Amphetamine abuse

Amphetamine abuse

Definition

Amphetamines were originally widely used for medical reasons such as appetite suppressants and for insomnia, but are now recreationally used. Medical use of amphetamine (and derivatives) is now limited to selected cases of narcolepsy and attention deficit hyperactivity disorder.

There are several derivatives of amphetamine, such as methamphetamine, which can be smoked, and there-fore became popular for their increased speed of on-set and intense effect. Amphetamines can be taken orally, intranasally, smoked or injected. Street names for amphetamine include ‘speed, whizz, sulphate’, and for methamphetamine ‘meth, ice’.

Incidence/prevalence

Amphetamine and derivatives (including ecstasy) are the second most common class of illegal drug used after cannabis.

Pathophysiology

Amphetamines are stimulant drugs with cardiovascular, neuropsychiatric and other physiological effects. Multiple doses, taken to maintain euphoria, can lead to intox-ication, and feelings of anxiety and paranoia. Tolerance to amphetamines can take place with increased doses or a different method of administration, e.g. smoking or injecting rather than oral. In psychological dependence withdrawal can cause depression, profound lethargy and hunger. Street amphetamine usually only contains ∼5% of the drug, mixed with other substances including baby milk powder, lead, caffeine and paracetamol or codeine. This makes it particularly dangerous to inject. The excretion of amphetamine depends on urine pH – acid urine increases its clearance.

Clinical features

Physical effects of an amphetamine-intoxicated state include tachypnoea, tachycardia, decreased appetite and increased motor activity. A history should be taken of recent and previous recreational drug use, including methods of administration, and alcohol intake. A psychiatric and social history should be taken, as well as a medical history and examination.

Complications

Medical complications include seizures, coma, tach-yarrhythmias, hyperthermia and hypertension. Acute hepatic failure has been reported. Psychiatric complications include paranoia, eating disorders, hallucinations and panic attacks. Loss of judgement, e.g. when car driving or a bad trip can lead individuals to become uncharacteristically aggressive and violent, causing harm to themselves or others.

Investigations

If the individual is euphoric, but with no physical side-effects, there is no need for specific investigations and should be monitored for 4 hours. If physical side-effects are present, U&Es, liver function tests, creatine kinase and an ECG should be performed. The core temperature should be checked.

Management

In more than mild toxicity, patients should have cardiac monitoring.

1.     Seizures and agitation are treated with diazepam or lorazepam.

2.     Hypertension should be treated with diazepam or if this is ineffective, intravenous glyceryl trinitrate (GTN).

3.     Hypovolaemia should be treated with fluid resuscitation, consider inotropes, and treat metabolic acidosis with sodium bicarbonate as necessary.

4.     Cardiac arrhythmias or refractory hypertension require specialist advice, for example from the NPIS.

5.     Amphetamine abusers should be offered drug rehabilitation counselling.