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68 (2), FUNDAMENTOS DE LAS INTERACCIONES FARMACOCINÉTICAS

sorción-intercambio iónico, formación de quelatos o complejos, procesos de competición
por un portador, modificación del tránsito gastrointestinal, etc.

En las interacciones que afectan a la distribución de los fármacos por el orga-
nismo suelen estar implicados procesos de desplazamiento del compuesto unido a las
proteínas plasmáticas. La consecuencia más importante de una interacción por despla-
zamiento sería el aumento de la respuesta farmacológica y, probablemente, también de la
toxicidad del agente que es desplazado. Sin embargo, hay que tener en cuenta que dichos
aumentos tienen carácter transitorio, debido a la acción compensatoria que supone la
mayor eliminación del fármaco, por lo que las repercusiones clínicas de este tipo de
interacciones son, en general, de escaso relieve y si se conocen los mecanismos, se pue-
den prever sus consecuencias.

Palabras clave: Interacciones farmacocinéticas. Absorción. Distribución.

SUMMARY

The basis of drug pharmacokinetic interactions ( I )

Nowadays, it is a very common practice to use simultaneously more than one
drug for the treatment of one or more coexisting pathological states. Under these circum-
stances, it is of special interest to determine if the specific drug combination used pro-
duces an interaction, that is, if the effects of one drug are changed by the presence of
another drug, food, drink or by some environmental chemical agent.

Sometimes a drug interaction can be beneficial and valuable, such as the delib-
erate co-prescription of antihypertensive drugs and diuretics in order to achieve anti-
hypertensive effects possibly not obtainable with either drug alone. However, in the
majority of cases, the consequences of a drug interaction are adverse and undesirable. A
solution to this problem would be to adjust the doses or the dosage regimen although, if
possible, the easiest solution would be to choose a non-interacting alternative.

The purpose of this work is to study the basis of the pharmacokinetic interac-
tions which affect the processes by which drugs are absorbed and distributed in the body.
The first ones arise mainly when the drugs are given orally and, very many drugs which
interact do so, not by a single mechanism, but often by two or more of the following
ones: modification of the gastrointestinal pH, adsorption, quelation and other complex-
ing mechanisms, active transport competition, changes in gastrointestinal transit, etc.

When referring to those interactions which affect the process by which drugs
are distributed within the body, the mechanism mainly involved is the displacement of
the primary drug from its plasma binding site, leading to altered kinetics and in some
instances changed drug effects in the patient and, possibly, toxicity. However, these

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