Morphine pharmacokinetics after pulmonary administration from a novel aerosol delivery system

Recent advances in drug delivery to the central nervous system by inhalation

INTRODUCTION

Drugs need to enter the systemic circulation efficiently before they can cross the blood-brain barrier and reach the central nervous system. Although the respiratory tract is not a common route of administration for delivering drugs to the central nervous system, it has attracted increasing interest in recent years for this purpose.

AREAS COVERED

In this article, we compare pulmonary delivery to three other common routes (parenteral, oral, and intranasal) for delivering drugs to the central nervous system, followed by summarising the devices used to aerosolise neurological drugs. Recent studies delivering drugs for different neurological disorders via inhalation are then discussed to illustrate the strengths of pulmonary delivery.

EXPERT OPINION

Recent studies provide strong evidence and rationale to support inhaling neurological drugs. Since inhalation can achieve improved pharmacokinetics and rapid onset of action for multiple drugs, it is a non-invasive and efficient method to deliver drugs to the central nervous system. Future research should focus on delivering other small and macro-molecules via the lungs for different neurological conditions.

Drivers of absolute systemic bioavailability after oral pulmonary inhalation in humans

There are few studies in humans dealing with the relationship between physico-chemical properties of drugs and their systemic bioavailability after administration via oral inhalation route (Fpulm). Getting further insight in the determinants of Fpulm after oral pulmonary inhalation could be of value for drugs considered for a systemic delivery as a result of poor oral bioavailability, as well as for drugs considered for a local delivery to anticipate their undesirable systemic effects. To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters. As a result of the small sample set, the performance of the different models as predictive of Fpulm were quite average with random forest algorithm displaying the best performance. As a whole, the different models captured between 50 and 60% of the variability with a prediction error of less than 20%. Tmax data suggested a significant positive influence of lipophilicity on absorption rate while charge apparently had no influence. A significant linear relationship between Cmax and dose (R² = "0.79) highlighted that Cmax was primarily dependent on dose and absorption rate and could be used to estimate Cmax in humans for new inhaled drugs.

Nebulized versus intravenous morphine titration for the initial treatment of severe acute pain in the emergency department: study protocol for a multicenter, prospective randomized and controlled trial, CLIN-AEROMORPH

BACKGROUND

Intravenous morphine titration (IVMT) is the French gold standard for opioid treatment in the emergency department (ED). Nebulized morphine titration (NMT) may represent an alternative without venous access, but it has not been adequately studied in adults. We test the hypothesis that NMT is at least as effective as IVMT to initially manage severe acute pain in the ED.

METHODS/DESIGN

We designed a multicenter (10 French EDs), single-blind, randomized and controlled trial. Adults between 18 and 75 years with visual analog scale (VAS) ≥ 70/100 or numeric rating scale (NRS) ≥ 7/10 will be enrolled. We will randomize 850 patients into two groups to compare two routes of MT as long as VAS >  30 or NRS >  3. In group A (425), patients will receive an initial NMT for 5-25 min associated with titration of an intravenously (IV) administered placebo of physiologic serum (PS). In group B (425), patients will receive IVMT plus nebulized PS placebo. NMT is defined as a minimum of 1 and a maximum of 3 5-min nebulized boluses of 10 mg or 15 mg (weight ≥ 60 kg), at 10-min fixed intervals. IVMT is defined as a minimum of 1 and a maximum of 6 boluses of 2 mg or 3 mg (weight ≥ 60 kg), at 5-min fixed intervals. Nebulized placebo titration will be performed every 10 min. IV titration of PS will be performed every 5 min. In both groups, after 25 min, if VAS > 30/100 or NRS > 3/10, routine IVMT will be continued until pain relief. Pain severity, vital signs, bronchospasm, and Ramsay score will be recorded every 5 min. The primary outcome is the rate of relief obtained 1 h from the start of drug administration. Complete pain relief in both groups will be compared with a non-inferiority design. Secondary outcomes are pain relief at 30 min (the end of NMT) and at 2 h and median pain relief. We will compare final doses, and study the feasibility and tolerance of NMT (protocol deviations, respiratory or hemodynamic depression, sedation, and minor vegetative side effects). Co-analgesia will be recorded. Discharge criteria from the ED and hospital are defined.

DISCUSSION

This trial is the first multicenter randomized and controlled NMT protocol for severe pain in the ED using the titration concept. We propose an original approach of combined titration with an endpoint at 1 h and a non-inferiority design.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03257319 . Registered on 22 August 2017.

Dosimetrically administered nebulized morphine for breathlessness in very severe chronic obstructive pulmonary disease: a randomized, controlled trial

BACKGROUND

Systemic morphine has evidence to support its use for reducing breathlessness in patients with severe chronic obstructive pulmonary disease (COPD). The effectiveness of the nebulized route, however, has not yet been confirmed. Recent studies have shown that opioid receptors are localized within epithelium of human trachea and large bronchi, a target site for a dosimetric nebulizer. The aim of this study was to compare any clinical or statistical differences in breathlessness intensity between nebulized 2.0% morphine and 0,9% NaCl in patients with very severe COPD.

METHODS

The study was a double-blind, controlled, cross-over trial. Participants received morphine or NaCl during two 4-day periods. Sequence of periods was randomized. The primary outcome measure was reduction of breathlessness intensity now by ≥20 mm using a 100 mm visual analogue scale (VAS) at baseline, 15, 30, 60, 120, 180 and 240 min after daily administration, during normal activities.

RESULTS

Ten of 11 patients included completed the study protocol. All patients experienced clinically and statistically significant (p < 0.0001) breathlessness reduction during morphine nebulization. Mean VAS changes for morphine and 0.9% NaCl periods were 25.4 mm (standard deviation (SD): 9.0; median: 23,0; range: 14.0 to 41,5; confidence interval (CI): 95%) and 6.3 mm (SD: 7.8; median: 6.8; range: -11,5 to 19,5; CI: 95%), respectively. No treatment emergent adverse effects were noted.

DISCUSSION

Our study showed superiority of dosimetrically administered nebulized morphine compared to NaCl in reducing breathlessness. This may have been achieved through morphine's direct action on receptors in large airways, although a systemic effect from absorption through the lungs cannot be excluded.

TRIAL REGISTRATION

Retrospectively registered (07.03.2017), ISRCTN14865597.

The function and performance of aqueous aerosol devices for inhalation therapy

OBJECTIVES

In this review paper, we explore the interaction between the functioning mechanism of different nebulizers and the physicochemical properties of the formulations for several types of devices, namely jet, ultrasonic and vibrating-mesh nebulizers; colliding and extruded jets; electrohydrodynamic mechanism; surface acoustic wave microfluidic atomization; and capillary aerosol generation.

KEY FINDINGS

Nebulization is the transformation of bulk liquids into droplets. For inhalation therapy, nebulizers are widely used to aerosolize aqueous systems, such as solutions and suspensions. The interaction between the functioning mechanism of different nebulizers and the physicochemical properties of the formulations plays a significant role in the performance of aerosol generation appropriate for pulmonary delivery. Certain types of nebulizers have consistently presented temperature increase during the nebulization event. Therefore, careful consideration should be given when evaluating thermo-labile drugs, such as protein therapeutics. We also present the general approaches for characterization of nebulizer formulations.

SUMMARY

In conclusion, the interplay between the dosage form (i.e. aqueous systems) and the specific type of device for aerosol generation determines the effectiveness of drug delivery in nebulization therapies, thus requiring extensive understanding and characterization.

Nebulizers for drug delivery to the lungs

INTRODUCTION

Nebulizers are the oldest modern method of delivering aerosols to the lungs for the purpose of respiratory drug delivery. While use of nebulizers remains widespread in the hospital and home setting, certain newer nebulization technologies have enabled more portable use. Varied fundamental processes of droplet formation and breakup are used in modern nebulizers, and these processes impact device performance and suitability for nebulization of various formulations.

AREAS COVERED

This review first describes basic aspects of nebulization technologies, including jet nebulizers, various high-frequency vibration techniques, and the use of colliding liquid jets. Nebulizer use in hospital and home settings is discussed next. Complications in aerosol droplet size measurement owing to the changes in nebulized droplet diameters due to evaporation or condensation are discussed, as is nebulization during mechanical ventilation.

EXPERT OPINION

While the limelight may often appear to be focused on other delivery devices, such as pressurized metered dose and dry powder inhalers, the ease of formulating many drugs in water and delivering them as aqueous aerosols ensures that nebulizers will remain as a viable and relevant method of respiratory drug delivery. This is particularly true given recent improvements in nebulizer droplet production technology.

Prediction of morphine dose in humans

BACKGROUND

Morphine is widely used throughout the human life span. Several pharmacokinetic models have been proposed to predict how morphine clearance changes with weight and age. This study uses a large external data set to evaluate the ability of pharmacokinetic models to predict morphine doses.

METHODS

A data set of morphine clearance estimates was created from published reports in premature neonates, full-term neonates, infants, children, and adults. This external data set was used to evaluate published models for morphine clearance as well as other models proposed for use in neonates and infants. Morphine clearance predictions were used to predict morphine dose rates to achieve similar target concentrations in all age groups.

RESULTS

An allometric ¾ power model using weight combined with a sigmoid maturation model using postmenstrual age successfully predicted the morphine dose rate (within 25% of target) in all age groups except infants [predicted dose 30% under target (95% CI, 7-46%)]. Other published models based on empirical allometric scaling all made unacceptable predictions (>100% of target) in at least one age group.

CONCLUSIONS

Clearance based on empirical allometric scaling predicted unacceptable doses. Theory-based allometric scaling combined with a maturation function has been confirmed by external evaluation to provide a sound basis for describing clearance and predicting morphine doses in humans of all ages.

Pulmonary delivery of therapeutic compounds for treating CNS disorders

Delivering therapeutic compounds via the lungs presents potential advantages relative to other routes of administration. Depending on the compound and the disease state, these advantages may include: non-invasive medication delivery, ease of administration, higher bioavailability leading to dose sparing and lower systemic toxicity, potentially greater blood–brain barrier penetration and rapid pharmacodynamic effect. The practice of inhaling drugs has been around for centuries, including both medical and recreational usage. It is only more recently that formal clinical development programs have been undertaken specifically to use medication delivery via the lung to achieve systemic blood levels for the treatment of CNS disorders. At present, there are several CNS therapies being developed for pulmonary administration, with some of those programs at or near the marketing authorization stage. While there are still regulatory hurdles before these therapies can be put into practice, the success of these programs thus far demonstrates the scientific viability of inhalation therapies for treating CNS disorders.

Morphine inhalation by cancer patients: a comparison of different nebulization techniques using pharmacokinetic, spirometric, and gasometric parameters

Despite numerous case reports suggesting the value of morphine (M) nebulization in the treatment of breathlessness, only a few clinical trials have been able to support this. The reason for this could lie in the lack of understanding of the localization of opioid receptors in the airways and the biopharmaceutics and pharmacokinetics of nebulized morphine. In the present study, we compared two different methods of pneumodosimetric nebulization: the Bronchial Control Treatment System-Sidestream (BCTS-S) and the Bronchial Control Treatment System-Micro Cirrus (BCTS-MC). The first method delivers relatively large aerosol particles (2-5microm) preferentially to the bronchial tree and trachea. In the BCTS-MC method, small aerosol particles (0.5-2microm) mostly reach the alveoli. Ten patients with cancer were randomly assigned to either the BCTS-S or BCTS-MC inhalation of 5 mg morphine HCl. Patients using the BCTS-S method inhaled a morphine dose in 6.6+/-2 minutes, whereas with the BCTS-MC method, the inhalation time was 28.8+/-8 minutes. The areas under the curve of morphine and glucuronides were several times higher after BCTS-S than after BCTS-MC. The proportion of morphine-3-glucuronide to morphine-6-glucuronide (M6) was, on average, close to one for both methods. From the same amount of morphine in the BCTS-S method, five times more M6 was produced. In both methods, the time to maximum concentration for morphine metabolites was 20-40 minutes, much shorter than expected from oral, intranasal, or intravenous administration. The study shows that the method of inhalation may have a profound effect on the pharmacokinetics of morphine. It is possible that the lungs metabolize morphine to glucuronides themselves and in different proportions from those seen after systemic administration. The BCTS-S method was found to be potentially superior to the BCTS-MC method in local action in the lungs.

Current therapies and technological advances in aqueous aerosol drug delivery

Recent advances in aerosolization technology have led to renewed interest in pulmonary delivery of a variety of drugs. Pressurized metered dose inhalers (pMDIs) and dry powder inhalers (DPIs) have experienced success in recent years; however, many limitations are presented by formulation difficulties, inefficient delivery, and complex device designs. Simplification of the formulation process as well as adaptability of new devices has led many in the pharmaceutical industry to reconsider aerosolization in an aqueous carrier. In the acute care setting, breath-enhanced air-jet nebulizers are controlling and minimizing the amount of wasted medication, while producing a high percentage of respirable droplets. Vibrating mesh nebulizers offer advantages in higher respirable fractions (RFs) and slower velocity aerosols when compared with air-jet nebulizers. Vibrating mesh nebulizers incorporating formulation and patient adaptive components provide improvements to continuous nebulization technology by generating aerosol only when it is most likely to reach the deep lung. Novel innovations in generation of liquid aerosols are now being adapted for propellant-free pulmonary drug delivery to achieve unprecedented control over dose delivered and are leading the way for the adaptation of systemic drugs for delivery via the pulmonary route. Devices designed for the metered dose delivery of insulin, morphine, sildenafil, triptans, and various peptides are all currently under investigation for pulmonary delivery to treat nonrespiratory diseases. Although these devices are currently still in clinical testing (with the exception of the Respimat), metered dose liquid inhalers (MDLIs) have already shown superior outcomes to current pulmonary and systemic delivery methods.

The pharmacokinetics and bioavailability of prochlorperazine delivered as a thermally generated aerosol in a single breath to volunteers

A thermally generated aerosol (TGA) system can effect reliable delivery of excipient-free drug to alveoli, resulting in rapid systemic drug absorption. We developed a pharmacokinetic model of prochlorperazine, administered by inhalation and as a rapid intravenous infusion, and we determined absolute TGA bioavailability in eight healthy volunteers in this institutional review board-approved, two-period crossover study. After the drug was administered as either a 5-s intravenous infusion or a TGA single-breath inhalation, blood was collected at various times for up to 24 h. Plasma prochlorperazine concentrations were measured using liquid chromatography-tandem mass spectrometry. Inhalation and rapid intravenous administration produced similar plasma prochlorperazine concentration profiles. Intravenous and inhalation pharmacokinetics were well characterized by a simultaneous two-compartment model with multiple absorption delays. Prochlorperazine pharmacokinetic parameters were similar to those reported for single intravenous doses. The geometric mean bioavailability after TGA delivery was 1.10. The administration of prochlorperazine by inhalation resulted in pharmacokinetics similar to that seen after intravenous administration, in terms of speed, extent, and consistency of absorption.

Morphine bioavailability from a topical gel formulation in volunteers

Although available therapies provide relief to many patients with cancer-related pain, swallowing difficulties or intestinal obstruction may preclude oral analgesic delivery in some. Topical morphine might provide an alternate delivery form but morphine bioavailability from a topical gel formulation has not been reported in humans. We conducted a randomized, placebo-controlled, double-blind, crossover study of five volunteers after they provided institutionally-approved, written, informed consent. They were admitted to the Northwestern University General Clinical Research Center twice, being randomly assigned to receive either 1mL of morphine compounded at 10mg/mL in pluronic lecithin organogel (PLO) base applied to the wrist and 1mL of normal saline administered subcutaneously, or 1mL of topical drug-free PLO base and 1mL of subcutaneous morphine, 3mg/mL, the first time and the opposite combination the second. Seventeen blood samples were collected from 5minutes to 10hours after dose administration for morphine concentration determination. Plasma samples were prepared by solid-phase extraction and morphine concentrations measured by a mass spectrometric technique with a linear range of 0.5-500ng/mL. Bioavailability of the topical formulation relative to the subcutaneous dose was to be estimated from doses and the plasma morphine concentration versus time relationships. Because morphine was seldom detected in plasma samples after topical administration and was unquantifiable when it was, the low bioavailability of topical morphine was unquantifiable. These results suggest that topical administration of morphine compounded in a PLO base for transdermal drug delivery is unlikely to provide relief of cancer-related pain.

Ultra-fast absorption of amorphous pure drug aerosols via deep lung inhalation

A deficiency of most current drug products for treatment of acute conditions is slow onset of action. A promising means of accelerating drug action is through rapid systemic drug administration via deep lung inhalation. The speed of pulmonary drug absorption depends on the site of aerosol deposition within the lung and the dissolution rate and drug content of the deposited particles. Alveolar delivery of fast-dissolving, pure drug particles should in theory enable very rapid absorption. We have previously shown that heating of thin drug films generates vapor-phase drug that subsequently cools and condenses into pure drug particles of optimal size for alveolar delivery. Here we present a hand held, disposable, breath-actuated device incorporating this thermal aerosol technology, and its application to the delivery of alprazolam, an anti-panic agent, and prochlorperazine, an anti-emetic with recently discovered anti-migraine properties. Thermal aerosol particles of these drugs exist in an amorphous state, which results in remarkably rapid drug absorption from the lung into the systemic circulation, with peak left ventricular concentrations achieved within 20 s, even quicker than following rapid (5 s) intravenous infusion. Absorption of the thermal aerosol is nearly complete, with >80% absolute bioavailability found in both dogs and human normal volunteers.

Pulmonary delivery of opioids as pain therapeutics

Pulmonary opioid delivery, on the basis of the fact that small molecular entities can be rapidly and completely absorbed from the peripheral lung, poses a unique opportunity for the treatment of severe (breakthrough) pain, which currently is treated with intravenous therapy. Early clinical studies involving inhaled opioids were focused on treatment of dyspnoea and not pain management, but they showed that inhalation of various opioid compounds is safe, even in severely ill patients. The advent of specialized and efficient pulmonary drug delivery systems has facilitated the evaluation of inhaled opioids, such as morphine and fentanyl, for management of severe pain associated with surgery or malignant disease. This review will summarize recent literature on the pharmacokinetics and pharmacodynamics of inhaled opioids and will discuss safety and efficacy in comparison to injection and other opioid dosage forms available for pain therapy. Finally, regulatory considerations will be discussed towards the approval of this new delivery paradigm for opioid drugs.

Development of pharmaceutical heroin preparations for medical co-prescription to opioid dependent patients

Presently, there is a considerable interest in heroin-assisted treatment: co-prescription of heroin to certain subgroups of chronic, treatment-resistant, opioid dependent patients. In 2002, nine countries had planned (Australia, Belgium, Canada, France, Spain) or ongoing (Germany, The Netherlands, Switzerland, United Kingdom) clinical trials on this subject. These trials (and the routine heroin-assisted treatment programs that might result) will need pharmaceutical heroin (diacetylmorphine) to prescribe to the patients. Research into the development of pharmaceutical forms of heroin for prescription to addicts can benefit from the large amount of knowledge that already exists regarding this substance. Therefore, in this paper we review the physicochemical and pharmaceutical properties of diacetylmorphine and the clinically investigated routes of administration, as well as routes of administration utilised on the street in the context of developing pharmaceutical heroin formulations for prescription to addicts. Patient acceptability of the formulation is essential, because heroin-assisted treatment is aimed at treatment-resistant addicts, who often have to be encouraged to participate (or to maintain participation) in a treatment program. This means that the most suitable products would have pharmacokinetic profiles mimicking that of diacetylmorphine for injection, with rapid peak concentrations of diacetylmorphine and 6-acetylmorphine, ensuring the 'rush effect' and the sustained presence of morphine(-6-glucuronide) creating the prolonged euphoria. Diacetylmorphine for inhalation after volatilisation (via 'chasing the dragon') seems to be a suitable candidate, while intranasal and oral diacetylmorphine are currently thought to be unsuitable. However, oral and intranasal delivery systems might be improved and become suitable for use by heroin dependent patients.

Stability and characterization of perphenazine aerosols generated using the capillary aerosol generator

Perphenazine (a potent antiemetic) was aerosolized using capillary aerosol generator to generate respirable condensation aerosols from drug in propylene glycol (PG) solutions, by pumping the liquids through a heated capillary tube. The study characterized the stability of perphenazine during and following aerosol generation. The stability-indicating HPLC method (C-8 column with a mobile phase of 52% 0.01 M pH 3.0 acetate buffer+48% acetonitrile) also enabled the study of perphenazine stability in solution under acidic, basic, oxidizing and photolysing conditions. An LC-MS (ESI+) method was used to characterize the degradation products. Perphenazine was found to be stable in acidic and basic conditions, while perphenazine sulfoxide was the major product formed in dilute peroxide solutions. Two photo-degradation products were formed in PG that were tentatively identified by LC-MS; one of these was synthesized and confirmed to be 2-[4-(3-phenothiazin-10-yl-propyl)-piperazino]-ethanol. Both photolysis products showed that aromatic dechlorination had occurred and one appeared to also result from interaction with the solvent. Within an aerosolization energy window of 84-95 J, fine particle aerosols were generated from perphenazine PG formulations with no significant degradation. Small amounts of degradation products were produced in all samples during aerosolization at elevated (non-optimal) energies. These were largely consistent with those seen to result from oxidation and photolysis in solution, showing that oxidation and dehalogenation appeared to be the main degradation pathways followed when the CAG system was overheated.

[Dyspnea and morphine aerosols in the palliative care of lung cancer]

OBJECTIVE

To evaluate the effectiveness of morphine aerosols in the treatment of dyspnoea in the palliative care of patients with lung cancer.

MATERIALS AND METHODS

During a randomised, double blind, cross-over study 12 patients receiving palliative care for lung cancer and suffering from dyspnoea despite conventional treatments were given, for two periods of 48 hours separated by a 24 hour wash-out period, 4 mls of morphine sulphate and 4 mls of normal saline 4 hourly by a jet nebuliser. Before and after each nebulisation respiratory rate and capillary oxygen saturation were measured and dyspnoea was quantified with the aid of a visual analogue scale by the patient and various other observers (doctors, students, nurses, care assistants and physiotherapists).

RESULTS

The aerosols of normal saline and morphine produced the same improvements in the dyspnoea scores independently of the mass nebulised. Furthermore the nebulisations did not produce any significant change in respiratory rate or oxygen saturation.

CONCLUSION

The fact that both aerosols lead to a similar improvement in dyspnoea scores suggests that humidification of the airways rather than a pharmacological action may be beneficial in the treatment of dyspnoea in terminally ill patients.

Initial pharmacokinetic, safety and efficacy evaluation of nasal morphine gluconate for breakthrough pain in cancer patients

Patients with controlled background pain associated with cancer frequently also experience episodes of moderate to severe intensity breakthrough pain. Opioid pharmacotherapy, particularly with oral morphine, remains the cornerstone for the management of cancer pain. Nasal administration of opioids provides a mechanism for more rapid drug absorption and more rapid onset of pain relief compared with oral dosing. This non-randomized, open-label, uncontrolled investigation evaluated the pharmacokinetics, safety and efficacy of a single 40 mg dose of nasal morphine gluconate, administered to cancer patients in response to an episode of breakthrough pain. Single dose nasal morphine gluconate administered to 11 patients was associated with effective plasma morphine concentrations (mean C(max) 64 ng/ml; range 33.8-121 ng/ml) and low plasma morphine metabolites (morphine-6-glucuronide mean C(max) 114 ng/ml; range 46-189 ng/ml; morphine-3-glucuronide mean C(max) 572 ng/ml; range 257-990 ng/ml). Side effects were minor and limited to nasal irritation. Patients reported rapid onset of pain relief (perceptible pain relief achieved in 10/11 patients, time to onset 2.4+/-2.1 min; and meaningful pain relief, achieved in five patients, 6.8+/-7.3 min to onset, mean t(max) 0.36 h). Pain intensity scores were significantly reduced at all times after dosing; pain relief scores were unchanged. Patient satisfaction ratings were high. These results show that nasal morphine has rapid absorption and apparent onset of effect. Additional multi-dose, dose-ranging and placebo-controlled studies of nasal morphine for cancer pain are warranted.

Pharmacotherapy of cancer-related episodic pain

Episodic pain is a transient increase in pain intensity over background pain. Episodic pain occurs commonly in cancer patients; it is a heterogeneous phenomenon that is incapacitating, debilitating and can have a significant impact on quality of life. Episodic pain can be difficult to manage; it is often unpredictable, typically of fast onset, of short duration and feels similar to background pain except that it may be more severe. The successful management of episodic pain can only be achieved following a thorough assessment. The subsequent management usually involves both pharmacological and non-pharmacological strategies integrated into the overall care and appropriate for the stage of the patient's disease. Pharmacological management includes the implementation of primary therapies (e.g., chemotherapy for the underlying aetiology of the pain, optimising the scheduled medication (e.g., analgesics and adjuvant analgesics) and specific pharmacological interventions for the episodic pain (e.g., rescue medication).

Constitutive expression of p-glycoprotein in normal lung alveolar epithelium and functionality in primary alveolar epithelial cultures

The multidrug resistant (MDR) transporter P-glycoprotein (P-gp) is constitutively expressed in normal tissues, where its spatial distribution defines it as an important element reducing the systemic exposure and tissue access of potentially harmful xenobiotics. We sought to determine whether P-gp is functionally expressed within alveolar epithelium of lung, in particular within the predominant cell type of this barrier, the alveolar epithelial (AE) type I cell. By immunohistochemistry, MDR-1/mdr-1 P-gp was localized to luminal membranes of AE type I epithelium within normal human and rat lung tissue. Using a primary rat cell culture model affording study of AE type II to AE type I differentiation, we observed increased expression (reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunoflow cytometry techniques) of mdr-1a and mdr-1b P-gp in the cultures as they adopted an AE type I phenotype; freshly isolated AE type II cells were negative for mdr-1/P-gp. The functionality of P-gp within the AE cultures was demonstrated by a flow cytometric accumulation-retention assay using rhodamine-123 as substrate, and also by the polarized transport of vinblastine across confluent AE type I monolayers (basal-to-apical permeability was 3-fold that of apical-to-basal permeability), which was found to be comparable with the P-gp transport barrier presented by Caco-2 cell monolayers. The implications of localizing P-gp within alveolar epithelium is of significance to studies of fundamental respiratory cell biology as well as to further clarifying the nature of the barrier to xenobiotic transfer from alveolar airspace to pulmonary interstitium and capillary blood.

Aerosolization of lipoplexes using AERx Pulmonary Delivery System

The lung represents an attractive target for delivering gene therapy to achieve local and potentially systemic delivery of gene products. The objective of this study was to evaluate the feasibility of the AERx Pulmonary Delivery System for delivering nonviral gene therapy formulations to the lung. We found that "naked" DNA undergoes degradation following aerosolization through the AERx nozzle system. However, DNA formulated with a molar excess of cationic lipids (lipoplexes) showed no loss of integrity. In addition, the lipoplexes showed no significant change in particle size, zeta (zeta) potential, or degree of complexation following extrusion. The data suggest that complexation with cationic lipids had a protective effect on the formulation following extrusion. In addition, there was no significant change in the potency of the formulation as determined by a transfection study in A-549 cells in culture. We also found that DNA formulations prepared in lactose were aerosolized poorly. Significant improvements in aerosolization efficiency were seen when electrolytes such as NaCl were added to the formulation. In conclusion, the data suggest that delivery of lipoplexes using the AERx Pulmonary Delivery System may be a viable approach for pulmonary gene therapy.

Evaluation of the AERx pulmonary delivery system for systemic delivery of a poorly soluble selective D-1 agonist, ABT-431

PURPOSE

ABT-431 is a chemically stable, poorly soluble prodrug that rapidly converts in vivo to A-86929, a selective dopamine D-1 receptor agonist. This study was designed to evaluate the ability of the AERx pulmonary delivery system to deliver ABT-431 to the systemic circulation via the lung.

METHODS

A 60% ethanol formulation of 50 mg/mL ABT-431 was used to prepare unit dosage forms containing 40 microL of formulation. The AERx system was used to generate a fine aerosol bolus from each unit dose that was collected either onto a filter assembly to chemically assay for the emitted dose or in an Andersen cascade impactor for particle size analysis. Plasma samples were obtained for pharmacokinetic analysis after pulmonary delivery and IV dosing of ABT-431 to nine healthy male volunteers. Doses from the AERx system were delivered as a bolus inhalation(s) (1, 2, 4, and 8 mg) and intravenous infusions were given over 1 hr (5 mg). Pharmacokinetic parameters of A-86929 were estimated using noncompartmental analysis.

RESULTS

The emitted dose was 1.02 mg (%RSD = 11.0, n = 48). The mass median aerodynamic diameter of the aerosol was 2.9 +/- 0.1 microm with a geometric standard deviation of 1.3 +/- 0.1 (n = 15). Tmax (mean +/- SD) after inhalation ranged from 0.9 +/- 0.6 to 11.5 +/- 2.5. The mean absolute pulmonary bioavailibility (as A-86929) based on emitted dose ranged from 81.9% to 107.4%.

CONCLUSIONS

This study demonstrated that the AERx pulmonary delivery system is capable of reproducibly generating fine nearly monodisperse aerosols of a small organic molecule. Aerosol inhalation utilizing the AERx pulmonary delivery system may be an efficient means for systemic delivery of small organic molecules such as ABT-431.

On computational control of flow in airblast atomisers for pulmonary drug delivery

Among different approaches to successful pharmacotherapy the pulmonary drug delivery (PDD) mode plays an increasingly important role. In this paper PDD systems based on air-blast atomisation have been analysed mathematically. In order to allow the bioengineer to estimate the degree of effectiveness of a specific system prototype and to lay the basic principles for design, a conservation-law-based mathematical model is discussed. Key control parameters that allow improvement in the efficiency of the system have been identified and main characteristics of the system have been analysed numerically as functions of these parameters.

Trends in the pharmacology of opioids: implications for the pharmacotherapy of pain

Some 25 years ago, it was popular to write a figurative equation for drug treatment: Patient + drug --> effect. Clearly, this was too simplistic for the reliable pharmacotherapy of pain. The 'patient' with pain is a complex individual and the 'drug' is not the same in effect to every patient, regardless of being an opioid analgesic. Besides, the 'effect' needs specification: it really means an acceptable balance between therapeutic and side-effect--to that patient. These days, neural plasticity and neuromodulation associated with nociception are well-known. Psychological involvement in the physical domain of nociception is similarly well-known. Given these complexities, it is surprising that the pharmacological control of pain through the application of relatively simple analgesics can be so effective. Opioid analgesics have been administered by every possible route. Because the degree of invasion of the patient differs between routes, the balance between simplicity, aesthetic appeal, and efficacy of the various routes needs to be considered. The effectiveness of opioid analgesics depends in large measure on the application of the right agent, in the right dose, by the right route, at the right time for that patient. To assist in this task, researchers have produced patient-controlled analgesia and 'pharmacologically engineered' analgetic molecules to achieve receptor selectivity and pharmacokinetic predictability. Also, much relevant data concerning the time courses of analgetic drug (+/- metabolite) concentrations in the body and in the ways in which these properties are modified by different normal and pathophysiological variations have been gathered, and the philosophy of 'opioid rotation' has arisen to maintain therapeutic benefits when tolerance or metabolite-induced side-effects prevail. This essay discusses some of the trends in opioid pharmacotherapy over the past 25 years.

Delivery options and devices for aerosolized therapeutics

Although inhalation is one of the oldest modes of drug delivery, it is currently receiving renewed attention. Prior to 1987, aerosolized therapeutics were delivered via systems that relied on chlorofluorocarbon propellant systems. The subsequent ban on all nonmedical uses of these inert gases stimulated pharmaceutical companies to investigate other propellant systems. Two hydrofluoroalkanes were effective. However, in some instances, the change in propellant required reformulation of the drugs to be delivered. In some cases, bioequivalence could be achieved at lower doses with reduced toxicity. Pressurized metered-dose inhalers (pMDIs) have been used to deliver many types of inhaled therapeutics since the 1960s. Their major limitation is that drug delivery and effectiveness are affected by patient factors, including coordination difficulties and problems related to breathing and breath holding in patients with airway disease. Dry-powder inhalers are being developed to deliver powdered formulations of drugs such as bronchodilators and anti-inflammatory drugs for the treatment of asthma and COPD, and, eventually, proteins, peptides, recombinant products, and gene therapeutics. These devices have been proven to be as efficient as pMDIs in clinical trials. In some cases, they deliver a greater amount of the drug to the lungs. Percentages of the emitted dose deposited in the lungs range from 15 to 40% with the current generation of these devices. Finally, metered-dose liquid inhalers also are under development. Drug deposition in the lung with devices that are currently being tested ranges from 30 to 80% of the emitted dose. The choice of delivery system depends on the effective dose, drug deposition, patient ability, patient acceptance, and cost. Patient education in the correct use of each device is essential to maximize the therapeutic benefit.

The ascent of pulmonary drug delivery

The origins of inhalation therapy can be traced back to the early civilizations but this route of administration was relatively uncommon until recently. Direct delivery of drugs to the lung by inhalation for the treatment of respiratory disease grew rapidly in the second half of the 20th century as a result of the availability of effective asthma drugs in convenient, portable delivery systems. In the search for non-invasive delivery of biologics, it was discovered that the large highly absorptive surface area of the lung could be used for systemic delivery of proteins such as insulin. New delivery systems with efficiency and reproducibility to match the high cost and therapeutic constraints of biologics are currently in late stage clinical trials. Even small molecular weight drugs previously administered by injection are tested via the inhalation route either to provide non-invasively rapid onset of action, or to improve the therapeutic ratio for drugs acting in the lung. Gene therapy of pulmonary disease is still in its infancy but could provide valuable solutions to currently unmet medical needs. The beginning of the new millennium is therefore likely to witness development of many valuable therapeutic products delivered by inhalation.

Comparison of in vitro and in vivo efficiencies of a novel unit-dose liquid aerosol generator and a pressurized metered dose inhaler

Gamma scintigraphic imaging was employed in 10 healthy volunteers to compare the total and regional lung deposition of aerosols generated by two delivery platforms that permitted microprocessor-controlled actuation at an optimal point during inhalation. An aqueous solution containing 99mTc-DTPA was used to assess the deposition of aerosols delivered by inhalation from two successive unit-dosage forms (44 microl volume) using a prototype of a novel liquid aerosol system (AERx Pulmonary Delivery System). This was compared with aerosol deposition after inhalation of two 50 microl puffs of a 99mTc-HMPAO-labeled solution formulation from a pressurized metered dose inhaler (MDI). The in vitro size characteristics of the radiolabeled aerosols were determined by cascade impaction. For the AERx system, the predicted lung delivery efficiency based on the product of emitted dose (60.8%, coefficient of variation (CV)=12%) and fine particle fraction (% by mass of aerosol particles <5.7 microm in diameter) was 53.3% (CV=13%). For the solution MDI, the emitted dose was 62.9% (CV=13%) and the predicted lung dose was 44. 9% (CV=15%). The AERx system demonstrated efficient and reproducible dosing characteristics in vivo. Of the dose loaded into the device, the mean percent reaching the lungs was 53.3% (CV=10%), with only 6. 9% located in the oropharynx/stomach. In contrast, the lung deposition from the solution MDI was significantly less (21.7%) and more variable (CV=31%), with 42.0% of the radiolabel detected in the oropharynx/stomach. Analysis of the regional deposition of the radioaerosol indicated a homogeneous pattern of deposition after delivery from the AERx system. A predominantly central pattern of distribution occurred after MDI delivery, where the pattern of deposition was biased towards a central zone depicting the conducting airways. The AERx system, in contrast to MDIs, seems highly suited to the delivery of systemically active agents via pulmonary administration.

Targeted delivery of inhaled drugs: current challenges and future goals

Past success of topical delivery to the lung stems more from the therapeutic nature of drugs used rather than the delivery device. Both the pressurized metered dose inhaler (pMDI) and the dry powder inhaler (DPI) are inefficient, placing a small fraction of the dose at the site of action. Most of the drug deposits in the mouth and is swallowed. Modifications to the pMDI may redress this by improving the coordination of dose generation and inspiration, or by the use of spacers. The DPI can be improved by the use of special excipients. Nevertheless, fundamental weaknesses that limit improvements in targeting drugs to the lung remain. Ideally, a stationary or slow-moving cloud of a selected particle size distribution should be generated at the source by the device. The rate of cloud generation should be such that a patient can accommodate it during a slow inspiration. Many new devices are in development, harnessing one or more of these principles. Respimat (Boehringer Ingelheim, Ingelheim am Rhein, Germany), a soft mist inhaler, shows particular promise. It generates a fine slow-moving cloud over a period exceeding 1 second and incorporates many design features to win patient acceptance.

Nebulized opioids to treat dyspnea

Breathlessness secondary to cancer and nonmalignant disease is very distressing and exhausting to patients and families. Patient quality of life and functionality can be greatly improved with effective management. The pathophysiology and treatment of dyspnea are where the science of pain management was 20 years ago. While the optimal therapy for dyspnea would be to treat the underlying cause, this is frequently not possible. Research results evaluating dosages and effectiveness of nebulized morphine are conflicting. Some researchers have reported dramatic benefit to patients in relieving the symptoms of dyspnea, increasing exercise endurance, and improving function. Other studies have reported no significant differences between nebulized morphine and saline with or without oxygen. Studies that administer single predetermined doses that are not titrated to relief in patients that do not have end-stage lung or cardiac disease may report false-negative results. Other factors such as the placebo effect of saline and oxygen, if not controlled, may cause false-positive results. The dramatic positive benefits documented warrant further investigation on the appropriate patient selection criteria and therapeutic potential. Clearly, large scale randomized trials on opioid nebulized treatments for patients with severe dyspnea need to be published to reach a clear consensus outlining efficacy and administration parameters. Until that time, we must rely on anecdotal reports for treatment options. Such reports of the effectiveness of nebulized morphine as an alternative to hospital or hospice admission are encouraging for patients and family members managing severe dyspnea in the home.

The effect of duration of dose delivery with patient-controlled analgesia on the incidence of nausea and vomiting after hysterectomy

AIMS

Postoperative nausea and vomiting (PONV) may be exacerbated by postoperative opioid analgesics and may limit patients' successful use of these medications when used with patient controlled analgesia (PCA). We tested the hypothesis that the rapid change in blood morphine concentration associated with PCA bolus delivery contributed to PONV, and that prolonging its delivery to a brief infusion would result in decreased PONV.

METHODS

Patients, who were receiving morphine for pain relief via patient-controlled analgesia (PCA) after total abdominal hysterectomy, received 1 mg morphine sulphate incremental doses either over 40 s with a 5 min lockout interval or over 5 min delivery with a 1 min lockout interval. Episodes of nausea, retching and vomiting, along with the use of morphine and the pain relief obtained, were recorded.

RESULTS

Data from 20 patients in each group were analysed. Contrary to expectations, most patients in both groups reported nausea postoperatively. Those patients receiving morphine over 5 min experienced more episodes of emesis (36) than those receiving the dose over 40 s (17). Most patients receiving the 40 s doses vomited in the first 12 h (median time 8 h), while those receiving the 5 min doses vomited between 12 and 24 h (median time 19 h) (P = 0.01). There were no differences between groups in the visual analogue pain scores or use of morphine between groups.

CONCLUSIONS

Reasons for these unexpected findings remain speculative. The high incidence of PONV appears to be inherently high in gynaecological surgery patients and standard antiemetic medication regimens appear to be poorly efficacious. Reasons for the differences in the time-course of emetic episodes between the two groups may be related to differences in the time-course of central opioid receptor occupancy.