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A G Burm

Publications and source records attributed to A G Burm.

At least 19 recordsLinked to original sources

Pharmacokinetics of alfentanil before and after cardiopulmonary bypass in pediatric patients undergoing cardiac surgery: Part I.

Changes induced by cardiopulmonary bypass (CPB) may markedly affect the pharmacokinetics of drugs. Therefore, the pharmacokinetics of alfentanil before and after CPB were compared in infants and children undergoing cardiac surgery, who had been anesthetized with nitrous oxide in oxygen and low inspiratory concentrations of halothane. Six infants and six children were investigated. Before CPB, alfentanil, 200 micrograms/kg, and after CPB, alfentanil, 80 micrograms/kg, was infused in 10 minutes. Arterial blood samples were obtained before and after CPB for determination of plasma alfentanil concentrations. Bi-exponential functions were fitted to the plasma concentration-time data using weighted least-squares nonlinear regression analysis. A correction was made to account for the contribution of the first infusion to the plasma concentrations measured during and after the second infusion. Total sampling time before CPB (45 to 75 minutes) was too short to allow full characterization of the pharmacokinetics of alfentanil, but allowed estimation of the initial volume of distribution. The initial volume of distribution before CPB was smaller (68 +/- 37 mL/kg in infants and 80 +/- 32 mL/kg in children) than after CPB (235 +/- 58 mL/kg in infants and 179 +/- 99 mL/kg in children; P less than 0.001). The normalized area under the plasma concentration-time curve from 0 to 45 minutes was larger before CPB (17.9 +/- 2.9 mg.min/L in infants and 18.3 +/- 5.4 mg.min/L in children) than after CPB (11.1 +/- 2.9 mg.min/L in infants and 12.9 +/- 3.4 mg.min/L in children; P less than 0.001). Despite intravenous administration of atropine, arterial blood pressure and heart rate decreased significantly after alfentanil was given.

Alfentanil

Pharmacokinetics of alfentanil before and after cardiopulmonary bypass in pigs: Part II.

The pharmacokinetics of alfentanil before and after cardiopulmonary bypass (CPB) were investigated in six pigs undergoing mitral valve replacement. Before bypass, alfentanil, 100 micrograms/kg, was infused in 10 minutes and after bypass, alfentanil, 40 micrograms/kg, was infused in 10 minutes. Low inspiratory concentrations of halothane were given concomitantly. Arterial blood was obtained before and after CPB for determination of plasma alfentanil concentrations by gas chromatography. Bi-exponential functions were fitted to the plasma concentration-time data using weighted least-squares nonlinear regression analysis. The steady-state volume of distribution (Vss; 258 +/- 70 mL/kg), elimination clearance (Cle; 10.7 +/- 3.0 mL/kg/min), and distribution clearance (Cld; 6.8 +/- 3.3 mL/kg/min) before CPB were smaller than the Vss (1,107 +/- 373 mL/kg; P less than 0.01), Cle (20.0 +/- 3.0 mL/kg/min; P less than 0.002), and Cld (23.0 +/- 6.7 mL/kg/min; P less than 0.02) after CPB. The distribution half-life (t1/2 lambda 1; 2.8 +/- 0.8 minutes) was longer and the elimination half-life (t1/2 lambda 2; 36 +/- 8 minutes) was shorter before CPB than the t1/2 lambda 1 (1.7 +/- 0.2 minutes; P less than 0.05) and t1/2 lambda 2 (68 +/- 20 minutes; P less than 0.02) after CPB.

Alfentanil

Uptake of sufentanil, alfentanil and morphine in the lungs of patients about to undergo coronary artery surgery.

We have studied the pulmonary extraction and retention of sufentanil, alfentanil and morphine using a double indicator technique in 30 patients undergoing elective aortocoronary bypass surgery. Patients were allocated to three groups (10 each) to receive sufentanil 43 micrograms, alfentanil 672 micrograms or morphine 1887 micrograms, mixed with indocyanine green as indicator. After sufentanil, mean peak extraction was 93.7% (95% confidence interval 87.1-100.4%) and release occurred after 16.1 (13.8-18.4) s; first-pass retention was 61.1 (51.3-70.9)%. After alfentanil, peak extraction was 67.4 (42.7-92.0)% and release occurred after 9.9 (8.5-11.3) s; first-pass retention was 10.1 (3.5-16.7)%. After morphine, peak extraction was 58.3 (44.4-72.2)% and release occurred after 7.2 (4.4-10.1) s; first-pass retention was 7.1 (-4.7-19.9)%. Both peak extraction and first-pass retention were significantly greater after sufentanil. There was no significant difference in the peak extraction and first-pass retention between alfentanil and morphine.

Alfentanil

Pharmacodynamics of alfentanil. The role of plasma protein binding.

The role of protein binding in relation to the pharmacodynamics of alfentanil was investigated in 15 female and 13 male patients, aged 21-85 yr, ASA physical status 1 or 2, undergoing upper abdominal surgery. All patients had normal cardiac, hepatic, renal, and pulmonary function. None was receiving medication or had a history of alcohol or other drug abuse. Anesthesia was induced and maintained with 66% nitrous oxide in oxygen and alfentanil. Alfentanil was administered by a computer-controlled infusion pump. If, during surgery, the patient exhibited signs of inadequate anesthesia (i.e., response), the target alfentanil plasma concentration was increased by 50-100 ng/ml. If there was no response during a 15-min period, the target concentration was decreased by 50-100 ng/ml. Arterial blood samples were taken before any change of the target concentration and 4 min after the computer had indicated that the new target concentration had been reached. In addition, blood samples were taken before intubation, skin incision, and in the patients in whom ventilation recovered spontaneously before extubation. In the remaining patients a blood sample was taken before the administration of naloxone. Plasma alfentanil concentrations were determined by capillary gas chromatography. Alfentanil protein binding was determined by equilibrium dialysis in an arterial blood sample taken before induction of anesthesia. Alfentanil concentration-effect data were evaluated by logistic regression, where effect was either response or no response to perioperative stimuli. The average free fraction of alfentanil was 9.3 +/- 3.9% (range 3.7-19.1%). For intubation, skin incision, and postanesthesia ventilation, it was not possible to characterize the concentration-effect curves based on total plasma concentrations with logistic regression.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen

Pharmacodynamics of propofol in female patients.

Although the clinical properties of propofol have been studied extensively, the pharmacodynamics have not yet been described fully. We studied the propofol concentration-effect relationships for loss of eyelash reflex, loss of consciousness, and hemodynamic changes in 18 female patients, ASA physical status 1, aged 20-49 yr. Propofol was given by computer-controlled infusion. The initial target concentration of 0.5-1 microgram/ml was increased every 12 min by 0.5-1 microgram/ml until the patients lost consciousness. Every 3 min, loss of eyelash reflex and loss of consciousness were tested and an arterial blood sample was taken for analysis of the blood propofol concentration. The concentration-response relationships for loss of eyelash reflex and loss of consciousness were defined by fitting a sigmoid Emax function (where Emax = the maximum effect that can be reached; i.e., 100% of the patients showing loss of eyelash reflex or loss of consciousness) to the response/no response data versus the propofol concentration, using nonlinear regression. The effect of propofol on hemodynamic parameters was analyzed by linear regression. The propofol concentrations at which 50% and 90% of the patients showed loss of eyelash reflex were 2.07 and 2.78 micrograms/ml, respectively. The corresponding values for loss of consciousness were 3.40 and 4.34 micrograms/ml. The systolic and diastolic blood pressure decreased with increasing blood propofol concentration. The correlation coefficients for the decrease in systolic and diastolic blood pressure versus the blood propofol concentration were r2 = -0.663 and r2 = -0.243, but heart rate did not change. In conclusion, propofol concentrations inducing loss of eyelash reflex are less than those inducing loss of consciousness.

Adult

The effect of age on the systemic absorption, disposition and pharmacodynamics of bupivacaine after epidural administration.

The influence of age on the systemic absorption and disposition of bupivacaine following epidural administration in 20 male patients (22 to 81 years) was examined using a stable isotope method to determine whether pharmacokinetics play a role in age-related pharmacodynamic changes seen with the drug. After epidural bupivacaine administration a deuterium-labelled analogue was administered intravenously. Bi- and triexponential functions were fitted to plasma concentration-time data of deuterium-labelled bupivacaine. The systemic absorption was described by 2 parallel first-order absorption processes. The upper level of analgesia and the duration of analgesia at dermatome T-12 increased with age (r = 0.68, p less than 0.001; r = 0.56, p less than 0.01, respectively). The time to maximal caudad spread of analgesia and the time to onset of motor block decreased with age (r = -0.76, p less than 0.0001; r = -0.72, p less than 0.001, respectively). Age did not influence systemic absorption or disposition of bupivacaine. We conclude that the changes in the clinical profile of bupivacaine with age are not due to altered pharmacokinetics, but may be related to changes in the pharmacodynamics of the drug.

Absorption

Continuous interpleural infusion of bupivacaine for postoperative analgesia after surgery with flank incisions: a double-blind comparison of 0.25% and 0.5% solutions.

Postoperative analgesia, as assessed by visual analogue scale scores (0-10) and patient-controlled analgesia morphine requirements, pulmonary function (forced vital capacity and forced expiratory volume in 1 s), and plasma bupivacaine concentrations were studied in patients receiving interpleural blockade with bupivacaine after surgery with a flank incision. Two groups of 10 patients received either 0.5% or 0.25% bupivacaine, both with epinephrine (5 micrograms/mL). Pain relief was initiated when patients had visual analogue scale scores greater than or equal to 4. Patients received 21 mL of bupivacaine 0.25% or 0.5% in a double-blind fashion. One hour later, a continuous infusion of 5 mL/h of the study solution was started. At the same time, patient-controlled analgesia became accessible to the patients. The onset time of pain relief and the area under the visual analogue scale score-time curves over the first 8 h were similar in both groups. Patient-controlled analgesia morphine use was also similar in the 0.25% (21.3 +/- 14.6 mg) and 0.5% (21.0 +/- 16.0 mg) groups (mean +/- SD). In both groups, forced vital capacity and forced expiratory volume in 1 s improved significantly within 60 min (P less than 0.05). Peak plasma concentrations (Cmax) and the area under the plasma concentration-time curve (AUC) over 24 h were higher (P less than 0.001) in the 0.5% group (Cmax, 1.47 +/- 0.37 micrograms/mL; AUC, 1511 +/- 323 micrograms.mL-1.min) than those in the 0.25% group (Cmax, 0.55 +/- 0.22 micrograms/mL; AUC, 680 +/- 118 micrograms.mL-1.min) (mean +/- SD).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

The effect of age on systemic absorption and systemic disposition of bupivacaine after subarachnoid administration.

In order to evaluate the role of the pharmacokinetics of the age-related changes in the clinical profile of spinal anesthesia with bupivacaine, we studied the influence of age on the systemic absorption and systemic disposition of bupivacaine after subarachnoid administration in 20 male patients (22-81 yr), ASA Physical Status 1 or 2, by a stable isotope method. After subarachnoid administration of 3 ml 0.5% bupivacaine in 8% glucose, a deuterium-labeled analog (13.4 mg) was administered intravenously. Blood samples were collected for 24 h. Plasma concentrations of unlabeled and deuterium-labeled bupivacaine were determined with a combination of gas chromatography and mass fragmentography. Biexponential functions were fitted to the plasma concentration-time data of the deuterium-labeled bupivacaine. The systemic absorption was evaluated by means of deconvolution. Mono- and biexponential functions were fitted to the data of fraction absorbed versus time. The maximal height of analgesia and the duration of analgesia at T12 increased with age (r = 0.715, P less than 0.001; r = 0.640, P less than 0.01, respectively). In 18 patients the systemic absorption of bupivacaine was best described by a biexponential equation. The half-life of the slow systemic absorption process (r = -0.478; P less than 0.05) and the mean absorption time (r = -0.551; P less than 0.02) decreased with age. The total plasma clearance decreased with age (r = -0.650, P less than 0.002), whereas the mean residence time and terminal half-life increased with age (r = 0.597, P less than 0.01; r = 0.503, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

Age does not influence the serum protein binding of bupivacaine.

The serum protein binding of bupivacaine was studied in 74 subjects, 39 males and 35 females, aged 20-90 years, without evidence of acute or chronic inflammatory disease or malignancy. Subjects were drug free for at least 1 month. The free fractions of bupivacaine did not change with age in either males or females. This is in keeping with the lack of effect of age on AAG concentrations. Free fractions of bupivacaine were slightly higher in females as compared with males. The previously observed decline in clearance of bupivacaine with age probably reflects a concomitant decline in the metabolic activity of hepatic enzymes.

Adult

Pharmacokinetics and EEG effects of flumazenil in volunteers.

The effect of intravenous flumazenil 10 mg on the electroencephalogram (EEG) was investigated in 7 volunteers in a placebo-controlled, randomised, double-blind, crossover study. The EEG was recorded between Fp1-M1 and Fp2-M2 and analysed using an aperiodic analysis technique. Two volunteers were excluded from the study because of significant asymmetry between baseline EEG recordings of the left and right hemisphere, in the remainder there were no changes in the beta-frequency range (12 to 30 Hz) or in other ranges of the EEG during or after flumazenil or placebo administration, with regard to the parameters total number of waves per second or total amplitude per second. There were no changes in heart rate, respiratory rate or blood pressure after administration of flumazenil or placebo. Three volunteers reported feelings of 'pressure to move' during the initial 2 min of the flumazenil infusion. The pharmacokinetics of flumazenil were investigated in the same volunteers. Flumazenil 10 mg was administered intravenously over 10 min; the data from 1 volunteer were excluded from this analysis because of blood sampling problems. The plasma concentration-time data of the remaining 6 volunteers were characterised by a biexponential function. The pharmacokinetic parameters were (mean +/- SD): initial volume of distribution, 16 +/- 5.7L; volume of distribution at steady-state, 64.8 +/- 12.5L; total body clearance, 53.8 +/- 1.2 L/h; distribution half-life, 4.1 +/- 1.3 min; and elimination half-life, 70.2 +/- 9.9 min. The authors conclude that flumazenil has no significant EEG effects. The rapid distribution and elimination of flumazenil may explain its previously reported short duration of action after intravenous anaesthesia with high doses of midazolam.

Adolescent

Pharmacokinetic-pharmacodynamic modelling of the interaction between flumazenil and midazolam in volunteers by aperiodic EEG analysis.

The CNS effects resulting from the combined administration of midazolam and flumazenil were studied in 8 healthy volunteers to develop a model of the pharmacokinetic-pharmacodynamic interaction. Electroencephalograms (EEG) were recorded between Fp1-M1 and Fp2-M2. The EEG parameter total number of waves between 12 and 30 Hz (TNW12-30) derived by aperiodic analysis was used to quantify the effect. Following a 15 min baseline EEG recording, infusion of placebo or flumazenil was started. Infusion regimens for flumazenil were designed so that 'steady-state' concentrations of 10 and 20 micrograms/L were obtained. Doses of midazolam 15, 30 and 60 mg over 5 min were given 30 min after the start of placebo infusion (session A) or flumazenil infusion to 10 micrograms/L (session B) or 20 micrograms/L (session C), respectively. Venous blood samples were taken until 8 h after the start of the flumazenil or placebo infusion. A sigmoid maximum effect (Emax) model was used to characterise the relationship between the plasma concentration of midazolam which is in equilibrium with the effect compartment concentration (Cem) [Cem/Kp] and TNW12-30. Within 2 to 5 min of starting the midazolam infusion all subjects fell asleep, with loss of eyelid reflex. They awoke between 25 and 82 min later in all 3 sessions. The mean (+/- SD) plasma drug concentrations of midazolam corresponding to half the maximum increase in TNW12-30 (EC50) were 276 +/- 64, 624 +/- 187 and 1086 +/- 379 micrograms/L in sessions A, B and C, respectively. The half-lives reflecting equilibration between plasma concentration and effect (t1/2ke0), estimated by a nonparametric method, were 2.2 +/- 1.2, 3.3 +/- 3.3 and 2.9 +/- 1.2 min for the 3 different sessions. Emax and N were not affected by flumazenil. In each subject the plot of the average measured steady-state plasma flumazenil concentration versus the EC50 of midazolam showed a linear relationship. The plasma concentration of flumazenil that doubled the EC50 of midazolam (Cf,2) was 6.5 +/- 1.0 micrograms/L. The observed interaction is consistent with the competitive nature of the antagonism of midazolam by flumazenil.

Adult

The effect of age on serum concentrations of albumin and alpha 1-acid glycoprotein.

1. Human serum albumin (HSA) concentrations and alpha 1-acid glycoprotein (AAG) concentrations were measured in 68 subjects, 35 males and 33 females, aged 20-90 years without evidence of acute or chronic inflammatory disease or malignancy. Subjects were drug free for at least 1 month. HSA and AAG concentrations were measured using rate nephelometry. 2. Age had no effect on alpha 1-acid glycoprotein concentration, whereas plasma albumin levels decreased as a function of age in both sexes. We observed no differences between males and females in the plasma concentrations of HSA and AAG. 3. These data show that in healthy subjects the HSA concentration decreases with increasing age, whereas age, uncomplicated by disease does not influence AAG concentration.

Adult

Single-dose interpleural versus intercostal blockade: nerve block characteristics and plasma concentration profiles after administration of 0.5% bupivacaine with epinephrine.

Analgesic effects and plasma concentration profiles after interpleural (IP) or intercostal (IC) administration of 21 mL of 0.5% bupivacaine with epinephrine (5 micrograms/mL) were studied in 24 patients (IP group: n = 12; IC group: n = 12) who had undergone cholecystectomy or renal surgery. The number of blocked dermatomes, as assessed by pinprick, was more variable between patients in the IP group (2-9 dermatomes) than in the IC group (6-8 dermatomes). The mean time intervals from the injection to two-dermatome regression and to first need for additional pain medication were 4 h (IP) and 5.5 h (IC) (P less than 0.02) and 5.3 h (IP) and 9.8 h (IC) (P = 0.002), respectively. The degree of postoperative pain was evaluated by means of a visual analogue scale. This gradually increased during the first 4 h in the IP group (P less than 0.001), but not in the IC group. Peak bupivacaine concentrations in arterial plasma were approximately 10% higher than those in venous plasma and were attained more rapidly. Peak arterial plasma concentrations after IP injection (2.07 +/- 0.53 micrograms/mL) were significantly higher (P less than 0.005) than those after IC administration (1.36 +/- 0.48 micrograms/mL). Peak venous plasma concentrations showed a similar difference (IP: 1.86 +/- 0.45 micrograms/mL; IC: 1.21 +/- 0.48 micrograms/mL; P less than 0.005). Peak concentrations were attained later after IP injection both in arterial (IP: 16.3 +/- 4.6 min; IC: 8.8 +/- 5.4 min; P less than 0.002) and venous plasma (IP: 20.0 +/- 7.1 min; IC 13.3 +/- 6.9 min; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

Comparison of midazolam and propofol in combination with alfentanil for total intravenous anesthesia.

Hemodynamic function during induction of anesthesia, the alfentanil and naloxone requirements, and the speed of recovery from total intravenous anesthesia with alfentanil/midazolam (group M, n = 10) or alfentanil/propofol (group P, n = 10) were compared in patients undergoing lower limb surgery. Twenty patients were randomly assigned to receive either 2 mg/kg propofol in 5 min followed by 9 mg.kg-1.h-1 for 30 min and 4.5 mg.kg-1.h-1 until skin closure, or 0.42 mg/kg midazolam in 5 min followed by 0.125 mg.kg-1.h-1 until skin closure. Simultaneously, a variable-rate infusion of alfentanil was given. Patients were ventilated with 30% oxygen in air. In both groups blood pressure and heart rate decreased significantly (P less than 0.02) and to a similar extent during induction. The total dose of alfentanil was similar in both groups. No patient in group P and nine patients in group M needed naloxone (average dose 130 +/- 70 micrograms, P less than 0.001). Recovery, as judged by psychomotor tests (90% score was reached at 1 h in the P group and at about 4 h in the M group, P less than 0.001), sedative scores, and orientation in time and place, was shorter in group P than in group M. The conclusion is reached that propofol is superior to midazolam in total intravenous anesthesia with alfentanil.

Adult

Quantification of the EEG effect of midazolam by aperiodic analysis in volunteers. Pharmacokinetic/pharmacodynamic modelling.

The effects of midazolam on the EEG were related to plasma midazolam concentrations in 8 healthy male volunteers in order to develop a pharmacokinetic-pharmacodynamic model. The EEG parameters were derived by aperiodic analysis. The EEG was recorded between Fp1-M1 and Fp2-M2. Following a 15-minute baseline EEG registration, midazolam 15 mg was given intravenously over 5 minutes. Venous blood samples were taken until 8 hours after the start of the infusion. Within 2 to 4 minutes of starting the infusion all subjects became asleep, with loss of eyelid reflex. The most obvious EEG changes, in the beta frequency range (12 to 30 Hz), were observed within 2 minutes of the start of drug administration. Seven subjects awoke 60 to 70 minutes after the start of the infusion and 1 awoke after 45 minutes. The EEG parameter that best characterised the effect of midazolam was the total number of waves per second in the frequency range 12 to 30 Hz (TNW12-30). This was used as the effect parameter in the pharmacokinetic-pharmacodynamic modelling. The plasma concentration-time data were characterised by a triexponential function for all subjects. To allow for a possible delay between plasma midazolam concentration and EEG effect, a hypothetical effect compartment was included in the pharmacokinetic-pharmacodynamic model. A sigmoid maximum effect (Emax) model was used to characterise the effect compartment midazolam concentration-TNW12-30 data. The plasma drug concentration corresponding to half the maximum increase in TNW12-30 (EC50) was 290 +/- 98 micrograms/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

Influence of age on the pharmacokinetics of alfentanil. Gender dependence.

Studies on the effects of age on the pharmacokinetics of alfentanil are inconclusive. A possible factor in explaining the differences between various studies could be the effect of gender. The authors studied the effects of age on the pharmacokinetics of alfentanil in female (n = 21) and male (n = 15) patients undergoing lower abdominal surgery under nitrous oxide alfentanil anaesthesia. There was a significant negative correlation (r = -0.79, p less than 0.001) between plasma alfentanil clearance (CL) and age in women (less than 50y, median CL 24.84 L/h; greater than 50y, median CL 14.52 L/h), but not in men (less than 50y, median CL 19.44 L/h; greater than 50y, median CL 16.2 L/h). The conclusion is drawn that the effects of age on the pharmacokinetics of alfentanil are gender-dependent.

Adult

Alcohol consumption alters the pharmacodynamics of alfentanil.

Two groups of women, ASA physical status 1, undergoing surgery for primary breast cancer, were studied to assess the effect of alcohol intake on alfentanil pharmacodynamics. Patients in group 1 (n = 6) had an average daily consumption of 20-40 g alcohol. Patients in group 2 (n = 8) were life-long abstainers or drank only occasionally (less than 60 g per year). Anesthesia was induced and maintained with 66% N2O in O2 and alfentanil. Alfentanil was administered by a computer-controlled infusion pump. If during surgery the patient exhibited somatic, hemodynamic, or other autonomic signs of inadequate anesthesia (response), the target alfentanil plasma concentration was increased by 50-100 ng/ml. If there was no response during a 15-min period, the target concentration was decreased by 50-100 ng/ml. Arterial blood samples were taken before any change of the target concentration, 4 min after a new predicted target concentration was achieved, and at extubation. Plasma concentrations were determined by capillary gas chromatography. Alfentanil protein binding was measured by equilibrium dialysis. Plasma alfentanil concentration-effect data were analyzed by nonlinear regression, where effect was either response or no response to surgical stimuli. The average total alfentanil requirement was significantly (P less than 0.005) higher in group 1 (3.7 +/- 1.2 micrograms.kg-1.min-1) than in group 2 (1.9 +/- 0.4 micrograms.kg-1.min-1). The average Cp50 (the plasma concentration for which the probability of no response during surgery is 50%) was significantly (P less than 0.001) higher in group 1 (522 +/- 104 ng/ml) than in group 2 (208 +/- 26 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Drinking