Dose (toxicology, medicine)

(Needs differentiation from existing articles for "dose" in different meanings)

Dose is a term, broadly defined, that is used to describe the quantity of an agent (chemical, biological, or physical) that impacts (is given to, eaten by, absorbed by, etc.) a biological entity (DNA, cell, tissue, organ, whole organism). In medicine, the term is usually applied to a deliberate exposure to an agent for therapeutic purposes; in toxicology it may refer to the amount of a harmful agent to which something is exposed. Thus, it is related to exposure.

In addition to actual quantity of agent, effects of exposure are also strongly affected by route (ingestion, skin contact, respiratory, whole body vs. part), concentration, and temporal considerations (the same quantity of chemical may be poisonous when given all at once but not if given over a long period of time). Thus, dosage is often referred to "oral dose" or "inhaled dose" etc., as well as by concentration (particles per cubic meter, grams per liter, etc.), and quantity per time unit (e.g. mg per hour, etc.).

Chemicals, including medications, are the most commonly referenced agents for which a dose is calculated. For humans, most doses of medications are measured in milligrams (mg.). For some nonmedicinal poisons, an effective dose may be less than one microgram (mcg.) or as large as six liters (in the case of water, itself a toxin in such a large dose).

Biological agents (bacteria, viruses, parasites) may have different dosage units. This is because it is the ability of the organism to cause effects that is the important unit, not a specific quantity by weight, volume or even numerical count. Often the unit used is CFU (colony forming units), which is proportionate to the number of organisms present multiplied times the number able to reproduce on a culture medium such as a Petri dish.

Physical agents (heat, cold, forceful blows, vibration, noise, non-ionizing radiation, ionizing radiation) have a variety of dose units that reflect the wide variety of entities included in this category. For instance, forceful blows = ergs or joules; noise = decibels; X-rays = grays or seiverts; cold = wind chill factor; (add to/ edit list of units for each).

In the realm of toxicology, several measures are commonly used to describe toxic dosages according to the degree of effect on an organism or a population, and some are specifically defined by various laws or organizational usage. For instance, LD50 = (lethal dose for 50%), a dose which will kill 50% of a population exposed to the agent for a specified time; NOEL = No Observed Effect Level, the highest dose known to show no effect; NOAEL = No Observed Adverse Effect Level, the highest dose known to show no adverse effects; PEL = Personal Exposure Limit, the highest permissible concentration or dose per time unit; STEL = Short Term Exposure Limit, the highest permissible concentration for even instantaneous exposure; TWA = Time Weighted Average, the average amount of an agent's dose over a specified period of time, usually an 8-hour workday; (add to/ edit list of terms with definitions and organizations)