The basic assumptions underlying therapeutic drug monitoring are that drug metabolism varies from patient to patient and that the plasma level of a drug is more closely related to the drug’s therapeutic effect or toxicity than is the dosage. For certain drugs that are intended for long-term use, close monitoring with appropriate routine hematology and chemistry tests may be necessary to avoid or minimize drug-associated adverse events.

Drugs Main Use Tests Suggested Frequency
Acarbose Diabetes mellitus, type 2 LFT, KFT Every 3 months during the first year, then periodically as clinically indicated
ACE inhibitors Hypertension, heart failure Electrolytes, KFT Every 3–6 months
Adalimumab Rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease CBC, KFT, LFT Every 2 months
Adefovir Chronic hepatitis B CBC, LFT, KFT Every 3 months
Alpha 1-antiproteinase (antitrypsin) inhibitor Emphysema related to alpha 1-antiproteinase (antitrypsin) deficiency LFT, KFT Annually
Amiodarone Cardiac arrhythmias TSH, LFT Every 6 months
Anakinra Neonatal-onset multisystem inflammatory disease, refractory rheumatoid arthritis, juvenile idiopathic arthritis CBC, LFT, KFT Every 3 months
Azathioprine Immunosuppression for various conditions CBC, LFT Every other week for the first 8 weeks, then every 3 months
Clozapine and other atypical antipsychotics (risperidone, olanzapine, quetiapine, ziprasidone, aripiprazole) Schizophrenia CBC/diff, LFT, HbA 1C or fasting glucose, fasting lipid profile Annually, except for CBC/diff which should be weekly for the first 6 months, then every other week or monthly
Cyclosporine Organ transplant (kidney, liver, heart), rheumatoid arthritis and other rheumatic diseases CBC/diff, CMP, magnesium Every 3 months
Darbepoetin Anemia (chronic kidney disease, chemotherapy, myelodysplasia) CBC Every 3 months
Entecavir Chronic hepatitis B, HIV/HBV coinfection CBC, LFT, KFT Every 3–6 months
Etanercept Rheumatoid arthritis, other rheumatic diseases CBC, LFT, KFT Every 2 months
Interferon beta-1α Multiple sclerosis CBC/diff, LFT Every 6 months
Lamivudine Chronic hepatitis B, HIV infection (in combination with other agents) CBC, LFT, KFT, amylase Every 3 months
Lithium Bipolar disorder TSH, KFT Every 3–6 months
Mercaptopurine Acute lymphoblastic leukemia (in combination with other agents) CBC/diff, LFT Every 3 months
Mesalamine Ulcerative colitis, Crohn disease LFT, KFT, CBC Every 6 months
Metformin Diabetes mellitus, type 2 CBC, KFT Every 6–12 months
Methotrexate Acute leukemia, lymphoma, cancer, rheumatic diseases CBC/diff, LFT, KFT Every 3 months
NSAIDS (chronic use) Chronic conditions with inflammation, pain and/or fever KFT Annually
Oxcarbazepine Seizures Electrolytes Every 6 months
Prednisone (oral >10 mg daily) Allergic conditions, dermatitis, endocrine conditions, inflammatory bowel disease, autoimmune disorders, leukemia/lymphoma, other conditions HbA 1c or fasting glucose, electrolytes Annually
Riluzole Amyotrophic lateral sclerosis LFT Every 3 months
Sirolimus Organ transplant (kidney, heart) CBC/diff, CMP, magnesium Every 3 months
Statins Prevention of cardiovascular disease, treatment of hypercholesterolemia and dyslipidemia Fasting lipid profile Every 6–12 months
Sulfasalazine Rheumatoid arthritis, ulcerative colitis CBC, LFT, KFT Every 3 months
Tacrolimus Organ transplant (kidney, heart, liver) CBC/diff, CMP, magnesium Every 3 months
Tenofovir HIV infection KFT Every 3 months for one year, then every 6 months
Tizanidine Muscle spasticity, acute low back pain LFT Every 6 months
Topiramate Seizures, migraine headache Electrolytes, KFT Annually
Valproate (valproic acid) Seizures, mania in bipolar disorder, migraine prophylaxis CBC, LFT, PT/PTT Every 6 months
Warfarin Prophylaxis and treatment of thromboembolic disorders PT/INR Frequency varies as clinically indicated
Zafirlukast Asthma, chronic urticaria LFT Every 6 months
CBC/diff, complete blood count with white cell differential; CMP, comprehensive metabolic panel; LFT, liver function tests; KFT, kidney function tests; PT/INR, prothrombin time/International Normalized Ratio; PTT, partial thromboplastin time; TSH, thyroid-stimulating hormone.

The basic principle underlying pharmacogenetics testing is that the identification of genetic factors that influence drug absorption, metabolism, or action at the target level may allow for individualized therapy and thereby help optimize drug efficacy and minimize drug toxicity.