Toxicology: Practice Question

An individual tests positive for PCP during a pre-employment drug screen. A follow up questionnaire reveals he is taking which of the following drugs that cross reacts with the PCP enzyme immunoassay?
  1. Dextromethorphan
  2. Sertraline
  3. Phenytoin
  4. Amitriptyline
  5. Pseudoephedrine
Show Answer and Explanations

Dextromethorphan — Correct answer

Correct. Dextromethorphan is commonly used as a cough suppressant and is available over-the-counter. It reacts with PCP EIA antibodies.

Sertraline

Incorrect. Sertraline reacts with benzodiazepine and LSD EIA antibodies.

Phenytoin

Incorrect. Phenytoin reacts with barbiturate EIA antibodies.

Amitriptyline

Incorrect. A number of drugs cross react with LSD EIA antibodies, including amitriptyline, sertraline, verapamil and metoclopramide.

Pseudoephedrine

Incorrect. Many drugs cross react with amphetamine EIA antibodies, including ephedrine, pseudoephedrine and phenylephrine found in decongestants and diet pills, as well as propranolol, bupropion and trazodone.

Summary

Summary: Dextromethorphan can cause a false positive PCP on drug screen. Sertraline can cause a false positive benzodiazepine and/or LSD on drug screen. Phenytoin can cause a false positive barbiturate on drug screen.
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