Courses:Pulmonary Drug Delivery/Introduction

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Introduction

Pulmonary drug delivery systems have been used for decades to deliver drugs for treatment of respiratory disorders. The lungs provide a huge surface area of alveoli with rich capillary network which acts as an excellent absorbing surface for administration of drugs. Throughout the past several years, rapid onset of action and higher efficiency has been responsible for the success of pulmonary delivery system for symptomatic relief in treatment of asthma and chronic obstructive pulmonary disease (COPD).

The principle behind pulmonary drug delivery is aerosolization, i.e., reduction in particle size of drug compound delivered to bronchioles and alveoli.

Anatomically the lung has a large surface of tubular system (Fig.1).

FIG 1: Anatomy of lung showing the major airway subdivisions

It is a series of bifurcating tubes which begin at the trachea, divide into the main bronchi, the conducting bronchioles and conclude in the terminal bronchioles and the alveoli, as shown in figure 2 The available delivery systems include metered dose inhalers (MDIs), dry powder inhalers (DPIs) and nebulizers. MDIs were the first of the systems introduced in the mid 1950s. Since then, the technology has advanced, improving drug delivery efficiency and patient convenience.

Chlorofluorocarbons (CFC)-based MDIs has been used with lot of success. However, with the discovery that CFCs cause depletion of the ozone layer they are being replaced with hydrofluoroalkane (HFA)-based MDIs. In addition, the use of DPIs has been increasing, especially after the 1987 Montreal Protocol. Nebulizers are generally used within hospital settings and provide continuous aerosol spray with the help of an external energy source. Patients who are unable to use inhalers also use nebulizers. In an attempt to develop products of pulmonary drug delivery technologies that are effective, safe, and cost-effective, companies are developing Liquid- based inhalers LBIs. Though LBIs are not available as of now, they are anticipated to be introduced in the coming years for treatment of asthma/COPD, cancer and diabetes. In this chapter emphasis has been on details of principle, formulation and manufacture of pharmaceutical aerosols for manufacture of MDIs.

FIG 2: Symmetrical branching model of the lung