Immunoassay screen for qualitative detection of PCP in urine.

Phencyclidine (PCP) was originally made available as a surgical anesthetic agent, but it was removed from clinical use due to undesirable side effects both during surgery and in recovery. The illicit use of the drug produces clinical symptoms ranging from confusion, disorientation, stupor, coma, and death in cases of overdose. The PCP screening assay is based on the competition of a drug labeled with enzyme, glucose-6- phosphate dehydrogenase (G6PDH), and the drug from the urine sample for a fixed amount of specific antibody binding sites. 

In the absence of the drug from the sample, the specific antibody binds the drug labeled with G6PDH and the enzyme activity is inhibited. This phenomenon creates a direct relationship between the drug concentration in urine and the enzyme activity. The G6PDH activity is determined spectrophotometrically at 340 nm by measuring its ability to convert nicotinamide adenine dinucleotide (NAD) to NADH.