Two-step process

The selection of essential drugs is a two-step process. Market approval of a pharmaceutical product is usually granted on the basis of efficacy, safety and quality, and rarely on the basis of a comparison with other products already on the market or of cost. The regulatory decision defines the availability of a drug in the market. In addition to this, most public drug procurement and insurance schemes have mechanisms to limit procurement or reimbursements of drug costs. For these decisions an evaluation process is necessary, based on a comparison between various drug products and on considerations of value for money. This second step leads to a list of essential drugs.

A list of essential drugs is best developed for different levels of care, and on the basis of clinical guidelines for common diseases and complaints that can and should be diagnosed and treated at that level. A good balance of expert opinions and evidence of effectiveness and cost-effectiveness should lead the development of clinical guidelines. Both these guidelines and the essential drugs lists for the different levels of care must be updated regularly, preferably every two years.

WHO Model List of Essential Drugs

The Model List of Essential Drugs is intended as a model for the second step in the selection process. It has been updated by the WHO Expert Committee on the Use of Essential Drugs every two years since 1977. The Model List of 1999 contains 306 active ingredients and is divided into a main list and a complementary list. 15 Drugs are specified by international nonproprietary name (INN) or generic name without reference to brand names or specific manufacturers.¹⁸

Selection criteria

The treatment recommended and the drugs selected depend on many factors, such as the pattern of prevalent diseases, treatment facilities, the training and experience of available personnel, financial resources, and genetic, demographic and environmental factors. The following criteria are used by the WHO Expert Committee on he Use of Essential Drugs:

• only drugs for which sound and adequate evidence of efficacy and safety in a variety of settings is available should be selected;

• relative cost-effectiveness is a major consideration in the choice of drugs. In comparisons between drugs, the total cost of the treatment - not only the unit cost of the drug - must be considered, and be compared with its efficacy;

• in some cases, the choice may also be influenced by other factors such as pharmaco-kinetic properties or by local considerations such as the availability of facilities for manufacture or storage;

• each drug selected must be available in a form in which adequate quality, including bioavailability, can be ensured; its stability under the expected conditions of storage and use must be determined;

• most essential drugs should be formulated as single compounds. Fixed-ratio combination products are acceptable only when the dosage of each ingredient meets the requirements of a defined population group, and when the combination has a proven advantage over single compounds administered separately, in terms of therapeutic effect, safety or patient adherence to treatment.

Selection process

The process by which drugs are selected is critical. An essential drugs list that is imposed from above will not reflect the needs of the users or be accepted by them. It is therefore very important that: the process is consultative and transparent; the selection criteria are explicit; selection of the drugs is linked to evidence-based clinical guidelines; and the clinical guidelines and the list are divided into levels of care, and that both are regularly reviewed and updated. Clinical guidelines and the list should be reviewed at least every two years, and their use and the impact should be monitored.

A standing committee should be appointed to give technical advice. This committee should include people from different fields, such as medicine, nursing, clinical pharmacology, pharmacy, public health, consumer affairs as well as health workers at grass-roots level. Formal and informal consultations should be organized with interested parties, including representatives of professional bodies, pharmaceutical manufacturers, consumer organizations and the government budget and finance group. However, the final drug selection by the committee members should be carried out independently.

An important principle that needs to be accepted by the committee is that not all evidence is equally strong. For example, the result of a meta-analysis of several clinical trials carries more weight than the result of an observational study without controls, and much more than the personal experiences of individual experts. The strength of the evidence defines the strength of the recommendation.

When the clinical guidelines and the essential drugs list are finalized and printed, they should be launched and made widely available. In case of an update, it may be useful to issue an information leaflet that summarizes the changes or to make the changes known through a newsletter or drug bulletin.