Nifedipine kinetics and dynamics during rectal infusion to steady state with an osmotic system

Nifedipine steady-state kinetics and dynamics were investigated in a placebo-controlled study of six healthy subjects. Nifedipine was given rectally through an osmotic system at a zero-order rate for 24 hr. Steady-state plasma concentrations of approximately 20 ng/ml were achieved within 6 to 8 hr. Nifedipine lowered diastolic blood pressure (DBP) and increased forearm blood flow (FBF) and plasma norepinephrine concentration. On the other hand, heart rate (HR) and systolic blood pressure were not affected. Changes in DBP and FBF were closely related to nifedipine plasma concentrations during and immediately after the infusion period. Our data indicate that nifedipine lowers blood pressure in subjects with normotension and that it is possible by infusing the drug at a relatively low rate to dissociate its effect on blood pressure from that on HR.     

Lung microdialysis study of levofloxacin in rats following intravenous infusion at steady state

Lung microdialysis has been used with rats to investigate antibiotic distribution after single-dose administration. However, conducting such experiments after intravenous infusion at steady state would constitute a more convenient alternative, which was evaluated here, using levofloxacin (LVX) as a test compound. Microdialysis probes were inserted in blood and muscle, used as a comparator, between 9:00 a.m. and 11:00 a.m. Intravenous LVX infusion was started 6 h later and maintained until the end of the experiment at a rate of 1.0 mg·h⁻¹. Lung microdialysis probes were inserted on the morning of the next day. Rats were kept anesthetized during dialysate collection. In vivo probe recoveries were estimated by retrodialysis using a calibrator method, with ciprofloxacin (CIP) as the calibrator. LVX and CIP were analyzed in dialysates by high-performance liquid chromatography. The steady-state tissue-to-blood unbound-drug concentration ratios were 1.00 ± 0.15 in muscle tissues and 1.06 ± 0.40 in lungs, suggesting passive distribution of LVX in tissue. Although providing no information on rate of distribution, microdialysis investigations following drug infusion at steady state appear to be an interesting approach for characterization of antibiotic distribution in rat lungs.     

Acyclovir kinetics after intravenous infusion.

The disposition and safety of the antiviral drug acyclovir were studied in 14 subjects with advanced malignancies. Acyclovir was administered by a 1-hr intravenous infusion at doses of 0.5, 1.0, 2.5, and 5.0 mg/kg. At the end of infusion, mean peak plasma levels (+/- SEM), determined by radioimmunoassay, were 6.4 +/- 0.7, 12.1 +/- 2.3, 14.9 +/- 2.7, and 33.7 +/- 7.1 microM. The plasma concentration-time profiles could be described by a biexponential equation. The half-life of acyclovir in the slow disposition phase ranged from 2.2 to 5 hr and the drug was detected in the plasma for at least 18 hr after infusion. The total body clearance ranged from 117 to 396 ml/min/1.73 m2. A proportionality between area under the curve and dose suggests that acyclovir exhibits dose-independent kinetics in the dose range studied. There was wide variation in cumulative urinary excretion of unchanged drug, ranging from 30 to 69% of the dose. From renal clearances of acyclovir, which were higher than creatinine clearances, it appears that both glomerular filtration and tubular secretion contribute to its renal excretion. Analysis of the urine by reverse-phase high-performance liquid chromatography revealed the presence of the metabolite 9-carboxymethoxymethylguanine. There was no indication of toxicity either clinically or from laboratory findings in any of the study subjects. This study demonstrates that in addition to selectivity and low toxicity, the kinetic profile and metabolic disposition of acyclovir make it an attractive candidate for therapy in a variety of herpes infections.     

Lag times to steady state drug delivery by continuous intravenous infusion: direct comparison of peristaltic and syringe pump performance identifies contributions from infusion system dead volume and pump startup characteristics

Journal of Clinical Monitoring and Computing - Time lags between the initiation of a continuous drug infusion and achievement of a steady state delivery rate present an important safety concern. At...     

Beta blockade by oral propranolol and labetalol

beta-Adrenergic blockade after single, oral doses of labetalol or propranolol was evaluated in a double-blind, placebo-controlled study by an isoproterenol sensitivity test and handgrip exercise in 10 healthy men. The tests were performed with subjects resting in a supine position. At the doses used, there was no effect on heart rate and blood pressure in either the resting position or in the isometric exercise phase. It is possible that exercise-induced changes in blood pressure and heart rate were reduced by higher vagal tone in this young group tested in the supine position. Isoproterenol increased heart rate and reduced diastolic blood pressure in a dose-dependent manner. The dose of isoproterenol at which heart rate increased 25 bpm above the resting rate (CD25; 1.36 +/- 0.18 microgram) was of the order of that at which diastolic blood pressure fell 25 mm Hg from baseline (HD25; 1.07 +/- 0.07 microgram). There was a significant positive correlation between CD25 and HD25 in the 10 subjects. Propranolol and labetalol induced a dose-dependent, parallel shift to the right in the dose-response curves of isoproterenol effects on heart rate and diastolic blood pressure, indicating that both drugs are nonselective, competitive antagonists of beta-adrenergic receptors. On the average, propranolol was 17 and 19 times more potent than labetalol in antagonizing the chronotropic and hypotensive actions of isoproterenol, respectively.     

Free and total cefazolin plasma and interstitial fluid concentrations at steady state during continuous infusion

Free and total concentrations of cefazolin were compared in plasma and interstitial fluid during continuous intravenous infusion therapy. Seven patients, median age 53 (25-74) years, were administered a constant infusion of cefazolin at a mean (+/-S.D.) dose of 3.5 g (+/-1.1) per 24 h for > or = 5 days. Four blisters were induced on the forearm of each patient for sampling of interstitial fluid. Free concentrations in plasma and interstitial fluid were similar, and correlated better than total concentrations (r(2) = 0.82, P = 0.005 versus r(2) = 0.54, P = 0.056). In all patients, the free concentrations in the interstitial fluid were at least two-fold the MIC(90) for Staphylococcus aureus.     

Plasma concentrations and the time-course of beta blockade due to propranolol.

The effectiveness of intravenously administered propranolol in antagonizing the chronotropic effect of isoproterenol and exercise has been investigated, and has been found at all times to be a predictable function of its plasma concentrations according to the classical drug-receptor theory for competitive antagonism. The data show further that the relationship between effectiveness and time depends on the way in which antagonism is measured. If the dose ratio to isoproterenol (DR) is measured, then (DR-1) declines with time in parallel with drug concentration. On the other hand, if propranolol's effects are measured as percentage reduction in a given response, then this declines linearly with time, even though plasma concentrations decline exponentially. This fact explains why confusion has in the past arisen concerning the relationship of the duration of beta blockade and pharmacokinetic half-life.     

Autonomic blockade by propranolol and atropine to study intrinsic myocardial function in man

Blockade of cardiac autonomic nervous activity by an intravenous injection of 0.2 mg/kg propranolol and 0.04 mg/kg atropine was used with cardiac catheterization to study intrinsic cardiac function in 47 patients with normal hearts and known graded myocardial disease. After blockade, significant hemodynamic abnormalities became apparent at rest in the majority of patients with known disease, many of whom had normal control findings. This occurred partly through a reduction in the normal range of cardiac function at rest, and partly through changes in the abnormalities associated with disease: after blockade, diseased hearts had normal stroke volumes, but beat more slowly, and had higher left ventricular filling pressures. The heart rate after blockade was fixed; this was defined as the intrinsic heart rate (IHR); it ranged from 57 to 126 beats/min in different patients. Both the IHR and left ventricular end-diastolic pressure after blockade were sensitively and quantitatively related to the severity of myocardial disease. When, after blockade, arterial pressure was raised by angiotensin, the IHR was unchanged; normal hearts maintained their stroke volume and increased stroke work; diseased hearts maintained stroke volume less well and stroke work was unchanged or fell. Abnormal ventricular responses corresponded well with abnormal ventricular function at rest.In different patients the IHR was significantly related to each available index of left ventricular function. Other studies in animals have shown that the IHR is closely related to intrinsic myocardial contractility in certain forms of experimental heart failure. An analogous relationship existing between the IHR and myocardial function in patients with heart disease is suggested as the explanation for the IHR/ventricular function relationship in this study. If so, the IHR may prove valuable as an index of myocardial function in man, since it can be measured simply and safely in clinical practice.     

The origin, kinetics, and characteristics of the kupffer cells in the normal steady state

Enzymatic digestion with pronase and DNAase was used to isolate Kupffer cells from mouse liver. The characteristics of these cells were found to be similar to those of peritoneal macrophages, except that in the initial suspension the percentage of Kupffer cells with Fc receptors was low, C receptors were absent and the ingestion of opsenized bacteria was very poor, because of the effect of pronase on the cell membrane. After 24 h incubation in vitro all these characteristics return. The in vitro and 1 h-pulse [(3)H]thymidine labeling of the Kupffer cells is low (0.8 and 1 percent, respectively) indicating that in essence these cells do not divide. It was also shown that the small percentage of in vitro labeled Kupffer cells was recently derived from the circulation. After an intravenous injection of zymosan the in vitro labeling index of the Kupffer cells increased 16-fold, but it was proven that these dividing cells were immature mononuclear phagocytes very recently recruited from the bone marrow. The labeling of Kupffer cells aider one or four injections of [(3)H]thymidine reached a peak of 10.4 percent at 48 h or 24.1 percent at 60 h, respectively, indicating that these cells are derived from labeled monocytes. Further evidence for this conclusion was obtained by the absence of an increase of labeled Kupffer cells during treatment with hydrocortisone, which causes a monocytopenia during which no circulating monocytes are available to migrate to the tissues. Labeling studies in animals X-irradiated with hind-limb shielding gave a Kupffer cell labeling index of 5-10 percent of the normal values, which confirms their bone marrow origin. A quantitative study on the production of labeled monocytes in the bone marrow and their transit through the circulation showed that in the normal steady state at least 56.4 percent of the monocytes leaving the circulation become Kupffer cells. Considering the Kupffer cells as kinetically homogeneous this gives a mean turnover time of the total population of Kupffer cells of 21 days.     

Uptake kinetics of 2',3'-dideoxyinosine into brain and cerebrospinal fluid of rats: intravenous infusion studies

The pharmacokinetics of 2',3'-dideoxyinosine (ddl) and its distribution to plasma, brain tissue and cerebrospinal fluid (CSF) were determined during and after 2-hr i.v. infusions of ddl (125 mg/kg/hr) in rats to define its specific pharmacokinetic parameters for subsequent studies of prodrugs designed to target this compound to the brain. Steady-state plasma concentrations of 50 micrograms/ml were obtained within 30 min after the start of infusions corresponding to a total clearance of 2.4 l/kg/hr. Postinfusion, ddl concentrations declined biphasically from plasma with alpha T1/2 = 3 min and beta T1/2 = 35 min. STeady-state concentrations of ddl in brain tissue and CSF were 2.6 micrograms/g in tissue and 0.81 microgram/ml in CSF, respectively. These values represent 4.7 and 1.5%, respectively, of the simultaneously determined plasma concentration. The estimated brain vascular space contribution to the observed brain uptake was 4.1%, obtained by least squares fitting of a compartmental pharmacokinetic model to the uptake data. Postinfusion, the elimination of ddl from the brain and CSF was significantly slower than from plasma, resulting in increased brain/plasma and CSF/plasma ratios after the infusions. The low steady-state brain/plasma or CSF/plasma ratios suggest rapid disappearance of ddl from the CNS relative to its rate of entry. These data indicate that ddl penetrates poorly into the brain. Thus, prodrugs with enhanced blood-brain barrier transport may improve the delivery of ddl to the brain.     

Metabolic effects of low and high doses of insulin during beta-receptor blockade in dogs

Summary. Metabolic effects of low and high doses of insulin during beta-receptor blockade were studied in eight dogs. Beta-receptor blockade was induced by 0.5 mg/kg propranolol which caused depression of heart performance. This was accompanied by a significant reduction in myocardial blood-flow and oxygen consumption. There was also a significant reduction in arterial concentrations and myocardial uptake of free fatty acids, while arterial concentrations and myocardial uptake of glucose and lactate were not significantly changed. Fifteen minutes after beta receptor blockade, an intravenous (i.v.) bolus injection of 0.5IU/kg, of insulin, free of glucagon and calcium, was given followed by a continuous infusion of 0.5 IU/kg/h. Glucose and potassium were given to maintain constant levels of these factors. After 30 min another bolus dose of 300 IU insulin was injected. Thirty minutes after a low dose of insulin, a significant increase in heart performance was recorded at unaltered myocardial oxygen consumption. Arterial concentrations of free fatty acids were significantly reduced while levels of glucose and lactate were unchanged. Myocardial uptake of glucose increased significantly while uptake of lactate and free fatty acids was unchanged. After a high dose of insulin there was a considerable improvement in heart performance. Myocardial blood-flow and oxygen consumption were not changed, nor were there alterations in arterial concentrations and myocardial uptake of glucose, lactate and free fatty acids. It is concluded that, during beta-receptor blockade high doses of insulin improve the mechanical performance of the heart through mechanisms that are independent of insulin's effects on substrate metabolism.     

Polymorphic ability to metabolize propranolol alters 4-hydroxypropranolol levels but not beta blockade

The ability to hydroxylate debrisoquine is known to be polymorphically distributed, with about 8% to 9% of the North American Caucasian population being poor metabolizers. We have shown that the ability to 4-hydroxylate propranolol is also polymorphically determined and that it cosegregates with ability to metabolize debrisoquine, such that poor debrisoquine metabolizers produce much less 4-hydroxypropranolol (4-OH propranolol) than do extensive metabolizers. There was no significant difference, however, between plasma propranolol concentrations after either single or multiple doses in the two groups. Despite the substantial difference in production of the pharmacologically active 4-OH metabolite, no difference was seen in the extent of beta-blockade induced in the extensive and poor metabolizers, which implies that 4-OH propranolol does not contribute substantially to beta-blockade.     

Tolerance to alprazolam after intravenous bolus and continuous infusion: psychomotor and EEG effects

A study was undertaken to compare the time course of changes in psychomotor performance and spectral edge (SE) of the EEG and to relate these changes to alprazolam concentrations in a pharmacokinetic/pharmacodynamic tolerance model. Digit symbol substitution (DSS) tests were administered and EEG data were obtained for SE calculation in a four-way crossover study in four normal men. Each treatment consisted of a 2-minute bolus injection followed by an 8-hour infusion. Treatment A, placebo, consisted of a 50% propylene glycol injection followed by a saline infusion. Active drug treatments were: B, 0.5 mg alprazolam plus saline infusion; C, 2.0 mg alprazolam plus saline; and D, 1.0 mg plus 72 micrograms alprazolam/hr for a total dose of 1.576 mg in 8 hours. For both DSS and SE data, three distinct effect-concentration curves result from the three alprazolam treatments, with successive shifts to the right as dose increases. A tolerance rate constant (kt) of 0.15 hr-1 was calculated from the DSS vs. time data during the 8 hour alprazolam infusion. The Hill equation was altered by using kt in an exponential modification of EC50. The resulting tolerance model describes both DSS and SE vs. concentration data from the rapid-injection and continuous-infusion treatments.     

定时摇晃输液瓶 规范静脉输注胰岛素

[目的]探讨定时摇晃输液瓶,以规范静脉输注胰岛素的操作方法。[方法]取500mL 10％葡萄糖溶液玻璃瓶6瓶,分别在输液瓶中注入12U胰岛素摇匀,将各瓶挂于输液架上模拟人体输液过程,自然输注,滴速为50gtt／min,其中3瓶设为摇晃组,每隔10min摇晃1次,另外3瓶设为非摇晃组;每隔50mL（记录时间为20min）取液,采用紫外分光光度法测定液体中胰岛素浓度。[结果]摇晃组胰岛素浓度较为均匀,而非摇晃组胰岛素浓度发生明显变化。[结论]采取定时摇晃输液瓶的方法,规范静脉输注胰岛素可有效提高病人输注胰岛素的安全性。