Phencyclidine Confirmation, Meconium
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Phencyclidine (PCP) was originally developed as an anesthetic in the 1950s but later was abandoned because of a high frequency of postoperative delirium with hallucinations. It was classed as a dissociative anesthetic because, in the anesthetized state, the patient remains conscious with staring gaze, flat facies, and rigid muscles.(1) PCP binds with high affinity to sites located in the cortex and limbic structures, resulting in blocking of N-methyl-D-aspartate (NMDA)-type glutamate receptors.(1) PCP became a drug of abuse in the 1970s because of its hallucinogenic effects.(1,2)
PCP is approximately 65% protein bound and has a volume of distribution (Vd) of 5.3 to 7.5 L/kg. The drug is metabolized by the liver via oxidative hydroxylation and has a dose-dependent half-life ranging from 7 to 46 hours.(2)
Meconium is the first fecal material passed by the neonate. Meconium forms in the first trimester of pregnancy but is seldom excreted before the 34th week. It is composed of approximately 70% water, bile acids, cholesterol, squamous cells, protein and drug metabolites, and no bacteria are normally present. Prebirth excretion of meconium is a sign of fetal distress.
Because drugs and metabolites can accumulate in meconium, assessment of meconium for the presence of illicit drugs can be an indicator of maternal drug use during pregnancy. Illicit drug use during pregnancy can have a profound effect on fetal development.
The disposition of drug in meconium is not well understood. The proposed mechanism is that the fetus excretes drug into bile and amniotic fluid. Drug accumulates in meconium either by direct deposit from bile or through swallowing of amniotic fluid.(3) The first evidence of meconium in the fetal intestine appears at approximately the 10th to 12th week of gestation, and slowly moves into the colon by the 16th week of gestation.(4) Therefore, the presence of drugs in meconium has been proposed to be indicative of in utero drug exposure during the final 4 to 5 months of pregnancy, a longer historical measure than is possible by urinalysis.(3)
Detection of in utero drug exposure up to 5 months before birth
The presence of phencyclidine in meconium is indicative of in utero drug exposure up to 5 months before birth.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Because the results of this test may have legal ramifications, it is recommended that testing be performed using chain of custody. A kit including all the materials necessary to complete chain of custody is available to ensure the test results are appropriate for legal proceedings.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Positives are reported with a quantitative LC-MS/MS result.
PCP by LC-MS/MS: >10 ng/g
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. O'Brien CP: Drug addiction and drug abuse. In Goodman and Gilman's the Pharmacological Basis of Therapeutics. 11th edition. Edited by LL Brunton, JS Lazo, KL Parker. McGraw-Hill Book Company, Inc, 2006
2. Baselt RC: Phencyclidine. In Disposition of Toxic Drugs and Chemicals in Man. Eighth edition. Edited by RC Baselt. Foster City, CA, Biomedical Publications, 2008, pp 1735
3. Ostrea EM Jr, Brady MJ, Parks PM, et al: Drug screening of meconium in infants of drug-dependent mothers: an alternative to urine testing. J Pediatr 1989 Sep;115(3):474-477
4. Ahanya SN, Lakshmanan J, Morgan BL, Ross MG: Meconium passage in utero mechanisms, consequences, and management. Obstet Gynecol Surv 2005 Jan;60(1):45-56; quiz 73-74