Clinical effects of interaction between drugs. Review of points at which drugs can interact.

The prescribing of mixtures is unfortunately traditional and has a psychological appeal, which is being encouraged by many manufacturers. Doctors must have a sound working knowledge of the mode of action of modern drugs in order to use them effectively and safely, particularly when they are used together.In this context ;drug' means any biologically active substance. Interaction between drugs can be inapparent (if equal and opposite), antagonistic or synergistic. This includes summation and potentiation.INTERACTION BETWEEN DRUGS CAN ARISE IN A VARIETY OF WAYS: directly; in the intestine or other absorptive site; in transit; at the receptor or at another site in the same biological system; by accelerating or slowing drug metabolism; or by influencing excretion.Most of these mechanisms are considered in detail in this Symposium. With greater understanding of underlying mechanisms many of the untoward interactions now being increasingly reported might be foreseen and avoided.