When two drugs are taken together, or when the drugs is taken in combination in certain foods or with alcohol, this may produce effects different from those produced when the drugs is taken alone, In many cases this is beneficial, and physicians frequently make use of interactions to increase the effectiveness of a treatment. very often, more than one drug may be prescribe to treat cancer or high blood pressure ( hypertension)
Many interactions, however are unwanted and may be harmful. They may occur not only between prescriptions drugs, but also between prescription and over the counter that does the physician does not know about.
A drug may interact with another drug or with food or alchol for a number of reason.
The Main type of interactions are:
1. Altered absorption
Alcohol and some drugs (especially narcotic) slow down the digestive system process that empties the stomach content into the intestine. This may delay the absorption, and therefore the effect, of another drug taken at the same time. Other drugs for (example, metoclopramide, an anti emetic drug) may speed the rate at which the stomach empties and therefore may increase the rate at which another drug is absorbed and takes effect.
some drug are also combine with another drug or a food in the intestine to form a compound that is not so readily absorbed. this occurs when tetracycline and iron tablets or antacids are taken together. milk also reduce the absorption of certain drugs in this way.
2. Enzyme effects
some drugs increase the production of enzymes in the liver that break down drugs, while others may inhibit or reduce enzyme production. then therefore they affect the rate at which other drugs are activated or inactivated.
3. Excretion in urine
A drugs may reduce the kidney’s ability to excrete another drug, thereby raising the level of the drug in the blood and increasing its effect.
4. Receptor effects
Drugs which acts on the same Receptors sometime redouble each other stimulating effect on the body. or they may compete with each other in occupying particular receptors sites. Naloxone, for instance, blocks the receptors used by narcotic drugs, thereby helping to reverse the effects of narcotic poisoning.
5. Similar effects
Drugs that produce similar effects (even thought they do not act on the same receptors) may be given together so that a smaller dose of each is required,reducing the side effect of each. this is common practice in the treatment of high blood presure, in giving anticancer drugs, and also in the treating pain. sometimes two antibiotics may be given simultaneously. though their effects may be similar, the infecting organisms are less likely to develop resistance.
6.Reduced protein binding
Some drugs circulate around the body in the bloodstream with a proportion of the drug attached to the proteins of the blood plasma. this means that the amount of the drug attached to plasma protein is inactive, if another drug is taken, some of the second drug may also attached itself to the plasma proteins and displace the first drug; more of the first drug is then active in the body.