Dry powder inhalers (DPIs)
Dry powder inhalers (DPIs)
Introduction
The principle of dry powder inhalers (DPIs) differs from that of MDIs in that, with DPIs, the inspiration must be rapid to break up powdered drug agglomerates into respirable-sized particles. DPIs are inappropriate for infants and children under 5 years, and possibly for people with severe airflow obstruction.
The Turbuhaler multidose device contains dry powder, which is loaded by rotating the base. Other multidose devices include Accuhaler and Diskhaler. Single-dose devices include Spinhaler, HandiHaler, Rotahaler and Aerolizer. Some of the powder formulations contain a lactose filler.
When comparing the delivery of inhaled corticosteroids, DPIs are equivalent to MDIs with regard to safety and efficacy in individuals with asthma (both adults and children); however, there appears to be greater systemic absorption with the DPI compared with the MDI plus spacer in children with asthma.
The pH of dry powder antiasthma preparations is significantly less than that of MDI formulations, with most DPI antiasthma drugs having a pH below 5.5 in powdered form. As tooth substance begins to dissolve at pH 5.5, regular use of these drugs may lead to formation of dental caries. Doctors should advise children (and their parents) to rinse their mouths with water and spit out directly after taking these drugs. A spacer and MDI may be used as an alternative to a dry powder device if topical adverse effects are a problem.
Technique
Patient technique must be checked to ensure appropriate use.
Common errors for all DPIs include:
holding loaded single-dose device upside down before inhaling
exhaling into the device
inhaling too slowly
believing there is no drug delivery because of lack of taste or lack of propellant blast.
Common errors with the Turbuhaler device include:
failing to load the device properly (eg Turbuhaler not in a vertical position—the correct loading position can be demonstrated by asking the patient to put the base of the device on a flat surface and load)
trying to double the dose with 2 clicks of the device.
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