Over twenty million Americans suffer from asthma or chronic obstructive pulmonary disease (COPD). These diseases are characterized by periods of relative normalcy punctuated by acute attacks (exacerbations) that may be severe enough to require hospitalization. Typically, an attack is preceded by a progressive increase in a patient's use of “rescue” medication to alleviate respiratory difficulties and a decrease in lung function, as measured by peak expiratory flow rate. These changes usually occur several days or weeks before an attack and can serve as a signal for initiating preemptive treatment. Unfortunately, patients often lack the time or resolve to keep accurate records of drug usage. As a result, they may not become aware that their condition is deteriorating until it is too late to prevent an attack requiring urgent medical attention. Also, pediatric, elderly, or impaired patients may lack the capacity for carefully monitoring changes in drug use patterns.
Many different types of inhalation devices have been developed and used by respiratory patients for delivering a carefully controlled dosage of medication (see, e.g., U.S. Pat. Nos. 6,223,746; and 6,532,955). Some of these devices have microprocessors and sensors for counting the number of doses administered (U.S. Pat. Nos. 6,138,669; and 5,593,390) or have other adaptations to improve delivery characteristics (U.S. Pat. No. 5,477,849). However, most continue to rely upon patients to monitor their own drug use patterns.
To the extent that devices that can be used to detect and monitor patient self-administration of inhaled drugs have been described in the prior art (e.g., WO01/024690; U.S. Pat. No. 5,363,842), they are typically used to monitor patient compliance with physician instructions, or to ensure that a patient receives no more than a certain dose of a medication. Generally, there has not been a focus on monitoring inhaled drug usage to recognize when a patient's condition is likely to be deteriorating.
Moreover, in the existing devices, the mechanism for detecting that a dose has been dispensed is usually within the device, often in a position in which it can be easily fouled by dirt or accumulated medication. The positioning of the detection mechanism often makes the design of the devices relatively complex, and increases the possibility of failure. Monitoring devices that are more robust and more compatible with conventional types of inhalers would be beneficial.