create a single, fully searchable in silico drug resource that links sequence, structure and mechanistic data about drug molecules (including biotech drugs) with sequence, structure and mechanistic data about their drug targets. Beyond its obvi- ous educational value, this kind of database could potentially allow researchers to easily visualize and explore 3D drug interactions, compare drug similarities or perform in silico drug (or drug target) discovery. Here, we wish to describe just such a database—called DrugBank. DATABASE DESCRIPTION Fundamentally, DrugBank is a dual purpose bioinformatics– cheminformatics database with a strong focus on quantitative, analytic or molecular-scale information about both drugs and drug targets. In many respects it combines the data-rich molecular biology content normally found in curated sequence databases such as Swiss-Prot and UniProt (6) with the equally rich data found in medicinal chemistry textbooks and chemical reference handbooks. By bringing these two disparate types of information together into one uniﬁed and freely available resource, we wanted to allow educators and researchers from diverse disciplines and backgrounds (academic, indus- trial, clinical, non-clinical) to conduct the type of in silico learning and discovery that is now routine in the world of genomics and proteomics. The diversity of data types and the required breadth of domain knowledge, combined with the fact that the data were mostly ‘paper-bound’ made the assembly of DrugBank both difﬁcult and time-consuming. To compile, conﬁrm and validate this comprehensive collection of data, more than a dozen textbooks, several hundred journal articles, nearly 30 different electronic databases, and at least 20 in-house or web-based programs were individually searched, accessed, compared, written or run over the course of four years. The team of DrugBank archivists and annotators included two accredited pharmacists, a physician and three bioinform- aticians with dual training in computing science and molecular biology/chemistry. DrugBank currently contains >4100 drug entries, corres- ponding to >12 000 different trade names and synonyms. These drug entries were chosen according to the following rules: the molecule must contain more than one type of atom, be non-redundant, have a known chemical structure and be identiﬁed as a drug or drug-like molecule by at least one reputable data source. To facilitate more targeted research and exploration, DrugBank is divided into four major categor- ies: (i) FDA-approved small molecule drugs (>700 entries), (ii) FDA-approved biotech (protein/peptide) drugs (>100 ent- ries), (iii) nutraceuticals or micronutrients such as vitamins and metabolites (>60 entries) and (iv) experimental drugs, including unapproved drugs, de-listed drugs, illicit drugs, enzyme inhibitors and potential toxins (3200 entries). These individual ‘Drug Types’ are also bundled into two larger categories including all FDA drugs (Approved Drugs) and All Compounds (Experimental + FDA + nutraceuticals). DrugBank’s coverage for non-trivial FDA-approved drugs is 80% complete. In addition, >14 000 protein (i.e. drug target) sequences are linked to these drug entries. More com- plete information about the numbers of drugs, drug targets and Nucleic Acids Research, 2006, Vol. 34, Database issue D669 Table 1. Summary of the data fields or data types found in each DrugCard Drug or compound information Drug target or receptor information Generic name Brand name(s)/synonyms IUPAC name Chemical structure/sequence Chemical formula PubChem/KEGG/ChEBI Links Swiss-Prot/GenBank Links FDA/MSDS/RxList Links Molecular weight Melting point Water solubility pKa or pI LogP or hydrophobicity NMR/MS spectra MOL/SDF/PDF text files MOL/PDB image files SMILES string Indication Pharmacology Mechanism of action Biotransformation/absorption Patient/physician information Metabolizing enzymes Target name Target synonyms Target protein sequence Target no. of residues Target molecular weight Target pI Target gene ontology Target general function Target specific function Target pathways Target reactions Target Pfam domains Target signal sequences Target transmembrane regions Target essentiality Target GenBank protein ID Target Swiss-Prot ID Target PDB ID Target cellular location Target DNA sequence Target chromosome location Target locus Target SNPs/mutations A more complete listing is provided on the DrugBank home page. non-redundant drug targets (including their sequences) is available in the DrugBank ‘download’ page. The entire data- base, including text, sequence, structure and image data occu- pies nearly 16 gigabytes of data—most of which can be freely downloaded. DrugBank is a fully searchable web-enabled resource with many built-in tools and features for viewing, sorting and extracting drug or drug target data. Detailed instructions on where to locate and how to use these browsing/search tools are provided on the DrugBank homepage. As with any web- enabled database, DrugBank supports standard text queries (through the text search box located on the home page). It also offers general database browsing using the ‘Browse’ and ‘PharmaBrowse’ buttons located at the top of each DrugBank page. To facilitate general browsing, DrugBank is divided into synoptic summary tables which, in turn, are linked to more detailed ‘DrugCards’—in analogy to the very successful GeneCards concept (7). All of DrugBank’s summary tables can be rapidly browsed, sorted or reformatted (using up to six different criteria) in a manner similar to the way PubMed abstracts may be viewed. Clicking on the DrugCard button found in the leftmost column of any given DrugBank summary table opens a webpage describing the drug of interest in much greater detail. Each DrugCard entry contains >80 data ﬁelds with half of the information being devoted to drug/chemical data and the other half devoted to drug target or protein data (see Table 1). In addition to providing comprehensive numeric, sequence and textual data, each DrugCard also con- tains hyperlinks to other databases, abstracts, digital images and interactive applets for viewing molecular structures (Figure 1). In addition to the general browsing features, Drug- Bank also provides a more specialized ‘PharmBrowse’ feature. This is designed for pharmacists, physicians and medicinal chemists who tend to think of drugs in clusters of indications or drug classes. This particular browsing tool