Dose/Response Relationship

When we consider Paracelsus's famous phrase, "The right dose differentiates a poison and a remedy", the relationship between dose and response is crucial in understanding what may be harmful to our body and what may be beneficial for intake. In toxicology, the basic principle to understand is that for every dose, there is a response. According to Dose-Response Relationships in Toxicology, An important assumption in this relationship is that there is almost always a dose below which no response occurs or can be measured. A second assumption is that once a maximum response is reached any further increases in the dose will not result in any increased effect. 

The basis for establishing this relationship comes primarily from experimental data using laboratory animals, in vitro studies, and information from humans. The quantitative relationship provides information to assess the relative toxicity of a chemical when compared with others tested under similar conditions of exposure.  

Toxicity Rating

MicroCare discusses toxicity ratings which include the threshold limit value (TLV) , Personal Exposure Limit (PEL), and Assigned Exposure Limit (AEL). The best ratings are known as the TLV ratings. These are only assigned by the organization ACGIH. The Extension Toxicology Network states that the threshold limit value (TLV) for a chemical is the airborne concentration of a the chemical (expressed in ppm) that produces no adverse effects in workers exposed for eight hours a day per five days per week. This value is usually set to prevent minor toxic effects like skin or eye irritation.  

Dose

The administered or applied dose is considered the amount presented to an absorption barrier and available for absorption (although not necessary having yet crossed the outer boundary of the organism). This is otherwise specified. The internal does is more of a general term denoting the amount absorbed without respect to specific absorption barriers or the exchange boundaries. The delivered dose is the amount of the chemical available for interaction with any particular organ or cell. 

Reference Dose

NCBI states that the reference dose has been introduced in the field of toxicology in order to avoid use of prejudicial terms, such as "safety" and "acceptable", to promote greater consistency in the assessment of noncarcinogenic chemicals, and to maintain the functional separation between risk assessment and risk management. 

Median Doses

Deranged Physiology states that ED50 is the dose required to achieve 50% of the desired response pr intended use in 50% of the population. TD50 is the dose to achieve 50% of the population reporting this specific toxic effect. LD50 is defined as the dose that is required to achieve 50% morality from toxicity. EC50 is the concentration of a drug at which 50% of its maximum response is observed. LC50 is when the concentration of half of the drug at which 50% of mortality from toxicity is observed. 

The dose/response relationship is highly dependent on the interactions with exposure time (how long the subject has been exposed) and exposure route (how the substance entered the body). Understanding this relationship within the subject of toxicology is extremely important.