A medicine blood level test that measures how much of your medicine is in your blood. We check it to make sure that pets are taking a safe and effective dose of anything that we prescribe them. This testing is called therapeutic drug monitoring.
Therapeutic Drug Monitoring - TDM
Therapeutic drug monitoring is the measurement of specific drugs and/or their breakdown products (metabolites) at timed intervals to maintain a relatively constant concentration of the medication in the blood. Some of the monitored drugs tend to have a narrow "therapeutic index," which is a ratio between the toxic and therapeutic (effective) dose of medication.
As soon as a drug enters the body, different processes start removing the drug from the body. The amount of time it takes for the body to reduce the drug concentration to half from the initial value is called a half-life of the drug. It generally takes around five half-lives to remove a drug completely from the body.
Generally, a pet must be given a drug dose at regular intervals to ensure that the effective or the therapeutic concentration of the drug is maintained in the body. For some drugs, maintaining this steady state is not as simple as giving a standard dose of medication. Each pet will absorb, metabolize, utilize and eliminate drugs at different rates based upon their age, general state of health and genetic makeup. The drug concentration in the body may be enhanced or decreased by the interference of other medications that you may be taking along with the drug which has to be motioned. This is also known as drug-drug interaction.
Many of the drugs that require therapeutic monitoring are taken for a lifetime. They must be maintained at steady concentrations year after year while the pet ages and goes through life events that may alter that pet's therapeutic level. Over time, pets may acquire other chronic conditions that also require lifetime medication and that may affect the processing of their monitored drugs.
Therapeutic drug monitoring follows these changes and accommodates them. It identifies when a pet does not take the medication regularly as prescribed (patient noncompliance) and the effect of drug interactions, which may cause drug concentrations that are higher or lower than expected at a given dosage, and helps to personalize a dose to fit the specific needs of a patient. Along with tests such as BUN, creatinine, and liver function tests, therapeutic drug monitoring can help identify decreases in the efficiency of and dysfunctions in the body's ability to metabolize and eliminate therapeutic drugs. Testing may also determine how a medication interacts with other necessary drugs.