Therapeutic  drug monitoring (TDM) is the practice of determining the concentration of the drugs in the plasma, blood, or serum at pre-defined intervals. The information is used to individualize dosage and maintain the optimum drug levels in the patient’s body. For diagnostic and treatment purposes, the drug concentration can also be determined from other body fluids such as saliva, urine, and sweat.

In some cases, drug metabolism varies from one patient to another. For example, concentration-dependent drugs with a very narrow target range have inter-individual variations. The TDM information helps, in this case, to manage dosage regimen and improve the clinical effect of the drugs.

Why is Therapeutic Drug Monitoring Important?

The primary aim of therapeutic drug monitoring is to help design the specific dosage regimen for the patient. Other benefits include helping to enhance the efficiency of drugs, reducing the toxicity of drugs, and other diagnostic purposes. Therapeutic Drug Monitoring can be used in conjunction with traditional clinical reasoning to optimize medical outcomes and overall patient management.

Which drugs require Therapeutic Drug Monitoring?

When an individual experiences effects such as pain or changes in blood pressure after administration of medication, the dose of the drugs must be adjusted based on the response. The drug concentration in the blood should also be monitored, especially when used to prevent adverse outcomes such as toxicity or graft rejection. The drugs should satisfy the following criteria to qualify for therapeutic drug monitoring:

• Significant pharmacokinetic variability
• Narrow target range
• The established target concentration range
• The established relationship between clinical effects and plasma concentrations

The most common monitored drugs are valproate, carbamazepine, and digoxin.

Information required for Therapeutic Drug Monitoring

• The clinical condition of the patient
• Purpose of TDM, i.e., whether for toxicity, efficacy, or diagnostic purposes.
• Pharmacokinetics of the drug
• Dosage regimen
• Clinical history of the patient relating to the recent therapeutic responses
• Sampling time
• Patient’s clinical responses

Indications for Therapeutic Drug Monitoring

Most drug essay methods are costly. Thus, it is prudent to understand the benefits of TDM. For most drugs, TDM helps to minimize toxicity, increase efficacy, and diagnose medications. However, routine drug monitoring is not advocated for most drugs, apart from those with meaningful clinical tests.

The appropriate indications for drug monitoring include:

1.    Toxicity

• Avoiding toxicity, especially for aminoglycosides or cyclosporine
• Toxicity diagnosis, particularly for the undifferentiated clinical syndrome

2.    Dosing

• Assessment of patient’s adequate loading dose
• After dose adjustment, especially when a steady-state has been reached
• Forecasting the patient’s dose to predict the dose requirements

3.    Monitoring

• Diagnosing failed therapy (TDM can help distinguish between non-compliance, ineffective, and adverse effects which show similar characteristics to the underlying disease)
• Diagnosing under treatment, especially with prophylactic drugs like immunosuppressants and anticonvulsants
• Assessing compliance, especially anticonvulsant concentrations for individuals with frequent seizures

The target drug concentration depends on indications. For instance, the target concentration for digoxin largely depends on whether it is aimed at treating congestive heart failure or atrial fibrillation.

Therapeutic drug monitoring assists in individualizing doses, detecting toxicity to improve clinical outcomes, and optimizing patient management. Contact us today at Tesis Biosciences to learn why therapeutic drug monitoring should be part of your standard of care.

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