Laboratory Studies
In general, routine laboratory workup in patients who present with toxicity involving phenylcyclohexyl piperidine (PCP), also known as phencyclidine, should be focused on the following:
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Renal function
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Fluid balance
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Electrolyte abnormalities
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Lactic acidosis
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Serum creatine phosphokinase (CPK) level
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Urine myoglobin level
Quantitative laboratory analysis is generally not very helpful because serum and urine levels do not reflect the drug's vast lipid storage, nor does the precise serum concentration correlate with the clinical effect. Results of toxicologic urine screening may remain positive for several weeks because of PCP's large volume of distribution.
Qualitative plasma or urine levels may help establishing the diagnosis but should be interpreted with care. Urine screening for PCP should be part of the diagnostic workup in children and infants presenting with acute dystonic reactions. [20]
Ketamine levels, as well as norketamine levels, can be determined in urine; however, these specific tests are generally not readily available and are not clinically useful. PCP may cross-react with ketamine assays.
Diphenhydramine and dextromethorphan (which are also frequently abused N-methyl-D-aspartate [NMDA] receptor antagonists) can produce false-positive urine drug screens for PCP because of their similar chemical structures.
Other useful tests to determine the presence of rhabdomyolysis, renal dysfunction, and hypoglycemia include measurements of electrolytes, glucose, BUN, creatinine, and total creatine kinase levels, as well as a urinalysis (myoglobin). An arterial blood gas (ABG measurement may be indicated to assess the occurrence of metabolic acidosis and hypoxemia. A urine pregnancy test is indicated in female patients of childbearing age.
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Phenylcyclohexyl piperidine (PCP), also known as phencyclidine, in tablet form. Image courtesy of the US Drug Enforcement Administration.
