Drug sensitivity is broadly defined as an exaggerated response to a drug in a patient in comparison to the expected response in the general population. Drug sensitivity can range from increased side effects to complete drug intolerance, whereby patients exhibit severe side effects or death. These side effects are often irreversible, as in aspirin induced Tinnitus.
Why Do Some People Suffer from Drug Sensitivity?
Drug sensitivity should not be confused with drug hypersensitivity. Drug hypersensitivities are caused by a patient’s body mounting an immune response to a drug. These can also be severe, but are different to drug sensitivities. Drug sensitivity results solely from genetic differences in a patient. How can your genetics impact drug metabolism and action? Through polymorphisms of genes coding for enzymes or receptors that directly affect how the body responds to the drug.
For instance, an article in Pharmacogenetics and Genomics “VKORC1 Pharmacogenomics Summary” (Oct 2011) states that polymorphisms in the gene VKORC1, which codes for the enzyme Vitamin K epoxide reductase, regulates a patient’s sensitivity to the common anti-coagulant drug Warfarin. The enzyme is the limiting step in the vitamin K cycle and Warfarin acts to inhibit this enzyme, inhibiting Vitamin K’s downstream coagulation effects. Variants 1639A and 1173T require a lower Warfarin dose whereas patients with allele 9041A need a higher dose.
Drug Intolerance and Severe Side Effects
Drug intolerance can cause severe side effects in a patient. These are usually rare but in some instances are reasonably common. For instance, Tinnitus is a drug intolerant side effect to the drug Aspirin. At higher doses, aspirin is nown to cause tinnitus according to a study Frontiers in Systems Neuroscience “Salicylate toxicity model of tinnitus” (April 2012), but some patients experience the symptom after a normal dose of the drug.
Other examples of drug intolerance include liver failure to Paracetamol, fatal poisoning in infants who breastfeed on mothers who are taking the pain relief drug codeine, hypotension (low blood pressure) in patients taking heart drug Enalapril and hallucinations in patients taking codeine, according to research in Australian Family Physician, “Adverse drug reactions” (Feb 2013).
The number of genes that might cause drug sensitivity is massive and many are still not known. At Rxight® we sequence VKORC1 and a panel of other genes to identify how patients will react to more than 200 clinically relevant medications. Genetic testing for drug sensitivity is a faster, cheaper and far safer alternative than watching patients undergo adverse drug reactions and adjusting the dose accordingly.