Implantable drug-delivery systems

Differential Drug Release Kinetics from Paclitaxel-Loaded Polydioxanone Membranes and Capsules

BACKGROUND

Drug laden implantable systems can provide drug release over several hours to years, which eventually aid in the therapy of both acute and chronic diseases. The present study focuses on a fundamental evaluation of the influence of implant properties such as morphology, architecture, porosity, surface area, and wettability in regulating the drug release kinetics from drug-loaded polymeric matrices.

METHODS

For this, Polydioxanone (PDS) was selected as the polymer and Paclitaxel (Ptx) as the model drug. Two different forms of the matrix implants, viz., reservoir type capsules developed by dip coating and matrix type membranes fabricated by phase inversion and electrospinning, were utilized for the study. Drug release from all the four different matrices prepared by simple techniques was evaluated in vitro in PBS and ex vivo in peritoneal wash fluid for ~4 weeks. The drug release profiles were thereafter correlated with the physicochemical parameters of the polymeric implants.

RESULTS

Reservoir-type capsules followed a slow and steady zero-order kinetics, while matrix-type electrospun and phase inversion membranes displayed typical biphasic kinetics.

CONCLUSION

It was inferred that the slow degradation rate of PDS polymer as well as the implant properties like porosity and wettability play an important role in controlling the drug release rates.

Advanced drug delivery 2020 and beyond: Perspectives on the future

Drug delivery systems are developed to maximize drug efficacy and minimize side effects. As drug delivery technologies improve, the drug becomes safer and more comfortable for patients to use. During the last seven decades, extraordinary progress has been made in drug delivery technologies, such as systems for long-term delivery for months and years, localized delivery, and targeted delivery. The advances, however, will face a next phase considering the future technologies we need to overcome many physicochemical barriers for new formulation development and biological unknowns for treating various diseases. For immediate and long-term progress into the future, the drug delivery field should use time and resources for more translatable research ideas. The drug delivery discipline has to continue working on basic, applied, translational, and clinical research in a concerted manner to produce drug delivery systems that work for patients. It is a time to focus our attention on things that matter. It is also a time to develop realistic research goals and outcomes, diversify drug delivery technologies, and take the collective responsibility for our actions.

Simple minimally-invasive automatic antidote delivery device (A2D2) towards closed-loop reversal of opioid overdose

With approximately 48,000 attributed deaths in 2017, the opioid overdose is now the leading cause of death amongst Americans under the age of 50. The overdose process can be interrupted by the administration of naloxone, a safe and effective opiate antagonist that can reverse the effects of overdose and minimizing the delay in administering the antidote is critical in preventing permanent damage to patients. A closed-loop implantable drug delivery system is an ideal solution to minimize the response time, however, they often feature complex designs that are expensive to fabricate and require a more invasive surgical implantation. Here we propose a simple, low-cost, minimally-invasive automatic antidote delivery device (A2D2) that can administer a large dose of naloxone upon detection of overdose-induced respiratory failure. The subcutaneously placed device can be activated using an externally applied time varying magnetic field from a wearable device. Using a custom magnetic field generator, we were able to release the drug within 10 s. Our bench-top evaluation showed that A2D2 can release 1.9 mg of powdered drug within 60 s and up to 8.8 mg in 600 s. We also performed in vivo evaluation to demonstrate rapid drug releasing capability in the subcutaneous space of mice. However, we saw a small amount of leakage (1.75% of payload) over the course of 1000 h of simulated implantation. Thus, additional research is needed to verify the long term stability of our device and to demonstrate the closed-loop release mechanism to revive overdosed animals. Nevertheless, our preliminary results show the potential of using a simple, low-cost, subcutaneous device for emergency drug delivery application.

Sequential and controlled release of small molecules from poly(N-isopropylacrylamide) microgel-based reservoir devices

Devices capable of releasing two different small molecules independently, at defined release kinetics, were prepared and their behavior characterized.

Engineered therapeutic-releasing nanoporous anodic alumina-aluminum wires with extended release of therapeutics

In this study, we present a nanoengineered therapeutic-releasing system based on aluminum wires featuring nanoporous anodic alumina layers and chitosan coatings. Nanoporous anodic alumina layers are produced on the surface of aluminum wires by electrochemical anodization. These nanoporous layers with precisely engineered nanopore geometry are used as nanocontainers for bovine serum albumin molecules labeled with fluorescein isothiocyanate (BSA-FITC), which is selected as a model drug. The surface of these therapeutic-releasing implants is coated with a biocompatible and biodegradable polymer, chitosan, in order to achieve a sustained release of protein over extended periods of time. The performance of this therapeutic-releasing device is systematically assessed through a series of experiments under static and dynamic flow conditions. In these experiments, the effect of such parameters as the number of layers of chitosan coating and the temperature and pH of the eluting medium is established. The obtained results reveal that the proposed therapeutic-releasing system based on nanoporous aluminum wires can be engineered with sustained release performance for up to 6.5 weeks, which is a critical factor for medical treatments using sensitive therapeutics such as proteins and genes when a localized delivery is desired.

Nanoengineered drug-releasing aluminium wire implants: comparative investigation of nanopore geometry, drug release and osteoblast cell adhesion

In this study, drug-releasing aluminium (Al) wire implants featuring nanoporous alumina (NPA) layers produced by different anodization approaches are systematically investigated as potential platforms for localized drug delivery and bone therapy.

Controlled release of polypeptides and other macromolecules

The use of polymeric matrices for the controlled release of polypeptides and other macromolecular drugs is reviewed. Three principal mechanisms of release include diffusion of the polypeptide through the polymer, erosion of the polymer matrix, and the application of magnetic fields to force more drug out of the matrix. The diffusion controlled systems generally utilize ethylene-vinyl acetate copolymer. The advantage of these systems is facile manipulation of the pore structure to obtain desired release kinetics. Release of many different polypeptides from these systems for periods of months has been demonstrated. Bioerosion provides the advantage that the polymer system does not need to be retrieved. Magnetism provides a mechanism whereby desired increases and decreases in polypeptide release rates can be achieved on demand.

Platelet lysates stimulate angiogenesis, neurogenesis and neuroprotection after stroke

Platelets contain chemo-attractants and mitogens that have a major role in tissue repair. Therefore we hypothesised that tissue regeneration secondary to activation of endogenous neural stem cells (eNSC) can be enhanced by delivering platelets to the ischaemic brain. To examine these potential therapeutic effects we injected platelet-poor plasma (PPP), fibroblast growth factor (FGF2) and platelet lysate (PLT) to the lateral ventricles after permanent middle cerebral artery occlusion (PMCAO) in rats. The animals were tested with the neurological severity score, and infarct volumes were measured at 90 days post-PMCAO. Immunohistochemistry was used to determine the fate of newborn cells and to count blood vessels in the ischaemic brain. Platelets significantly increased eNSC proliferation and angiogenesis in the subventricular zone (SVZ) and in the peri-lesion cortex. Functional outcome was significantly improved and injury size was significantly reduced in rats treated with PLT suggesting additional neuroprotective effects. In conclusion, local delivery of PLT to the lateral ventricles induces angiogenesis, neurogenesis and neuroprotection and reduces behavioural deficits after brain ischaemia.

Species and density of implant surface chemistry affect the extent of foreign body reactions

Implant-associated fibrotic capsule formation presents a major challenge for the development of long-term drug release microspheres and implantable sensors. Since material properties have been shown to affect in vitro cellular responses and also to influence short-term in vivo tissue responses, we have thus assumed that the type and density of surface chemical groups would affect the degree of tissue responses to microsphere implants. To test this hypothesis, polypropylene particles with different surface densities of -OH and -COOH groups, along with the polypropylene control (-CH2 groups) were utilized. The influence of functional groups and their surface densities on fibrotic reactions were analyzed using a mice subcutaneous implantation model. Our comparative studies included determination and correlation of the extents of fibrotic capsule formation, cell infiltration into the particles, and recruitment of CD11b+ inflammatory cells for all of the substrates employed. We have observed major differences among microspheres coated with different surface functionalities. Surfaces with -OH surface groups trigger the strongest responses, while -COOH-rich surfaces prompt the least tissue reactions. However, variation of the surface density of either functional group has a relatively minor influence on the extent of fibrotic tissue reactions. The present results show that surface functionality can be used as a powerful tool to alter implant-associated fibrotic reactions and, potentially, to improve the efficacy and function of drug-delivery microspheres, implantable sensors, and tissue-engineering scaffolds.

Microfluidic Rheology of Non-Newtonian Liquids

We investigate the rheological properties of a non-Newtonian glass-former liquid within lithographically defined microchannels in the range of temperatures above the vitrification region. The non-Newtonian behavior of the fluid, as evidenced by rotational rheology, is well described by a power law dependence of the viscosity on the shear rate. Taking into account such non-Newtonian character in the equations for the microfluidic motion, we relate the penetration dynamics into capillaries with the liquid rheological properties. The temperature dependence of the viscosity, determined over 1 order of magnitude in the temperature range 286-333 K and for shear rates between 0.07 and 1 s-1, can be described by a Vogel-Fulcher-Tamman law, consistent with the fragile nature of the investigated compound. Microfluidics is a promising analytical approach for the investigation of the rheology of non-Newtonian fluids within confined microenvironments.

Streaming potential and electroosmotic flow in heterogeneous circular microchannels with nonuniform zeta potentials: requirements of flow rate and current continuities

Real surfaces are typically heterogeneous, and microchannels with heterogeneous surfaces are commonly found due to fabrication defects, material impurities, and chemical adsorption from solution. Such surface heterogeneity causes a nonuniform surface potential along the microchannel. Other than surface heterogeneity, one could also pattern the various surface potentials along the microchannels. To understand how such variations affect electrokinetic flow, we proposed a model to describe its behavior in circular microchannels with nonuniform surface potentials. Unlike other models, we considered the continuities of flow rate and electric current simultaneously. These requirements cause a nonuniform electric field distribution and pressure gradient along the channel for both pressure-driven flow (streaming potential) and electric-field-driven flow (electroosmosis). The induced nonuniform pressure and electric field influence the electrokinetic flow in terms of the velocity profile, the flow rate, and the streaming potential.

Lattice Boltzmann model of microfluidics in the presence of external forces

We present here a lattice Boltzmann model in the presence of external force fields to describe electrokinetic microfluidic phenomena and consider pressure as the only external force to drive liquid flow. Our results from a 9-bit square lattice Boltzmann model are in good agreement with recent experimental data in a pressure-driven microchannel flow that could not be fully described by electrokinetic theory. The differences between the predicted and the experimental Reynolds numbers from pressure gradients are well within 5%. Results suggest that the lattice Boltzmann model described here is an effective computational tool for predicting the more complex microfluidic systems that might be problematic using conventional methods.

Oscillating laminar electrokinetic flow in infinitely extended rectangular microchannels

This paper has addressed analytically the problem of laminar flow in microchannels with rectangular cross-section subjected to a time-dependent sinusoidal pressure gradient and a sinusoidal electric field. The analytical solution has been determined based on the Debye-Hückel approximation of a low surface potential at the channel wall. We have demonstrated that Onsager's principle of reciprocity is valid for this problem. Parametric studies of streaming potential have shown the dependence of the electroviscous effect not only on the Debye length, but also on the oscillation frequency and the microchannel width. Parametric studies of electroosmosis demonstrate that the flow rate decreases due to an increase in frequency. The obtained solutions for both the streaming potential and electroosmotic flows become those for flow between two parallel plates in the limit of a large aspect ratio.

Oscillating laminar electrokinetic flow in infinitely extended circular microchannels

This article addresses the problem of oscillating laminar electrokinetic liquid flow in an infinitely extended circular microchannel. Based on the Debye-Huckel approximation for low surface potential at the channel wall, a complex variable approach is used to obtain an analytical solution for the flow. The complex counterparts of the flow rate and the current are linearly dependent on the pressure gradient and the external electric field. This property is used to show that Onsager's principle of reciprocity continues to be valid (involving the complex quantities) for the stated problem. During oscillating pressure-driven flow, the electroviscous effect for a given value of the normalized reciprocal electrical double-layer (EDL) thickness is observed to attain a maximum at a certain normalized frequency. In general, an increasing normalized frequency results in a reduction of EDL effects, leading to (i). a volumetric flow rate in the case of streaming potential approaching that predicted by the theory without EDL effects, and (ii). a reduction in the volumetric flow rate in the case of electroosmosis.

Effect of liquid slip in electrokinetic parallel-plate microchannel flow

Liquid slip at hydrophobic surfaces in microchannels has frequently been observed. We present here an analytical solution for oscillating flow in parallel-plate microchannels by combining the electrokinetic transport phenomena with Navier's slip condition. Our parametric results suggest that electrokinetic transport phenomena and liquid slip at channel walls are both important and should be considered simultaneously. Their significance depends on channel wall material, electrolyte concentration, and pH. For pressure-driven-flow, liquid slip counteracts the effect by the electrical double layer and induces a larger flow rate. A higher apparent viscosity would be predicted if slip is neglected. For electroosmotic flow, liquid slip alters the flow rate by about 20% for a thick electrical double layer. Our results provide design guidelines to precisely control time-dependent microflow in hydrophobic microfluidic microelectromechanical system devices.

Drug delivery systems. 4. Implants in drug delivery

In comparison with many of the other drug delivery systems, implantable pumps and implants for variable rate delivery are at a crude stage of development. Although exceptions exist, the typical implantable pump consists of an electromechanically complex mechanism to regulate drug delivery from a percutaneous refillable reservoir, while power to drive the system comes from a transcutaneous energy transmission system. The potential for electrical or mechanical failure is high, and the systems are not yet sufficiently convenient or easy to use to recommend in a routine therapy. Problems with refilling of an apparently well designed implanted reservoir have been observed while, at the same time, cutaneous energy transmission systems are not well established. In most instances, the development of an elementary osmotic pump system dosage form follows a well defined path of physical-chemical formulation and clinical testing. The benefits most often provided by the dosage form are expected to be (1) increase in selectivity of drug action achieved by the system's zero-order release rate, and (2) decrease in frequency of administration. The success in achieving these values is quantifiable from the pharmacology of the drug substance and its pharmacokinetics. Osmotic and other technical approaches to producing economical, rate-controlled dosage forms will make it possible for all new pharmaecutical products to carry kinetic specification of rate as well as static specification of content. This review considers the characteristics of the ideal implantable pump, the clinical situations which require pumps, the limitations of portable pumps, and the detailed characteristics of existing implantable pumps and implants. Most of the review, however, focuses on insulin delivery because of the importance of this subject.

Infusional versus systemic chemotherapy for liver metastases from colorectal cancer

It is clear from these studies that intrahepatic arterial infusion of floxuridine produces significantly higher response rates than does systemic infusion of the same drugs. Nevertheless, survival is the most important consideration when comparing two methods of treatment, and at present, there is only a slightly improved survival rate in those patients who receive intrahepatic infusional therapy. However, palliation of the patient and the effect on the quality of life should be taken into account, and these high response rates suggest an effective palliative measure to be offered to patients with this advanced disease. It is hoped that in the future the development of methods to identify those patients who will respond to this form of therapy, together with new ways to increase drug uptake by the tumors, will translate the better response rates achieved into better survival rates.

[A totally implantable permanent central venous access, long-term experience with subcutaneous infusion chambers]

Subcutaneously implanted infusion chambers represent a new method of central venous access. In 57 evaluable out of 70 patients, four different models of infusion chambers with an accumulative observation time of 57 years were implanted. In 72% of the patients, up to 12 cycles of polychemotherapy were administered. Parenteral nutrition and blood drawing were also performed. After 4,970 punctions of the system and 12.2 years of use 46 complications in 38 patients were observed, however, most were minor ones, such as temporary occlusions (12) and extravasations (14). Septum luxation (1), septum perforation (1), catheter fracture (1) and catheter migration (2) as well as 7 cases of septicemia or port-pocket-infection required explanation. Infusion chambers seem to be particularly suitable for intermittent and long-term chemotherapy and emergency bolus injections with a significant advantage (10 complications per one thousand days of use) compared to externally placed venous catheters. However, follow-up and care must be performed by a skilled team.

Survival following self-administered chemotherapy for liver metastases

Fifty-three patients with unresectable liver metastases from colorectal cancer either self-administered or had a family member administer 5-fluorouracil (5-FU) (12 mg/kg/day for 5 days in alternate weeks) through intraoperatively placed hepatic artery and/or portal vein catheters. Twenty percent had failed previous systemic chemotherapy. Seventeen who were symptomatic received additional radiotherapy. Metastasis was confined to the liver in 38, while 15 also had extrahepatic metastases. Median survival for those with hepatic metastases only was 21 months from diagnosis and 16 months from catheter insertion. There are three long-term survivors in this group, alive 58, 69, and 86 months, respectively, from diagnosis. Median survival for those with hepatic and extrahepatic metastases was 10 months from diagnosis and 6 months from catheter insertion. No patient in this group has survived long term. Catheter-related complications occurred in 20% of the patients; none were fatal. Drug toxicities were minor. Self-administered chemotherapy is a safe, effective, and simple method of achieving prolonged survival in patients with unresectable hepatic metastasis from colorectal cancer.

Targeted drug delivery

Cancer chemotherapy drugs are neither specific, i.e., they do not act exclusively on the metabolic pathways of cancer cells, nor are they targeted solely toward cancer cells. However, recent research has begun to address, in part, the latter issue. Improved delivery of chemotherapeutic agents to tumor tissue in man appears to be an achievable goal in the next decade. Improved drug delivery includes developing predictive models that allow for laboratory assessment of the best treatment for a patient's cancer without exposing the patient to an empirical trial or to the possible morbidity from exposure to a less useful drug, or to the loss of time in the fight against cancer because of ineffectual therapy. Monoclonal antibodies directed against tumor-associated antigens have the potential to achieve major advances in targeted drug delivery. Monoclonal antibodies may have direct antitumor effects, or they can be used as "homing devices" when attached to a payload and can guide diagnostic or therapeutic agents to the targeted tissues. Carrier systems of all types have become available; these include liposomes and polymeric compounds which can carry drugs, radionuclides, toxins, or other materials in a protected environment. These carriers can also be bound to monoclonal antibodies for possible targeted delivery. Pharmacological sanctuaries have been recognized as a problem in cancer treatment. The best known of these is the central nervous system (CNS). Techniques to temporarily disrupt the blood-brain barrier are now appearing. Mechanisms to administer therapy directly into the CNS are also being reassessed. Implantable pumps and reservoirs have been used to treat selected organs or for regional perfusions. Other treatments that are regional in scope include administration directly into a cavity or into a tumor. Computerized implantable devices should play a major role in cancer therapy in the future, in pain control as well as antibiotic and hormone administration. In recent years, mathematical models have been developed that can more accurately predict drug distribution and metabolism in various tissues of the body. Such models point the way to more logical designs of chemotherapeutic administration. The expanded use of autologous bone marrow transplantation, along with improving techniques of "purging" the marrow of tumor cells before reinfusion can be anticipated. Pro-drugs are substances that must be biotransformed in vivo to exert their pharmacologic effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Diffusivity of 125I-calmodulin through collagen membranes: effect of source concentration and membrane swelling ratio

Diffusivity of 125I-calmodulin (MW congruent to 17,000) through collagen membranes was studied as a model for the release of macromolecules from collagen matrices. The diffusion coefficient of calmodulin through collagen membranes was determined from time-lag experiments conducted in a dialysis cell at 24 degrees C. Based on time-lag experiments, the diffusion coefficient was observed to be a function of source concentration and membrane swelling ratio after denaturation. The dependence of the diffusion coefficient on source concentration was consistent with a model involving calmodulin immobilization by the collagen membrane. At high source concentrations the diffusion coefficient of calmodulin through collagen membranes was observed to vary from about 10(-8) for uncrosslinked membranes to 10(-9) cm2/s for highly crosslinked membranes. Based on theoretical calculations, the release rate from collagen matrices may be altered by a factor of three. It was concluded that the release rate of biologically active molecules from collagen matrices can be controlled by varying the extent of crosslinking and the macromolecular concentration. Further studies are necessary to characterize the release of other macromolecules from collagen matrices.

Outpatient dobutamine infusion using a totally implantable infusion pump for refractory congestive heart failure

A patient with refractory congestive heart failure was treated, on an outpatient basis, with intermittent dobutamine using a totally implantable infusion pump. Dobutamine was infused for 48 hours every week and resulted in sustained clinical improvement. Symptoms and signs of congestive heart failure remained well controlled until his death from a stroke eight months after implantation of the pump.

A prospective study of continuous hepatic perfusion with implantable pump

The delivery of chemotherapy through the implantable hepatic infusion pump in the management of patients with hepatic metastases secondary to carcinoma of the colon and rectum is evaluated in this preliminary prospective study. Patients were selected according to hepatic lobar distribution and magnitude, age, and general systemic evaluation. Infusion pumps were implanted in a total of 14 patients who were judged to be unsuitable for hepatic resection. After pump implantation all patients were alive and well and receiving regional perfusion chemotherapy. For the nine patients in this study who have been monitored for a full six months, the median decrease in CEA levels was 49 percent. On computerized axial tomography (CT) and/or liver-spleen scan, five patients showed greater than 50 percent reduction in tumor size. All patients have demonstrated minimal systemic toxicity and have maintained a good quality of life. The results encourage further evaluation of perfusion chemotherapy.

Extended immunosuppression with cyclophosphamide using controlled-release polymeric implants

An effective method of prolonged immunosuppressive therapy using cyclophosphamide incorporated into acrylic bone cement has been developed. We have studied the effect of this form of administration of cyclophosphamide on circulating immune cells and the inflammatory response. When the slow release mode of cyclophosphamide administration was compared with conventional systemic therapy, it was found to produce a more rapid and prolonged immunosuppression. A dose-response relationship was established and the biological effects of varying the composition and surface area of the implant were determined. The inflammatory response, assessed by measuring the mobilisation of cells into subcutaneously implanted sponges, was also depressed using this mode of administration. These results, coupled with the commercial availability and existing clinical approval of Simplex P bone cement, suggest that the procedure could lead to useful clinical protocols.

Microencapsulation and controlled release of insulin from polylactic acid microcapsules

Insulin has been encapsulated in biodegradable polylactic acid microcapsules and non-biodegradable ethylcellulose microcapsules by using an emulsification-solvent evaporation process. Gelatin and polyvinylalcohol were used as protective colloids. The concentrations and types of protective colloids affecting the micromeritic properties and release behavior of insulin microcapsules were studied. The higher the concentration of protective colloids the smaller the particle size of microcapsules. The median diameter of microcapsules decreased with the increase of the viscosity of protective colloids. Scanning electron microscopic observations suggested that microcapsules prepared from higher concentrations of polyvinylalcohol solution resulted in a nonporous and compact surface on the microcapsules, compared to the porous microcapsules prepared from gelatin solution. The residual crystals and porous structure of microcapsules affected the release rate of microcapsules. After the initial burst effect the release rate of insulin from microcapsules was found to be constant, so that prolonged release was obtainable. Three percent of polyvinylalcohol was the best choice for the preparation of polylactic acid microcapsules.

Treatment alternatives. Head and neck cancers

No tumor system is more amenable to multidiscipline therapy than head and neck cancers. Diagnosis is enhanced by fine-needle cytology, computerized tomography (CT) scan, and tumor markers. Modified surgical techniques, CO2 laser, and immediate myocutaneous flap reconstruction have enhanced surgery. Endocurie therapy, radiosensitizers, and particle therapy supplementation have enhanced radiotherapy. Combination chemotherapy, immunotherapy, prostaglandin synthesis inhibitors, and retinoids have enhanced chemotherapy. Induction chemotherapy followed by surgery with or without postoperative radiotherapy is optimum multidisciplinary therapy. Reduction in exposure to tobacco, alcohol, sunlight, gamma irradiation, occupational toxins, and Epstein-Barr virus, and recognizing high-risk hereditary conditions, can help prevent these cancers.

Cancer pain relief using chronic morphine infusion. Early experience with a programmable implanted drug pump

Fourteen patients were implanted with drug pumps to provide chronic epidural or intrathecal morphine to relieve pain due to cancer. A new programmable pump was used in seven of the patients and a constant infusion device was used in the other seven patients. Results, judged by subjective pain reports (on a 0 to 10 scale), decrease in oral narcotics, and change in activity level, were excellent in eight patients, good in five patients, and poor in one patient. The programmable device has the obvious advantage of being able to vary dose according to patient need and requires less frequent refilling. Four programmable pump failures occurred, two requiring replacement.

A prospective phase II clinical trial of continuous FUDR regional chemotherapy for colorectal metastases to the liver using a totally implantable drug infusion pump

A prospective phase II evaluation of regional FUDR chemotherapy using a totally implantable drug infusion pump was conducted in 81 patients with colorectal metastases to the liver. The survival results were compared to a historical control group of 129 patients with isolated liver metastases. The two groups were comparable with respect to their dominant prognostic factors. The pump patients received their continuous chemotherapy on an outpatient basis and had an 88% response rate, as evidenced by a fall in their serum CEA levels by one-third or greater after two cycles of chemotherapy. By four criteria, the regional chemotherapy patients had an improved survival rate compared to the control series. First, the 1 year survival and median survival was better for the entire group of pump patients vs. controls (82% vs. 36%, 26 months vs. 8 months, p less than 0.0001). The survival for the regional chemotherapy patients was not influenced by the extent of tumor involvement, whether previous systemic 5-FU was given, or whether the patient had symptomatic disease. Second, the entire group of regional chemotherapy patients (including nonresponders) had a greater 1 year survival compared to the most favorable subgroup of control patients with the following characteristics: normal liver function tests, no symptoms, and only one lobe involved (82% vs. 66%, p = 0.009). Third, a subgroup of 49 pump patients, whose initial treatment for metastatic disease was regional chemotherapy (within 3 months of diagnosis) had a better 1 year survival than an exactly matched group of 49 control patients (67% vs. 30%, p = 0.000003). Fourth, the actuarial survival for all 81 pump patients was significantly better than predicted by a mathematical model constructed to predict the patient's clinical course based upon the seven dominant prognostic variables identified in a multifactorial analysis (82% survival at 1 year vs. 33% predicted survival). While liver metastases could be controlled in most patients, the major cause of death was tumor progression in extrahepatic sites, particularly lung metastases and abdominal carcinomatosis. Although it appears that regional chemotherapy with an implantable pump appears to prolong life by 12 to 18 months more than matched historical controls, these results must be confirmed by a randomized (phase III) prospective clinical trial.

Biomaterials for drug delivery systems

Drug delivery systems have unusual materials requirements which derive mainly from their therapeutic role: to administer drugs over prolonged periods of time at rates that are independent of patient-to-patient variables. The chemical nature of the surfaces of such devices may stimulate biorejection processes which can be enhanced or suppressed by the simultaneous presence of the drug that is being administered. Selection of materials for such systems is further complicated by the need for compatibility with the drug contained within the system. A review of selected drug delivery systems is presented. This leads to a definition of the technologies required to develop successfully such systems as well as to categorize the classes of drug delivery systems available to the therapist. A summary of the applications of drug delivery systems will also be presented. There are five major challenges to the biomaterials scientist: (1) how to minimize the influence on delivery rate of the transient biological response that accompanies implantation of any object; (2) how to select a composition, size, shape, and flexibility that optimizes biocompatibility; (3) how to make an intravascular delivery system that will retain long-term functionality; (4) how to make a percutaneous lead for those delivery systems that cannot be implanted but which must retain functionality for extended periods; and (5) how to make biosensors of adequate compatibility and stability to use with the ultimate drug delivery system-a system that operates with feedback control.

Long-term intravenous infusion of antiarrhythmic drugs using a totally implanted drug delivery system

In vitro and in vivo testing was performed to establish the feasibility of a totally implantable pump system to deliver antiarrhythmic agents. In vitro flow characteristics suggested predictable day to day delivery with acceptably small variations in flow with changes in reservoir volume or temperature. During 3 months of in vitro testing, procainamide and bretylium were found suitable for long-term delivery. Delivery of lidocaine was limited by high viscosity and corrosion of steel elements within the pump. The pump was implanted in a subcutaneous pocket in four dogs. Procainamide (0.5 g/ml), delivered at 4 ml/day (70 mg/kg body weight per day), provided a mean steady state drug concentration of 5.3 micrograms/ml. Bretylium (50 mg/ml), delivered at 8 ml/day (13 mg/kg per day), provided a steady state concentration of 0.8 micrograms/ml (range 0.4 to 1.4). Long-term intravenous administration of therapeutic doses of bretylium and procainamide with this delivery system has been demonstrated in dogs and appears to be feasible in human subjects.