Should adults on antidepressants, such as Monoamine Oxidase Inhibitors (MAOIs) or Tricyclic Antidepressants (TCAs), or Selective Serotonin Reuptake Inhibitors (SSRIs), have regular bloodwork done?

Bloodwork Monitoring for Adults on Antidepressants

Routine bloodwork monitoring is not universally recommended for all adults on antidepressants, but is strongly indicated for specific antidepressant classes (TCAs, MAOIs) and in certain clinical situations. 1

Recommendations by Antidepressant Class

Tricyclic Antidepressants (TCAs)

• Therapeutic drug monitoring (TDM) is strongly recommended for TCAs due to their narrow therapeutic window and risk of potentially lethal toxicity 1
• Plasma level monitoring helps avoid intoxications and optimize dosing to achieve therapeutic levels 1
• TDM is particularly valuable for TCAs in cases of inadequate response, toxicity concerns, or suspected poor compliance 2
• Monitoring is especially important in elderly patients due to higher risk of cardiovascular effects and higher plasma concentrations of active metabolites 3

Monoamine Oxidase Inhibitors (MAOIs)

• While a clear plasma level-clinical effectiveness relationship has not been established for MAOIs, TDM may still be useful in situations of noncompliance, nonresponse, adverse effects, or suspected intoxication 1
• Monitoring can help identify potential drug interactions, which are particularly dangerous with MAOIs 1

Selective Serotonin Reuptake Inhibitors (SSRIs)

• Routine TDM is not generally required for SSRIs but can be cost-effective as it helps determine minimum effective doses 1
• Blood monitoring may be useful in specific situations such as nonresponse, adverse effects, or suspected noncompliance 1

Specific Clinical Scenarios Requiring Bloodwork

Age-Related Considerations

• Older Adults (>65 years):

  • Monitoring is recommended due to age-related changes in pharmacokinetics 1
  • Particularly important when SSRIs are used in older adults due to increased risk of upper gastrointestinal bleeding, which rises significantly with age (from 4.1 hospitalizations per 1000 adults aged 65-70 years to 12.3 per 1000 octogenarians) 1
  • Liver function tests are particularly important in elderly patients as hepatic adverse events have been reported, though rarely 3

• Children and Adolescents:

  • TDM is generally indicated for all psychotropic medications in this population due to developmental differences in pharmacokinetics 1

Medical Conditions

• Hepatic Impairment:

  • Bloodwork monitoring is recommended for patients with liver disease, especially when using antidepressants that undergo significant hepatic metabolism 4
  • Regular liver function tests are recommended, particularly for TCAs 3

• Concomitant Medications:

  • Blood monitoring is important when antidepressants are used with medications that inhibit cytochrome P450 2D6 (including other antidepressants, phenothiazines, and certain antiarrhythmics) 3
  • Particularly important when SSRIs are used with NSAIDs due to significantly increased bleeding risk (adjusted OR: 15.6 [CI, 6.6 to 36.6]) 1

Special Populations

• Pregnant or Lactating Women:

  • Antidepressants should be monitored to minimize drug exposure to the fetus or infant 1

• Patients with Treatment Resistance:

  • Blood level monitoring can help determine if nonresponse is due to inadequate dosing or pharmacokinetic factors 1

Monitoring Parameters and Frequency

• For TCAs:

  • Plasma drug concentrations should be measured to ensure levels fall within established therapeutic windows 1
  • Cardiovascular function, particularly arrhythmias and blood pressure fluctuations, should be monitored in elderly patients 3

• For SSRIs:

  • Monitoring for gastrointestinal bleeding risk is important, especially in older adults or those on concomitant NSAIDs 1
  • Monitoring for hyponatremia is recommended, particularly within the first month of treatment in older adults 1

• For all antidepressants:

  • Consider monitoring for suicidality, particularly in the first month of treatment when risk is highest 1
  • Blood levels should be checked when switching between brand name and generic formulations, though evidence for significant pharmacokinetic differences is limited 1

Common Pitfalls and Caveats

• Relying solely on blood levels without clinical correlation can lead to inappropriate treatment decisions; therapeutic windows should be interpreted in the context of the clinical situation 1
• Failure to monitor drug interactions, particularly with medications that affect cytochrome P450 enzymes, can lead to unexpected toxicity or treatment failure 3
• Not considering pharmacogenetic factors that affect drug metabolism can result in unexpected blood levels; combining pharmacogenetic testing with TDM may be beneficial in certain cases 1
• Overlooking the need for monitoring in special populations (elderly, children, pregnant women) where pharmacokinetics may differ significantly from the general adult population 1