How does the route of administration affect cocaine toxicity?

Updated: Sep 01, 2018
  • Author: Lynn Barkley Burnett, MD, EdD, LLB(c); Chief Editor: Sage W Wiener, MD  more...
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Answer

Cocaine enters the United States in the form of a hydrochloride salt, having undergone numerous steps in refinement from the original coca leaf. In its hydrochloride form, cocaine may be absorbed topically across all mucosal membranes, including the oral, nasal, GI, rectal, urethral, and vaginal membranes. It may also be injected intravenously or ingested. Ingested cocaine is poorly absorbed from the stomach because it is a weak base with a pKa of 8.6, but it is readily absorbed from the duodenum. Cocaine may be inhaled through a straw or rolled-up paper currency, or snorted from a coke spoon, typically containing 5-20 mg of the drug. A 1-inch line typically contains 25-100 mg of the drug.

Crack is produced when the hydrochloride molecule is removed by ether extraction, which frees the basic cocaine molecule, or "freebase". Heating does not destroy freebase, rather it melts at 98°C and vaporizes at higher temperatures. These physical properties allow it to be smoked.

Crack is lipid soluble and therefore rapidly absorbed in the pulmonary capillaries. The term crack describes the crackling sound heard when cocaine freebase is smoked. Crack may be smoked in a pipe bowl containing 50-100 mg or in a cigarette with as much as 300 mg. Smoking crack bypasses the vasoconstriction that results when cocaine is snorted; therefore, the effects are similar to taking cocaine intravenously. Crack smokers may aggressively inhale against a small pipe and then perform a Valsalva maneuver before exhaling against pursed lips or forcefully blow the drug into a partner's mouth. These techniques are reputed to enhance the euphoria of cocaine.

Table 1. Onset of Effects, Peak Effects, Duration of Euphoria, and Plasma Half-Life by Routes of Administration (Open Table in a new window)

Route

Onset

Peak Effect (min)

Duration (min)

Half-Life (min)

Inhalation

7 s

1-5

20

40-60

Intravenous

15 s

3-5

20-30

40-60

Nasal

3 min

15

45-90

60-90

Oral

10 min

60

60

60-90

All of the cocaine injected intravenously is delivered to the circulatory system, versus 20-30% of cocaine that is ingested or inhaled. With repeated use, tolerance develops so that the intensity and duration of effect decrease. People who use cocaine long term may dose themselves as frequently as every 10 minutes, binge as long as 7 days at a time and use as much as 10 g/d. Reverse tolerance, with onset of seizures and paranoid ideation at decreased doses, has been observed in animals and is thought to occur in humans as well.


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