Possibility of occurrence of drug interactions increases with the number of drugs administered. Drug interactions can be classified in a number of ways using different basis as well as terminology. Drugs may interact with other drugs, foods, beverages, contrast media, and herbs; outside or inside the body. The term “drug-condition interaction” is sometimes used when the existing medical condition makes certain drugs potentially harmful. Knowledge of In vitro interactions is essential to avoid loss of activity of drugs before administration. Although every theoretical drug interaction may not manifest in practice, “drug interactions” is a prominent cause of adverse or undesired events related to drug administration or treatment failure. Amongst the herbs, St. John’s wort has a potential of producing significant drug interactions due to its capacity to induce metabolism of number of drugs. In vivo interactions at pharmacokinetic level affect absorption, distribution, biotransformation or excretion of drugs. Induction or inhibition of cytochrome P450 (CYP450) enzymes forms a major basis of drug interactions. As compared to induction, inhibition is a fairly rapid process. Number of precipitant drugs which inhibit the metabolism is much more than those that produce induction of enzymes; hence inhibition of metabolism may lead to serious and acute adverse events by aggravating the toxicity of substrate drugs. Role of drug transporters, especially P-glycoprotein (P-gp), in causation of drug interactions is being increasingly identified. P-gp affects absorption, distribution and excretion, and hence plays a major role in pharmacokinetic drug interactions. Additionally, P-gp works hand in hand with CYP450 enzymes. In pharmacodynamic interactions, the drugs synergise or antagonise the effects at the level of target of action. Clinically beneficial and reparative drug interactions are explored to obtain useful drug combinations. Interactions of drugs with contrast media should be remembered and carefully prevented. Extensive research has led to the development of a large number of In vitro and In vivo methods to detect and predict drug interactions.“Drug interaction softwares” is an additional and significant tool for analysis and prediction of probable drug interactions. Appropriate awareness and knowledge of possible drug interactions is crucial in prevention of harmful drug interactions and their consequences.
Dr. Madhav Mutalik (MBBS, MD (Pharmacology), MBA)
Professor and Head, Departmentof Pharmacology, D Y Patil Dental School,Pune, India.
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