The aim of any drug administration therapy is to alleviate symptoms of a condition, (e.g. We take Aspirin to get rid of a headache), or to eliminate the causes of an illness (e.g. We take antibiotics to treat a bacterial infection). To achieve this the person responsible for the administration will determine a dosage which will achieve the desired effect.

In general this means that an estimate will be made of the level of drug which will circulate in the bloodstream to achieve the desired effect. So we will decide to take one, two or three aspirin depending on the severity of the headache.

The level at which a drug becomes effective can be termed the therapeutic level, and the aim of any administration is to achieve this level for a specified period of time. This is difficult to determine precisely as the rate of absorption of the drug into the bloodstream is variable, and of course the drug will get metabolized in the body chemistry which will reduce this effect.

The diagram below shows how the blood level of a drug will vary with time as the result of a single injection, or oral dose of medicine.

The injection will not reach the therapeutic level in the blood until some time after the dose has been administered. In general, however, for the drug to be effective over a period of time the initial dosage will cause the blood levels to rise significantly above the desired therapeutic level. This is to ensure that the drug is not eliminated from the body so quickly that it cannot be effective.

In many cases, of course, this may not be particularly important. However, unfortunately, many of the drugs that we take can be toxic, or have unpleasant side effects, if the blood levels become too high. It then becomes a difficult exercise to get the appropriate balance between effectiveness and limitation of side effects.

Examples of drugs where this may be important are Insulin, Diamorphine for pain relief, and many Chemotherapy agents which can be highly toxic.

In effect pumps can be considered to be giving frequent small injections, and would provide a pattern as shown below.

A short while after the administration has started the drug will have achieved its therapeutic level. Then the frequent addition of small doses of the drug will maintain this level, without producing the excessive, and possibly toxic, levels provided by the more conventional route.

Pumps are widely used in the hospitals to give continuous infusion of a variety of medications. AMT, however, is concerned exclusively with those therapies which use portable pumps to allow individuals to receive the treatment away from the hospital environment.