Therapeutic Drug Levels Normal Lab Values

Monitoring the therapeutic levels of certain medications is often conducted when the patient is taking medications with a narrow therapeutic range where a slight imbalance could be critical. Drug monitoring includes drawing blood samples for peak and trough levels to determine if blood serum levels of a specific drug are at a therapeutic level and not a subtherapeutic or toxic level. The peak level indicates the highest concentration of the drug in the blood serum while the trough level represents the lowest concentration. The following are the normal therapeutic serum medication levels:

• Acetaminophen (Tylenol): 10 to 20 mcg/mL
• Carbamazepine (Tegretol): 5 to 12 mcg/mL
• Digoxin (Lanoxin): 0.5 to 2 ng/mL
• Gentamicin (Garamycin): 5 – 10 mcg/mL (peak); <2.0 mcg/mL (trough)
• Lithium (Lithobid) 0.5 to 1.2 mEq/L
• Magnesium sulfate: 4 to 7 mg/dL
• Phenobarbital (Luminal): 10 to 30 mcg/mL
• Phenytoin (Dilantin): 10 to 20 mcg/mL
• Salicylate: 100 to 250 mcg/mL
• Theophylline: 10 to 20 mcg/dL
• Tobramycin (Tobrex): 5 – 10 mcg/mL (peak); 0.5 – 2.0 mcg/mL (trough)
• Valproic acid (Depakene): 50 – 100 mcg/mL
• Vancomycin (Vancocin): 20 – 40 mcg/mL (peak); 5 – 15 mcg/mL (trough)