Therapeutic duplication occurs when a patient is taking more than one drug that does exactly the same thing as another.


Therapeutic duplication may involve:

(1) two or more medications from the same drug class with the same therapeutic use

(2) two drugs, one of which is a prodrug that is metabolized to the second. A classic example involves mercaptopurine and azathioprine.


An exemption may be use of systemic and topical use of a drug.


Risk factors for therapeutic duplication:

(1) A patient who sees multiple physicians.

(2) Failure to identify all of the medications that a patient may be taking.

(3) Failure to understand pharmacology on the part of the prescribing physician.

(4) Failure of the patient to understand that an over-the-counter medication has the same purpose as one that is prescribed.


Hazards of therapeutic duplication:

(1) increased risk of adverse effects from overdosage, especially if there is a narrow therapeutic range

(2) increased cost


A person whose drug therapy shows therapeutic duplication may avoid the adverse effects of nonadherence if only one of the drugs is not taken.


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