A novel method for efficient drug delivery

Local delivery of anti-thrombotic and anti-restenotic drugs is desired to achieve high concentrations of agents which may be rapidly degraded systemically or which exhibit very short half-lives in vivo. In this article, the operating characteristics of a novel local drug delivery method are described and its effectiveness demonstrated computationally and experimentally. Computational models used a finite volume method to determine the concentration field. Optical dye density measurements of Evans blue in saline were performed in an in vitro steady flow system. Modeling parameters were kept in the physiologic range. Experimental flow visualization studies demonstrated high concentrations of infusate near the vessel wall. Computational studies predicted high, clinically significant drug concentrations along the wall downstream of the infusion device. When the radial infusion velocity is large (infusion flow rate, Qinf>0.5% of the main flow rate, Q), the wall concentration of the infused drug remains high, e.g., levels are greater than 80% of the infusate concentration 5 cm downstream of the infusion device. At lower infusion rates (Qinf<0.001Q), the drug concentration at the wall decreases exponentially with axial distance to less than 25% of the infusate concentration 5 cm downstream of the infusion device, although therapeutic drug levels are still readily maintained. The near wall drug concentration is a function of flow conditions, infusion rate, and the drug diffusivity. Good agreement was obtained between computational and experimental concentration measurements. Flow simulation and experimental results indicate that the technique can effectively sustain high local drug concentrations for inhibition of thrombosis and vascular lesion formation.     

Pharmacokinetic-based minibolus delivery as an alternative to continuous infusion for drugs that exhibit a biophase lag

The presence of a biophase compartment in a pharmacokinetic model indicates that the response to an administered dose of drug is damped such that the time to peak effect occurs after the peak concentration in the bloodstream. This phenomenon, which is common to most intravenous anesthetic agents, can be exploited by a drug delivery method that administers minibolus doses of drug rather than a continuous infusion. Through analysis of the frequency response behavior of the biophase compartment, a bolus magnitude and dose frequency or interval (1/frequency) can be chosen such that the oscillation in drug effect is minimized even though the plasma concentration may be changing significantly with each supplemental dose. A pharmacokinetic and pharmacodynamic based method for calculating the bolus dose size and dosing interval is presented. The trade-off between dose interval and change in drug effect is exemplified through computer simulation of this strategy applied to delivery of the neuromuscular blocking agent pancuronium. The method provides a repetitive perturbation to the pharmacokinetic and pharmacodynamic system that can aid in model parameter identification during closed loop applications.     

Comparison of 14C-sucrose delivery to the brain by intravenous, intraventricular, and convection-enhanced intracerebral infusion

OBJECT: The authors evaluated convection-enhanced delivery (CED) of 14C-sucrose to the rat brain as a method of enhancing cerebral drug delivery and compared it with intravenous (i.v.) and intraventricular (i.v.t.) routes of administration. METHODS: Groups of rats received 14C-sucrose by bolus i.v. infusion, i.v.t. infusion for 1, 2, or 7 days at 0.17 microl/minute, or CED at rates from 0.01 to 0.5 microl/minute for periods from 1 hour to 7 days. Radioisotope distribution and concentration in tissue were analyzed using quantitative autoradiography. Intravenously administered sucrose reached the entire brain, but levels in tissue were low. After i.v.t. administration, sucrose levels in tissue were high at, and declined exponentially away from, the ventricular surface. Chronic CED administration maintained high levels of sucrose in tissue that focally were up to 10,000 times higher than in the i.v. group. The isotope distribution pattern after chronic CED infusions indicated a central component that resulted from convention and a peripheral component in gray matter that was the result of diffusion. The brain influx (0.42 microl/g/min) and diffusion constants of sucrose (2.8 x 10(-6) cm2/second) were similar to reported values. The total brain efflux constant was 0.0044 minute, whereas the blood-brain barrier (BBB) efflux constant was 0.0016 minute. There were no pathological changes in the brains after CED except those associated with cannula insertion. Sucrose, which was thought to be inert, was found to interact with brain tissue; up to 25% was bound to an unidentified tissue component. CONCLUSIONS: Chronic CED appears to be a potentially useful method for significantly circumventing the BBB and increasing delivery of water-soluble drugs to the brain.     

The effects of the HIV-1 envelope protein gp120 on the production of nitric oxide and proinflammatory cytokines in mixed glial cell cultures

Previous studies showed that intracarotid artery perfusion of biotinylated vasoactive intestinal peptide analog (bio-VIPa) coupled to a blood-brain barrier (BBB) drug delivery vector, OX26/avidin, causes an increase in brain blood flow by 65% in N2O-anesthetized rats. OX26 is a murine monoclonal antibody to the rat transferrin receptor and undergoes receptor-mediated transport through the BBB in vivo. The present investigation examined the central nervous system effects of bio-VIPa after conventional i.v. injection to conscious rats. The VIPa was monobiotinylated (bio) with an-XX-noncleavable (amide) linker, and the bio-XX-VIPa conjugated to OX26/streptavidin (SA) maintained affinity for the VIP receptor in radioreceptor assays. Brain uptake of the bio-XX-VIPa coupled to the OX26/SA vector after i.v. injection was at least 10-fold higher than that of the free bio-XX-VIPa, because of both an increased plasma area under the concentration curve and BBB permeability-surface area product. Administration of the free bio-XX-VIPa increased salivary gland blood flow by 350%, but had no effect on brain blood flow. By contrast, bio-XX-VIPa/OX26-SA conjugate at equal doses (20 micrograms/kg) after i.v. injection increased brain blood flow by 60% in conscious rats, but had no effect on salivary gland blood flow. In summary, the use of the BBB peptide drug delivery system targeted the drug to the central nervous system, and optimized the therapeutic index of the VIPa by enhancing cerebral blood flow and by attenuating side effects in peripheral organs such as salivary gland.     

Boundary layer drug delivery using a helical catheter

BACKGROUND: A catheter-based approach for local endovascular drug delivery has been developed. The catheter is deployed percutaneously, while the end of the catheter is in the form of a helix that is placed just proximal to the vascular site to be treated. The helices are in contact with the vessel wall. A number of small holes is drilled in the coils of the catheter through which drug is infused, so that the infused drug remains within the blood fluid 'boundary layer' adjacent to the vessel wall. This approach is expected to be highly efficient for administration of antithrombotic and antiproliferative agents that target processes leading to vascular occlusion, heart attacks, and strokes. METHODS: The helical catheter was qualitatively evaluated using optical dye density measurements of Evans blue dye infused using an in vitro steady flow system under a physiologic range of conditions. To further demonstrate the efficiency of the technique, its capacity to inhibit thrombosis was evaluated in a baboon thrombosis model. The catheter was inserted into a femoral arteriovenous shunt (blood flow rate = 100 ml/min) and placed proximal to a segment of highly thrombogenic Dacron vascular graft (4.0 mm i.d.). Integrelin (an inhibitor of platelet glycoprotein IIb/IIIa; doses: 0.25-1.0 microg/min) and hirudin (an antithrombin; doses: 10-100 microg/min) were used to inhibit thrombus formation. RESULTS: Experimental flow visualization studies demonstrated that high concentrations of the infused Evans blue dye were retained near the vessel wall. In the animal experiments, platelet deposition on the Dacron graft surface was reduced by 82-97% (Integrelin) and 68-92% (hirudin) over 1-2 h of blood exposure. The local antithrombotic effects produced were found to be 200-fold and 30-fold more efficient than systemic administration of the same agents. CONCLUSIONS: Local drug infusion using the helical catheter approach can achieve high drug concentration levels at target sites, may avoid systemic effects, and can reduce cost of therapy by reducing total drug requirements.     

Regulation of lymphocyte migration into lymph nodes by high endothelial venules

The transgenic (Tg) mice carrying the human gene for poliovirus receptor (PVR) are susceptible to poliovirus intravenously (i.v.) inoculated as well as intracerebrally or intraspinally inoculated. Thus, i.v.-inoculated poliovirus may invade the central nervous system (CNS) through the blood-brain barrier (BBB). To know the contribution of PVR to tissue distribution and BBB permeability of i.v.-inoculated polioviruses, these dissemination processes were investigated and compared between the Tg mice and non-Tg mice. Distribution profile of i.v.-inoculated poliovirus in various tissues of the Tg mice is similar to that in non-Tg mice. The data suggest that tissue distribution of the virus occurs independently of the transgene for PVR. The amount of poliovirus delivered to the CNS suggested the existence of a specific delivery system of the virus to the CNS. Virus accumulation in the CNS of the Tg mice was measured up to 7.5 hr after the i.v. inoculation. The viruses, regardless of whether the virulent or attenuated strain, seem to accumulate at a constant rate of approximately 0.2 microliter/min/g tissue. Similar phenomena were observed when the viruses were inoculated into non-Tg mice. The rates of the virus accumulation in the CNS are more than 100 times higher than that of albumin, which is considered not to permeate through the BBB via a specific transport system, and only three times lower than that of monoclonal antibody against transferrin receptor (OX-26), which is a potential candidate as a drug delivery vehicle specific to the CNS. These data suggest that polioviruses permeate through the BBB at a fairly high rate, independently of PVR and virus strains.     

Safety and cost of rapid i.v. injection of famotidine in critically ill patients

The safety and cost of famotidine in intensive care patients given the drug by rapid i.v. injection or slow i.v. infusion were studied. All patients admitted to the medical-coronary care and surgical intensive care units (ICUs) at a university teaching hospital over a two-month period who had orders for at least one dose of famotidine injection for any indication were randomly assigned to receive the drug by rapid i.v. injection or slow i.v. infusion via volumetric chamber. Data on patient demographics, drug administration time, adverse effects, cardiovascular variables, and costs (including drug acquisition, supply, and nursing personnel costs) were collected prospectively. Fifty-three patients received famotidine by i.v. injection (a total of 1041 doses) and 52 by i.v. infusion (1006 doses). The mean +/- S.D. duration of famotidine administration was 44 +/- 12 seconds in the i.v.-injection group and 19 +/- 5 minutes in the i.v.-infusion group. Adverse effects possibly related to famotidine occurred in three injection-group patients and two infusion-group patients. No significant difference between the groups in cardiovascular variables (mean arterial pressure, heart rate, and respiratory rate) was noted. Cost savings for the injection group relative to the infusion group totaled $2886 for the two-month study period. Half of the savings came from reduced supply costs and half from reduced personnel costs. The annualized savings to the institution would be about $17,300. Rapid i.v. injection of famotidine appeared to be as safe in ICU patients as giving the drug by slow i.v. infusion and was less costly.     

An analysis of the effect of venous resistance on the performance of gravity-fed intravenous infusion systems

OBJECTIVE: Our objective was to assess the effect of venous resistance in a clinically relevant range on flow rates through intravenous (i.v.) cannulae. METHODS: Since resistances in series are additive, the sum of the resistance of the i.v. cannula and the vein equates to the total resistance to flow. Using resistance data from earlier work, the total resistance for various combinations of cannula and vein size was calculated, allowing a prediction to be made of the comparative flow rates between these combinations for a given driving pressure. Next, the clinical situation was simulated by measuring flow rates through i.v. cannulae connected in series to a variety of infusion devices with resistances known to be within the range of clinically relevant venous resistance. RESULTS: The effect of venous resistance was greatest on large-bore cannulae, with significant reductions in flow occurring when even low levels of venous resistance were added. Throughout much of the range of venous resistances encountered clinically, total flows through two small-gauge cannulae exceeded that through a single large-gauge cannula. CONCLUSION: To achieve maximum benefit from a large-bore cannula, a suitably large vein must be chosen. Further, where venous access is difficult and high flow potential from an infusion system is required, two separate infusions through small cannulae may be a preferable option to a single large bore.     

Enhanced intracoronary thrombolysis with urokinase using a novel, local drug delivery system. In vitro, in vivo, and clinical studies

BACKGROUND: Current pharmacological regimens for treating intracoronary thrombus in the cardiac catheterization laboratory generally involve the administration of thrombolytic agents that result in a systemic fibrinolytic state and/or require prolonged arterial drug infusion. The purpose of the present study was to assess a new technique for treating intracoronary thrombus consisting of the local infusion of limited quantities of urokinase with a novel drug delivery device. METHODS AND RESULTS: THe Dispatch coronary infusion catheter is a new local drug delivery system that allows for the prolonged infusion of therapeutic agents at an angioplasty site while distal coronary flow is maintained. Three experimental protocols were performed to determine the in vitro, in vivo, and clinical efficacy of this device. First, in vitro thrombolysis of fresh, porcine thrombus trapped in a 4-mm plastic tube with a 50% constriction and perfused with 20% porcine plasma was measured. Twenty-three thrombi were weighed before and after no treatment (n = 5), "systemic" urokinase administration (n = 4), local infusion of 150,000 U urokinase with a standard end-hole catheter (n = 4), local infusion of saline with the Dispatch catheter (n = 5), and local infusion of 150,000 U urokinase with the Dispatch catheter (n = 5). Second, 25 porcine coronary arteries in 23 pigs were dilated in vivo with conventional balloon angioplasty and then treated with 123I-labeled urokinase that was administered either by the Dispatch catheter (150,000 U; n = 16), intravenous systemic bolus (1,000,000 U; n = 3), guiding catheter infusion (500,000 U; n = 3), or local end-hole catheter infusion (150,000 U; n = 3). All vessels were subsequently harvested to quantify intramural deposition and subsequent washout of urokinase at the angioplasty site. Finally, 19 patients with angiographic evidence of intracoronary thrombus were treated with local urokinase infusion with the Dispatch catheter either before or after balloon angioplasty or directional atherectomy. In vitro studies demonstrated that infusion of urokinase with the Dispatch catheter decreased thrombus weight by 66% compared with no treatment (-25%), "systemic" urokinase administration (25%), end-hole catheter urokinase infusion (32%), or infusion of saline by the Dispatch catheter (32%) (P < or = .005). In vivo studies demonstrated immediate deposition of 0.12% of the urokinase delivered by the Dispatch catheter to the angioplasty site, compared with 0.0007% with systemic bolus, 0.003% with guiding catheter infusion, and 0.007% with local infusion with an end-hole catheter (P < .001). Urokinase deposited by the Dispatch catheter persisted intramurally for at least 5 hours. Patient studies demonstrated reduction of thrombus-containing stenoses and complete disappearance of intracoronary thrombus in all cases in which 150,000 U urokinase was locally infused over 30 minutes. There was no evidence of abrupt closure, distal embolization, or no reflow in any patient. CONCLUSIONS: Local urokinase delivery with the Dispatch catheter can result in rapid and complete intracoronary thrombolysis using substantially less drug than standard thrombolytic techniques. Intramural deposition of drug with this technique creates a local reservoir of urokinase that may provide prolonged thrombolytic activity at the infusion site.     

Differential permeability of a human brain tumor xenograft in the nude rat: impact of tumor size and method of administration on optimizing delivery of biologically diverse agents

To assess how to maximize drug delivery to intracerebral tumors and surrounding brain, this study examined the effects of route and method of administration and tumor size on the distribution of three agents in a nude rat intracerebral tumor xenograft model. Aminoisobutyric acid (M(r) 103), methotrexate (M(r) 454), and dextran 70 (M(r) 70,000) were administered i.v. or intra-arterially (i.a.) with or without osmotic blood-brain barrier disruption (BBBD) at 8, 12, or 16 days after tumor cell inoculation (n = 72). A 2.2- to 2.5-fold increase in delivery to tumor and surrounding brain was observed when i.a. was compared with i.v., and a 2.5- to 7.6-fold increase was observed when BBBD was compared with the saline control. The combined effect of i.a. administration and BBBD was to increase delivery 6.3-16.7-fold. The greatest benefit of BBBD was seen in animals with 8-day tumors, whereas BBBD had less benefit in improving delivery to intracerebral tumor and brain around tumor as the tumors grew larger. Regional delivery decreased as the molecular weight of the agent increased. Based on these results, we suggest that i.a. administration of antitumor agents may be adequate to obtain initial responses in large, very permeable, intracerebral tumors. However, in smaller, less permeable tumors or after an initial response to treatment, there may be a significant therapeutic advantage to i.a. agent administration and BBBD.     

Patient maintained alfentanil target-controlled infusion for analgesia during extracorporeal shock wave lithotripsy

PURPOSE: The purpose of this study was to determine whether alfentanil given by a pharmacokinetic-based target controlled infusion (TCI) system under patient control is a suitable analgesic technique for extracorporeal shock wave lithotripsy (ESWL). METHODS: The design was an open, unblinded, noncomparative, prospective study. Forty outpatients undergoing ESWL were given patient maintained alfentanil TCI. Pain, nausea and sedation were assessed every 300 shocks. Vital signs were recorded every three minutes, pulse oximetry and electrocardiography being monitored continuously. Blood alfentanil concentration was measured for comparison with the predicted value. RESULTS: Alfentanil consumption (median 1.34 mg, range 0.8-3.6) and measured levels following treatment (median 60 ng.ml-1, range 15.6-134.3) varied widely. The precision of the TCI system and the median prediction error (bias) were both 49%. The median of pain scores recorded during treatment was 4 (range 0-8). The median respiration rate was 15 bpm (range 10-23), three patients required oxygen (SaO2 < 92%) cardiovascular measurements were stable and there was no excessive sedation. The incidence of nausea was 15%. All patients were ready for hospital discharge within one hour following treatment. CONCLUSIONS: Patient maintained alfentanil TCI provides good analgesia for ESWL in the majority of patients with little sedation. Respiratory depression is uncommon but supplementary oxygen should be given prophylactically. There is considerable interindividual variation in demand for alfentanil indicating the usefulness of the patient control method. The TCI system underestimated alfentanil blood concentrations but this did not affect its clinical usefulness.     

Tat-induced lesions in transgenic mice do not correlate with the HIV-1 LTR transactivation

A pilot study was conducted in 7 normal volunteers to demonstrate the feasibility of employing pharmacokinetic tailoring to achieve matching plasma opioid concentration-time curves after epidural (e.p.) and intravenous (i.v.) alfentanil administration. Each subject participated in 1 pretest and 2 test sessions. Our pain model was cutaneous electrical stimulation of the finger and toe, adjusted to produce a baseline pain report of 5 (strong pain on a 0-5 scale). On test day 1, subjects received e.p. alfentanil (750 micrograms) and an i.v. saline infusion. Serial measurements of analgesia, end tidal CO2, pupil size, subjective side effects, and plasma alfentanil concentrations were conducted before and at various time intervals over a 4-h period after alfentanil administration. On test day 2, subjects received e.p. saline and a pharmacokinetically tailored i.v. infusion (using individual pharmacokinetics determined on the pretest day) designed to achieve a plasma concentration-time profile identical to that observed on the epidural day. The same battery of effect measurements was administered as on the 1st test day. Plasma alfentanil was measured to verify the accuracy of the tailored infusion. Plasma alfentanil concentration profiles were nearly identical on both test days. Peak plasma alfentanil concentrations were near the reported minimum effective analgesic concentration (MEAC). Overall, analgesia was slightly greater with e.p. administration. Onset of pain relief was rapid, and duration was approximately 1.5 h with e.p. and 1 h with i.v. alfentanil. There were no differences in pupil size, ETCO2, or subjective side effects between e.p. versus i.v. administration. We conclude that systemic redistribution from the epidural space appears to account for most, but not all, of the analgesia.     

Acute liver injury following infection with a cytopathic strain of duck hepatitis B virus

It is well established that systemic inflammation induces a counter-regulatory anti-inflammatory response particularly resulting in deactivation of monocytes/macrophages. However, recently we demonstrated a systemic anti-inflammatory response without preceding signs of systemic inflammation in patients with brain injury/surgery and release of cytokines into the cerebrospinal fluid (CSF). In order to analyze the mechanisms and pathways of systemic immunodepression resulting from sterile cerebral inflammation we established an animal model using continuous intra-cerebroventricular (i.c.v.) or intra-hypothalamic (i.h.) infusion of rat recombinant (rr) tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta for 48 h. Controls received intra-venous (i.v.) cytokine administration. Interestingly, i.c.v. and i.h. infusion of IL-1beta but not TNF-alpha produced distinct signs of central nervous system (CNS) inflammation. Correspondingly, i.c.v. infusion of IL-1beta particularly diminished the TNF-alpha but increased the IL-10 concentration in whole blood cultures after endotoxin stimulation. All parameters normalized within 48 h after termination of the infusion. Blocking the hypothalamic-pituitary-adrenal (HPA) axis by hypophysectomy (HPX) led to complete recovery of the diminished TNF-alpha concentration and temporarily inhibited the IL-10 increase. Blocking the sympathetic nervous system (SNS) transmission by application of the beta2-adrenoreceptor antagonist propranolol not only inhibited the increase but further downregulated the endotoxin induced IL-10 concentration in the media of whole blood cell cultures, whereas the TNF-alpha decrease was only partially prevented. Interestingly, HPX and propranolol also diminished the cell invasion into the CSF. In summary, activation of both the HPA axis and the SNS plays an important role in systemic anti-inflammatory response resulting from cytokines in brain and cerebral inflammation.     

Clearance of morphine in postoperative infants during intravenous infusion: the influence of age and surgery

We analyzed morphine clearance values in infants receiving the drug by continuous i.v. infusion for analgesia after surgery, because we found lower steady-state morphine concentrations than we expected from our previous studies. Infants received morphine after a loading dose of 0.05 mg/kg and continuous infusion calculated to reach a steady-state concentration of 20 ng/mL. Blood was sampled twice on Postoperative Day 1 at times separated by at least 2 h, and morphine and morphine-6-glucuronide (M-6-G) concentrations were determined by high-performance liquid chromatography. Clearance of morphine was calculated as infusion rate divided by the steady-state morphine concentration. Morphine given to 26 infants by continuous i.v. infusion after major noncardiac surgery has rapidly increasing clearance values, from a median value of 9.2 mL x min(-1) x kg(-1) in infants 1-7 days old, 25.3 in infants 31-90 days old, and 31.0 in infants 91-180 days old to 48.9 in infants 180-380 days old. Adult clearance values are reached by 1 mo of age, more quickly than in infants of the same age previously studied who received morphine after cardiac surgeries. M-6-G was measured in all infants. The ratio of M-6-G to morphine concentrations was 1.9-2.1 in these infants, which is lower than ratios reported in older infants or adults by others, but higher than those reported in newborns. Infants with normal cardiovascular systems undergoing surgery clear morphine more efficiently than infants of the same age undergoing cardiac surgery. Implications: Morphine removal from the body is slow in newborns but increases to reach adult values in the first months of life. Calculating the clearance of morphine from blood samples drawn during continuous i.v. infusions after surgery shows that this maturation occurs more quickly in infants undergoing noncardiac surgery (by 1-3 mo of age) than in those receiving morphine after cardiac surgery (by 6-12 mo of age).     

Cardiopulmonary and anesthetic effects of propofol in wild turkeys

OBJECTIVE: To determine safety, anesthetic variables, and cardiopulmonary effects of i.v. infusion of propofol for induction and maintenance of anesthesia in wild turkeys. ANIMALS: 10 healthy, adult wild turkeys. PROCEDURE: Anesthesia was induced by i.v. administration of propofol (5 mg/kg of body weight) over 20 seconds and was maintained for 30 minutes by constant i.v. infusion of propofol at a rate of 0.5 mg/kg/min. Heart and respiratory rates, arterial blood pressures, and arterial blood gas tensions were obtained prior to propofol administration (baseline values) and again at 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30 minutes after induction of anesthesia. All birds were intubated immediately after induction of anesthesia, and end-tidal CO2 concentration was determined at the same time intervals. Supplemental oxygen was not provided. RESULTS: Apnea was observed for 10 to 30 seconds after propofol administration, which induced a decrease in heart rate; however, the changes were not significant. Compared with baseline values, respiratory rate was significantly decreased at 4 minutes after administration of propofol and thereafter. Systolic, mean, and diastolic pressures decreased over the infusion period, but the changes were not significant. Mean arterial blood pressure decreased by 30% after 15 minutes of anesthesia; end-tidal CO2 concentration increased from baseline values after 30 minutes; PO2 was significantly decreased at 5 minutes after induction and thereafter; PCO2 was significantly (P < 0.05) increased after 15 minutes of anesthesia; and arterial oxygen saturation was significantly (P < 0.05) decreased at the end of anesthesia. Two male turkeys developed severe transient hypoxemia, 1 at 5 and the other at 15 minutes after induction. Time to standing after discontinuation of propofol infusion was 11 +/- 6 minutes. Recovery was smooth and unremarkable. CONCLUSION: Propofol is an effective agent for i.v. induction and maintenance of anesthesia in wild turkeys, and is useful for short procedures or where the use of inhalational agents is contraindicated.     

Nitric oxide and the haemodynamic profile of endotoxin shock in the conscious mouse

1. The release of cytokines following administration of endotoxin and the contribution of nitric oxide (NO) to the subsequent haemodynamic profile were investigated in the conscious mouse. 2. Administration of endotoxin (E. Coli, 026:B6, 12.5 mg kg(-1), i.v.) elevated the concentration of tumour necrosis factor-alpha (TNF-alpha) in the plasma within 0.5 h, reaching a maximum at 2 h and returning to control concentrations by 4 h. In addition, the concentration of interleukin-6 (IL-6) in the plasma was also elevated within 1 h, reaching a maximum at 3 h and remaining elevated throughout the 12 h of study. 3. Endotoxin (12.5 mg kg(-1), i.v.) induced the expression of a Ca2+-independent (inducible) NO synthase in the mouse heart and elevated the concentrations of nitrite and nitrate in the plasma within 4 h, reaching a maximum at 12 h. This was accompanied by a progressive fall in blood pressure over the same period. 4. The vasopressor effect of noradrenaline (0.5-4 microg kg(-1) min(-1), i.v.) administered as a continuous infusion was significantly attenuated 7 h after endotoxin (12.5 mg kg(-1), i.v). 5. The NO synthase inhibitor NG-monomethyl-L-arginine HCl (L-NMMA; 1-10 mg kg(-1), i.v. bolus) reversed the fall in blood pressure when administered 7 h after endotoxin (12.5 mg kg(-1), i.v.). 6. In an attempt to maintain a constant blood concentration, L-NMMA was administered as a continuous infusion (10 mg kg(-1) h(-1), i.v.), beginning 4 h after a lower dose of endotoxin (6 mg kg(-1), i.v.). Such treatment prevented the fall in blood pressure and the elevation of nitrite and nitrate in the plasma throughout the 18 h of observation. 7. The fall in blood pressure following endotoxin (3 mg kg(-1), i.v.) was significantly reduced throughout the 18 h of observation in homozygous mutant mice lacking the inducible NO synthase. 8. In summary, we have developed a model of endotoxin shock in the conscious mouse in which an overproduction of NO by the inducible NO synthase is associated with the haemodynamic disturbances. This model, which exhibits many of the characteristics of septic shock in man, will enable the study of the pathology of this condition in more detail and aid the investigation of potential therapeutic agents both as prophylactics and, more importantly, as treatments.     

pH in human tumor xenografts and transplanted rat tumors: effect of insulin, inorganic phosphate, and m-iodobenzylguanidine

Various strategies to improve the therapeutic index of anticancer agents aim at inducing, by stimulation of aerobic glycolysis, temporary pH differences between malignant and normal tissues which can be exploited to activate cytotoxic agents selectively in tumors. We have investigated whether the pH reduction induced by glucose, the "drug" commonly used to increase lactic acid production in malignant tissues, can be augmented by pharmacological manipulation of tumor cell glycolysis. At normal plasma glucose concentration (6 +/- 1 mM), inorganic phosphate, a modifier of hexokinase and phosphofructokinase activity, had no effect on pH in two transplanted rat tumors and a human tumor xenograft line (average pH, 6.80; range, 6.65-6.95). When plasma glucose concentration was raised to 30 +/- 3 mM by i.v. infusion of glucose, inorganic phosphate reduced the pH in those tumors which exhibited only a moderate pH response to glucose per se (mean pH, 6.60) to an average value of 6.20 (range, 6.05-6.35). In the same setting, insulin, continuously infused at dose rates up to 600 milliunits/kg body weight/min, did not result in acidification of tumor tissue exceeding that induced by glucose alone. However, the H+ ion activity in both transplanted rat tumors and human tumor xenografts was increased by m-iodobenzylguanidine (MIBG), an inhibitor of mitochondrial respiration. For example, at normoglycemia, MIBG reduced the mean pH in a human mesothelioma xenograft from 6.90 to 6.70. This pH value was further reduced to 6.20 by simultaneous low-dose i.v. glucose infusion (plasma glucose concentration, 14 +/- 3 mM). The acidosis induced by inorganic phosphate and MIBG was tumor specific. Normal tissues of tumor-bearing hosts were only marginally sensitive to hyperphosphatemia or MIBG administration. These results indicate that the known stimulatory effect of exogenous glucose on lactic acid production in malignant tumors in vivo can be further accentuated or, as in the case of MIBG, partially replaced by pharmacological manipulation of aerobic glycolysis using clinically established drugs.     

New approaches to the evaluation of pulmonary circulation in surgical patients with tuberculosis

Home care is replacing the traditional hospital stay for a variety of acute and chronic illnesses. The delivery of home antibiotic infusion therapy is an innovative treatment approach for stable term infants with suspected or confirmed infection. Neonates are a unique group of home i.v. therapy recipients, and programs specific to the needs of this population must be developed. This article describes one such program in detail.     

A four-hour topotecan infusion achieves cytotoxic exposure throughout the neuraxis in the nonhuman primate model: implications for treatment of children with metastatic medulloblastoma

The purpose of this study was to define the length of topotecan (TPT) i.v. infusion necessary to attain a cytotoxic exposure for medulloblastoma cells throughout the neuraxis. In vitro studies of human medulloblastoma cell lines (Daoy, SJ-Med3) were used to estimate the length and extent of TPT systemic exposure associated with inhibition of tumor cell growth or the exposure duration threshold (EDT). We evaluated TPT systemic and cerebrospinal fluid (CSF) disposition in six male rhesus monkeys (8-12 kg) that received TPT 2.0 mg/m2 i.v. as a 30-min or 4-h infusion. Plasma and CSF samples were assayed for TPT lactone by high-performance liquid chromatography, and the CSF exposures were compared with the estimated EDT. Results of the in vitro studies defined an EDT as a TPT lactone concentration of > 1 ng/ml for 8 h (IC99) daily for 5 days. The mean +/- SD for systemic clearance (CL(SYS)), penetration into fourth ventricle (%CSF(4th)), and penetration into lumbar space (%CSF(LUM)) were similar for the 30-min and the 4-h infusions. At a TPT lactone systemic exposure (AUC(PL)) of 56.7 +/- 19.9 ng/ml x h, time above 1 ng/ml in the fourth ventricle was 1.4-fold greater for a 4-h infusion compared with a 30-min infusion. At a TPT lactone AUC(PL) of 140 ng/ml x h, the 4-h infusion achieved the desired TPT exposure throughout the neuraxis (lateral and fourth ventricles and lumbar space), whereas the 30-min infusion failed to achieve it in the lumbar space. In conclusion, prolonging TPT i.v. infusion from 30-min to 4-h at a targeted AUC(PL) achieves the EDT throughout the neuraxis and represents an alternative method of TPT administration that will be tested prospectively in patients with high-risk medulloblastoma.     

Local intraluminal infusion of biodegradable polymeric nanoparticles. A novel approach for prolonged drug delivery after balloon angioplasty

BACKGROUND: Several perfusion balloon catheters are under investigation for local drug delivery; however, sustained tissue drug levels are difficult to achieve with these techniques. To overcome this problem, sustained-release, biodegradable nanoparticles represent a potential alternative for prolonged local delivery. METHODS AND RESULTS: A biodegradable polylactic-polyglycolic acid (PLGA) copolymer was used to formulate nanoparticles. Fluorescent-labeled nanoparticles were intraluminally administered in a single, 180-second infusion after balloon injury in the rat carotid model. Localization and retention at different time points and biocompatibility of nanoparticles were evaluated. To evaluate the potential of the system in the prevention of neointimal formation, dexamethasone was incorporated into the particles and delivered locally as above. Nanoparticles were seen in the three layers of the artery at 3 hours and 24 hours. At 3 days, they were mainly present in the adventitial layer, decreasing at 7 days, with no fluorescent activity at 14 days. The PLGA nanoparticles appeared to be fully biocompatible. In the dexamethasone nanoparticle study, a significant amount of dexamethasone was present in the treated segment for up to 14 days after a single infusion, with no plasma levels detected after the first 3 hours. There was a 31% reduction in intima-media ratio in animals treated with local dexamethasone nanoparticles compared with control. CONCLUSIONS: Nanoparticles successfully penetrated into the vessel wall and persisted for up to 14 days after a short, single intraluminal infusion. Local administration of nanoparticles with incorporated dexamethasone significantly decreased neointimal formation. This methodology appears to have important potential for clinical applications in local drug delivery.