Therapeutic Drug Monitoring Reagents

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Therapeutic drugs are used to heal, control, or prevent certain diseases and conditions, and are often required throughout a person’s lifetime to treat chronic conditions. Most therapeutic drugs have a narrow therapeutic index and require regular monitoring to ensure correct levels of the drug in the blood are maintained; therapeutic index refers to the difference in the amount that causes a therapeutic effect, and the amount that causes toxicity. Toxic levels may occur as a result of other factors affecting a person’s ability to absorb the drug i.e. change in health, additional medication that may be reacting with the drug, and, overdose. In addition, sub-therapeutic levels may occur where the patient’s level of the drug is inadequate for their treatment.

To read more about each of our therapeutic drug assays use the drop-down menu below. Alternatively, read on for more information about the different types of therapeutic drugs and the relevance of Randox therapeutic drug assays.

Therapeutic Drug Monitoring products available from Randox

Initial doses are measured to ensure suitability for each individual…

Therapeutic drugs are monitored upon initial dosage to evaluate dosage suitability for the individual; standardised doses are not effective as each person absorbs, metabolises and eliminates drugs at different rates. Depending upon test results, drug dosage may be increased or decreased, and monitored until the blood level reaches the therapeutic range.

Regular monitoring of therapeutic drugs ensures toxic levels are not reached…

The majority of therapeutic drugs require monitoring due to their narrow therapeutic index (the difference between safe therapeutic doses and toxic doses). Therapeutic drugs are administered for chronic conditions, and as a result are required throughout a person’s lifetime. Steady concentrations must be maintained year after year, and as a result monitoring at regular intervals is required; this is largely due to the fact that age and life events including pregnancy, infection, illness and stress can contribute to a change in the rate at which an individual absorbs, metabolises and eliminates drugs from the body.

Therapeutic drugs which may require monitoring include:

  • Carbamazepine, an anti-epileptic drug used in the treatment of seizures; side effects of incorrect dosage can include breathing difficulties, drowsiness and in severe cases seizures, development of lupus and fatal skin reactions
  • Digoxin, a cardiovascular drug used in the treatment of heart conditions such as arrhythmias and heart failure; digoxin toxicity can be associated with health issues such as changes in heart rate and rhythm, gastrointestinal problems and fatigue
  • Gentamicin, an antibiotic drug used to treat a wide range of bacterial infections; gentamicin toxicity complications include ear and hearing problems as well as kidney damage, numbness, muscle twitching and seizures
  • Lithium, used for the treatment of the manic phase of affective disorders, mania, and manic-depressive illness; early symptoms of intoxication include apathy, sluggishness, drowsiness, lethargy, speech difficulties, irregular tremors, myoclonic twitching, muscle weakness and ataxia
  • Phenobarbital, an anti-epileptic drug and sedative-hypnotic drug; incorrect dosage can cause drowsiness, depression, headaches and dizziness with severe cases leading to renal failure, coma and hypotension
  • Phenytoin, an anti-epileptic drug used to control generalised seizures; incorrect dosage can lead to side effects such as insomnia, nausea, confusion and fatigue, with symptoms of high level toxicity including seizures, unusual bleeding and difficulty breathing or swallowing

If you currently take or are due to start taking any of the drugs mentioned discuss your monitoring schedule with your doctor!

Tests may also be sought for a variety of other reasons…

There are a variety of other reasons when a test may be requested; this includes situations where a patient is experiencing side effects to determine if the dose needs to be adjusted; if a patient has experienced a change in health i.e. kidney function, thyroid problems, cancer, or stomach or intestinal issues; if a patient begins taking another medication; if a doctor suspects the patient is not taking the recommended dose of medication; and, if an overdose is suspected. For some therapeutic drugs such occasions are the only cause for levels to be tested i.e. Valproic Acid (an anti-epileptic drug); incorrect dosage can result in severe liver impairments, renal function failure and pancreatic function impairments.

If you are experiencing side effects, have experienced a change in health, or are about to start a new medication or change of dosage, ask your doctor for a test to ensure you are on the correct dosage!

Upon overdose, seek help immediately!

The tests mentioned above are also used to diagnose an overdose and assess the risk of damage to the organs. It is important that you seek medical attention immediately after taking an overdose. For medication such as painkillers, accidental overdose can easily occur if you do not keep track of the timing between doses. Paracetamol and Aspirin can be extremely dangerous if overdose occurs:

  • Paracetamol (Acetaminophen) can cause liver and kidney damage in the event of prolonged use, and can lead to hepatic failure if an overdose is left untreated; treatment, in the form of an antidote, must begin within 15 hours of overdose. It is important to note that symptoms may not occur for 2-3 days after overdose even if a potentially fatal dose has been taken, and therefore it is vital that you seek medical help if you have taken above the recommended amount, regardless of whether you feel well
  • Aspirin (Salicylate) can cause metabolic acidosis, gastrointestinal and central nervous system disturbances, encephalopathy and renal failure in the event of overdose. Monitoring of this drug may occur for patients who take a high dose for the treatment of conditions such as rheumatoid arthritis, osteoarthritis or systemic lupus erythematosus, or to treat rheumatic fever or Kawasaki disease

Effective monitoring of therapeutic drugs is crucial for patient health!

Therapeutic drugs can present a danger to patients if the wrong dosage is recommended and if a change which may affect their absorption is missed i.e. changes in health, life or medication. This is because their levels may be increasing their risk of toxicity, or be inadequate for the treatment of their condition. In particular, therapeutic drugs with a narrow therapeutic index should be monitored at the beginning of treatment to ensure the patient has been recommended the correct dosage for them, and routine monitoring throughout treatment should take place to ensure consistently safe levels of the drug in the patient’s blood.

A range of therapeutic drugs assays are available for the evaluation and/or routine monitoring of anti-epileptic medications such as Carbamazepine, Phenobarbital, Phenytoin and Valproic Acid in addition to Digoxin (used in the treatment of heart conditions); Gentamicin (used to treat a wide range of bacterial infections; and, Lithium (used for the treatment of the manic phase of affective disorders, mania, and manic-depressive illness).

We also have assays for the diagnosis of overdose of Acetaminophen (paracetamol) and Salicylate (Aspirin). In addition our Salicylate assay enables routine monitoring of patients who take a high dose of Salicylate for the treatment of rheumatoid arthritis, osteoarthritis or systemic lupus erythematosus or to treat rheumatic fever of Kawasaki disease; this is important to ensure toxic concentrations are detected on time!

Ask your laboratory for these tests to ensure patients are monitored effectively!

Know when to test a patient’s therapeutic drug levels…

The tests mentioned above should also be sought if a patient is experiencing side effects, if a patient’s health status has changed, if a patient begins taking another medication, if you suspect the patient of non-compliance with their treatment, and, if you suspect an overdose. This is to determine if the dose needs to be adjusted to facilitate therapeutic effects and ensure the patient is safe from toxicity.

Therapeutic drugs have the potential to lead to patient drug addiction!

It is important to note that therapeutic drugs can be addictive due to the physical and mental changes experienced from the drug; the Family Doctor Association suggest that across the UK abuse of sleeping pills, antidepressants and painkillers is increasing. This raises another reason why routine monitoring is so crucial.

If you would like more information or require informative materials for your laboratory please contact us. Alternatively, download our therapeutic drugs monitoring brochure.

Randox offers 9 therapeutic drug testing kits including Acetaminophen, Carbamazepine, Digoxin, Gentamicin, Lithium, Phenobarbital, Phenytoin, Salicylate and Valproic Acid.

Offering approximately 100 tests per kit our reagents are cost-effective and offer various other benefits including:

  • Liquid-ready-to-use reagents for increased convenience
  • Extensive measuring ranges for ultimate detection of ranges outside the therapeutic range
  • Applications for a wide range of analysers to allow flexibility
  • Multi-analyte controls and calibrators to decrease costs
    • Our TDM controls are lyophilised for enhanced stability, 100% human serum providing a matrix similar to the patient sample, and have a reconstituted stability of 4 weeks at 2-8oC reducing waste and helping to keep costs low
  • Strong correlation to reference methods
  • Latex-enhanced immunoturbidimetric method; the majority of our TDM assays use this method to ensure high sensitivity and performance, superior curves and long life (robust under high temperatures)
    • Exceptions are our Lithium colorimetric assay which offers quicker and less expensive testing than traditional ISE/Photometry methods, and our Acetaminophen and salicylate enzymatic assays

To order your TDM test kits visit our online store or contact reagents@randox.com to get in touch with your local sales representative. Alternatively, contact us to request a kit insert or refer to our individual product pages for further information.

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