The science of health technology assessment--clinical effectiveness of therapeutic interventions

Important information is not, and cannot, be available at the time a new drug enters the market. Delaying registration is not the answer because most of this information can only be obtained in a real life situation. Several types of postmarketing (phase IV studies) can be identified. The active pharmacovigilance cohort who allows large number of patients to be followed for long periods of time can answer questions about the incidence of rare events (less than one of 3000 patients). The prospective effectiveness cohort can answer questions on long term efficacy (more than two years). The simplified clinical trial, which implies randomly assigning patients and then following them with a 'naturalistic' protocol can answer questions about effectiveness (efficacy in real life). The drug use study is the only way to answer questions of key importance to drug plan managers such as 'which drug(s) is it going to replace?' and 'is it going to be used as first line or second line?'. Phase IV studies, which in some cases should be mandatory (conditional registration), are essential for the protection of the patients and the proper use of public funds to reimburse drugs.