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Unit Code 80339:
Haloperidol, Serum

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Useful For

Optimizing dosage, monitoring compliance, and assessing toxicity

Clinical Information

Haloperidol (Haldol) is a member of the butyrophenone class

of neuroleptic drugs used to treat psychotic disorders (e.g.,

schizophrenia).  It is also used to control the tics and verbal utterances

associated with Tourette's syndrome and in the management

of intensely hyperexcitable children who fail to respond to other

treatment modalities.

 

The daily recommended oral dose for patients with moderate symptoms

is 0.5-2.0 mg; for patients with severe symptoms, 3-5 mg may be used.

However, some patients will respond only at significantly higher doses.

 

Haloperidol is metabolized in the liver to reduced haloperidol, its major

metabolite (1,2).

 

Use of haloperidol is associated with significant toxic side

effects, the most serious of which include tardive dyskinesia which

can be irreversible, extrapyramidal reactions with Parkinson-like

symptoms, and neuroleptic malignant syndrome.  Less serious side

effects can include hypotension, anticholinergic effects (blurred vision,

dry mouth, constipation, urinary retention), and sedation.  The risk of

developing serious, irreversible side effects seems to increase with

increasing cumulative doses over time (1,3).

Reference Values

HALOPERIDOL

      5-16 ng/mL

REDUCED HALOPERIDOL

      10-80 ng/mL

Interpretation

Studies show a strong relationship between dose and blood serum

concentration (4); however, there is a modest relationship of clinical

response or risk of developing long-term side effects to either dose

or serum concentration.

 

A therapeutic window exists for haloperidol;

patients who respond at serum concentrations between 5-16 ng/mL

show no additional improvement at concentrations >16-20 ng/mL

(3,5).  Some patients may respond at concentrations <5 ng/mL, and

others may require concentrations significantly >20 ng/mL before an

adequate response is attained.

 

Because of such inter-individual variation, the serum concentration

should only be used as 1 factor in determining the appropriate dose

and must be interpreted in conjunction with the clinical status.

 

Although the metabolite, reduced haloperidol, has minimal

pharmacologic activity, evidence has been presented suggesting that

an elevated ratio of reduced haloperidol-to-haloperidol (i.e., >5) is

predictive of a poor clinical response (3,6). A reduced haloperidol-

to-haloperidol ratio <0.5 indicates noncompliance; the metabolite does

not accumulate except during steady-state conditions.

Cautions

Potentially interfering drugs include hydroxyzine (interferes with

haloperidol), tiagabine (interferes with reduced haloperidol),

and quetiapine (interferes with internal standard resulting in

artificially low haloperidol).

Clinical Reference

1.   Lawson GM:  Monitoring of serum haloperidol. Mayo Clin Proc

      1994;69:189-190

2.   Ereshefsky L, Davis CM, Harrington CA, et al: Haloperidol and

      reduced haloperidol plasma levels in selected schizophrenic

      patients. J Clin Psychopharmacol 1984;4:138-142

3.   Volavka J, Cooper TB: Review of haloperidol blood level and

      clinical response: looking through the window. J Clin Psycho-

      pharmacol 1987;7:25-30

4.   Moulin MA, Davy JP, Debruyne JC, et al:  Serum level monitoring

      and therapeutic effect of haloperidol in schizophrenic patients.

      Psychopharmacology 76:346-350, 1982

5.   Van Putten T, Marder SR, Mintz J, Polant RE:  Haloperidol plasma

      levels and clinical response: a therapeutic window relationship.

      Am J Psychiatry 1992;149:500-505

6.   Shostak M, Perel JM, Stiller RL, et al: Plasma haloperidol and

      clinical response: a role for reduced haloperidol in antipsychotic

      activity?  J Clin Psychopharmacol 1987;7:394-400

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