Phencyclidine

Phencyclidine (a contraction of the chemical name phenylcyclohexylpiperidine), abbreviated PCP, is a dissociative drug formerly used as an anesthetic agent, exhibiting hallucinogenic and neurotoxic effects. It is commonly known as Angel Dust.

PCP was commercially developed in the 1950s by the Parke-Davis pharmaceutical company. PCP is listed as a Schedule II drug in the United States under the Convention on Psychotropic Substances.

Chemistry and pharmacology
Chemically PCP is an arylcyclohexylamine derivative, and pharmacologically, it is a member of the family of dissociative anesthetics. PCP works primarily as an NMDA receptor antagonist which blocks the activity of the NMDA Receptor. Other NMDA receptor antagonists include ketamine, tiletamine, and dextromethorphan. Although the primary psychoactive effects of the drug only last hours, total elimination from the body is prolonged, typically extending over weeks.

More than 30 different analogues of PCP were reported as being sold on the street during the 1970s and 1980s, mainly in the USA. The best known of these were PCPy (Rolicyclidine, 1-(1-phenylcyclohexyl)pyrrolidine); PCE (Eticyclidine, N-ethyl-1-phenylcyclohexylamine); and TCP (Tenocyclidine, 1-(1-(2-Thienyl)cyclohexyl)piperidine). These compounds were never widely used and did not seem to be as well accepted by users as PCP itself, however they were all added onto Schedule I of the Controlled Substance Act because of their presumably similar effects.

The generalised structural motif required for PCP-like activity is derived from structure-activity relationship studies of PCP analogues and summarised below. All of these analogues would presumably have somewhat similar effects to PCP itself, although with a range of potencies and varying mixtures of anaesthetic, dissociative and stimulant effects depending on the particular substituents used. In some countries such as the USA, Australia and New Zealand, all of these compounds would be considered controlled substance analogues of PCP and are hence illegal drugs, even though many of them have never been made or tested.



Danger
Like other NMDA Receptor Antagonists, it is postulated that phencyclidine can cause a certain kind of brain damage called Olney's Lesions. Studies conducted on rats have shown that high doses of the NMDA receptor antagonist MK-801 caused vacuoles to form in certain regions of test rats' brains, and experts say that it is possible that similar brain damage can occur in humans.

Medical and veterinary use
PCP was first tested after World War I as a surgical anesthetic. Because of its adverse side-effects, it was shelved until the 1950s. It was then patented by Parke-Davis and named Sernyl (supposedly referring to serenity), but was again withdrawn from the market because of side effects. It was soon renamed Sernylan, and marketed as a veterinary anaesthetic, but again discontinued. Its side effects and long half-life in the human body made it unsuitable for medical applications.

Some PCP-like drugs have multiple targets but are also used, by virtue of their PCP-like effects, as antitremor drugs (procyclidine, biperiden, trihexphenidyl) in the symptomatic treatment of Parkinson's disease. They have side effects similar to those of PCP, the severity generally correlating with the efficacy of the drug in inhibiting NMDA receptors.

PCP is retained in fatty tissue and is broken down by the human metabolism into PCHP, PPC and PCAA. When smoked, some of it is broken down by heat into 1-phenyl-1-cyclohexene (PC) and piperidine.



Recreational use
PCP is consumed in a recreational manner mainly in the United States, where the demand is met by illegal production. It comes in both powder and liquid forms (PCP base dissolved most often in ether), but typically it is sprayed onto leafy material such as marijuana, mint, oregano, parsley or Ginger Leaves, and smoked. It is sometimes taken with Ecstasy &mdash; a practice known as "elephant flipping". PCP is a Schedule II substance in the United States and a Class A substance in Great Britain.

Biochemical action
The N-methyl-D-Aspartate (NMDA) receptor, a type of ionotropic receptor, is found on the dendrites of neurons and receives signals in the form of neurotransmitters. It is a major excitatory receptor in the brain. Normal physiological function requires that the activated receptor fluxes positive ions through the channel part of the receptor. PCP enters the ion channel from the outside of the neuron and binds, reversibly, to a site in the channel pore, blocking the flux of positive ions into the cell. PCP therefore inhibits depolarization of neurons and interferes with cognitive and other functions of the nervous system.

Similarly, PCP and analogues also inhibit nicotinic acetylcholine receptor channels (nAChR). Some analogues have greater potency at nAChR than at NMDAR. In some brain regions these effects act synergistically to inhibit excitatory activity.

Method of absorption


The term "embalming fluid" is often used to refer to the liquid PCP which a cigarette or joint is dipped in, to be ingested through smoking. Smoking PCP is known as "getting wet." There is much confusion over the practice of dipping cigarettes in "embalming fluid" leading some to think that real embalming fluid may actually be used. This is a misconception that may cause serious health consequences beyond those of consuming PCP.

In its powder form, PCP can be insufflated.

In its pure form, PCP is a white crystalline powder that readily dissolves in water. However, most PCP on the illicit market contains a number of contaminants as a result of makeshift manufacturing, causing the color to range from tan to brown, and the consistency to range from powder to a gummy mass.

Effects
PCP has potent effects on the nervous system altering perceptual functions (hallucinations, delusional ideas, delirium or confused thinking), motor functions (unsteady gait, loss of coordination, and disrupted eye movements or nystagmus), and autonomic nervous system regulation (rapid heart rate, altered temperature regulation). The drug alters mood states in an unpredictable fashion causing some individuals to become detached and others to become animated. Intoxicated individuals may act in an unpredictable fashion driven by their delusions or hallucinations. Included in the portfolio of behavioral disturbances are acts of self injury including suicide, and attacks on others or destruction of property. Unfortunately the anesthetic properties of the drug cause violent individuals to feel less pain at the time and persist in violent or injurious acts as a result. Recreational doses of the drug induce a psychotic state that resembles schizophrenic episodes.

Police and firefighters often consider individuals under the influence of PCP to be highly dangerous and unpredictable; members of the Los Angeles Police Department justified their use of violent force against Rodney King by claiming he appeared to be under the influence of the drug.

In popular culture, a widespread mythology has developed around PCP use, often attributing superhuman strength and self-mutilation to the effects of PCP consumption; for example the abnormal strength and actions of robots in the Terminator movies and vampires in Buffy the Vampire Slayer are written off by authorities as those of PCP junkies.