Biostatistics

Biostatistics or biometry is the application of statistics to a wide range of topics in biology . It has particular applications to medicine .

ADME

ADME is an acronym in pharmacokinetics and pharmacology for Absorption, Distribution, Metabolism, and Excretion, and describes the disposition of a pharmaceutical compound within an organism. The four criteria all influence the drug levels and kinetics of drug exposure to the tissues and hence influence the performance and pharmacological activity of the compound as a drug :

Absorption

Before a compound can exert a pharmacological effect in tissues, it has to be taken in to the bloodstream — usually via mucous surfaces like the digestive tract (intestinal absorption). Uptake into the target organs or cells needs to be ensured, too. This can be a serious problem at some natural barriers like the blood-brain barrier . Factors such as poor compound solubility, chemical instability in the stomach, and inability to permeate the intestinal wall can all reduce the extent to which a drug is absorbed after oral administration. Absorption critically determines the compound’s bioavailability. Drugs that absorb poorly when taken orally must be administered in some less desirable way, like intravenously or by inhalation (e.g. zanamivir ).

Distribution

The compound needs to be carried to its effector site, most often via the bloodstream. From there, the compound may distribute into tissues and organs, usually to differing extents.

Metabolism

Compounds begin to be broken down as soon as they enter the body. The majority of small-molecule drug metabolism is carried out in the liver by redox enzymes, termed cytochrome P450 enzymes. As metabolism occurs, the initial (parent) compound is converted to new compounds called metabolites. When metabolites are pharmacologically inert, metabolism deactivates the administered dose of parent drug and this usually reduces the effects on the body. Metabolites may also be pharmacologically active, sometimes more so than the parent drug.

Excretion

Compounds and their metabolites need to be removed from the body via excretion, usually through the kidneys (urine) or in the feces. Unless excretion is complete, accumulation of foreign substances can adversely affect normal metabolism.

Sometimes, the potential or real toxicity of the compound is taken into account (*ADME-Tox* or ADMET). When the Liberation of the substance (from protective coating, or other excipients ) is considered, we speak of LADME.

Pharmacodynamics

Pharmacodynamics is the study of the biochemical and physiological effects of drugs and the mechanisms of drug action and the relationship between drug concentration and effect. It is often summarily stated that pharmacodynamics is the study of what a drug does to the body, whereas pharmacokinetics is the study of what the body does to a drug.

Pharmacokinetics

Pharmacokinetics is a branch of pharmacology dedicated to the study of the time course of substances and their relationship with an organism or system. In practice, this discipline is applied mainly to“drug”:http://en.wikipedia.org/wiki/Medication substances, though in principle it concerns itself with all manner of compounds residing within an organism or system, such as nutrients, metabolites, endogenous hormones, toxins, etc. So, in basic terms, while pharmacodynamics explores what a drug does to the body, pharmacokinetics explores what the body does to the drug.

Drug Metabolism

Drug metabolism is the metabolism of drugs , their biochemical modification or degradation, usually through specialized enzymatic systems. Drug metabolism often converts lipophilic chemical compounds into more readily excreted polar products. Its rate is an important determinant of the duration and intensity of the pharmacological action of drugs.

Drug metabolism can result in toxication or detoxication – the activation or deactivation of the chemical. While both occur, the major metabolites of most drugs are detoxication products.

Drugs are almost all xenobiotics . Other commonly used organic chemicals are also drugs, and are metabolized by the same enzymes as drugs. This provides the opportunity for drug-drug and drug-chemical interactions or reactions.

Mass spectrometry

Mass spectrometry (also known as mass spectroscopy (deprecated)1 or in common speech “mass-spec”) is an analytical technique used to measure the mass-to-charge ratio of ions . It is most generally used to find the composition of a physical sample by generating a mass spectrum representing the masses of sample components. The technique has several applications, including:

• identifying unknown compounds by the mass of the compound molecules or their fragments
• determining the isotopic composition of elements in a compound
• determining the structure of a compound by observing its fragmentation
• quantifying the amount of a compound in a sample using carefully designed methods (mass spectrometry is not inherently quantitative)
• studying the fundamentals of gas phase ion chemistry (the chemistry of ions and neutrals in vacuum)
• determining other physical, chemical or even biological properties of compounds with a variety of other approaches

A mass spectrometer is a device that measures the mass-to-charge ratio of ions. This is achieved by ionizing the sample and separating ions of differing masses and recording their relative abundance by measuring intensities of ion flux. A typical mass spectrometer comprises three parts: an ion source , a mass analyzer, and a detector system.