volunteers undergo an exhaustive medical examination before the tests and are
strictly monitored at all times during the trial. The trials are conducted in either
in house-clinics or specialist outside facilities. The objective of these trials on
healthy humans is to ascertain the behaviour of the new drug in the human
body. They also yield information on the dosage form, absorption, distribution,
bioavailability, elimination and side effects of the new drug. The relation of the
side effects to specific metabolites allows medicinal chemists to eliminate the side
effects by designing new analogues that do not give rise to that metabolite (see
section 9.8.). In addition, the trials give information concerning the level of the
drug in the blood after intravenous and oral dosing, rate of excretion in the
urine and via the bowel and the effect of gender on these parameters. At all
times in the trials the function of the kidney and other organs in the body are
monitored for adverse reactions. The dose administered to the volunteers is
initially a small fraction of that administered by the same route to animals.
Once the safety of the drug has been assessed in healthy volunteers the testing
programme moves toPhase IItrials. However, before these trials can be carried
out in Britain the company must obtain a clinical trials certificate, which is
issued by the regulating authority. Phase II trials are conducted on small
numbers of patients with the condition that the drug has been designed to
treat. They assess the drug’s effectiveness in treating the condition and also
help establish a dose level and dosage regimen for the drug. The success of this
phase leads toPhase IIItrials, where the the new product is tried out on large
numbers of patients. In Britain, Phase II trials may only be carried out after a
local ethics committee has evaluated and approved the trials programme (see
section 11.8). Phase III trials are carried out using both placebos and compari-
son standards. They are particulary useful for obtaining safety and efficacy data
in order to satisfy the product licencing authorities. In both Phase II and III
trials a few subjects will exhibit adverse drug reactions(ADRs). These are
described as responses that are either unwanted or harmful, which occur at
the doses used for therapy. They exclude therapy failure. These ADRs are noted
and added to the drug’s data sheet. However, unless a high percentage of
subjects exhibit the same ADR they do not usually result in the drug being
withdrawn from use.
When the new drug has been released onto the market the performance of the
drug is monitored using very large numbers of patients both in hospital and
general practice. This monitoring is often refered to as thePhase IVtrials. It
provides more information about the drug’s safety and efficiacy. In addition
trials are conducted on specific aspects of the drug’s use with smaller specialist
groups, for example, its kinetics in the elderly, infants, neonates and ethnic
groups.
PHARMACOLOGICAL AND TOXICOLOGICAL TESTING 233