A drug product combines pharmacologic activity with pharmaceutical properties. Desirable performance characteristics are physical and chemical stability, ease of processing, accurate and reproducible delivery to the target organ, and availability at the site of action. For the dry powder inhaler (DPI), these goals can be met with a suitable powder formulation, an efficient metering system, and a carefully selected device. This review focuses on the DPI formulation and development process. Most DPI formulations consist of micronized drug blended with larger carrier particles, which enhance flow, reduce aggregation, and aid in dispersion. A combination of intrinsic physicochemical properties, particle size, shape, surface area, and morphology affects the forces of interaction and aerodynamic properties, which in turn determine fluidization, dispersion, delivery to the lungs, and deposition in the peripheral airways. When a DPI is actuated, the formulation is fluidized and enters the patient's airways. Under the influence of inspiratory airflow, the drug particles separate from the carrier particles and are carried deep into the lungs, while the larger carrier particles impact on the oropharyngeal surfaces and are cleared. If the cohesive forces acting on the powder are too strong, the shear of the airflow may not be sufficient to separate the drug from the carrier particles, which results in low deposition efficiency. Advances in understanding of aerosol and solid state physics and interfacial chemistry are moving formulation development from an empirical activity to a fundamental scientific foundation.

http://rc.rcjournal.com/content/respcare/50/9/1209.full.pdf

Dry powder inhaler formulation.

Background Asthma and chronic obstructive pulmonary disease (COPD) are common diseases of the airways and lungs that have a major impact on the health of the population. The mainstay of treatment is by inhalation of medication to the site of the disease process. This can be achieved by a number of different device types, which have wide variations in costs to the health service. A number of different inhalation devices are available. The pressurised metered-dose inhaler (pMDI) is the most commonly used and cheapest device, which may also be used in conjunction with a spacer device. Newer chlorofluorocarbons (CFC)-free inhaler devices using hydrofluoroalkanes (HFAs) have also been developed. The drug is dissolved or suspended in the propellant under pressure. When activated, a valve system releases a metered volume of drug and propellant. Other devices include breath-actuated pMDIs (BA-pMDI), such as Autohaler and Easi-Breathe. They incorporate a mechanism activated during inhalation that triggers the metered-dose inhaler. Dry powder inhalers (DPI), such as Turbohaler, Diskhaler, Accuhaler and Rotahaler, are activated by inspiration by the patient. The powdered drug is dispersed into particles by the inspiration. With nebulisers oxygen, compressed air, or ultrasonic power is used to break up solutions or suspensions of medication into droplets for inhalation. The aerosol is administered by mask or by a mouthpiece. There has been no previous systematic review of the evidence of clinical effectiveness and cost-effectiveness of these different inhaler devices. Objectives To review systematically the clinical effectiveness and cost-effectiveness of inhaler devices in asthma and COPD. Methods The different aspects of inhaler devices were separated into the most clinically relevant comparisons. Methods involved systematic searching of electronic databases and bibliographies for randomised controlled trials (RCTs) and systematic reviews. Pharmaceutical companies and experts in the field were contacted for further information. Trials that met the inclusion criteria were appraised and data extraction was under-taken by one reviewer and checked by a second reviewer, with any discrepancies being resolved through agreement. RESULTS--IN VITRO CHARACTERISTICS VERSUS IN VIVO TESTING AND CLINICAL RESPONSE: There is evidence that when comparative testing is performed on inhaler devices using the same methods, there is some correlation between particle size measurements and clinical response. However, the measurements are dependent upon the methods used, and a single measure of a device in isolation is of limited value. Also, there is little data on comparing devices of different types. There is currently insufficient data to verify the ability of in vitro assessments to predict inhaler performance in vivo. RESULTS--EFFECTIVENESS OF METERED-DOSE INHALERS FOR THE DELIVERY OF CORTICOSTEROIDS IN ASTHMA: The review of three trials in children and 21 trials in adults demonstrated no evidence to suggest clinical benefits of any other inhaler device over a pMDI in corticosteroid delivery. RESULTS--EFFECTIVENESS OF METERED-DOSE INHALERS FOR THE DELIVERY OF BETA-AGONISTS IN STABLE ASTHMA: In children, 11 studies were reviewed, of which seven compared the Turbohaler with the pMDI. One study found a significant treatment difference in peak expiratory flow rate, although there were differences in the patients' baseline characteristics. In adults, a review of 70 studies found no demonstrable difference in the clinical bronchodilator effect of short-acting b2-agonists delivered by the standard pMDI compared with that produced by any other DPI, HFA-pMDI or the Autohaler device. The finding that HFA-pMDIs may reduce treatment failure and oral steroid requirement in beta-agonist delivery needs further confirmatory research in adequately randomised clinical trials. RESULTS--EFFECTIVENESS OF NEBULISERS VERSUS METERED-DOSE INHALERS FOR THE DELIVERY OF BRONCHODILATORS IN STABLE ASTHMA: In children, three included trials compared different devices with a nebuliser and demonstrated no evidence of clinical superiority of nebulisers over inhaler devices in bronchodilator delivery. A total of 23 studies in adults found no equivalence for the main pulmonary outcomes and no evidence of difference in other outcomes. RESULTS--EFFECTIVENESS OF METERED-DOSE INHALERS FOR THE DELIVERY OF BETA-AGONISTS IN COPD: Only two studies were included in this review. No evidence of clinical difference was found in beta-agonist delivery. RESULTS--EFFECTIVENESS OF NEBULISERS VERSUS METERED-DOSE INHALERS FOR THE DELIVERY OF BRONCHODILATORS IN COPD: Evidence from 14 trials demonstrated equivalence for the main outcomes of pulmonary function. For other outcomes there was no evidence of treatment difference in bronchodilator delivery. RESULTS--PATIENTS' ABILITY TO USE METERED-DOSE INHALERS: Differences among studies and the heterogeneity of the results make it difficult to draw conclusions about inhaler technique differences between device types. The review of technique after teaching the correct technique suggests that there is no difference in patients' ability to use DPI or pMDIs. RESULTS--ECONOMIC ANALYSIS: The total number of NHS prescriptions for inhaler therapy for asthma in 1998 was over 31 million, with a net ingredient cost in excess of 392 million GB pounds. This economic assessment uses decision analysis to estimate the relative cost-effectiveness of inhaler devices for the delivery of bronchodilator and corticosteroid inhaled therapy. Overall, there were no differences in patient outcomes among the devices. On the assumption that the devices were clinically equivalent, pMDIs were the most cost-effective devices for asthma treatment. Conclusions This systematic review examined the evidence from clinical trials evaluating the clinical effectiveness of different inhaler devices in the delivery of inhaled corticosteroids and beta2-bronchodilators for patients with asthma and COPD. The evidence from the published clinical literature demonstrates no difference in clinical effectiveness between nebulisers and alternative inhaler devices compared to standard pMDI with or without a spacer device. The cost-effectiveness evidence therefore favours pMDIs (or the cheapest inhaler device) as first-line treatment in all patients with stable asthma unless other specific reasons are identified. Patients can use pMDIs as effectively as other inhaler devices as long as the correct inhalation technique is taught. CONCLUSIONS--RECOMMENDATIONS FOR RESEARCH: Further clinical trials are required to demonstrate any differences in the clinical effectiveness and cost-effectiveness of inhaler devices and nebulisers compared with pMDIs. These should be of sufficient statistical power and methodological rigour to demonstrate any clinical benefit. Trials should be undertaken in community settings to ensure the generalisability of results. Outcome measures should be more patient-centred and report adverse effects more completely. Reporting of data from trials should be improved.

/pdf/comparison-of-the-effectiveness-of-inhaler-devices-in-asthma-2rk1e4womd.pdf

Comparison of the effectiveness of inhaler devices in asthma and chronic obstructive airways disease: a systematic review of the literature

Evolution of dry powder inhaler design, formulation, and performance

The pulmonary route is an interesting route for drug administration, both for effective local therapy (asthma, chronic obstructive pulmonary disease or cystic fibrosis) and for the systemic administration of drugs (e.g., peptides and proteins). Well-designed dry powder inhalers are highly efficient systems for pulmonary drug delivery. However, they are also complicated systems, the the performance of which relies on many aspects, including the design of the inhaler (e.g., resistance to air flow and the used de-agglomeration principle to generate the inhalation aerosol), the powder formulation and the air flow generated by the patient. The technical background of these aspects, and how they may be tuned in order to obtain desired performance profiles, is reviewed. In light of the technical background, new developments and possibilities for further improvements are discussed.

/pdf/dry-powder-inhalers-for-pulmonary-drug-delivery-3aclgd783w.pdf

Dry powder inhalers for pulmonary drug delivery

Technological and practical challenges of dry powder inhalers and formulations

A metered-dose powder inhaler system has been developed. It is a multidose system that is easy to load and handle for the patient and that does not demand coordination between activation and inhalation. In addition, the new inhaler system is free of propellants, carriers, and other drug additives. Terbutaline sulfate has been selected as a suitable compound for evaluation of this inhaler. Clinical tests with the Turbuhaler have been performed and it has been compared with the conventional terbutaline pressurized metered-dose inhaler (MDI). The new powder inhaler can even be used at low inspiratory flow rates such as those present during acute asthma attacks.

Kjell Wetterlin

Papers

Turbuhaler: a new powder inhaler for administration of drugs to the airways.