Which Medications Require Blood Level Monitoring?

Most medications used to treat mental disorders do not require blood level monitoring. This is mainly due to the inconsistency and heterogeneity of responses to different doses of psychiatric medications.

Only a few medications have sufficient evidence suggesting a therapeutic range and threshold for toxicity. In fact, blood level monitoring is used more for preventing toxicity than ensuring therapeutic efficacy. 

Lithium has a narrow therapeutic index, which means the threshhold for therapeutic effect and toxicity are close together. The normal therapeutic blood level for lithium is between 0.6-1.2.

Valproic acid (Depakote) does not have an agreed upon therapeutic level, but most experts report toxic effects with blood levels over 150.

Clozapine does not require monitoring of drug levels per se, but instead requires repeated neutrophil counts because neutropenia (i.e., low white blood cells) and agranulocytosis are rare yet serious adverse effects of clozapine treatment. 

Below is a table outlining the most common medications requiring blood level monitoring, their recommended therapeutic ranges, and the recommended frequency of monitoring. 

DrugTherapeutic rangeLabs
Antipsychotics ---▪Baseline/yearly: CBC, CMP, Hba1c, TSH, Lipid panel
▪Monitor weight
▪Consider Baseline EKG
▪Yearly AIMS*
Clozapine ---▪Same as above (except CBC scheduling)
▪CBC (ANC) Schedule:
Check at baseline, weekly for 6 months, then biweekly for 6 months, then monthly after 1 year
Lithium▪Acute: 0.8-1.2mEq/L▪Baseline/2-3x per year: CBC, Cr, BUN, TSH, CMP
▪Chronic: 0.50-0.75mEq/L▪Consider baseline EKG in pts >50yo
▪Monitor weight
▪Check Li levels after 4-5 half lives (blood should be collected prior to next dose)
▪Recheck Li levels after dose changes, addition of other drugs, or if suspecting toxicity
Valproic acid▪ 45-125ug/ml▪Baseline/q6-12mos: CBC, LFTs, Electrolytes, TSH
(Manic patients may require/ tolerate higher levels)
Carbamazepine ---▪Baseline: Na, CBC, BUN, Cr, LFTs, TSH
▪Monitor weight
▪Follow CBC and Na q2-4wks for 8 wk then q3-6mos
▪Follow BUN, Cr, LFTs, and TSH q6-12mos
SNRIs, Bupropion, TCAs, MAOIs---▪Monitor blood pressure & HR

*(—) No definitive evidence correlating levels with efficacy 

Lithium Level Monitoring

Lithium MonitoringTarget Lithium LevelRecommended Labs
Acute Mania0.8-1.2mEq/LBaseline: CBC, CMP, Cr, BUN, TSH, Weight, EKG (in pts>50yo or with cardiac disease)
Maintenance0.6-1.0 mEq/LAfter 1 week, 1 month, 6 months, and 12 months of starting lithium: Lithium Level, TSH, BUN/Cr, Electrolytes, monitor weight
Every 6-12 months: Lithium Level, TSH, BUN/Cr, Electrolytes, monitor weight
NOTE: Check Lithium levels after 4-5 half lives (blood should be collected prior to next dose); Also check lithium levels after dosage changes, addition of other drugs, or if suspecting toxicity

Clozapine & Absolute Neutrophil Count (ANC) Monitoring

References

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