Medline and Embase are the two most comprehensive databases of medical literature. They both include the major medical journals but they have different content, so ideally they should both be searched. Access outside the public hospital or university setting may be limited. If Medline and Embase are not available, then use PubMed and TRIP. SHPA members can access Medline through the EBSCOhost interface on the SHPA website.
PubMed and TRIP are very easy to search, PubMed contains the same information as Medline. It uses keyword searches but no subheadings so it is harder to narrow down the results than with a well-constructed Medline search. TRIP contains a subset of PubMed and includes a selection of tools to assist with searching.
Taking the time to learn to search Medline and Embase effectively is well worth the investment. It will save you time and improve the quality of the information obtained.
This section cannot replace hands-on experience.
Experiment with as many different databases as you can.
General tips on searching bibliographical databases
- When starting a new search, don’t use too many search terms. If you retrieve too many hits, you can always narrow your search.
- Many databases operate using a concept called ‘Boolean logic’. If you want to combine two terms in a search, you can use the Boolean operators AND, OR and NOT. For example:
- cats AND dogs will produce articles that mention both cats and dogs in the same article. This is the most commonly used Boolean term.
- cats OR dogs will produce some articles that mention cats and some articles that mention dogs and some that mention both cats and dogs.
- cats NOT dogs will produce articles that only mention cats. Articles that mention cats and dogs will not be included.
- Many databases use a thesaurus which can help make your search more effective. Each article is read by an indexer, who decides what the key concepts are and assigns keywords to the article from the thesaurus. When you search the database using your chosen keyword from the thesaurus, you will retrieve all the articles with your keyword assigned.
You may need to use US drug names and spellings if you are using an American system. For example, paediatric (pediatric), salbutamol (albuterol) Some databases will automatically convert US and UK spellings and names.
Established in 1966, Medline (Medical Literature, Analysis, and Retrieval System Online) is the US National Library of Medicine’s (NLM) bibliographic database. It contains over 23 million references to journal articles in clinical sciences and biomedical research and covers over 5600 journals.
There are several different ways to access Medline. Many hospitals have access via OVID Medline.
Medline does not provide the full text of a journal article; in most cases an abstract is provided. If the journal can be accessed electronically there may be a hyperlink to the relevant website; some of these may be free or may be available via your organisation’s subscription. There is usually a lag-time between articles being published and being indexed in Medline.
There is no right or wrong way to search Medline. It can be searched using the thesaurus, an author’s name, a journal title, or a word in the text or title of the article abstract. If you are not looking for a single specific article, use the thesaurus for the best results.
Using the Thesaurus
Using the thesaurus is essentially searching for a subject. The Medline thesaurus is called ‘MeSH’ which stands for Medline Subject Headings. MeSH terms are arranged into ‘trees’, where very broad search terms are the ‘trunk’ of the tree and more narrow terms are the branches and twigs.
In the example shown below ‘Cardiovascular Diseases’ is the broadest term and ‘Shock, Cardiogenic’ is the narrowest term.
If you explode a MeSH term you will include all the terms listed under your selected term in the thesaurus tree.
Using the example tree above about cardiovascular diseases; if you just want very broad articles about cardiovascular diseases, that may not mention myocardial infarction specifically, then do not explode the term. However, if you want to search for articles about cardiovascular diseases (including those that definitely mention myocardial infarction), then you need to explode the term cardiovascular diseases. The explode facility will therefore include all the specific terms ‘beneath’ it in the tree hierarchy.
When the term that you select is further down the branch of a tree it will narrow your searching.
OVID Medline does not automatically explode terms for you. To explode a term using OVID you will need to tick the ‘Explode’ box.
If you use the PubMed version of Medline it will automatically explode your chosen term.
If you are in any doubt, always explode; you’ve nothing to lose because you can always limit your search later on if too many results are obtained.
If your search is producing too many hits, consider using a subheading, also called a ‘qualifier’. Subheadings are terms that you can add onto your MeSH term to make your search more specific (e.g. drug therapy, adverse effects, metabolism, pathology). For example you might want to add ‘drug therapy’ into your search about myocardial infarction to only search for articles about the drug treatment of myocardial infarction. For most versions of Medline there is a screen where you can choose to add subheadings.
In addition to MeSH terms and subheadings, each article is tagged with a variety of terms such as the age group of the population studied, the nature of the participants (e.g. human vs. animal) and the type of article (e.g. review). If, despite adding a subheading to your search, you still have too many results, consider adding one of these ‘tags’ or ‘limits’. If your search about the drug therapy of myocardial infarction has produced too many hits then consider adding a ‘human’ limit or the limit for review articles.
Most Medline records have between six and fifteen MeSH terms assigned to them. Two or three of these are marked as the article’s major MeSH terms, which describe the main topics of the paper. In the Medline record these terms will be marked with an asterisk. On some versions of Medline you can choose to find papers that consider your search term as one of the major topics. This process is called ‘focussing’.
There is a lag-time between the development of new drugs and their entry into the thesaurus. During this time some versions of Medline (e.g. PubMed) refer to them as ‘supplementary concepts’. If the thesaurus indicates that your term is a supplementary concept, it will normally give you a ‘registry number’ to use instead. Alternatively you can just use your new term anyway, turn the thesaurus off and Medline will search the title or text of an article abstract for it. This is also known as a text word or keyword text search.
The use of Boolean logic applies to Medline searches and you can combine MeSH headings and supplementary concepts using AND, OR and NOT.
Your oncology pharmacist asks you for help in finding recent evidence to support the use of lenalidomide in patients with multiple myeloma.
So far you have two MeSH headings – lenalidomide and multiple myeloma. You also have one subheading for multiple myeloma – drug therapy.
You have now constructed your Medline search. These will be the terms you will enter into the version of Medline that you have available to you.
A pharmacist asks you to perform ‘a quick Medline search’ about the clinical trial evidence for benralizumab for uncontrolled, severe eosinophilic asthma for a committee meeting in half an hour.
As in example 1, first take time to think about your terms.
You can try searching for asthma/drug therapy, eosinophilia/drug therapy. Depending on how may results you get you might combine the terms. Or for a narrower search you might combine eosinophilia/drug therapy AND benralizumab.
For newly marketed drugs you may not want to add limits to your search. In this example if you get too many hits with your first search, consider adding limits for clinical trials.
Now it’s your turn. Read the following enquiry and try to find the terms in the thesaurus that will enable you to perform a Medline search.
Your neurology pharmacist calls into your office to find out if peripheral neuropathy has been associated with simvastatin.
What MeSH headings will you use?
Simvastatin, Peripheral Nervous System Diseases.
What subheadings, if any, will you use?
Do you need to add limits?
What extra information would be helpful to this search?
Peripheral Nervous System Diseases is a general term, more information about the peripheral neuropathy may be helpful in choosing a more specific term further down the tree
What terms did you use for your search?
Simvavastatin/adverse effects AND Peripheral Nervous System Diseases (MeSH)
Although less well known than Medline, in many ways Embase is better for medicines information enquiries. It includes references to over 32 million articles in 2900 indexed journals. The basic structure is similar to Medline, although search terms may differ between the two databases. The main advantages of Embase over Medline are:
- it covers a larger number of biomedical journals. In particular, it is more comprehensive for pharmaceutical, European and drug-related journals.
- the subheading and limit functions are more comprehensive; for example, you can limit searching to a specific route of drug administration.
- the thesaurus includes more drug names.
CINAHL is the Cumulative Index of Nursing and Allied Health Literature. It provides indexing for over 5000 nursing and allied health journals. The CINAHL subject headings follow the MeSH structure, as used in Medline. The database provides abstracts or full text papers for selected journals. It is helpful for enquiries with a nursing theme, e.g. nurse prescribing, nurse-led admission clinics etc. SHPA members can access Medline through the EBSCOhost interface on the SHPA website.
PsycINFO is a bibliographic database that provides systematic coverage of the professional and academic literature in psychology and related disciplines, including medicine, psychiatry, nursing, sociology, education, pharmacology, physiology, and linguistics. PsycINFO contains coverage of articles and books.
The Cochrane Collaboration is an international organisation that aims to promote evidence-based medicine. The Cochrane Library, the Collaboration’s database, is comprised of five sections, the most helpful being The Cochrane Database of Systematic Reviews and The Database of Abstracts of Reviews of Effectiveness (DARE). The Database of Systematic Reviews contains protocols and reviews prepared by the Cochrane Collaboration. DARE is composed by the NHS Centre for Reviews and Dissemination at the University of York and contains good quality systematic reviews performed by groups other than Cochrane. In Australia, access to the Cochrane Library is funded by the Federal Government.
In-house archiving databases
Many Medicines Information Services have an in-house database to archive the details of past enquiries. As enquiries are entered into the database they are usually given an individual identifying code and can be keyworded. Examples of software databases used in Australia include MiDatabank and ANDIN.