Terminology

Absorption	The movement of a drug from its site of administration into the systemic circulation
Active drug	The drug takes effect immediately. Example - morphine
Adverse drug reaction	An unintended, harmful reaction to medicines.
ADME	Absorption, distribution, metabolism and elimination (the key components of pharmacokinetics)
Allele	One of two or more forms of a single gene. Each person inherits two alleles for each gene, one from each parent.
Base pair	Two nucleotides on complementary DNA strands.
Candidate gene	A gene predicted to be associated with a particular trait e.g disease, adverse reaction to a drug
Cytochrome P450	A group of enzymes involved in drug metabolism and found in high levels in the liver. These enzymes change many drugs, including anticancer drugs, into less toxic forms that are easier for the body to excrete. Examples include CYP2D6, CYP2C19 and CYP2C9
DNA	(Deoxyribonucleic acid) is the chemical name for the molecule that carries genetic instructions for all living things
Enzyme	A biological catalyst, usually a protein, that speeds up the rate of a specific chemical reaction. The body contains thousands of different enzyme molecules, each specific to a particular chemical reaction.
Efficacy	The maximum beneficial or therapeutic response that a drug can produce, and is a measure of clinical effectiveness. It can be expressed in terms of the percentage of recipients who show a therapeutic response at a given, standard dose.
Excretion	A pharmacokinetic term that refers to the irreversible removal of a drug in the unchanged form. Excretion is one of two processes (metabolism, excretion) that account for the elimination of a drug from the body.
Exome	Part of the genome formed by DNA sequences that encode genes (exons).
Gene	The basic physical unit of inheritance
Genotype	An individual’s collection of genes
Genome-Wide Association Study (GWAS)	A study to assess common genetic variations across the entire genome of a large population of individuals in order to study whether any of the investigated variations is associated with a phenotype of interest.
Haplotype	A haplotype can be thought of as a collection of genetic variants, such as SNPs, that always travel together (are inherited together) on the same individual allele
Heterozygosity	When two different alleles are present on the chromosome pair
Homozygosisty	When two identical alleles are present on the chromosome pair.
Metaboliser	Poor Metabolizers Poor metabolizers have two non-functional alleles and therefore have little to no enzyme activity. Intermediate Metabolizers Intermediate metabolizers have one non-functional allele and one normally functioning allele, and therefore have decreased enzyme activity. Extensive Metabolizers Extensive metabolizers have 2 normally functioning alleles and therefore have normal enzyme activity. Ultra-Rapid Metabolizers Ultra-rapid metabolizers have one or more alleles which result in increased enzyme activity compared to extensive metabolizers.
Nucleotides	The building blocks of DNA. Four nucleotides make up DNA: adenine (A), cytosine (C), guanine (G), and thymine (T)
Pharmacodynamics	The biochemical and physiological effects of drugs, particularly those that define the drugs mechanism of action on the body.
Pharmacokinetics	The absorption, distribution, metabolism, and excretion (ADME) of bioactive drugs following their administration to higher organisms including man
Pharmacogenetics	The identification of genetic variations and their association with variations in drug treatment response.
Pharmacogenomics	The incorporation of multiple pharmacogenetic results to develop a gene-based phenotypic characterization. Pharmacogenomic uses include identifying responsive or side-effect prone patients in clinical practice and in drug development trials.
Phase I metabolism	Small chemical changes that make a compound more hydrophilic, so it can be effectively eliminated by the kidneys. These reactions usually involve either adding or unmasking a hydroxyl group, or some other hydrophilic group such as an amine or sulphydryl group, and usually involve hydrolysis, oxidation or reduction mechanisms. Cytochrome P450 enzymes are responsible for most phase I reactions.
Phase II metabolism	Takes place if phase I is insufficient to clear a compound from circulation, or if phase I generates a reactive metabolite. These reactions usually involve adding a large polar group (conjugation reaction), such as glucuronide, to further increase the compound’s solubility. Often, the functional groups generated in phase I reactions are required for attachment of the phase II polar groups (though in some cases phase II reactions can occur on their own). Transferase enzymes are responsible for most phase II reactions, e.g. uridine diphosphoglucuronosyl transferase (UGT), N-acetyl transferase (NAT), glutathione S-transferase (GST), and sulphotransferase (ST).
Phase III	Involves drug transporters, which influence the effect, absorption, distribution and elimination of a drug. Drug transporters move drugs across cellular barriers, and as such can target sites of accumulation. They are located in epithelial and endothelial cells of the liver, gastrointestinal tract, kidney, blood-brain barrier and other organs.
Phenotype	Observable physical characteristic (such as enzyme activity)
Polymorphism	A variant that has two or more alleles and is present at a frequency of at least 1% of the population.
Prodrug	A precursor (forerunner) of a drug. A prodrug must undergo chemical conversion by metabolic processes before becoming an active pharmacological agent. For example, codeine is a prodrug.
Single nucleotide polymorphism (SNP)	A single nucleotide locus with two or more naturally occurring alleles defined by a single base pair substitution.