Dose-response relationship

Dose-response relationship
Semi-log plots of two agonists with different Kd.

The dose-response relationship, or exposure-response relationship, describes the change in effect on an organism caused by differing levels of exposure (or doses) to a stressor (usually a chemical) after a certain exposure time[1] . This may apply to individuals (e.g.: a small amount has no significant effect, a large amount is fatal), or to populations (e.g.: how many people or organisms are affected at different levels of exposure).

Studying dose response, and developing dose response models, is central to determining "safe" and "hazardous" levels and dosages for drugs, potential pollutants, and other substances to which humans or other organisms are exposed. These conclusions are often the basis for public policy. The U.S. Environmental Protection Agency has developed extensive guidance and reports on dose-response modeling and assessment, as well as software [2]

It should be realized that dose-response relationships will generally depend on the exposure time and exposure route (e.g., inhalation, dietary intake); quantifying the response after a different exposure time or for a different route leads to a different relationship and possibly different conclusions on the effects of the stressor under consideration. This limitation is caused by the complexity of biological systems and the often unknown biological processes operating between the external exposure and the adverse cellular or tissue response.

Contents

Dose-response curve

A dose-response curve is a simple X-Y graph relating the magnitude of a stressor (e.g. concentration of a pollutant, amount of a drug, temperature, intensity of radiation) to the response of the receptor (e.g. organism under study). The response may be a physiological or biochemical response, or even death (mortality), and thus can be counts (or proportion, e.g., mortality rate), ordered descriptive categories (e.g., severity of a lesion), or continuous measurements (e.g., blood pressure)[3]. A number of effects (or endpoints) can be studied, often at different organizational levels (e.g., population, whole animal, tissue, cell).

The measured dose (usually in milligrams, micrograms, or grams per kilogram of body-weight for oral exposures or milligrams per cubic meter of ambient air for inhalation exposures) is generally plotted on the X axis and the response is plotted on the Y axis. Other dose units include moles per body-weight, moles per animal, and for dermal exposure, moles per square centimeter. In some cases, it is the logarithm of the dose that is plotted on the X axis, and in such cases the curve is typically sigmoidal, with the steepest portion in the middle. Biologically based models using dose are preferred over the use of log(dose) because the latter can visually imply a threshold dose when in fact there is none.

The first point along the graph where a response above zero (or above the control response) is reached is usually referred to as a threshold-dose. For most beneficial or recreational drugs, the desired effects are found at doses slightly greater than the threshold dose. At higher doses, undesired side effects appear and grow stronger as the dose increases. The more potent a particular substance is, the steeper this curve will be. In quantitative situations, the Y-axis often is designated by percentages, which refer to the percentage of exposed individuals registering a standard response (which may be death, as in LD50). Such a curve is referred to as a quantal dose-response curve, distinguishing it from a graded dose-response curve, where response is continuous (either measured, or by judgment).

Statistical analysis of dose-response curves may be performed by regression methods such as the probit model or logit model, or other methods such as the Spearman-Karber method. Empirical models based on nonlinear regression are usually preferred over the use of some transformation of the data that linearizes the dose-response relationship [4].

Dose-response curves can be fit to the Hill equation (biochemistry) to determine cooperativity.

Problems with linear model

Problems exist regarding non-linear relationships between dose and response, thresholds reached and 'all-or-nothing' responses. These inconsistencies can challenge the validity of judging causality solely by the strength or presence of a dose-response relationship. A threshold model or linear no-threshold model may be more appropriate, depending on the circumstances.

Endocrine disruptors have also been cited with producing one effect at high dose and a different effect at low doses.

References

  1. ^ Crump, KS; Hoel DG, Langley CH, Peto R. (1976). "Fundamental Carcinogenic Processes and Their Implications for Low Dose Risk Assessment". Cancer Research 36 ((9_Part1)): 2973–2979. 
  2. ^ U.S. EPA (2009). Benchmark Dose Software (BMDS) Version 2.1 User's Manual Version 2.0, DRAFT. Doc No.: 53-BMDS-RPT-0028. Washington, DC: Office of Environmental Information.. 
  3. ^ Altshuler, B (1981). "Modeling of Dose-Response Relationships". Environ Health Perspect 42: 23–27. 
  4. ^ Bates, D. and D. Watts (1988). Nonlinear regression analysis. New York: John Wiley and Sons. pp. 365. 

See also

External links


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • dose-response relationship — dozės ir atsako ryšys statusas T sritis biomedicinos mokslai apibrėžtis ↑Ryšys, kai didėjant veiksnio dozei (kiekiui, trukmei, koncentracijai), didėja ↑populiacijos dalis, kuriai pasireiškia poveikio rezultatas. atitikmenys: angl. dose response… …   Lithuanian dictionary (lietuvių žodynas)

  • dose-response curve — noun Medicine the relationship between the size of a dose and the extent of the response to it …   English new terms dictionary

  • dose-response curve — /dohs ri spons / a curve plotting the relationship between the dose of a drug administered and its pharmacological effect. [1970 75] * * * …   Universalium

  • dose-response curve — /dohs ri spons / a curve plotting the relationship between the dose of a drug administered and its pharmacological effect. [1970 75] …   Useful english dictionary

  • relationship — ryšys statusas T sritis biomedicinos mokslai apibrėžtis Vieno ↑kintamojo priklausomybė nuo kito ar keleto kitų kintamųjų. Ryšys tarp dviejų kintamųjų yra teigiamasis (positive), jeigu didėjant vieno kintamojo reikšmėms, didėja ir kito kintamojo… …   Lithuanian dictionary (lietuvių žodynas)

  • dose-re|sponse — «DOHS rih SPONS», adjective. showing the relationship of dosage (of a drug, gas, radiation, or other substance) to the physiological effect produced: »A dose response chart would have a line going from zero to maximum dose, with the risk… …   Useful english dictionary

  • relationship — The state of being related, associated, or connected. dose response r. r. in which a change in the amount, intensity, or duration of exposure is associated with a change in risk of a specified outcome. dual relationships relationships in which a… …   Medical dictionary

  • Median lethal dose — This article is about the toxicological term. For the album by Mudvayne, see L.D. 50 (album). For other uses, see LD50 (disambiguation). In toxicology, the median lethal dose, LD50 (abbreviation for “Lethal Dose, 50%”), LC50 (Lethal Concentration …   Wikipedia

  • Effective dose — An effective dose in pharmacology is the amount of drug that produces a therapeutic response in 50% of the people taking it, sometimes also called ED 50. In radiation protection it is an estimate of the stochastic effect that a non uniform… …   Wikipedia

  • Relation dose-effet — Courbes dans un repère semi logarithmique montrant le pourcentage d effet de deux stresseurs. La relation dose effet ou relation exposition réponse exprime le changement d effet, sur un organisme, provoqué par une quantité différente de… …   Wikipédia en Français

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”