Spacer devices in the treatment of asthma

Amount of drug delivered to the patient can vary greatly

Spacer devices are becoming increasingly popular for the delivery of inhaled drugs in the treatment of asthma. They reduce the problems of poor inhaler technique with metered dose inhalers, largely eliminate oral absorption of inhaled corticosteroids,1 and have been shown to be as effective as nebulisers in the treatment of acute severe asthma. By the attachment of facemasks they can be adapted to treat patients of all ages.2 Their popularity has led to a rapid increase in the number of different types of spacer available.

As with other inhalation devices, such as nebulisers, the proportion of the dose of the drug that the patient actually inhales may vary greatly with different spacers. Despite the apparent simplicity of the designs, spacer choice and method of use may dramatically alter the amount of drug available for inhalation. Recent laboratory studies,3 4 5 6 7 supported by emerging pharmacokinetic evidence and radiolabelled deposition studies,8 9 10 demonstrate where the incorrect use of a spacer can affect the amount of drug delivered.

Multiple actuations of the metered dose inhaler into the spacer before inhalation may reduce the proportion of the drug inhaled.3 4 5 6 Five actuations of a corticosteroid inhaler into a large volume spacer before inhalation will deliver a similar dose as if a single dose had been actuated into the same spacer and inhaled immediately.5 Several clinical studies have used multiple actuations into the spacer before inhalation,11 12 which may affect their interpretation.

In one study in which inhaled corticosteroids were given via a spacer the theoretical dose administered enabled patients to be weaned off oral steroids.11 Multiple actuations of drug into the spacer were used (personal communication). If a similar nominal dose is given as a series of single actuations before a series of inhalations, a considerably larger dose will be achieved. Another example is a dose equivalence study between salmeterol and salbutamol.11 This concluded that salmeterol was 10 times more potent, but the salbutamol metered dose inhaler was actuated five times into a large volume spacer before inhalation, reducing the amount of salbutamol available to the patient by about 60% compared with five single actuations followed by inhalation.6 Thus, the true potency of salmeterol may be nearer to four times that of salbutamol.

Delay between putting the metered dose into the spacer and inhalation may also reduce the amount of drug available to the patient.3 4 5 6 Spacers reduce the need for patients to coordinate inhalation with actuation of the metered dose inhaler, but to maximise the drug delivery period, inhalation should start as soon as possible after actuation of the inhaler. If a health professional or a carer is actuating the inhaler for the patient this should be done only when the patient is ready and the spacer in place.

Static electricity accumulates on many polycarbonate and plastic spacers, attracting drug particles, which become charged when they are produced by the metered dose inhaler. Highly charged spacers deliver less drug than those with an antistatic lining.4 13 A simple way of reducing any charge on a spacer is to wash it,14 which has a similar effect on drug delivery as antistatic paint,4 8 but the charge may reaccumulate. Spacers made of antistatic materials or metals may reduce this problem.15 If a patient or general practitioner carries a new plastic spacer for occasional use, it should be regularly washed to reduce the charge.

Spacer size may also affect the amount of drug available for inhalation, but this will vary with the drug prescribed.16 17 Preparations differ in the speed and volume of their aerosol cloud,18 and this may alter the amount of drug delivered from different spacers. For example, a recent laboratory study showed that the amount of sodium cromoglycate recovered in particles smaller than 5 µm in diameter from the Fisonair, a large volume spacer, was 118% of that recovered when the standard metered dose inhaler was used alone.19 The dose recovered from smaller volume spacers was a third of that from the metered dose inhaler alone. These large differences between spacers were not found in tests using budesonide: the amount of the drug recovered in small particles from large and small spacers was similar. Doctors should be aware that data about a spacer derived from studies with one drug may not apply to other drugs. Changing from one spacer to another may be unimportant with some drugs but be critical for others. The size of the spacer may be less important in young children, in whom breathing pattern has an important effect on the dose of drug received.7 17

Newer formulations in which hydrofluoroalkanes have replaced older propellents may behave very differently in spacers. In one study the amount of drug delivered by a new salbutamol preparation via a spacer device was double that from a conventional metered dose inhaler delivered via the same spacer.20

Much of the available information about spacers has come from laboratory studies in which the drug was collected on filters or in particle sizing apparatus. Recent pharmacokinetic studies have supported the laboratory findings. Maximizing drug output from spacers may improve therapeutic responses and reduce costs. Despite the recent increase in the popularity and number of spacers, little information is available (and little is demanded by regulatory authorities) on the amount of drug available for inhalation from various spacers.

What advice can be given in the light of currently available evidence? Introduce the drug into the spacer by repeated single actuations of the metered dose inhaler, each followed by inhalation. Keep delay to a minimum between actuation of the inhaler and inhalation from the spacer. In certain spacers reduce any static charge by washing and drying in air before first use. Finally, the choice of a spacer must take compliance into account. The first choice on scientific grounds may come second to the one that the patient prefers.