Comparison between the next generation impactor and the twin glass impinge as model pulmonary drug delivery devices

Background and objective: The British Pharmacopoeia contains four apparatus for testing inhalers. Two of these are the next generation impactor, and the twin glass impinge which differs in their use. The next generation impactor apparatus should ideally have at least five stages; even though the twin glass impinge has only two stages, it is still listed in the British Pharmacopoeia. The next generation impactor is more accurate, reliable and sophisticated than the twin glass impinger. This study gives a detailed comparison of the two pieces of equipment. Methods: Carriers including mannitol, lactose monohydrate, trehalose and sucrose with active pharmaceutical ingredient; salbutamol sulphate were delivered by dry powder inhaler using the next generation impactor and twin glass impinger at a constant flow rate of 60L/min. Results: The twin glass impinge respirable fractions of the powders were higher than the next generation impactor for each carrier. As expected, mannitol powder had the lowest percentage remaining in the capsule compared to lactose monohydrate, trehalose and sucrose had the greatest percentage remaining for both inhaler devices. Conclusion: Even though both apparatus are important for in-vitro studies of drug delivery into the lungs using inhaler devices, the next generation impactor is better suited when a specific size range is required. The twin glass impinger is useful for simple inhaler testing, and the inclusion within the British Pharmacopoeia is justified.