Types of Drug Interaction

Pharmaceutical drugs are used for a variety of reasons in medicine. Drugs can be used therapeutically to treat diseases or symptoms; preventively or even as a diagnostic agent helpful in the initial diagnosis of a disease. The Center for Disease Control and Prevention notes that 1.9 billion drugs were ordered or provided in doctor's offices in 2006. As the use of multiple drugs by one person and the use of alternative and complementary therapies like herbs and supplement becomes increasingly popular, understanding interactions between these groups have become even more important.

Drug-Drug Interactions

Polypharmacy is regarded as the daily use of multiple drugs by a single person. Susan M. Turley, author of the book "Understanding Pharmacology for Health Professionals, 4th edition," notes that drug-drug interactions can occur because of polypharmacy, synergism and antagonism. Synergism is noted as the action that two drugs of similar function have for one another. When two drugs work in a similar fashion, their combined use can result in an effect greater than their independent actions. This synergistic effect can cause the drug to reach toxic levels in the body or lead to side effects and adverse effects. Turley notes that two drugs can exert an antagonistic or contradictory effect in the body when taken together. The antagonistic effect of a drug-drug interaction produces a combined product that is less than the intended effect of either one used alone.

Drug-Nutrient Interactions

Drug nutrient interactions are also known as drug-food interactions. They can also have antagonistic or synergistic effects in the body. The most well known drug-food interaction is caused by the grapefruit. Turley states that drinking grapefruit juice blocks an enzyme in the intestine that normally processes drugs before they enter the blood stream. When this enzyme becomes blocked, more of the drug than was intended will enter the bloodstream and toxic levels of the drugs can be reached. Turley notes two other common drug-nutrient interactions. Patients should not take the tetracycline antibiotic class of drugs with milk because the milk binds up the drug in the stomach and makes it ineffective. Additionally, the they not take antidepressant MAO inhibitor drugs with foods high in the amino acid tyramine. The tyramine-MAO interaction can cause high blood pressure, headaches and strokes. Foods rich in tyramines include aged cheeses, red wine, bananas, liver, avocados and chocolate.

Drug-Herb Interactions

People have used herbs to treat various ailments since the beginning of time and in many cases, those same herbs became the sources of many modern medicines. Turley notes that cinchona bark was the original source of the modern anti-malarial drug, quinine. She further adds that penicillin originated from mold and aspirin from the plant, white willow bark. Even the periwinkle plant provided the ingredients active in the chemotherapy drugs vinblastine and vincristine. The 2002 Critical Care Nurse article notes that herbs can affect the effects of drugs at all levels of their metabolism. Absorption can become affected because certain herbs that don't absorb well in water bind to drugs when taken together. The bound drug becomes inactive. Other herbs such as rhubarb and Aloe Vera affect how fast food moves through the digestive tract. By acting as a laxative, drugs can move out of the digestive tract before they have had the opportunity to become absorbed into the bloodstream. Other herbs that may work to increase the function of the liver may cause certain drugs to metabolize to fast or metabolize into ineffective or toxic forms. Valerian, a herb commonly used to induce sleep, can increase the sedative effects of antidepressants and the action of drugs like gingko may affect the blood thinning effects of drugs like warfarin.