Drug Interactions: A Comprehensive Update | Chapter 6 | Modern Advances in Pharmaceutical Research Vol. 1
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.
Author(s) Details
Dr. Madhav Mutalik (MBBS, MD (Pharmacology), MBA)
Professor and Head, Departmentof Pharmacology, D Y Patil Dental School,Pune, India.
Professor and Head, Departmentof Pharmacology, D Y Patil Dental School,Pune, India.
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