E–I

efficacy The ability of a DRUGto produce a pre-
dictable effect in the body. Many factors influence
a drug’s efficacy, from foods and other drugs to
health conditions and a person’s metabolic charac-
teristics. An individual’s age, weight, gender, and
level of activity also may affect the rate at which a
drug enters, and how long it stays in, the BLOOD
circulation. Efficacy is a key factor in determining
a drug’s potential effectiveness to treat a particular
condition in a specific individual. Some drugs
have greater efficacy in younger people, for exam-
ple. Other factors that are also relevant include
BIOAVAILABILITYand BIOEQUIVALENCE.
See also CYTOCHROME P 450 (CYP 450 ) ENZYMES;
THERAPEUTIC WINDOW.

formulary A list of the prescription drugs a
health plan or insurance company, including state
and federal health insurance programs, will cover.
Typically a committee of physicians and pharma-
cists makes the determinations about what drugs
appear in the formulary and why. Factors for con-
sideration include

• the DRUG’s EFFICACY


• whether generic products are available


• similarity to other drugs that are less expensive
  or have fewer side effects


• NARROW THERAPEUTIC INDEX(NTI) status


• the need for the drug within the insurer’s
  patient population


• whether over-the-counter forms of the drug are
  available


• the drug’s approved uses

Most insurers update their formularies at least
annually. An insurer may pay a smaller percent-

age of the cost for a nonformulary drug or may

choose not to cover (pay for) nonformulary drugs

at all except within the parameters of specifically

defined criteria. A doctor may prescribe a drug

that is not on the formulary even though the

insurer may refuse to pay for it. The person may

still receive the drug by paying for the prescrip-

tion. Drug formularies help establish consistent

prescribing practices as well as control costs for the

insurer.

See also GENERIC DRUG; ORANGEBOOK, THE; OVER-

THE-COUNTER (OTC) DRUGS; PHARMACOPEIA; SIDE

EFFECT.

generic drug A DRUGthat has BIOEQUIVALENCEand

THERAPEUTIC EQUIVALENCEto its INNOVATOR DRUG(the

first drug to receive approval for use). Generic

drugs became significant in the health-care indus-

try in the 1970s when manufacturing require-

ments and procedures became standardized and

patents began to expire on innovator drugs, con-

verging factors that opened the market for compe-

tition within the pharmaceutical industry. Most

generic drugs are significantly less expensive than

their innovator counterparts, and most states have

laws allowing pharmacies to substitute generic

drugs when filling prescriptions unless the pre-

scribing provider specifies otherwise. The intent

behind such laws is to provide consumers with

cost-effective alternatives for prescription drugs.

Generic products are also available for many OVER-

THE-COUNTER(OTC) DRUGS, allowing consumers to

choose either generic or trade name products.

The US Food and Drug Administration (FDA),

the federal regulatory agency that approves drugs

for use in the United States, establishes the criteria

for potency, purity, consistency, and efficacy all

drugs must meet. These criteria are the same for

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