Techniques of postmarketing surveillance. An overview

Postmarketing Surveillance of Drugs: An Overview

The complete safety profile of a drug cannot be made before marketing because of the limited scope of the controlled clinical trials. Postmarketing surveillance (PMS) is the collection and analysis of information about a drug after it has been marketed. A PMS system ideally must be able to detect a rare event, determine its incidence, and validate the causality. Because an ideal system has not been devised, a combination of methods is used. The advantages and limitations of various methods of adverse drug reaction (ADE) reporting are described, and problems and concerns associated with ADE reporting are discussed. Postmarketing surveillance will continue to benefit from spontaneous reporting of ADEs by clinicians (ie, literature reports, reports to manufacturers and national regulatory agencies) to detect rare events and will be complemented by the selective use of formal PMS methods in appropriate circumstances. Increased clinician awareness of serious, potentially drug-related events together with comprehensive and complete reporting of these events will begin to address the problems of underreporting, assessment of causality, and misclassification of events.

Toxicity of nonsteroidal anti-inflammatory drugs. An overview of the epidemiological evidence

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used throughout the world. This paper reviews the epidemiological data linking NSAID administration with gastrointestinal, hepatic, renal, haematological, and hypersensitivity reactions. Meta-analysis has demonstrated that NSAIDs are associated with serious upper gastrointestinal disorders, with a relative risk of 2.7 in patients receiving NSAIDs compared with subjects not receiving NSAIDs. An increase in the dose and duration of NSAIDs and age > 60 are associated with an increase in the risk of upper gastrointestinal toxicity. The current data strongly support a causal relationship between NSAIDs and gastrointestinal disorders. Case-control studies have demonstrated an association between some NSAIDs and neutropenia, with a relative risk of between 3 and 9 in patients treated with NSAIDs compared with nonusers of these drugs. NSAIDs have also been linked with hypersensitivity reactions, although the incidence of such reactions is very low. However, there are inconsistent data on the potential associations between NSAIDs and renal disease, and there are no epidemiological studies linking NSAIDs with acute liver disease. Overall, the incidence of serious adverse reactions associated with NSAIDs is low, and this class of drugs can be regarded as being reasonably safe.

Assessing risk in postmarketing surveillance

We need to find some way to assess the probability of risk for individuals taking medications for a prolonged period of time either singly or, as is usually more likely, in combinations. It is not possible to perform detailed, controlled studies for all combinations of drugs, not even those most commonly administered. Therefore, we must rely primarily on data from various case studies of attending physicians. Since this data is not collected in a controlled setting, we require a statistical technique that can do the following: be modified to handle data sequentially as information continues to accumulate, be very robust for dependent data, make minimal assumptions concerning the underlying distribution of the data, and be used for multivariate data. A statistical technique--nonparametric density estimation--is available that will satisfy all of the above requirements. We will demonstrate its use in postmarketing surveillance.

Adverse effects of hypolipidaemic drugs

Cholestyramine, colestipol, clofibrate, gemfibrozil, nicotinic acid (niacin), probucol, neomycin, and dextrothyroxine are the most commonly used drugs in the treatment of hyperlipoproteinaemic disorders. While adverse reaction data are available for all of them, definitive data regarding the frequency and severity of potential adverse effects from well-controlled trials using large numbers of patients (greater than 1000) are available only for cholestyramine, clofibrate, nicotinic acid and dextrothyroxine. In adult patients treated with cholestyramine, gastrointestinal complaints, especially constipation, abdominal pain and unpalatability are most frequently observed. Continued administration along with dietary manipulation (e.g. addition of dietary fibre) and/or stool softeners results in diminished complaints during long term therapy. Large doses of cholestyramine (greater than 32 g/day) may be associated with malabsorption of fat-soluble vitamins. Most significantly, osteomalacia and, on rare occasions, haemorrhagic diathesis are reported with cholestyramine impairment of vitamin D and vitamin K absorption, respectively. Paediatric patients have been reported to experience hyperchloraemic metabolic acidosis or gastrointestinal obstruction. Concurrent administration of acidic drugs may result in their reduced bioavailability. Serious adverse reactions to clofibrate will probably limit its role in the future. Of particular concern are ventricular arrhythmias, induction of cholelithiasis and cholecystitis, and the potential for promoting gastrointestinal malignancy which far outweigh the reported benefits in preventing new or recurrent myocardial infarction, cardiovascular death and overall death. Patients with renal disease are particularly prone to myositis, secondary to alterations in protein binding and impaired renal excretion of clofibrate. Drug interactions with coumarin anticoagulants and sulphonylurea compounds may produce bleeding episodes and hypoglycaemia, respectively. Nicotinic acid produces frequent adverse effects, but they are usually not serious, tend to decrease with time, and can be managed easily. Dermal and gastrointestinal reactions are most common. Truncal and facial flushing are reported in 90 to 100% of treated patients in large clinical trials. Significant elevations of liver enzymes, serum glucose, and serum uric acid are occasionally seen with nicotinic acid therapy. Liver enzyme elevations are more common in patients given large dosage increases over short periods of time, and in patients treated with sustained release formulations.(ABSTRACT TRUNCATED AT 400 WORDS)