HEALTH TOPICS A TO Z

Adverse Drug Reactions

Medicines help to bring improved and longer life to humanity. However, they are not without risk and may cause lesser or greater harm to many people, alongside the large number who benefit. Harmful side effects are generally referred to as Adverse Drug Reactions (ADRs).

Classical examples of ADRs are:

Hospital admissions due to ADRs may be more than 10% of the total in some countries. For example, a 2004 study in the United Kingdom, published in the British Medical Journal, carried out a prospective analysis of 18 820 patients admitted into hospital over six months to assess the cause of admission. There were 1225 admissions related to an ADR, giving a prevalence of 6.5%, with the ADR directly leading to the admission in 80% of cases. The projected annual cost of such admissions to the National Health Service was £466 million (US$ 847 million).

According to a survey published in the Journal of American Pharmacists' Association in 2001, the cost of detected drug-related morbidity and mortality in the United States exceeded US$177 billion in 2000, with hospital admissions accounting for about 70% of total costs. Since 1995, the costs associated with drug related problems have more than doubled.

Figures from developing countries are not readily available but it is thought that adverse events are proportionately even higher than in wealthier regions.

Why adverse drug reactions?

A large proportion of negative reactions to medicines are due to irrational use or human error and are therefore preventable. The main ones are:

• Wrong diagnosis of the patient’s condition
• Prescription of the wrong drug or wrong dosage of the right drug
• Undetected medical, genetic or allergic condition in the patient which might cause a bad reaction to the drug
• Self-medication
• Lack of adherence to the prescribed course of the drug
• A large number of different drugs being taken by the patient (polypharmacy), which may interact.

However, it is important to remember that even when the above situations are carefully avoided, all medicines have side effects and some of those can be damaging. The effects of any medical intervention cannot be predicted with absolute certainty. No drug is totally devoid of risk.

For all medicines there is a trade-off between the benefits and the potential for harm. The harm can be minimized by ensuring that medicines of good quality, safety and efficacy are prescribed and used rationally.

Substandard and Counterfeit Drugs

Another factor that can cause adverse drug reactions is the existence on the market of substandard medicines. These are products whose composition and ingredients do not meet the correct scientific specifications and which are consequently ineffective and often dangerous to the patient. Substandard products may occur as a result of negligence, human error, insufficient human and financial resources or counterfeiting.

Counterfeit medicines are part of the broader phenomenon of substandard pharmaceuticals. The difference is that they are deliberately and fraudulently mislabelled with respect to identity and/or source. Counterfeiting can apply to both branded and generic products and counterfeit medicines may include products with the correct ingredients but fake packaging, with the wrong ingredients (some of which may be toxic), without active ingredients or with insufficient active ingredients.

In wealthier countries the most frequently counterfeited medicines recently have been cholesterol lowering medicines, drugs used for treatment of growth hormone deficiency and for cancer. In developing countries the most counterfeited medicines are those used to treat life-threatening conditions such as malaria, tuberculosis and HIV/AIDS. Antibiotics are also often found among counterfeit medicines.

Drug Safety Monitoring

Access to medicines must be accompanied by quality assurance of those medicines - that is, there must be controls and checks to ensure that the medicines ultimately reaching patients are of good quality, safe and effective.

Pharmaceutical companies are required by law in all countries to have tested their drugs on healthy and patient volunteers before making them widely available. The declared purpose of 'pre-marketing' clinical trials (tests carried out before the drug is available for purchase) is to discover:

• If a drug works and how well;
• if it has any harmful effects;
• if there is potential harm how serious is it and how does it weigh against the benefits.

Clinical trials generally do tell a good deal about how well a drug works for a defined disease and what potential harm it may cause. However they provide no information for larger populations with different characteristics from the trial group - age, gender, state of health, ethnic origin and so on.

Therefore, for many medicines, and particularly new, complex products, safety monitoring does not stop at the manufacturing stage; it must be followed by careful patient monitoring and by further scientific data collection. This aspect of drug monitoring is called post-marketing surveillance.

WHO Activities in Drug Safety Monitoring

WHO promotes drug safety through its International Drug Monitoring Programme, which began to operate in 1968. Initially a pilot project in 10 countries with established national reporting systems for ADRs, the network has expanded significantly as more countries worldwide develop national pharmacovigilance centres for the recording of ADRs. Currently, 86 countries participate in the programme.

The most important task of the Drug Monitoring Programme is to identify 'signals' of drug safety problems as early as possible. A signal is defined by WHO as 'reported information on a possible causal relationship between an adverse event and a drug' which has not been previously detected.

Reported cases of ADRs are forwarded from national pharmacovigilance centres to the WHO Collaborating Centre for International Drug Monitoring in Uppsala, Sweden. The case reports are stored in the ADR data base. Over 3.1 million case records are maintained in the data base, the most comprehensive source of international ADR information.

In addition, WHO also:

• has established a system for regular exchange of information between Member States on the safety and efficacy of pharmaceutical products, using a network of designated national information officers;
• ensures the prompt transmission to national health authorities of new information on serious adverse effects of pharmaceutical products;
• devises and disseminates guidelines to set up national drugs monitoring centres;
• trains doctors and drug safety monitoring experts across the globe on new and complex medicines (i.e. antiretrovirals);
• works with countries to strengthen drug regulatory authorities and establish reporting systems for ADRs;
• facilitates contacts between major stakeholders (regulatory authorities, police, customs officials, etc.) to combat counterfeit medicines at a national, regional and global level.

Future Perspectives

The future of global drug safety very much depends on countries' ability to build up local systems for drug monitoring, reporting and storing information. WHO intends to strengthen its technical assistance work with national Drug Regulatory Authorities to achieve greater global harmony in the way drug monitoring is carried out and how adverse drug reaction signals are handled nationally and globally. It is important for 'signals' to be rapidly transformed into policy decisions at the national level in order to safeguard patient safety.