The role of pharmacists in therapeutic drug monitoring

Pharmacists play a vital role in the detection, prevention, and management of drug-related problems. They are trained to understand the mechanisms of the action of drugs, their pharmacokinetics and pharmacodynamics, and the clinical context in which they are used. This enables them to optimize drug therapy and prevent or resolve drug-related problems.

Therapeutic drug monitoring (TDM) is the process of assessing the response of a patient to medication in order to optimize the drug’s efficacy and safety. It is a key element in the management of patients with chronic conditions, such as cancer, heart disease, and other complications.

The pharmacist’s role in TDM includes assessing the patient’s condition, evaluating the appropriateness of the drug regimen from different sets of medical solutions such as pain medications, and monitoring the patient’s response to the medication. In addition, pharmacists must keep up to date on the latest changes in TDM guidelines and research.

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Drug therapy monitoring

Therapeutic drug monitoring is the process of measuring and interpreting the concentration of blood plasma with the purpose of optimizing clinical outcomes and a patient’s drug therapy while reducing the risk of toxicity. It is most commonly used when the therapeutic window of a drug is narrow and blood concentration levels need to be monitored closely to ensure efficacy and avoid toxicity. The pharmacist tailors a patient’s dose regimen by maintaining the blood or plasma concentration within a specified range.

Here are the three key objectives that should be met in order to achieve optimal drug therapy:

  • Achieving maximum effect in the shortest time possible
  • Attaining desired drug’s pharmacological effect
  • Minimizing the risk of toxicity

Therapeutic drug monitoring is useful in drugs that:

  • Are highly protein-bound
  • Have a narrow therapeutic index
  • Metabolite might be toxic
  • Are liable to interact

Pharmacological principles of TDM

Pharmacological principles are the basic tenets or ideas behind the therapeutic effects of drugs and how they are used in the treatment of disease. They include a basic understanding of how drugs are metabolized and eliminated by the body, as well as how these processes can be affected by other drugs, diseases, and genetic factors. These principles guide the development of new drugs and the testing of their efficacy and safety. They also dictate the uses and dosages of existing drugs.

TDM requires an understanding of the relationship between drug concentration in the blood and the desired therapeutic effect. The goal is to achieve a therapeutic effect without the risk of harm to the patient. Achieving this goal varies with each drug, depending on its lipid solubility, protein binding, and excretion rate.

The following pharmacokinetic factors are used to derive therapeutic drug monitoring guidelines.

  • Patient’s response

The therapeutic effect does not necessarily result in the desired response. For example, about half of patients with low-dose aspirin for primary prevention of stroke who experience a reduction in the incidence of new strokes will experience no change in their risk for cardiovascular disease events. Aspirin therapy is useful for lowering cholesterol; however, it is not useful for lowering the risk of cardiovascular disease.

  • Therapeutic effect

The desired effect of a drug is the goal of any therapy. Most drugs have more than one desired effect, but only one effect is often the primary focus. For example, lowering cholesterol might be the primary goal in treating hypercholesterolemia, while lowering blood pressure is secondary.

  • Cascade drug interactions

When two drugs are given simultaneously, the effects of one might be altered by the other. Drugs that are commonly monitored for interactions include calcium channel blockers, some older antiarrhythmics, and warfarin. In some cases, the interaction between two drugs is synergistic; in others, it is antagonistic.

  • Residual drug

The amount of drug that remains in the blood after the target load is reached (such as a therapeutic dose) is called the residual effect. This term is not used when assessing nontherapeutic effects, such as addiction potential. The need to achieve a specific therapeutic response should be weighed against any residual effect on metabolism and toxic effects.

  • Drug metabolism

The rate at which a drug is metabolized by the body is important because it determines how quickly the drug concentration falls after each dose. It also affects how fast the drug can reach its site of action and exert its effect on enzymes or receptors.

  • Adverse effects

Adverse effects can be caused by drug interactions, drug metabolism, disease progression, and non-compliance. Side effects can also be caused by unsafe storage conditions, which can change the way the drug is metabolized and eliminated. These changes may affect therapeutic response and result in adverse events.

  • Previous treatment history

As with all drugs, therapy should be continued only if there has been no response or a worsening of the symptoms. Previous treatment responses or toxicities may require modification of dosage or other forms of therapy.

Role of pharmacist

A responsive and reliable therapeutic drug monitoring service relies on the teamwork of pharmacists, nurses, and technical staff, among others. Pharmacists assist in the interpretation of results and provide medical advice to medical staff on the appropriate timing and use of TDM. Pharmacists are also involved in:

  • Maintaining supplies of patient-specific TDM specimens
  • Following up with patients to ensure compliance in the collection of samples
  • Acting as a liaison between medical staff and laboratory personnel
  • Providing expert advice on the interpretation of results to medical staff
  • Undertaking risk management activities

The desired response of the drug is the goal of therapy. TDM service is established once the first dose is prescribed, and involves determining the level of drug present in a patient’s blood or plasma to ensure that the desired therapeutic concentration is attained as well as further aspects such as weight, age, and other clinical variables that are complementary with drug therapy.

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