In most states and in most hospitals, pharmacists have the option of supplying a generically equivalent drug product even if a proprietary name has been specified in the order. If the prescriber wants a particular brand of drug product dispensed, handwritten instructions to “dispense as written” or words of similar meaning are required. Some government-subsidized health care programs and many third-party insurance payers require that pharmacists dispense the cheapest generically equivalent product in the inventory (generic substitution). However, the principles of drug product selection by private pharmacists do not permit substituting one therapeutic agent for another (therapeutic substitution); that is, dispensing trichlormethiazide for hydrochlorothiazide would not be permitted without the prescriber’s permission even though these two diuretics may be considered pharmacodynamically equivalent. Pharmacists within managed care organizations may follow different policies; see below.
It cannot be assumed that every generic drug product is as satisfactory as the trade-named product, although examples of unsatisfactory generics are rare. Bioavailability—the effective absorption of the drug product—varies between manufacturers and sometimes between different lots of a drug produced by the same manufacturer. Despite the evidence, many practitioners avoid generic prescribing, thereby increasing medical costs. In the case of a very small number of drugs, which usually have a low therapeutic index, poor solubility, or a high ratio of inert ingredients to active drug content, a specific manufacturer’s product may give more consistent results. In the case of life-threatening diseases, the advantages of generic substitution may be outweighed by the clinical urgency so that the prescription should be filled as written.
In an effort to codify bioequivalence information, the FDA publishes Approved Drug Products with Therapeutic Equivalence Evaluations, with monthly supplements, commonly called “the Orange Book.” The book contains listings of multisource products in one of two categories: Products given a code beginning with the letter “A” are considered bioequivalent to a reference standard formulation of the same drug and to all other versions of that product with a similar “A” coding. Products not considered bioequivalent are coded “B.” Of the approximately 8000 products currently listed, 90% are coded “A.” Additional code letters and numerals are appended to the initial “A” or “B” and indicate the approved route of administration and other variables.
Mandatory drug product selection on the basis of price is common practice in the USA because third-party payers (insurance companies, health maintenance organizations, etc) enforce money-saving regulations. If outside a managed care organization, the prescriber can sometimes override these controls by writing “dispense as written” on a prescription that calls for a brand-named product. However, in such cases, the patient may have to pay the difference between the dispensed product and the cheaper one.
Within most managed care organizations, formulary controls have been put in place that force the selection of less expensive medications whenever they are available. In a managed care environment, the prescriber often selects the drug group rather than a specific agent, and the pharmacist dispenses the formulary drug
Aiken M, IMS Institute for Health Care Informatics: Medicines use and spending shifts: A review of the use of medicines in the U.S. in 2014. http:// www.imshealth.com/en/thought-leadership/quintilesims-institute/reports/ medicines-use-in-the-us-2014.