The role of genetic testing in ensuring drug safety in tertiary healthcare settings.

The Role of Genetic Testing Technology in Enhancing Efficiency and Safety of Medication Use in Tertiary Care Facilities

Advances in the field of Genomic Medicine have led to a paradigm shift in patient care from standard treatment to personalized medicine, also known as precision medicine. The core concept is understanding how different genetic characteristics affect drug response, a field of study known as Pharmacogenetics and Pharmacogenomics.

Studies have shown that genetic factors account for 20% to 95% of the variability in individual patient drug responses, especially for drugs with narrow therapeutic windows or those affecting critical body systems. This report aims to analyze the importance of testing for drug hypersensitivity genes and genes regulating enzyme functions in the body, covering key drug groups that impact safety and treatment efficacy, to provide foundational information for healthcare professionals and patients in hospital systems.

Introduction to Pharmacogenetics and the Mechanism of Gene Influence on Drug Response

The human body’s response to drugs involves complex biochemical processes, starting from drug absorption into the bloodstream, distribution to target organs, chemical structure modification by enzymes (metabolism), and drug excretion. Genes act as blueprints determining the quantity and efficiency of proteins involved in these processes, such as Cytochrome P450 (CYP) enzymes, drug transport proteins (Transporters), and drug receptors (Receptors).

Genetic variations or polymorphisms in these gene loci categorize individuals into four main groups based on their drug metabolism capacity: Poor Metabolizer (PM), Intermediate Metabolizer (IM), Normal Metabolizer (NM), and Ultra-rapid Metabolizer (UM). Identifying these statuses in advance helps prevent drug toxicity in PMs due to drug accumulation at high levels or treatment failure in UMs due to rapid drug breakdown that cannot maintain therapeutic concentrations.

Cardiovascular Drug Group: Precision in Critical Conditions

Cardiovascular drugs are among the most commonly applied pharmacogenetics in clinical practice because complications from inappropriate dosing can lead to recurrent thrombosis or severe bleeding.

CYP2C19 Genetic Testing for Clopidogrel

Clopidogrel is an antiplatelet drug that requires activation by the liver enzyme CYP2C19 to its active metabolite form. In the Thai and Asian populations, the prevalence of CYP2C19*2 and CYP2C19*3 alleles, which significantly reduce enzyme function, is notable. Patients with the Poor Metabolizer genotype have a high risk of major adverse cardiovascular events (MACE), such as acute myocardial infarction or stent thrombosis, due to insufficient Clopidogrel activation. Genetic testing before starting treatment helps physicians decide to switch to alternative drugs like Prasugrel or Ticagrelor, which do not depend on this enzyme for activation.

Anticoagulant Warfarin and CYP2C9, VKORC1 Genes

Warfarin is known for its challenging dose adjustment because the appropriate dose varies greatly among individuals. Studies in Thai patients confirm that variations in the CYP2C9 gene, responsible for drug metabolism, and the VKORC1 gene, the drug’s target site, affect initial dose calculations. Most Thai people carry the VKORC1 Haplotype A, which is more sensitive to Warfarin than African populations, requiring lower starting doses. Pharmacogenetic-based dosing formulas reduce the time to reach therapeutic INR levels and decrease the incidence of abnormal bleeding.

Statins and Muscle-Related Risks

Statin-associated muscle symptoms (SAMS) are a major cause for 7% to 29% of patients discontinuing lipid-lowering therapy. The SLCO1B1 gene controls the production of the OATP1B1 transporter protein, which facilitates statin uptake into the liver. Patients with the rs4149056 variant (SLCO1B1*5) have reduced transporter function, leading to elevated blood statin levels and muscle cell damage.

Neurological and Psychiatric Drugs: Preventing Severe Drug Hypersensitivity

Antiepileptic and psychiatric drugs are among the leading causes of severe cutaneous adverse reactions (SCARs) in Thailand, which have high mortality rates and cause disability.

Antiepileptic Carbamazepine and HLA-B*15:02 Gene

The HLA-B*15:02 gene is one of the most important pharmacogenetic markers for the Thai population, strongly associated with Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) caused by carbamazepine. Individuals with this risk gene have hundreds of times higher risk than normal. Pre-treatment screening is included as a basic benefit in Thailand. Other structurally similar drugs, such as Oxcarbazepine, also pose risks for hypersensitivity in carriers of this gene.

Phenytoin and Dual Risk

Phenytoin presents complexity because risks depend on both immune system genes and metabolic genes. The HLA-B*15:02 gene increases the risk of SJS/TEN, while reduced-function CYP2C9 alleles lead to elevated blood drug levels causing neurotoxicity, such as ataxia, diplopia, and nystagmus. Testing both gene loci is essential for appropriate drug selection and dose adjustment.

Antidepressants and Psychiatric Drugs

The CYP2D6 enzyme plays a key role in metabolizing tricyclic antidepressants (TCAs) like Amitriptyline and SSRIs/SNRIs. Ultra-rapid Metabolizers often experience treatment failure due to rapid drug breakdown, while Poor Metabolizers may suffer side effects such as dry mouth, dry throat, palpitations, or severe hypotension.

Anesthesiology and Malignant Hyperthermia: Life-Threatening Moments in the Operating Room

Malignant Hyperthermia (MH) is a surgical crisis often caused by genetic mutations in the RYR1 or CACNA1S genes. It is triggered by volatile anesthetics and the muscle relaxant Succinylcholine.

The disease mechanism involves continuous calcium leakage from the sarcoplasmic reticulum of skeletal muscle cells, causing muscle rigidity and massive energy consumption. Early signs include rapid rise in blood carbon dioxide levels (hypercapnia), followed by arrhythmia, acidosis, and body temperature that can reach up to 42°C within a short time. Screening for RYR1 mutations in individuals with a family history of MH is a critical safety measure before anesthesia.

Pharmacogenetics in Oncology: Reducing Chemotherapy Toxicity

Treatment failure in some cancers is not due to the disease itself but because patients cannot tolerate chemotherapy toxicity due to genetic differences.

5-Fluorouracil (5-FU) and DPYD Gene

The DPYD gene encodes the enzyme Dihydropyrimidine Dehydrogenase, which metabolizes over 80% of administered 5-FU and Capecitabine. Patients with DPYD mutations are at high risk of severe, potentially lethal toxicity, including bone marrow suppression, bloody diarrhea, and skin peeling. DPYD genetic testing before treatment allows dose reduction or switching to safer regimens.

Irinotecan and UGT1A1 Gene

Irinotecan is a key drug for colorectal cancer treatment. Its active metabolite SN-38 is highly toxic and eliminated by the UGT1A1 enzyme. Patients with UGT1A1*28 or UGT1A1*6 alleles have reduced SN-38 clearance, leading to severe neutropenia and diarrhea that may cause shock.

Antiviral, Antimicrobial Drugs and Prevention of Specific Side Effects

Infections are common in hospitals, and many anti-infective drugs have hypersensitivity reactions clearly linked to genetic markers.

HIV Antiviral Abacavir and HLA-B*57:01 Gene

Abacavir is specifically associated with the HLA-B*57:01 gene. Carriers of this gene experience severe hypersensitivity reactions affecting multiple organ systems, typically starting with fever, rash, nausea, vomiting, and respiratory symptoms. If this gene is detected, Abacavir must never be prescribed due to nearly 100% risk of hypersensitivity.

Dapsone and HLA-B*13:01 Gene Association

Dapsone is used to treat leprosy and other skin conditions and can cause Dapsone Hypersensitivity Syndrome (DHS), characterized by fever, rash, and hepatitis. Research in Thailand and East Asia identifies HLA-B*13:01 as a precise risk marker. Genetic testing before use is crucial in areas with high leprosy prevalence or for prophylaxis against opportunistic infections.

Tuberculosis Drug Isoniazid and NAT2 Gene

Isoniazid is metabolized by the enzyme N-acetyltransferase 2 (NAT2). Slow acetylators have a higher risk of drug-induced liver injury (DILI), while fast acetylators may face drug resistance due to insufficient blood levels. NAT2 genotyping helps physicians design balanced tuberculosis treatment regimens for efficacy and safety.

Painkillers and Antacids: Safety in Basic Medications

Even commonly accessible drugs have genetic risk factors that can turn treatment into harm.

Opioid Painkillers Codeine, Tramadol and CYP2D6 Enzyme

Codeine and Tramadol are prodrugs that require conversion to Morphine or O-desmethyltramadol by CYP2D6 to exert analgesic effects. Ultra-rapid Metabolizers convert these drugs too quickly and extensively, leading to acute opioid toxicity characterized by severe drowsiness, confusion, and respiratory arrest. Severe adverse events have been reported in children post-tonsillectomy, leading to warnings against use in young children without genetic testing.

Proton Pump Inhibitors (PPIs) and H. pylori Eradication

PPIs like Omeprazole are metabolized by CYP2C19. The effectiveness of Helicobacter pylori eradication depends on maintaining appropriate gastric pH levels. Ultra-rapid Metabolizers break down PPIs too quickly, reducing their efficacy and leading to treatment failure of gastric ulcers.

Testing Procedures and the Role of Benefits in Thailand

Pharmacogenetic testing in hospitals is designed to be convenient and integrated into standard laboratory testing.

Preparation and Sample Collection: Patients do not need to fast and samples can be collected via venous blood using EDTA tubes or by gently swabbing the buccal mucosa (buccal swab).

Turnaround Time and Interpretation: Molecular techniques such as Real-time PCR or Next-Generation Sequencing (NGS) take approximately 2 to 6 weeks for analysis. The test results remain valid for the patient’s lifetime and can be used for treatment decisions at any age.

Basic Benefits: Currently, the National Health Security Office (NHSO) includes key genetic tests such as HLA-B*15:02 (for Carbamazepine) and HLA-B*58:01 (for Allopurinol) as benefits for all Thai citizens to reduce costs and prevent drug hypersensitivity crises.

Summary and Future Outlook

Pharmacogenetic testing is a powerful tool to elevate safety standards in healthcare facilities. Transitioning from trial-and-error treatment to selecting the right drug, dose, and patient based on genetic codes not only saves lives from severe drug allergies but also reduces overall healthcare costs by improving treatment efficiency.

In the near future, pharmacogenetic data will be integrated into electronic health records and clinical decision support systems that alert physicians and pharmacists immediately when prescribing drugs that pose genetic risks to patients. Genetic testing is thus not just an option but a fundamental pillar of quality and sustainable healthcare for all.

Reference Table on Pharmacogenetics and Drug Hypersensitivity Testing