Therapeutic Drug Levels in Bipolar Disorder Treatment

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The therapeutic level of a drug in the bloodstream is the range within which that drug is expected to be effective. Your doctor can request a test to measure the amount of a specific drug in the serum portion of your blood. Your doctor will check those levels against established ranges for that drug to determine if the value is therapeutic or not.

Medication Dosage and Administration

The most important bipolar disorder drugs to be monitored regularly include the following mood stabilizers and tricyclic antidepressant:

The therapeutic levels of these drugs are dependent upon the half-life of the drugs as determined by the serum blood test. After test results are taken, proper dosage and administration of these mood stabilizers can commence. After your blood test is administered, usually by a phlebotomist in a lab setting, your results will be shared with your doctor who will determine if the amount of medication and the frequency with which you take them should be changed.

The goal is to maintain a "steady state" of drugs in your system, which will give you a therapeutic or effective dose of the medication without causing side effects or otherwise not working.

If your medication dosage is off you could experience symptoms that include mood swings or manic episodes, the very thing your psychoactive drugs are meant to prevent.

How Long Does It Take to Reach Therapeutic Levels?

From your serum blood test, your medical provider should be able to determine how many hours or days it will take for the medicine to reach therapeutic levels. While some medications have a half-life of only 1-4 hours, such as acetaminophen, some mood stabilizers have a half-life of 1-2 days. The longer the half-life of the drug, the longer it will take to reach a therapeutic level, i.e. for the drug to take effect.

While Tegretol (carbamazepine) has a variable half-life (initial half-life values range from 25-65 hours, decreasing to 12-17 hours on repeated doses), it also causes auto-induction of metabolism, so an initially therapeutic blood level can drop and that is why serum levels need to be followed more frequently initially with this medication.

Your doctor will explain how long it will take for your medicine to work, but you must work with him or her to ensure that you take the medication at the recommended dosage at the right time. Because of the long half-life, maintaining therapeutic levels takes attention to detail and focus, something that may be hard to maintain for those with bipolar disorders.

As you and your family members work through your diagnosis, be sure to keep track of your medications and have someone equally accountable for you so that you don't miss a dose and render your medication ineffective, or worse risk too much medication in your blood, which could be toxic.

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  • Medline Plus Medical Encyclopedia. Therapeutic drug levels. US National Library of Medicine and National Institutes of Health. 24 Aug 2009.

By Marcia Purse
Marcia Purse is a mental health writer and bipolar disorder advocate who brings strong research skills and personal experiences to her writing.