower than that of d-tubocurarine, with a feto-maternal ratio of 9 +/- 3% for atracurium and 12 +/- 5% for d-tubocurarine (P less than 0.05). The transplacental transfer of laudanosine was low at 14 +/- 5%, with blood levels of 0.101 +/- 0.032 microM.L-1 in the umbilical vein. Newborns in the two groups were comparable in terms of Apgar scores at one, five and ten minutes, as well as for NACS scores (neurological and adaptive capacity scoring test) at two and 24 hours after birth. However, at 15 min after birth, only 55% of newborns in whom the mothers received atracurium had a normal NACS score (greater than or equal to 35/40) compared with 83% of newborns in whom the mothers received d-tubocurarine (P less than 0.05). Further analysis of the five variables related to active muscle tone revealed that the modal score for active extension of the neck of newborns from the atracurium group was lower than for newborns from the d-tubocurarine group (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Intravenous↗
PubMed1991

Pharmacokinetics and pharmacodynamics of atracurium obtained with arterial and venous blood samples.

To determine the influence of sampling site on atracurium pharmacokinetic-pharmacodynamic relationships, blood was drawn simultaneously from the radial artery and peripheral vein during a 20-minute period after injection of atracurium, 0.2 mg/kg, in eight patients. Atracurium and laudanosine concentrations were measured by HPLC. Neuromuscular blockade was measured at the adductor pollicis, after stimulation of the ulnar nerve. Venous levels were lower than corresponding arterial values for up to 20 minutes, and this difference was marked for the early samples. Neuromuscular blockade was maximum after 5 to 7 minutes, much later than the peak venous concentration (1 to 3 minutes). Nonparametric analysis yielded (mean +/- SEM) a rate constant, concentration for 50% blockade, and slope of the effect-concentration relationship of 0.092 +/- 0.01 min-1, 379 +/- 27 ng/ml, and 7.3 +/- 1.67, respectively, when based on arterial samples. The values were statistically different (0.135 +/- 0.011 min-1, 235 +/- 42 ng/ml, and 3.41 +/- 0.37, respectively) when venous levels were used (p less than 0.05). It is concluded that forearm venous levels do not correspond to adductor pollicis neuromuscular blockade and the kinetics and kinetic-dynamic relationship for atracurium are heavily dependent on sampling site.

Adolescent↗
PubMed1991

Pharmacokinetics and pharmacodynamics of atracurium with and without previous suxamethonium administration.

Suxamethonium increases neuromuscular block produced by non-depolarizing agents administered subsequently. To determine if this effect has a pharmacokinetic or pharmacodynamic origin, 18 ASA physical status I or II adults received atracurium 0.2 mg kg-1, with (n = 10) or without (n = 8) previous injection of suxamethonium 1 mg kg-1, during a thiopentone-nitrous oxide-isoflurane (0.5% end-tidal) anaesthetic. Arterial blood samples were obtained and plasma atracurium concentration measured by HPLC. Train-of-four stimulation was applied to the ulnar nerve and the force of contraction of the adductor pollicis muscle was recorded. Mean (SEM) volume of distribution was slightly greater with previous suxamethonium (143 (13) ml kg-1) than without (109 (5) ml kg-1) (P less than 0.04). Mean elimination half-life was unaffected (20.3 (0.8) min and 20.4 (1.6) min, respectively). Neuromuscular block was more intense and recovery was slower with previous administration of suxamethonium. Atracurium concentration at 50% block (Cpss50) was 305 (30) ng ml-1 with and 454 (25) ng ml-1 without previous suxamethonium (P less than 0.01). It is concluded that suxamethonium may be associated with a slight increase in the volume of distribution of atracurium, but this effect is more than compensated by a decrease in atracurium concentration required for a given effect.

Adult↗
PubMed1991

Potentiation of atracurium neuromuscular blockade by enflurane: time-course of effect.

This study was designed to determine the time required for potentiation of atracurium neuromuscular blockade after the introduction of enflurane. Ten ASA physical status I and II adults anesthetized with thiopental, nitrous oxide, and alfentanil were given 0.4 mg/kg atracurium besylate. The force of contraction of the adductor pollicis muscle in response to train-of-four stimulation of the ulnar nerve was recorded. When the first twitch (T1) of the train-of-four recovered to 10% of control, an atracurium infusion was started and adjusted to keep the level of blockade constant. After 15 min of stable blockade, 1.6%-1.7% end-tidal enflurane was started and maintained for up to 2 h. Venous blood samples were drawn and plasma atracurium concentrations were measured 15 min before and 0, 5, 10, 15, 30, 45, 60, 90, and 120 min after the introduction of enflurane. Atracurium plasma concentrations were 730 +/- 127 (SEM) ng/mL at time 0. During the first 30 min, no significant decrease in plasma levels occurred; but at 45 min, concentrations were only 67% +/- 8% of their initial value (P less than 0.01) and 48% +/- 2% at 120 min (P less than 0.01). This suggests that the interaction between enflurane and atracurium is time-dependent. Clinically, the interaction between atracurium and enflurane is negligible during procedures of less than 45 min.

Adult↗
PubMed1990

Determination of atracurium and laudanosine in human plasma by high-performance liquid chromatography.

A high-performance liquid chromatographic method coupled with fluorometric detection has been developed for the determination of atracurium and its major end-product laudanosine in human plasma. The method enables good separation of atracurium from its metabolites after direct precipitation of plasma proteins. The assay is sensitive, reproducible and linear for atracurium concentrations ranging from 31.25 to 8000 ng/ml. In a clinical setting, drugs commonly administered during anesthesia did not interfere with the assay. This method provides a simple and time-saving alternative to existing methods.

Atracurium↗
PubMed1990

Influence of food on the bioavailability of diltiazem and two of its metabolites following the administration of conventional tablets and slow-release capsules.

The influence of food on the bioavailability of a conventional tablet and of a slow-release capsule of diltiazem was investigated in two separate groups of 24 healthy volunteers in two open crossover studies. Diltiazem, as a conventional tablet (2 x 30 mg, first group) or as a slow-release capsule (120 mg SR, second group), was administered in a fasting condition and 30 min after a breakfast of 784 kcal (23 per cent proteins, 55 per cent lipids, and 22 per cent of carbohydrates). Multiple blood samples were withdrawn during the next 24 h and diltiazem, desmethyldiltiazem, and deacetyldiltiazem were assayed by HPLC. Neither the rate of absorption, assessed by the rate constant of absorption, the peak plasma concentration, and the time required to reach the peak, nor the amount of drug reaching the systemic circulation, assessed by the area under the plasma concentration time curve (AUC infinity) were influenced by food, and that independently of the formulation. Compared to the fasting experiment, food did not affect either the rate of formation or the AUC infinity of desmethyldiltiazem or deacetyldiltiazem. The results of the present study show that the relative bioavailability of the single dose of diltiazem administered as a slow-release capsule is significantly higher (69 per cent) than that estimated after the administration of diltiazem in a conventional tablet. It was concluded that food does not influence the bioavailability of diltiazem administered as a conventional tablet or as a slow-release formulation.

Administration, Oral↗
PubMed1990

Influence of extreme obesity on the body disposition and neuromuscular blocking effect of atracurium.

The pharmacokinetics and pharmacodynamics of atracurium, a nondepolarizing neuromuscular blocking agent, were compared between morbidly obese patients and nonobese patients. Atracurium besylate (0.2 mg/kg) was administered intravenously as a bolus to patients who had received anesthesia. The force of contraction of the adductor pollicis was measured and plasma samples were collected for a 2-hour period. The concentrations of atracurium and its major end product, laudanosine, were determined by use of a chromatographic method. The pharmacokinetic-pharmacodynamic relationship was characterized by use of several models. No difference was observed between obese patients and nonobese patients in atracurium elimination half-life (19.8 +/- 0.7 versus 19.7 +/- 0.7 minutes), volume of distribution at steady state (8.6 +/- 0.7 versus 8.5 +/- 0.7 L), and total clearance (444 +/- 29 versus 404 +/- 25 ml/min). However, if values were expressed on a total body weight basis, there was a difference between obese and nonobese patients in the volume of distribution at steady state (0.067 versus 0.141 L/kg) and total clearance (3.5 +/- 0.2 versus 6.6 +/- 0.5 ml/min/kg). Although atracurium concentrations were consistently higher in obese patients than in nonobese patients, there was no difference in the time of recovery from neuromuscular blockade between the two groups. Consequently, the median effective concentration was higher in obese than in nonobese patients (470 +/- 46 versus 312 +/- 33 ng/ml).

Adult↗
PubMed1989

Determination of opiates and other basic drugs by high-performance liquid chromatography with electrochemical detection.

A procedure is described for the extraction and determination of morphine (M), hydromorphone (HM), codeine (C) and metoclopramide (MCP) present in human plasma. The drugs are separated by reversed-phase liquid chromatography and detected amperometrically at a glassy carbon electrode. The method provides high sensitivity and selectivity and has been used successfully in bioavailability studies.

Biological Availability↗
PubMed1987

Clinical pharmacology of carvedilol in normal volunteers.

The mechanism of the vasodilatory action of carvedilol (BM 14190), a new antihypertensive agent, was investigated in normal volunteers. Intra-arterial blood pressure and ECG were monitored continuously. Carvedilol (1 mg/min for 15 minutes) produced a rapid reduction in blood pressure and a transient increase in heart rate. At the end of infusion, systolic and diastolic blood pressure were reduced by 23% (-32.3 mm Hg) and 18% (-13.6 mm Hg), respectively, whereas heart rate was not different from baseline. At the doses used, the hypotensive effect of carvedilol was greater than that of labetalol (36 and 72 mg in 15 minutes). Carvedilol and labetalol antagonized isoproterenol-induced hypotension and tachycardia, at serum levels greater than or equal to 8 and 20 mg/ml, respectively. Both drugs antagonized phenylephrine pressor effects. A similar degree of inhibition (25% of control) of pressor effects was observed for carvedilol and labetalol when their respective serum concentrations were 23 ng/ml and 80 ng/ml. Neither carvedilol nor labetalol had any effect on AII pressor responses. Carvedilol serum levels as high as 150 ng/ml failed to inhibit AII-induced pressor responses. Our results suggest that at the doses used in this study, carvedilol has both alpha 1-and nonselective beta-receptor blocking properties. Moreover, carvedilol is approximately three to five times more potent than labetalol in blocking alpha 1-and beta-receptors and in reducing blood pressure.

Adult↗
PubMed1987

Mechanism of the vasodilatory effect of carvedilol in normal volunteers: a comparison with labetalol.

In a single blind parallel design, saline (n = 9), labetalol i.v. (40 mg n = 4, 80 mg n = 3), and carvedilol i.v. (15 mg n = 8) were given to volunteers with blood pressure (BP) recorded intraarterially. The effect of these treatments on the response to challenge doses of angiotensin II (to give a rise in mean BP of 20-25 mm Hg), isoproterenol (to give an increase in heart rate of 30-35 beats/min), and phenylephrine (to give a rise in mean BP of 20-25 mm Hg) were studied. The dose of i.v. carvedilol employed gave a greater fall in BP than the dose of labetalol used. Carvedilol appeared to be about four times more potent than labetalol in inhibiting the tachycardia to isoprenaline. Likewise, from inhibition of the pressor response to phenylephrine, it is concluded that carvedilol is four times more effective at the alpha receptor than labetalol. Neither drug was found to antagonize the pressor effects of angiotensin. Calculation of the half-life of carvedilol gave values of 2.2 to 9 h. The volume of distribution was found to be 1.54 l/kg and the total body clearance was 0.521 l/h/kg.

Adrenergic beta-Antagonists↗
PubMed1986

Liquid chromatographic assay and disposition of carvedilol in healthy volunteers.

Quantitative determination of serum concentrations of carvedilol [(+/-)-1-(carbazol-4-yloxy)-3-[[2-(o-methoxyphenoxy)ethyl) amino]-2-propanol], a combined alpha- and beta-adrenergic receptor antagonist, was obtained using HPLC with spectrofluorometric detection. Carvedilol was extracted from alkalinized serum with ether and was subsequently back extracted with diluted phosphoric acid. This method proved to be sensitive and reproducible (mean coefficient of variation of 6.1% for 0.25 to 150 nanograms per milliliter of serum). A single dose of carvedilol (5, 10, or 15 mg) was given as an intravenous infusion to three healthy volunteers. Carvedilol serum concentration-time profiles were fitted best to a three-compartment model and the pharmacokinetic data revealed the following mean values: Vdss of 1.97 L/kg, mean residence time (MRT) of 4.66 h, and CL of 0.437 L X h-1 X kg-1.

Antihypertensive Agents↗
PubMed1986

Effect of hypercapnia and/or hypoxemia and metabolic acidosis on kinetics and concentrations of phenytoin in the cerebrospinal fluid of conscious rabbits.

The present study was designed to determine the effect of changes in gases and pH in the blood on kinetics and passage to the cerebrospinal fluid (CSF) of phenytoin (DPH). Five groups of 6 rabbits were used, a control [with a mean partial pressure (Pa) of oxygen of 84 +/- 2 (SEM) mmHg, partial pressure of carbon dioxide (PaCO2) of 23 +/- 1 mmHg and pH = 7.512 +/- 0.018], a second group with hypercapnia (PaCO2 = 65 +/- 3 mmHg, pH = 7.244 +/- 0.008), a third group with hypoxemia (PaO2 = 48 +/- 2 mmHg), a fourth group with hypercapnia combined with hypoxemia (PaCO2 = 72 +/- 3 mmHg, PaO2 = 51 +/- 1 mmHg and pH = 7.252 +/- 0.008) and a fifth group with metabolic acidosis (pH = 7.232 +/- 0.011). All animals were conscious during the experiments following the administration of 10 mg/kg (i.v.) of phenytoin, hypoxemia decreased the clearance of phenytoin from 4.20 +/- 0.55 to 2.65 +/- 0.44 ml/min per kg (P less than 0.05) and consequently the area under the plasma concentration/time curve (AUC) for phenytoin increased (2575 +/- 319 to 4316 +/- 740 micrograms min/ml; P less than 0.05). Metabolic acidosis increased the volume of distribution of phenytoin from 780 +/- 70 to 1103 +/- 65 ml/kg (P less than 0.01). The protein binding of phenytoin was not affected by any of the experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1986

Intrahepatic circulation in liver disease.

Using the multiple indicator dilution approach, events occurring in the microvascular bed can be characterized in experimental animals with different types of cirrhosis and in man. Intrahepatic shunts can be found shunting blood away from sinusoids in both cirrhotic patients and cirrhotic animals. Such shunts were present in about one-third of cirrhotic patients with portal hypertension, and occurred mainly between the portal vein and hepatic veins. In cirrhotics, portohepatic anastomoses are usually large in diameter (more than 20 micron in diameter). Collagenization of the space of Disse and the progressive transformation of sinusoids into capillary-like channels decrease the extravascular space accessible to albumin and probably to other large molecules and protein-bound substances. However, unlike findings obtained in well-capillarized organs, these sinusoidal changes do not appear to limit the diffusion of sucrose, water, and lipophilic substances, such as lidocaine in the extravascular and intracellular spaces. The pattern observed for labeled sucrose curves following hepatic artery injection in cirrhotic patients could be secondary to the passage through the dense peribiliary capillary plexus originating from the enlarged arterial bed in cirrhosis. The difference in the perfusion of cirrhotic nodules with regard to the portal venous and hepatic artery routes introduces important new concepts in the overall mechanism of the elimination of endogenous and exogenous substances by the cirrhotic liver: blood entering the liver by the two afferent vessels will not flow through the same vascular bed before reaching the efferent hepatic veins.

Animals↗
PubMed1985

Hepatic microcirculation in the perfused cirrhotic rat liver.

Liver microcirculation in the perfused rat liver was assessed by the multiple indicator dilution technique. Comparative studies were carried out in noncirrhotic rats and in rats with cirrhosis secondary to chronic exposure to phenobarbital and carbon tetrachloride. The alterations of the sinusoidal bed were characterized by changes in the displacement of hepatic venous outflow curves of various diffusible substances (labeled albumin, sucrose, and water) relative to that of labeled erythrocytes (vascular reference). Outflow recoveries of lidocaine (a substance that penetrates the liver cell membrane freely and completely) and of labeled microspheres (15 microns diam) were also appraised. In all cirrhotic rats, unimodal erythrocytes and albumin curves were obtained. The sinusoidal space was significantly decreased when compared with normal rats (P less than 0.001) and the total space accessible to albumin became progressively restricted. In seven cirrhotic rats, the profiles of labeled sucrose and water curves were compatible with a flow-limited diffusion and the total distribution volumes were not significantly different from values found in noncirrhotic rats (P = NS), which indicates that sucrose and water were still able to diffuse into an extravascular space not accessible to albumin. In the other cirrhotic rats, labeled sucrose and water curves showed progressive bimodal changes not compatible with a flow-limited diffusion. Such alterations were not due to large intrahepatic shunts, since only 0.25% of the 15-microns microspheres were recovered in the outflow of cirrhotic rats. However, an early lidocaine outflow peak related in time to the peak erythrocyte curve was observed in cirrhotic, but not in noncirrhotic, rats. Lidocaine recovery varied greatly in cirrhotic rats and appeared to increase as the liver disease progressed. These data can be explained by capillarization of sinusoids and/or by the development of channels with poor permeability. Electron microscopic observations of these rat livers favored the latter. Thus, in cirrhotic rat liver, two kinds of alteration are likely: (a) the vascular space is decreased with collagenization of the extravascular space, limiting the diffusion of large molecules such as albumin; and (b) small channels with poorly permeable walls develop, limiting the diffusion of small molecules such as lidocaine, sucrose, and water. Large intrahepatic shunts are not a common feature.

Animals↗
PubMed1980

GLC-mass spectrometric procedure with selected-ion monitoring for determination of plasma concentrations of unlabeled and labeled barbital following simultaneous oral and intravenous administration.

A GLC-mass spectometric method employing specific-ion monitoring was developed for the determination of plasma concentrations of labeled (15N1,3, 13C2) and unlabeled barbital following simultaneous intravenous and oral administration. This method proved to be more sensitive and precise than the method employing GLC with flame-ionization detection or GLC with alkali flame-ionization detection. After extraction of [15N1,3, 13C2]barbital, barbital, and the internal standard, butalbital, from plasma with ether, the organic solvent is evaporated, and the labeled and unlabeled drug as well as the internal standard are converted into their N,N-dimethyl derivatives by treatment with diazomethane. The excess reagent is evaporated, and the resulting methyl derivatives are analyzed by GLC-mass spectrometry with selected-ion monitoring. The method is sufficiently sensitive to determine 0.5 microgram of the labeled and unlabeled drug/ml with a relative standard deviation of less than 5%. The application of the method to the determination of the plasma concentration of labeled and unlabeled drug over 6 days following simultaneous oral and intravenous administration of a single dose is demonstrated.

Administration, Oral↗