In this step you link the therapeutic objective to various drugs. Drugs that are not effective are not worth examining any further, so efficacy is the first criterion for selection. Initially, you should look at groups of drugs rather than individual drugs. There are tens of thousands of different drugs, but only about 70 pharmacological groups! All drugs with the same working mechanism (dynamics) and a similar molecular structure belong to one group. As the active substances in a drug group have the same working mechanism, their effects, side effects, contraindications and interactions are also similar. The benzodiazepines, beta-blockers and penicillins are examples of drug groups. Most active substances in a group share a common stem in their generic name, such as diazepam, lorazepam and temazepam for benzodiazepines, and propranolol and atenolol for beta-blockers.
There are two ways to identify effective groups of drugs. The first is to look at formularies or guidelines that exist in your hospital or health system, or at international guidelines, such as the WHO treatment guidelines for certain common disease groups, or the WHO Model List of Essential Drugs. Another way is to check the index of a good pharmacology reference book and determine which groups are listed for your diagnosis or therapeutic objective. In most cases you will find only 2-4 groups of drugs which are effective. In Annex 2 various sources of information on drugs and therapeutics are listed.
Look at a number of advertisements for new drugs. You will be surprised at how very few of these 'new' drugs are real innovations and belong to a drug group that is not already known.