Implantable Drug Delivery Systems and Foreign Body Reaction: Traversing the Current Clinical Landscape

Precise delivery of therapeutics to the target structures is essential for treatment efficiency and safety. Drug administration via conventional routes requires overcoming multiple transport barriers to achieve and maintain the local drug concentration and commonly results in unwanted off-target effects. Patients’ compliance with the treatment schedule remains another challenge. Implantable drug delivery systems (IDDSs) provide a way to solve these problems. IDDSs are bioengineering devices surgically placed inside the patient’s tissues to avoid first-pass metabolism and reduce the systemic toxicity of the drug by eluting the therapeutic payload in the vicinity of the target tissues. IDDSs present an impressive example of successful translation of the research and engineering findings to the patient’s bedside. It is envisaged that the IDDS technologies will grow exponentially in the coming years. However, to pave the way for this progress, it is essential to learn lessons from the past and present of IDDSs clinical applications. The efficiency and safety of the drug-eluting implants depend on the interactions between the device and the hosting tissues. In this review, we address this need and analyze the clinical landscape of the FDA-approved IDDSs applications in the context of the foreign body reaction, a key aspect of implant–tissue integration.

Narrative review of intrathecal drug delivery (IDD): indications, devices and potential complications

The management of chronic refractory pain (non-neoplastic and cancer-related pain) remains a therapeutic challenge. The continuous intrathecal (IT) administration of drugs may play an important role in the possible management options. Intrathecal drug delivery devices (IDDDs) may be effective for patients with refractory chronic pain. Therefore, they may be adopted for non-oncologic pain in patients with compression fractures, spondylolisthesis, spondylosis, back surgery failure syndrome and spinal stenosis. Oncologic patients can benefit from these treatments in a variable way according to tumor characteristics, prognosis, periprocedural imaging and risk of disease progression. In this review, we describe the most commonly used drugs (opioids and non-opioids), their pharmacokinetic and pharmacodynamic features and indications of use. The most used drugs are morphine, hydromorphone, fentanyl, methadone, bupivacaine, clonidine, and ketamine. Patient evaluation before the device implantation should be based on clinical examination, medical records assessment and psychometric evaluation. The infusion pumps available on the market are both non-programmable (with continuous IT deliver of drugs) and programmable (with variable deliver of drugs according to their flow rate). Moreover, we describe the procedure of implantation and the potential complications of IT drug delivery (such as bleeding, infection, loss of cerebrospinal fluid, wound seroma, loss of catheter pump propellant).

Intrathecal Drug Delivery

Targeted intrathecal (IT) drug delivery systems (IDDS) are well established as an effective treatment of patients with chronic nonmalignant or malignant pain, and as a tool for management of patients with severe spasticity. The risk to benefit ratio of IDD makes it a relatively safe therapy for both cancer- and noncancer-related pain, but it is not free of risks, so it should be managed at specific centers. Recent technological advances, new therapeutic applications, reported complications, and the costs as well as maintenance required for this therapy require the need to stay up to date about new recommendations that may improve outcomes. This chapter reviews all technological issues regarding IDDS implantation with follow-up and pharmacological recommendations published during recent years that provide evidence-based decision-making process in the management of chronic pain and spasticity in patients.

Remotely controlled nanofluidic implantable platform for tunable drug delivery

Chronic diseases such as hypertension and rheumatoid arthritis are persistent ailments that require personalized lifelong therapeutic management. However, the difficulty of adherence to strict dosing schedule compromises therapeutic efficacy and safety. Moreover, the conventional one-size-fits-all treatment approach is increasingly challenged due to the intricacies of inter- and intra-individual variabilities. While accelerated technological advances have led to sophisticated implantable drug delivery devices, flexibility in dosage and timing modulation to tailor precise treatment to individual needs remains an elusive goal. Here we describe the development of a subcutaneously implantable remote-controlled nanofluidic device capable of sustained drug release with adjustable dosing and timing. By leveraging a low intensity electric field to modify the concentration driven diffusion across a nanofluidic membrane, the rate of drug administration can be increased, decreased or stopped via Bluetooth remote command. We demonstrate in vitro the release modulation of enalapril and methotrexate, first-line therapeutics for treatment of hypertension and rheumatoid arthritis, respectively. Further, we show reliable remote communication and device biocompatibility via in vivo studies. Unlike a pulsatile release regimen typical of some conventional controlled delivery systems, our implant offers a continuous drug administration that avoids abrupt fluctuations, which could affect response and tolerability. Our system could set the foundation for an on-demand delivery platform technology for long term management of chronic diseases.

Characterization of Effect of Repeated Bolus or Continuous Intrathecal Infusion of Morphine on Spinal Mass Formation in the Dog

BACKGROUND

We determined whether intrathecally delivering the same daily dose of morphine (MS) at a fixed concentration of 25 mg/mL by periodic boluses versus continuous infusion would reduce intrathecal mass (IMs) formation in dogs.

METHODS

Adult dogs (hound cross, n = 32) were implanted with intrathecal catheters connected to SynchroMed II infusion pumps. Animals were randomly assigned to receive infusion of 0.48 mL/day of saline or MS dosing (12 mg/day at 25 mg/mL) as boluses: x1 (q24hour), x2 (q12hour), x4 (q6hour), or x8 (q3hour) given at the rate of 1000 μL/hour, or as a continuous infusion (25 mg/mL/20 μL/hour).

RESULTS

With IT saline, minimal pathology was noted. In contrast, animals receiving morphine displayed spinally compressing durally derived masses with the maximal cross-sectional area being greatest near the catheter tip. Histopathology showed that IMs consisted of fibroblasts in a collagen (type 1) matrix comprised of newly formed collagen near the catheter and mature collagen on the periphery of the mass. The rank order of median cross-sectional mass area (mm² ) was: Saline: 0.7 mm² ; x2: 1.8 mm² ; x4: 2.7 mm² ; x1: 2.7 mm² ; x8: 4.2 mm² ; Continuous: 8.1 mm² , with statistical difference from saline being seen with continuous (p < 0.0001) and x8 (p < 0.05). Bench studies with a 2D diffusion chamber confirmed an increase in dye distribution and lower peak concentrations after bolus delivery versus continuous infusion of dye.

CONCLUSIONS

Using multiple bolus dosing, IMs were reduced as compared to continuous infusion, suggesting relevance of bolus delivery in yielding reduced intrathecal masses.

Slow, continuous enzyme replacement via spinal CSF in dogs with the paediatric-onset neurodegenerative disease, MPS IIIA

Intra-cerebrospinal fluid (CSF) injection of recombinant human lysosomal enzyme is a potential treatment strategy for several neurodegenerative lysosomal storage disorders including Sanfilippo syndrome (Mucopolysaccharidosis type IIIA; MPS IIIA). Here we have utilised the MPS IIIA Huntaway dog model to compare the effectiveness of the repeated intermittent bolus injection strategy being used in the trials with an alternate approach; slow, continual infusion of replacement enzyme (recombinant human sulphamidase; rhSGSH) into the spinal CSF using a SynchroMed II® pump attached to a spinal infusion cannula. The ability of each enzyme delivery strategy to ameliorate lesions in MPS IIIA brain was determined in animals treated from ∼three- to six-months of age. Controls received buffer or no treatment. Significant reductions in heparan sulphate (primary substrate) were observed in brain samples from dogs treated via either cisternal or lumbar spinal CSF bolus injection methods and also in slow intra-spinal CSF infusion-treated dogs. The extent of the reduction differed regionally. Pump-delivered rhSGSH was less effective in reducing secondary substrate (G_M3 ganglioside) in deeper aspects of cerebral cortex, and although near-amelioration of microglial activation was seen in superficial (but not deep) layers of cerebral cortex in both bolus enzyme-treated groups, pump-infusion of rhSGSH had little impact on microgliosis. While continual low-dose infusion of rhSGSH into MPS IIIA dog CSF reduces disease-based lesions in brain, it was not as efficacious as repeated cisternal or spinal CSF bolus infusion of rhSGSH over the time-frame of these experiments.

Current and Future Issues in the Development of Spinal Agents for the Management of Pain

Targeting analgesic drugs for spinal delivery reflects the fact that while the conscious experience of pain is mediated supraspinally, input initiated by high intensity stimuli, tissue injury and/or nerve injury is encoded at the level of the spinal dorsal horn and this output informs the brain as to the peripheral environment. This encoding process is subject to strong upregulation resulting in hyperesthetic states and downregulation reducing the ongoing processing of nociceptive stimuli reversing the hyperesthesia and pain processing. The present review addresses the biology of spinal nociceptive processing as relevant to the effects of intrathecally-delivered drugs in altering pain processing following acute stimulation, tissue inflammation/injury and nerve injury. The review covers i) the major classes of spinal agents currently employed as intrathecal analgesics (opioid agonists, alpha 2 agonists; sodium channel blockers; calcium channel blockers; NMDA blockers; GABA A/B agonists; COX inhibitors; ii) ongoing developments in the pharmacology of spinal therapeutics focusing on less studied agents/targets (cholinesterase inhibition; Adenosine agonists; iii) novel intrathecal targeting methodologies including gene-based approaches (viral vectors, plasmids, interfering RNAs); antisense, and toxins (botulinum toxins; resniferatoxin, substance P Saporin); and iv) issues relevant to intrathecal drug delivery (neuraxial drug distribution), infusate delivery profile, drug dosing, formulation and principals involved in the preclinical evaluation of intrathecal drug safety.

Primary Hydromorphone-Related Intrathecal Catheter Tip Granulomas: Is There a Role for Dose and Concentration?

BACKGROUND

Intrathecal drug delivery therapy has been used effectively in treating patients with intractable chronic pain. The development of an intrathecal catheter tip granuloma (ICTG) related to delivery of intrathecal opiates is a relatively infrequent, but potentially devastating complication. While there are many morphine-related ICTG cases described, reports of hydromorphone-related ICTG are limited. In addition, studies suggest a strong correlation between the use of higher doses and concentrations of intrathecal opiates and ICTG formation.

OBJECTIVE

The objective of this study is to determine the incidence and the association of intrathecal hydromorphone dose, concentration, duration of treatment and concomitant agents with ICTG formation.

STUDY DESIGN

This is a retrospective analysis of 101 consecutive patients implanted with intrathecal infusion delivery devices. Data were collected from chart review, and records of pump refills from the division of Pain Medicine of University Hospitals or outsourced to a home pump refill service.

RESULTS

From a cohort of 101 consecutively implanted patients, 69 were treated with intrathecal hydromorphone and followed up postimplant for an average of 33.5 ± 24 months (range 0-93 months; 95% CI of 27-39 months). The incidence of ICTG in our patient population was 8.7% during this period of time postimplant with mean time to granuloma detection 35.1 ± 7.9 months. Patients developing granuloma (n = 6) were treated with a combination of intrathecal hydromorphone and bupivacaine infusion. Exposure time to intrathecal agents was not different between the granuloma and nongranuloma group. Monthly dose increase of hydromorphone was higher in granuloma group vs. non-granuloma group (58 ± 34 mcg/month n = 6 vs. 25 ± 8 mcg/month n = 63). Four out of six granuloma cases occurred with low dose and concentration of IT hydromorphone (160-370 mcg/day; 0.75-1.0 mg/mL concentration). Intrathecal bupivacaine dose was not different between groups. A subset of patients was treated with intrathecal fentanyl and bupivacaine. No intrathecal granulomas occurred in this patient cohort.

CONCLUSION

This is the first clinical report demonstrating an association of hydromorphone with intrathecal granulomas, particularly at low doses and concentrations of hydromorphone. This study supports the notion that using low dose of IT opioids might not protect against ICTG development but that the level of exposure and type of opioid used in IT space might be highly correlated with ICTG development. Further research and recommendations related to chronic intrathecal opioid infusions are necessary to raise awareness of significant incidence of ICTG and development of tests to isolate patient populations at high risk.

Intrathecal Catheterization and Drug Delivery in Guinea Pigs

Background

Intrathecal infusion of opioids in dogs, sheep, and humans produces local space-occupying masses. To develop a small-animal model, the authors examined effects of intrathecal catheterization and morphine infusion in guinea pigs.

Methods

Under isoflurane, polyethylene or polyurethane catheters were advanced from the cisterna magna to the lumbar enlargement. Drugs were delivered as a bolus through the externalized catheter or continuously by subcutaneous minipumps. Hind paw withdrawal to a thermal stimulus was assessed. Spinal histopathology was systematically assessed in a blinded fashion. To assist in determining catheter placement, ex vivo images were obtained using magnetic resonance imaging in several animals. Canine spinal tissue from previous intrathecal morphine studies was analyzed in parallel.

Results

(1) Polyethylene (n = 30) and polyurethane (n = 25) catheters were implanted in the lumbar intrathecal space. (2) Bolus intrathecal morphine produced a dose-dependent (20 to 40 μg/10 μl) increase in thermal escape latencies. (3) Absent infusion, a catheter-associated distortion of the spinal cord and a fibrotic investment were noted along the catheter tract (polyethylene &gt; polyurethane). (4) Intrathecal morphine infusion (25 mg/ml/0.5 μl/h for 14 days) resulted in intrathecal masses (fibroblasts, interspersed collagen, lymphocytes, and macrophages) arising from meninges proximal to the catheter tip in both polyethylene- and polyurethane-catheterized animals. This closely resembles mass histopathology from intrathecal morphine canine studies.

Conclusions

Continuous intrathecal infusion of morphine leads to pericatheter masses that morphologically resemble those observed in dogs and humans. This small-animal model may be useful for studying spinal drug toxicology in general and the biology of intrathecal granuloma formation in particular.

Advances in intrathecal drug delivery

PURPOSE OF REVIEW

Targeted intrathecal drug delivery systems (IDDS) are an option in algorithms for the treatment of patients with moderate-to-severe chronic refractory pain. This article is intended to review the literature regarding IDDS published over the last year, with special attention to the Polyanalgesic Consensus Conference 2012.

RECENT FINDINGS

The recommendations made by the Polyanalgesic Consensus Conference 2012 are reviewed. Separate considerations of intrathecal drug therapy for neuropathic and nociceptive pain syndromes and the new concept of 'microdosing' are discussed in this article.

SUMMARY

This review includes the recommendations for the use of IDDS, trialing, and recent reports of complications (especially, the occurrence of granulomas). In addition, the latest documents on cerebrospinal fluid and potential lines of future development are discussed.

Assessment of telemetry and fluidic control system used in the Medstream programmable infusion system: an in vivo and in vitro study

The MedStream Programmable Infusion Pump, an intrathecal pump indicated for the treatment of chronic intractable pain and severe spasticity (CE-mark) or severe spasticity (US), has a highly accurate medication delivery (within 10% of the programmed flow rate) and is certified for use in 3-Tesla magnetic resonance imaging systems (conditional). Performance of the telemetric link between external control-unit and implanted pump was assessed in sheep (in vivo) up to 26 weeks, resulting in 1040 communication sessions. The telemetric communication envelope (communication distance and maximum antenna tilt angles) and communication duration were characterized in an in vitro test. Capacitance measurements of the piezoelectric actuator of the valve, valve flow rates, and leak rates were measured in an in vitro cyclic accelerated aging test to assess reliability of the valve over 6,200 k cycles. The pump was well tolerated in vivo; all communication sessions between control-unit and pump were successful (P = 6.889 × 10(-14)). Mean communication distance between pump and control-unit was 3.8 cm, with the maximum antenna tilt angles being 40° (θy) and 50° (θx) for all test cases; the maximum communication duration was 5.5 s. Capacitance measurements, flow rates, and leak rates were within ±10 % range up to 6,200 k cycles corresponding to approximately 10 times the valve cycles over the specified service life of the pump (8 years), except for one flow-rate value, which can be explained by the measurement setup. These results demonstrate the reliability of the telemetry link and piezoelectric valve system of the MedStream Programmable Infusion Pump.

Role of Catheter's Position for Final Results in Intrathecal Drug Delivery. Analysis Based on CSF Dynamics and Specific Drugs Profiles

Intrathecal drug delivery is an effective and safe option for the treatment of chronic pathology refractory to conventional pain therapies. Typical intrathecal administered drugs are opioids, baclofen, local anesthetics and adjuvant medications. Although knowledge about mechanisms of action of intrathecal drugs are every day more clear many doubt remain respect the correct location of intrathecal catheter in order to achieve the best therapeutic result. We analyze the factors that can affect drug distribution within the cerebrospinal fluid. Three categories of variables were identified: drug features, cerebrospinal fluid (CSF) dynamics and patients features. First category includes physicochemical properties and pharmacological features of intrathecal administered drugs with special attention to drug lipophilicity. In the second category, the variables in CSF flow, are considered that can modify the drug distribution within the CSF with special attention to the new theories of liquoral circulation. Last category try to explain inter-individual difference in baclofen response with difference that are specific for each patients such as the anatomical area to treat, patient posture or reaction to inflammatory stimulus. We conclude that a comprehensive evaluation of the patients, including imaging techniques to study the anatomy and physiology of intrathecal environment and CSF dynamics, could become essential in the future to the purpose of optimize the clinical outcome of intrathecal therapy.

Role of meningeal mast cells in intrathecal morphine-evoked granuloma formation

BACKGROUND

Intrathecal morphine forms granulomas that arise from the adjacent arachnoid membrane. The authors propose that these inflammatory cells exit the meningeal vasculature secondary to meningeal mast cell degranulation.

METHODS

Three sets of experiments were accomplished in dogs: (1) ex vivo meningeal mast cell degranulation (histamine release was measured ex vivo from canine dura incubated with opiates); (2) in vivo cutaneous mast cell degranulation (flare areas on the dog abdomen were measured after subcutaneous opiates); and (3) in vivo granuloma pharmacology. Dogs with lumbar intrathecal catheters received infusion of intrathecal saline or intrathecal morphine. Intrathecal morphine dogs received (1) no other treatment (control); (2) twice-daily subcutaneous naltrexone; (3) intrathecal co-infusion of cromolyn; or (4) twice-daily subcutaneous cromolyn for the 24- to 28-day study course.

RESULTS

Morphine but not fentanyl evoked dural histamine release, which was blocked by cromolyn but not naloxone. Wheal/flare was produced by subcutaneous morphine, methadone, hydromorphone, but not fentanyl, and was unaffected by naltrexone but prevented by cromolyn. Granulomas occurred in all dogs receiving intrathecal morphine (15 of 15); subcutaneous naltrexone had no effect on granulomas (six of six) but was reduced by concurrent intrathecal cromolyn (zero of five) or twice-daily subcutaneous cromolyn (one of five).

CONCLUSIONS

The pharmacology of cutaneous/dural mast cell degranulation and intrathecal granulomas are comparable, not mediated by opioid receptors, and reduced by agents preventing mast cell degranulation. If an agent produces cutaneous mast cell degranulation at concentrations produced by intrathecal delivery, the agent may initiate granulomas.

Alfentanil: correlations between absence of effect upon subcutaneous mast cells and absence of granuloma formation after intrathecal infusion in the dog

BACKGROUND

We hypothesize that intrathecal (IT) granulomas arising from the IT infusion of several opiates may result from the degranulation of meningeal mast cells (MC). Given functional covariance between cutaneous and meningeal MC, we propose that opioids that do not degranulate cutaneous MC will not produce a granuloma. An opioid meeting this criteria is the phenylpiperadine alfentanil HCl.

METHODS

Three experiments were accomplished in dogs. 1) Cutaneous MC degranulation. Flare areas on the dog abdomen were measured after intradermal alfentanil, morphine, or compound 48-80. 2) Dose ranging of analgesic effects of IT alfentanil infusion. Dogs with lumbar IT catheters received continuous infusion for 24 hours of different concentrations (1-20 mg/mL/d) of alfentanil and analgesic effects were assessed. 3) Granuloma inducing effects. Dogs received IT alfentanil (20 mg/mL/d; N = 5; 22-28 days) or morphine (12 mg/mL/d; N = 3; 22-30 days) and spinal cord harvested for histopathology after 22-30 days of infusion.

RESULTS

1) Intradermal morphine (10 mg/mL) and compound 48-80 (1 mg/mL) but not alfentanil at concentrations up to 20 mg/mL produced a cutaneous flare. IT alfentanil infusion produced increases in thermal escape latency at concentrations as low as 2 mg/mL/day. A significant depression of arousal was noted in the dogs receiving 20 mg/mL. Over the 22- to 30-day infusion period, morphine (12 mg/mL/day) resulted in granulomas in all three animals examined whereas IT alfentanil at 20 mg/mL/day failed to initiate a granuloma in any animal.

CONCLUSIONS

These results support the hypothesis linking MC degranulation and IT granulomas.