used to form the dioxan ring. Finally, where appropriate, the use of sodium
ethanethiolate to remove the methyl protecting groups of any phenolic hydroxy
groups was avoided by the use of lithium diphenylphosphide. Demethylation
was simply carried out by adding the methyl ether to freshly prepared lithium
diphenylphosphide, which made this reaction highly suitable for large scale
production methods. It was reported that using the route outlined in Figure
11.5, products containing less than 1%of stereoisomers were produced on an
industrial scale.
11.3 Pharmacological and toxicological testing
Extensive pharmacological and toxicological testing must be carried out on any
new drug before it is marketed. These tests are carried out in two stages, namely,
preclinicalandclinical trials. These trials assess the risks involved with the use of
the new drug. They may also provide vital information concerning pharmaco-
kinetic properties of the drug, which can be used in other areas of the develop-
ment. Details of the trials are given in the MAA application which is submitted
to the appropriate government body (see section 11.8). This body will either
approve of the trials programme or specify modifications. To develop and
market the drug, the producer must comply with all the terms of the MAA,
which has replaced the older drug licience. It is essentially a scientific assessment
of the safety, efficacy and quality of the new product.
Preclinical trials are essentially toxicity and other biological tests carried out
by microbiologists on bacteria and pharmacologists on tissue samples, animals
and sometimes organ cultures to determine whether it is safe to test the drug on
humans. The animal tests investigate the effect of the drug on various body
systems such as the respiratory, nervous and cardiovascular systems. They are
carried out under bothin vivo(in the living organism) andin vitro(in an artifical
environment) conditions. These preliminary tests also provide other information
concerning the drug’s pharmacokinetic properties and its interaction with other
drugs and over-the-counter medicines. If necessary, any of these interactions that
enhance or reduce the drugs activity should be investigated further during the
clinical trials and the results noted in the product labelling and literature.
The preclinical tests should help decide whether it is safe to give the the drug to
humans and also the toxic dose for humans. This enables the investigators to set a
dose level to start the Phase I clinical trials. These will include dose-ranging
pharmacokinetic studies and bioavailability via chosen administration routes.
However, relating animal tests to humans is difficult and the results are only
acceptable if the dose–organ toxicity findings include a substantial safety margin.
PHARMACOLOGICAL AND TOXICOLOGICAL TESTING 231