Overdose, poisoning and drug abuse

Published on 27/05/2015 by admin

Filed under Internal Medicine

Last modified 27/05/2015

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 1688 times

CHAPTER 9 OVERDOSE, POISONING AND DRUG ABUSE

Overdose and poisoning 230
Investigations 231
Measures to reduce absorption/increase elimination of drugs 231
Antidotes 233
Intensive care management 234
Paracetamol 235
Salicylates (aspirin) 236
Benzodiazepines and opiods 237
Antidepressants 237
Insulin overdose 238
Carbon monoxide and cyanide poisoning 239
Methanol and ethylene glycol 240
Alcohol 241
Recreational drug abuse 242
Problems associated with intravenous drug abuse 243

OVERDOSE AND POISONING

The problems associated with overdose and poisoning (deliberate or accidental) are responsible for a significant portion of the acute medical workload in hospitals. While most overdoses and poisonings are not serious and can be managed on medical wards, some patients will require admission to intensive care. This may be the result of the specific nature and effects of the substance involved, respiratory or cardiovascular complications or occasionally due to the onset of multiorgan failure. Common complications associated with overdose and poisonings are shown in Table 9.1.

TABLE 9.1 Potential complications of overdose

General Hypothermia/hyperthermia
Pressure sores
Crush syndrome/rhabdomyolysis
Dehydration
Cardiovascular Hypotension/hypertension
Dysrhythmias
Cardiac arrest
Respiratory Respiratory depression
Aspiration
Pneumonia
CNS Coma
Hypoxic brain damage
Seizures
Confusional states/aggression
Renal ATN secondary to hypotension/dehydration
Effects of rhabdomyolysis
Direct toxic effects
Gastrointestinal/liver Diarrhoea/vomiting
Acute gastric erosions/gastrointestinal haemorrhage
Acute liver failure

This chapter provides general advice only. The UK National Poisons Information service (http://www.npis.org) operates TOXBASE®, which is an on-line poisons information service available at http://www.toxbase.org. This requires registration but should be available in most centres and should be consulted in the first instance. If additional advice is needed, this can be obtained from one of the regional poisons information services by telephone. Telephone numbers will be available through local hospital switch boards, via Toxbase® and from the British National Formulary (BNF: available on line at www.bnf.org).

INVESTIGATIONS

In the unconscious patient it is essential to exclude other treatable causes of loss of consciousness (e.g. head injury, subarachnoid haemorrhage, hypoglycaemia, meningitis), even if the patient has left a suicide note or is known to have taken an overdose previously. If in doubt, organize a CT scan of the brain and consider lumbar puncture and other investigations as appropriate.

The response to a (cautious) challenge of naloxone or flumazenil may occasionally be helpful in identifying opioid and benzodiazepine overdose, respectively (see below).

Aspirin (salicylate) and paracetamol assays should be performed in all cases. Alcohol levels can be measured in most centres and may be useful to distinguish intoxication from brain injury. The majority of other assays are unavailable at short notice, and the samples should be sent to regional centres. Aside from paracetamol, it is rare for assays to alter clinical management. Ask the laboratory to save serum in uncertain cases for later analysis and send urine for a toxicology screen. These samples may be invaluable if the patient subsequently dies and there is a Coroner’s inquest or other inquiry.

MEASURES TO REDUCE ABSORPTION/INCREASE ELIMINATION OF DRUGS

Gastric lavage

Historically, gastric lavage was frequently performed in an attempt to remove tablet debris from the stomach. This is no longer a routine procedure, as evidence suggests it is largely ineffective, does not improve survival and is associated with potentially serious adverse events including aspiration, airway compromise, hypoxia and death.

Gastric lavage should therefore only be performed when recommended by a poisons information centre. It is usually only indicated when patients present within one hour of ingestion of life threatening quantities of drugs. Contraindications include ingestion of corrosives or substances liable to cause lipoid pneumonias and refusal of consent. It is not usually performed in children.

In the rare cases where gastric lavage is indicated, the airway should be protected by endotracheal intubation. If necessary, seek help from an experienced anaesthetist.

image If the patient is very obtunded, it may be possible to intubate the trachea without any anaesthetic drugs.
image If not, perform a rapid sequence induction with preoxygenation, cricoid pressure, an intravenous induction agent and suxamethonium.
image Pass the gastric tube under direct vision and then perform lavage.
image Consider extubation in head-down, left lateral position.
image If the patient is not fit to extubate and/or send to the ward, keep the patient intubated and transfer to ICU.
image If respiratory effort is feeble, it is better to support ventilation for a few hours than leave the patient to breathe spontaneously with poor tidal volumes. This helps to maintain lung expansion, minimizes the tendency to atelectasis and provides ongoing airway protection.

Activated charcoal

Activated charcoal (oral or via a nasogastric tube) has two effects. It binds free drug within the lumen of the bowel and also actively absorbs drug from the circulation. It is absorption of ingested drug from the bloodstream that is the rationale for repeated use of activated charcoal in some cases. Indications for multiple-dose activated charcoal are shown in Box 9.1.

Box 9.1 Overdoses for which multiple-dose activated charcoal may be useful

Barbiturates

Carbamazepine

Chlormethiazole

Digoxin

Phenobarbital

Phenytoin

Quinine

Salicylates

Theophylline

A typical dose regimen is as shown:

image 50 g 4-hourly oral/NG.
image If nausea/vomiting are a problem, it can be given as 12.5 g hourly.

Forced alkaline diuresis

Traditionally, this has been used to increase the renal clearance of soluble, acidic drugs, particularly salicylates and barbiturates. It is now controversial due to problems with fluid overload and acid–base disturbance. Seek senior advice. A typical regimen is as follows:

image Use CVP to guide volume loading with normal saline/colloid.
image Give 0.25–0.5 g / kg mannitol 20% to promote diuresis > 200 mL / h.
image Give sodium bicarbonate (8.4%) 1 mmol / kg / h to achieve urinary pH > 7.5.

The role of loop diuretics to increase urine flow in this setting is controversial. Some authors recommend them if the response to mannitol is inadequate. They can, however, produce acidification in the renal tubule and promote precipitation of acid-soluble drugs and compounds such as myoglobin. (See Rhabdomyolysis, p. 320.)

Haemodialysis and haemoperfusion

Haemodialysis and haemoperfusion over activated charcoal are useful for some life-threatening overdoses. These are listed in Table 9.2. Seek specialist advice. There are also some reports of albumin dialysis (e.g. MARS®) being used in the treatment of heavy metal poisoning.

TABLE 9.2 Role of haemodialysis and haemoperfusion in overdose

Haemodialysis Haemoperfusion
Ethylene glycol Barbiturates
Methanol Theophylline
Lithium  
Salicylates  

ANTIDOTES

Some overdoses / poisonings have specific antagonists or antidotes which reduce the toxic effects and mortality. These should generally only be used for potentially life-threatening situations when the nature of the overdose or poison is known. Available antagonists / antidotes are shown in Table 9.3.

TABLE 9.3 Commonly available antagonists and antidotes

Drug Antagonist/antidote
Benzodiazepines Flumazenil
Copper Penicillamine
Digoxin Digoxin-specific antibodies
Ethylene glycol Ethanol, fomepizole
Heparin (unfractionated) Protamine
Iron Desferrioxamine
Lead Sodium calcium edetate
Methanol Ethanol, fomepizole
Opioids Naloxone
Organophosphates Atropine, pralidoxime
Paracetamol N-acetylcysteine
Warfarin Vitamin K, fresh frozen plasma, prothrombin complex concentrate (Beriplex)

INTENSIVE CARE MANAGEMENT

Related posts:

Organizational Issues Renal system Basic principles Trauma Metabolic and endocrine problems Respiratory system