Pharmacogenetics – Selecting Right Drugs For the Right Genes


Did you know that 87%of the total patients receiving cancer chemotherapy develop Adverse Drug Reactions (ADR)? It also causes 50 deaths out of 1000 patients in India. These statistics highlight the importance of correct drugs for the treatment.

Depending on your genetic makeup, some drugs may work more or less effectively for you than they do in other people. Likewise, some drugs may produce more or fewer side effects in you than in someone else.

Pharmacogenetics is the study of inherited genetic differences in drug metabolism which can affect individual responses to drugs, both in terms of therapeutic effect as well as adverse effects. It plays an important role in Oncology.

Now, doctors are able to use information about your genetic makeup to choose the drugs and drug doses that are helpful to you.

For example, if a patient asks for extra amount of codeine to relieve the pain, it can come across as a sign of an evading patient seeking narcotics. However, that patient can be breaking down the codeine within minutes of swallowing it and therefore not be able to create the intermediate molecule that relieves the pain. With this conclusion, the physician can suggest the suitable drugs.

image credits- static1.squarespace.com/
image credits- static1.squarespace.com/

Pharmacogenomics also help to save you time and money as the “best-fit” drug for you can be chosen from the beginning of the treatment to avoid the trial-and-error approach of giving you various drugs.

Besides pharmacogenomics, other factors may influence how a person reacts to a drug. These include:

  • Person’s age and gender.
  • How advanced the cancer is.
  • Person’s lifestyle habits, such as smoking and drinking alcohol.
  • Other diseases that they have and the medications they are on for these conditions.

FDA Guidelines for Pharmacogenetics

The U.S. Food and Drug Administration (FDA) has listed many drugs that need genetic testing before introducing them in the treatment. Some of them are Mercaptopurine and Irinotecan. FDA recommends genetic testing before giving the chemotherapy drug mercaptopurine (Purinethol) to patients with acute lymphoblastic leukemia. It also advises doctors to test colon cancer patients for certain genetic variants before administering irinotecan (Camptosar), which is part of a combination chemotherapy regimen.

Let us see some case studies so that we can understand how pharmacogenetic analysis helped patients with better drugs, and thus, treatment.

  1. A 62 year old male patient with colon cancer was started with a standard dose of FOLFOX and after 6 weeks, Irinotecan and Cetuximab were introduced. However, after the first cycle, sever Myelo-suppression was developed. It delayed the chemo for 3-15 days every cycle. At DGL, comprehensive pharmacogenetic analysis consisting of tumour mutation analysis was advised which confirmed ADR to Irinotekan and 5FU and capsitaben was recommended.
  1. 52 year old male Chronic Smoker diagnosed with adenocarcinoma of the Right Lung with liver metastasis was given Pemetrexed and Carboplatin- 6 cycles which showed partial response. He was advised comprehensive pharmacogenetic analysis at DGL consisting of Tumor mutation analysis for efficacy evaluation and Pharmacogenetics for toxicity profile that showed KRAS mutation which explains partial response to Pemetrexed. Other mutations detected suggestive of personalized targeted therapy.

Geneshield Test at DGL

This test at DGL requires sample of whole blood/ saliva and turnaround time is 2 weeks. The report will give you the information of the genetic mutations you carry that would affect the efficacy of drugs. This test also gives you information about the toxicity of these drugs on your body at the same time.

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It’s always better to maintain a good rapport with the doctor. Here are the few things which you should discuss with your doctor before starting a treatment.

  • Would you explain my treatment options?
  • Which treatment or combination of treatments do you recommend? Why?
  • What are the possible side effects of this treatment?
  • Is there a way to predict how the cancer will respond to this drug or whether I might experience severe side effects?
  • What are my options if the cancer does not respond to the drug or if I suffer from severe side effects?

Detecting the ill-effects of drugs and replacing them with proper ones under expert advice definitely help to give the treatment a right direction.

 

 

 

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