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.
