Formulations for inhalation routes of administration include both solid and liquid dosage forms. Inhalation solid dosage forms consist of dry powders and are delivered to the respiratory system through dry powder inhalers (DPI), rotahalers, spacers, etc. On the other hand, liquid inhalation formulations are constituted of solutions or suspensions and are delivered to the lungs via metered dose inhalers (MDI), nebulizers, etc. Delivery devices and dosage forms for drug delivery to the lungs are selected on the basis of multiple factors such as the expected indication, the target patient population, and the dose of the chosen drug product.
Inhalation solid dosage forms - Dry powders:
- Powders are dry, free-flowing formulations of drug products, which can be used internally and externally (e.g., external applications to the skin). Dry powders can be taken orally by some patients who are unable to swallow other solid dosage forms such as capsules. Dry powders can further be prepared for inhalation by spray-drying or micronization of a blend consisting of the drug and a suitable inert carrier.
Liquid inhalation formulations - Solutions & Suspensions:
- Solutions are clear liquid formulations containing one or more active pharmaceutical ingredients (API) dissolved in a suitable medium. Chronic respiratory diseases often involve inhalation therapy with nebulizers. There are a range of prescription drugs available for inhalation with a nebuliser including isotonic and hypertonic saline solutions.
- Suspensions may be defined as preparations containing finely divided drug particles distributed somewhat uniformly throughout a medium in which the drug exhibits a minimum degree of solubility. Budesonide, an anti-asthmatic drug used to control and prevent symptoms caused by asthma, is a liquid suspension which is administered via oral inhalation.