a. Drug. A drug may be broadly defined as any substance or group of substances, which affects living tissue. However, the term may be specifically defined as any substance used to prevent, diagnose, or treat disease or to prevent pregnancy.
b. Pharmacology. Pharmacology is the study of the actions and effects of drugs on living systems and their therapeutic uses.
c. Bioavailability. Bioavailability refers to the amount of drug that is available to the target tissue after the drug has been administered. In other words, it is the amount of the drug available to produce the desired effect.
d. Pharmacognosy. Pharmacognosy is the study of the characteristics of natural drugs.
e. Toxicology. Toxicology is the science of poisons. Toxicology includes the origin, chemical properties, toxic actions, detection, and proper antidotal therapy of poisons.
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.
(6) Single dose. The single dose of a drug is the amount of that substance to be taken at one time.
(7) 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 doses.
(8) 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.
(9) 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.
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