Terms

Before discussing drug interactions, it may be useful to review some basic pharmacological terms, abbreviations, and processes.

AUC is 'area under the curve'. To understand AUC, picture a graph where the y axis represents plasma drug concentration and the x axis is time. You would start to draw a line when a drug is taken. It would curve upwards and at the time of C_max, the line is at its highest point. As the drug concentration lessens, the line drifts downward until C_min is reached. The area where the drug is at a therapeutic concentration in the bloodstream is the 'area under the curve'.

Bioavailability is a measure of how much of an administered drug is absorbed into the bloodstream and actually reaches its intended site of action in the body. If a medication is designed to be taken on an empty stomach, taking it with food changes the drug's absorption rate and subsequent bioavailability. An example of this is seen with grapefruit juice. Grapefruit juice inhibits the enzymes that break down certain medications; this can increase their bioavailability to sometimes toxic levels. If a drug is not broken down by the same enzymes that break down grapefruit juice, then there will not be a variation in bioavailability. In most cases, a drug is active only until it is broken down, at which point it usually leaves the body.

C_max is the maximum concentration of drug in the bloodstream. This usually occurs just after taking a drug and is also known as 'peak concentration'.

C_min is the minimum concentration of a drug in the bloodstream. Usually by the time C_min has been reached, it is time for another drug dose. C_min is also known as the 'trough concentration'.

Half-life is the amount of time it takes for drug concentration in the body to fall by half.

IC refers to inhibitory concentration. This term comes from the laboratory. When studying the action of a drug in a test tube ('in vitro' meaning 'in glass'), researchers see how much drug is needed to slow down HIV production. When viral production is reduced by half, it has reached a level called IC₅₀. Ideally, a drug would have an IC₁₀₀. However, by the time a drug reached that level, the amount of drug in the bloodstream would probably be toxic.

Metabolism describes the biochemical processes taking place within cells that allow them to live, grow, and divide. Anabolism uses energy to build complex cell components from substances with a simple constitution; catabolism breaks down or transforms substances to produce energy. Some nutrients bind with drug ingredients, reducing their absorption or speeding elimination. Genetics can also affect metabolic processes.

P450 is an enzyme path used in the liver to break down many drugs.

PK stands for pharmacokinetics and generally refers to how drug levels in the body change over time.