Bioavailability of Drugs – Definition and Information

Definition of Bioavailability Bioavailability is the amount of a DRUG’S active ingredient the body absorbs and the length of time it takes for that ingredient to cause an effect in the body. A common means of determining bioavailability is to measure the concentrations of the drug in the BLOOD circulation or in the URINE at certain time intervals. Doctors know the spectrum […]

Read More

Narrow Therapeutic Index (NTI)

Definition of Narrow Therapeutic Index (NTI) Narrow Therapeutic Index (NTI) is a very close margin between the concentration in the BLOOD circulation of a DRUG that is therapeutic and the concentration that is lethal (deadly). Pharmacists generally express the therapeutic index as a ratio between the median effective DOSE (ED50) and the median lethal dose (LD50). A drug has a narrow therapeutic […]

Read More

Therapeutic Level

Definition of Therapeutic Level Therapeutic Level – the amount of a DRUG in the blood circulation that is necessary to achieve and sustain the desired effect for treatment, which is usually a steady state with little variation between the drug’s PEAK LEVEL and TROUGH LEVEL. Doctors calculate dosages to achieve a therapeutic level, factoring the person’s age, body weight, and […]

Read More

Bioequivalence Definition and Information

Definition of Bioequivalence Bioequivalence – a DRUG that has the same biological effect in the body as a substance the body makes naturally (such as a hormone supplement) or two or more drugs that have the same BIOAVAILABILITY and EFFICACY. Bioequivalence is a significant concern with NARROW THERAPEUTIC INDEX (NTI) drugs, which require precise and consistent dosing, as well […]

Read More

Off-Label Use

Definition of Off-Label Use Off-Label Use – Taking a DRUG for a purpose other than that for which it has received regulatory approval. In the United States the Food and Drug Administration (FDA) requires pharmaceutical manufacturers to demonstrate the safety and efficacy of a drug before approving it for use. Once a drug receives FDA approval, however, doctors […]

Read More

Therapeutic Window

Defintion of Therapeutic Window Therapeutic Window – the DOSAGE range within which most of a DRUG’s likely population will experience the expected EFFICACY and therapeutic value of the drug. The therapeutic window is important to doctors when they calculate dosages, providing a clinically valid starting point for most people. Individual characteristics such as other health conditions, other medications being […]

Read More

Cytochrome P450 (CYP450) Enzymes – Definition

Definition of Cytochrome P450 Enzymes Cytochrome P450 enzymes (CYP450)- a group of about 60 endogenous enzymes (enzymes the body produces) that participate in the metabolism of drugs. The CYP450 enzymes also participate in lipid (notably cholesterol) and steroid hormone synthesis. Most of enzymes, that are active in DRUG metabolism, are in the LIVER and the SMALL INTESTINE. The […]

Read More

Orange Book, The – FDA Document

Definition of Orange Book Orange Book is a document the US Food and Drug Administration (FDA) maintains that lists all the drugs, prescription and over-the-counter, that have FDA approval for use in the United States. As of 2005 The Orange Book is available only as an electronic document (www.fda.gov/cder/ob) on the FDA’s Web site (print editions […]

Read More

Trough Level of drugs

Definition of Trough Level Trough Level is the amount of a DRUG in the BLOOD circulation at the drug’s lowest therapeutic concentration. Generally the trough level occurs immediately before the person is due to take the next DOSE of the drug. The trough level helps the doctor determine if the dosage is appropriate to achieve the desired therapeutic effect and is useful […]

Read More

Dosage of Drugs

Definition of Dosage of Drugs Dosage – the therapeutic course of a DRUG, encompassing the drug’s DOSE (amount of the drug taken), the frequency of the doses, the health condition and status of the person (including age and gender), and the total length of time the drug the person needs to take the drug. For many drugs there are […]

Read More