A-Textbook-of-Clinical-Pharmacology-and-Therapeutics-5th-edition

434 DRUGS AND ALCOHOL ABUSE
• Drug availability and economic factors: Rates of dependence
are increased if a drug is easily available. This may
explain why dependence on nicotine and alcohol is a
much greater public health problem than dependence on
illegal drugs, because of their greater availability. Drug
use is sensitive to price (e.g. rates of alcoholism are
reduced by increasing alcohol prices).
• Biochemical reinforcement: Drugs of abuse and
dependence have a common biochemical pathway:
they all increase dopamine in the nucleus accumbens,
associated with mood elevation and euphoria.
Behaviourally, this is linked with reinforcement of drugtaking.
Dependence-potential of different drugs is related
to potency in releasing dopamine (cocaine is most potent).
The rate of dopamine release is also important, e.g.
smoked and intravenous drugs give a more rapid effect
than oral drugs.
GENERAL PRINCIPLES OF TREATING
ADDICTIONS
By the time an addict presents for assessment and treatment,
he or she is likely to have diverse and major problems. There
may be physical or mental illness, and emotional or attitudinal
problems, which may have contributed to the addiction
and/or resulted from it. Their financial and living circumstances
may have been adversely affected by their drug habit
and they may have legal problems relating to drug possession,
intoxication (e.g. drink–driving offences), or criminal activities
carried out to finance drug purchases. Attitudes to drug
use may be unrealistic (e.g. denial). The best chance of a successful
outcome requires that all of these factors are considered,
and the use of a wide range of treatment options is
likely to be more successful than a narrow repertoire.
Treatment objectives vary depending on the drug.
Complete abstinence is emphasized for nicotine, alcohol or
cocaine addiction, whereas for heroin addiction many patients
benefit from methadone maintenance. Other objectives are to
improve the health and social functioning of addicted patients.
Treatment success can only be determined over a long time,
based on reduction in drug use and improvements in health
and social functioning. A treatment programme should
include medical and psychiatric assessment and psychological
and social support. Addicts should be referred to specialist
services if these are available. Other services based in the voluntary
sector (e.g. Alcoholics Anonymous) are also valuable
and complementary resources. Medical and psychiatric assessment
may need to be repeated once the patient is abstinent, as
it is often difficult to diagnose accurately certain disorders in
the presence of withdrawal symptoms (e.g. anxiety, depression
and hypertension are features of alcohol withdrawal, but are
also common in abstinent alcoholics).
The pharmacological treatment of addictions, which includes
treatment of intoxication, detoxification (removal of the drug
from the body, including management of withdrawal symptoms)
and treatment to prevent relapse, is discussed below.
Table 53.1: Opioid drugs that are commonly abused
Drugs
Diamorphine a
Methadone
OPIOID/NARCOTIC ANALGESICS
Diamorphine (‘heroin’) is preferred by most opioid addicts.
It is often adulterated with other white powders, such as quinine
(which is bitter, like opiates), caffeine, lactose and even
chalks, starch and talc. Due to the variable purity, the dose
of black-market heroin is always uncertain. The drug is
taken intravenously, subcutaneously, orally or by inhalation of
smoked heroin. In addition to the illegal supply of heroin from
Afghanistan and elsewhere, opioids are obtained from pharmacy
thefts and the legal prescription of drugs for treatment of
the addiction. Some of the drugs used are listed in Table 53.1.
The pharmacological actions of opioids are described in
Chapter 25 and their effects on the central nervous system
(CNS) are summarized in Table 53.2.
MEDICAL COMPLICATIONS
Comment
Mainly obtained on the black market. It is of
variable purity and cut with quinine, talc,
lactose, etc. It is usually mixed with water,
heated until dissolved, and sometimes
strained through cotton. It may be used
intravenously (mainlining), subcutaneously
(skin popping) or inhaled (‘snorted’/
’chasing the dragon’, by heating up on foil
and inhaling the smoke) (t 1/2 60–90 min)
This is the mainstay of drug addiction clinics,
and is usually given as an elixir (long t 1/2
of 15–55 h). It is very difficult to use elixir
for injection
Dipipanone Previously much used by non-clinic doctors
( cyclizine treating addicts. It is easily crushed up and
Diconal®) a dissolved for intravenous use
Other opoids
All opioids, including mixed
agonists/antagonists (e.g. buprenorphine)
have the potential to cause dependence
a Diamorphine, dipipanone and cocaine (not an opioid) can only be
prescribed to addicts for treatment of their addiction by doctors with a
special licence.
Medical complications of opioid addiction are common and
some of them are listed in Table 53.3. The majority of these
relate to use of infected needles, the effects of contaminating
substances used to cut supplies or the life-style of opioid
addicts. These are the principal reasons for the development
of methadone clinics and needle-exchange programmes