e. Toxicology. Toxicology is the science of poisons. Toxicology includes the
origin, chemical properties, toxic actions, detection, and proper antidotal therapy of
f. Posology. Posology is the science of dosage. It deals with the amount of
drug necessary to produce a desired physiological, therapeutic, or prophylactic effect.
(1) Usual recommended dose. The usual recommended dose is the
amount of drug that will ordinarily produce the effect for which the drug is intended. In
addition to the usual recommended dose, the usual dosage range is indicated for many
drugs in the United States pharmacopoeia/National Formulary. The usual dose range
provides a guide in deciding whether the prescriber should be consulted about the
correctness of the prescribed dose.
(2) Minimum dose. The minimum dose is considered the smallest dose of
drug that produces the therapeutic effect.
(3) Maximum dose. The maximum dose is considered the largest dose of
a drug that can be safely administered.
(4) Toxic dose. The toxic dose of a drug is considered the amount of a
drug that will produce noxious (harmful) effects.
(5) Lethal dose. The lethal dose of a drug is the amount of substance that
will cause death. You will often see the term "LD50" in association with lethal dose.
LD50 means that 5O percent (or 1/2) of the animals given that amount of drug died.
The LD50 of a drug should be used as a guide, rather than an absolute number.
Single dose. The single dose of a drug is the amount of that
substance to be taken at one time.
Daily dose. The daily dose of a drug is the amount of that substance
to be taken in a 24-hour period. The daily dose of a drug is into several individual
Maintenance dose. The maintenance dose of a drug is the amount of
that substance taken to maintain or continue a desired therapeutic effect. Some drugs
must be taken on a daily basis in order to maintain the desired therapeutic effect. For
example, drugs used to treat high blood pressure often must be take daily to maintain a
lowered blood pressure.
Loading dose. The first dose given of a drug to achieve maintenance
drug levels quickly. Drugs that are given only one or two times a day may take two or
three days to reach a maximum effect. To overcome this time, a loading dose is given
to achieve the levels associated with the maximum effect more quickly. Loading doses
are often used in very sick patients.