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Lecture 42

Pharmacology 3620 Lecture 42: Lecture 42 Drugs of Abuse

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Pharmacology 3620
Rommel Tirona

42. Drugs of Abuse Why People Abuse Drugs  To Feel Good – To have novel:  To Feel Better – Self-medicating to lessen: o 1. Feelings o Anxiety o 2. Sensations o Worries o 3. Experiences o Fears o Share them o Depression o Hopelessness  Routes of Administration  Generally, drug abusers are looking for a “quick fix”  therefore, routes of administration are important  Typically used routes of administration include: o IV: Blood concentrations increase rapidly (b/c drug goes right into bloodstream) o Inhalation (smoking): By passes first metabolism. Contact with the large vascular bed in the lungs causes increases in blood concentration as rapidly as IV administration, because of fast rates to get to the brain. o Insufflation (snorting): By passes first metabolism. Rate of absorption is higher than inhalation of cocaine, but the intoxication levels are much lower. o Oral  Note: Plasma concentrations: IV > Insufflation > Oral > Inhalation o Intoxication levels: IV > Inhalation > Insufflation > Oral  Paraphernalia: Miscellaneous materials needed for insufflation (bumper), IV (needles), inhalation (bong)  Cocaine  History  Derived from the leaves of the coca plant - native to South America high in the mountains. o The coca leaves were chewed by natives and acted as a stimulant (increase breathing, oxygen intake and reduce appetite)  In late 1886 John Pemberton included cocaine in his new drink “Coca-Cola”. Initial version of Coca-Cola was thought to contain 9 grams of cocaine! Cocaine was removed from the beverage in the early 1900’s. o Nowadays, the stimulating effects of Coca-Cola are caused by caffeine, rather than cocaine.  In the early 1900’s cocaine was used as a local anesthetic and was sold over the counter.  Mechanism  Cocaine predominantly blocks dopamine re-uptake – increased dopamine in CNS causes increased stimulation o Cocaine is not 100% selective for DA; at high doses, cocaine also blocks re-uptake of serotonin and norepinephrine o Therefore, the mechanisms of cocaine are not specific for a particular transporter  Actions  Cocaine causes an acute increase in mental awareness, alertness and causes a general feeling of euphoria.  In the ANS, cocaine potentiates the actions of norepinephrine to induce the fight or flight response. o Cocaine also causes hyperthermia as it impairs sweating. o There is also increased respiratory rate and tachycardia (due to potentiated effects of norepinephrine)  Adverse Effects  Acute adverse effects of cocaine include agitation, paranoia, anxiety, hypertension and tachycardia.  Cocaine addicts will suffer from depression when withdrawing from use.  Long term cocaine use is associated with seizures, and potentially fatal cardiac arrhythmias.  If taken with alcohol, cocaine is metabolized to cocaethylene. o Cocaethylene = active metabolite w/ greater potency against dopamine transporters, less potency against norepinephrine and serotonin transporters. o Cocaethylene is very toxic and thought to contribute to the cardiotoxicity (i.e. poisonous to heart cells) of cocaine.  Crack vs. Cocaine  Cocaine is a white powder and is in the form cocaine hydrochloride (cocaine-HCL)  Crack is the free base form of cocaine. Crack can be made many ways but the most common is by heating a mixture of cocaine, NaHCO3 and water.  The major difference are the melting temperatures: o Cocaine is very unstable at high temperatures. If smoked it burns without effect (i.e. not vaporized). o In contrast, crack vaporizes at 90 C and can therefore be smoked. o Recall that inhalation allows much higher intoxication levels because it can get into the brain quicker  Both crack and cocaine-HCl can be injected IV but cocaine-HCl is water soluble and crack is not. Addicts often use lemon juice or vinegar to dissolve crack prior to injection, which can lead to health problems.  Opioids  Opioids bind to opioid receptors (mui and delta) and are critical in the management of pain.  Repeated use causes tolerance and physical dependence.  Opioid abuse is a major societal issue – both illegal (i.e. heroin) and prescription opioids are abused.  Opioids produce a powerful euphoria. Major side effects include: o Respiratory depression – Leads to death o Nausea o Constipation – People who abuse opioids have dead intestines which no longer contract and cannot move stool along  The relative potency of various opioids is always compared to morphine. E.g. Fentanyl is extremely potent (only a microgram is needed to treat pain), hydromorphone & oxycodone are a bit more potent, while codeine is not potent at all.  The addictive potential of opioids is associated with the fastest rise in brain concentrations. Therefore, more lipophilic opioids have the highest likelihood for abuse. o For example, heroin is just morphine with 2 methyl groups attached, such that it is more lipophilic and can enter the brain easier.  Opioid Pharmacokinetics  The behaviour of someone who uses heroin can be graphed as follows – When doses of opioids are within the red lines, they are in the asymptomatic stage where there is no euphoria or no withdrawal symptoms.  To treat opioid addicts, we want to keep their opioid plasma concentrations at a level within the asymptomatic zone.  The main drug used for this is methadone, an agonist for opioid receptors, which keeps the opioid receptors stimulated. o The half-life of methadone is long compared to heroin, so it is good for maintaining high body concentrations of opioid.  Note that methadone can be abused to get a euphoric high, but when used properly, it keeps people within the asymptomatic region.  Canada’s Opioid Crisis  An increase in therapeutic opioid sales were associated with an increase in opioid-related deaths and treatments.  It is unlikely that people are not currently undergoing more pain, so this increase in opioid sales is not for legitimate reasons (i.e. pain).  In addition, lots of people have been dying from fentanyl overdose – it is a lot cheaper for dealers to cut their opioids with fentanyl.  Oxycontin Controversy  Oxycodone is an opioid used in the treatment of pain.  Percocet contains 2.5 or 5 mg of oxycodone as well as some acetaminophen.  Oxycontin contains only oxycodone (10, 20, 40 or 80 mg) and is slow release. o Percocet relieves pain for 4-5 hours whereas the slow release in oxycontin gives it a 12-14 duration of effect.  The company that markets oxycontin originally advertised it as not addictive because of the slow release formulation.  But when the tablet is crushed, and taken by insufflation, injection or oral, an intense euphoric effect occurs.  Oxycontin is often referred to as Hillbilly Heroin and abuse is a major concern in North America.  Tamper Resistance - Oxyneo  In early 2012, Oxyneo was released in Canada as a replacement for oxycontin.  Oxyneo contains oxycodone but i
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