Opiate poisoning

What is opiate poisoning?

Opiate poisoning can occur at any time from birth (when pethidine given to the mother in labour may suppress ventilation) to terminal care. The outcome can range from minor adverse effects such as constipation to death from respiratory depression. See also the article on Opioid Analgesics.

How common is opiate poisoning? (Epidemiology)¹

• In 2020, 4,561 deaths related to drug poisoning were registered in England and Wales, which is 3.8% higher than the number of deaths registered in 2019.

• Two-thirds of registered drug poisoning deaths in 2020 were related to drug misuse, accounting for 52.3 deaths per million people.

• Rates of drug-misuse death continue to be elevated among those born in the 1970s, with the highest rate in those aged 45 to 49 years.

• The North East continues to have the highest rate of deaths relating to drug misuse. London had the lowest rate.

• Approximately half of all drug poisoning deaths registered in 2020 involved an opiate. 777 deaths involved cocaine.

Risk factors

• Studies of the psychosocial background of drug abusers who died from opiate poisoning show a strong correlation between mental health conditions, financial problems and crime. Being in a relationship tends to have a protective effect.

• A significant incidence in recently released prisoners has been identified. This has been found to be associated with extreme social disadvantage, multiple drug use and risky drug-use patterns.²

• Opiates produce tachyphylaxis. This means that, with time, larger and larger doses are needed to obtain the same effect and tolerance develops to the adverse effects. It is not uncommon to find a drug abuser or a patient in terminal care who is taking a daily dose that would be fatal to a normal person. If dosage is reduced or stopped this tolerance quickly fades. If they take what was formerly 'a good hit' it has become a fatal overdose.³

• Alcohol and other sedatives enhance the effect of opiates, especially respiratory depression. Drug abusers often like to enhance the effect of heroin with benzodiazepines. This is very dangerous.³

MHRA/CHM advice: Benzodiazepines and opioids: reminder of risk of potentially fatal respiratory depression (March 2020): Opioids co-prescribed with benzodiazepines and benzodiazepine-like drugs can produce additive CNS depressant effects, thereby increasing the risk of sedation, respiratory depression, coma, and death. Healthcare professionals are advised to only co-prescribe if there is no alternative and, if necessary, the lowest possible doses should be given for the shortest duration.⁴

The following groups are at risk of morphine toxicity and usually require a lower dose:⁴

• Reduce dose or avoid in renal impairment, the elderly and the debilitated.

• Hypotension.

• Hypothyroidism.

• Asthma (avoid during an attack) and decreased respiratory reserve.

• Prostatic hypertrophy.

Opiate poisoning symptoms⁵

• Opiate poisoning may be a chronic problem, in which case the main complaint will be of constipation. There may be nausea, vomiting or just loss of appetite. There may be sedation and craving for the next dose.

• Acute toxicity presents with drowsiness that will be more severe if there is also alcohol involved, or involvement of other sedatives. There may be nausea or vomiting.

Signs

• Respiratory depression may be apparent. Hypotension and tachycardia are possible. There are usually pinpoint pupils but this sign may be absent if other drugs are involved.

• The 'post-mortem sole incision' sign has been identified. This is an incision made in the sole by an acquaintance in the belief that the subsequent blood loss will reduce the likelihood of death in an individual who has taken an accidental overdose of an opiate.⁶

Differential diagnosis

There may be no clear indication of what the patient has taken. He or she may be a known drug abuser or there may be needle track marks on the limbs. Beware of multiple drug ingestion (eg, antidepressants, alcohol or benzodiazepines), especially in drug abusers or with suicidal intent. Consider other possible causes of coma:

• Diabetic ketoacidosis.

• Hypercalcaemia.

• Hypernatraemia.

• Hyperosmolar hyperglycaemic nonketotic coma.

• Hypoglycaemia.

• Hyponatraemia.

• Hypothermia.

• Meningitis.

• Stroke.

• Subdural haematoma.

• Syncope.

Investigations

• It is possible to obtain a urine screen for drugs of abuse and there are even some sticks available that will give a quick result. However, they merely detect the presence of opiates or methadone and give no indication of quantity.⁷

• A paracetamol blood level should be considered for all patients who have overdosed or self-poisoned.⁵

• Baseline pathology investigations should be performed in patients with moderate-to-severe toxicity, including FBC, metabolic screen, creatine kinase level and arterial blood gases.^{8 9}

• A CXR may be indicated if pulmonary oedema is suspected.⁹

• Abdominal X-ray has a poor pick-up rate in people suspected of ingesting drug packages and a combination of X-ray and CT scan is advisable.¹⁰

• ECG should, as a general rule, be considered in all patients.¹¹

Associated diseases¹²

Drug abusers may possibly carry hepatitis B (prevalence 5-10% in the UK). Intravenous abusers have a 60-80% chance of carrying hepatitis C. There may possibly be HIV infection. Nutrition and self-care are usually poor.

Opiate poisoning treatment and management

• Do not delay establishing a clear airway, adequate ventilation and oxygenation if consciousness is impaired.¹³

• Give naloxone intravenously. See BNF for dosage regimens.⁴
  

  • Give intramuscularly (IM) if no vein is available. Repeat the dose if there is no response within two minutes. Naloxone is a competitive antagonist and large doses (4 mg) may be required in a severely poisoned patient.

  • Failure of a definite opiate overdose to respond to large doses of naloxone suggests that another central nervous system (CNS) depressant, or brain damage, is present.

  • Observe the patient carefully for recurrence of CNS and respiratory depression. The plasma half-life of naloxone is shorter than that of all opioid analgesics. Repeated doses may be required.

  • If someone takes an overdose of IV heroin it is important to administer naloxone as soon as possible. Often this is done by paramedics but some people have advocated that users should have a supply in case one of their number overdoses and treatment can be started without delay.¹⁴

  • IV infusions of naloxone may be useful where repeated doses are required. Continuous infusion often maintains respiratory effort without promoting opiate withdrawal. Infusions are not a substitute for frequent review of the patient's clinical state.

• Give oral activated charcoal, provided the airway can be protected, if a substantial amount has been ingested within two hours.⁴

• Naltrexone:

  • Is recommended by the National Institute for Health and Care Excellence (NICE) as a treatment option for people who have been opioid-dependent but who have stopped using opioids and who are highly motivated to stay free from the drugs in an abstinence programme.¹⁵

  • It is a competitive opiate antagonist that will block the effect of heroin. It should only be given to people who have been told about the problems associated with treatment and with proper supervision. Treatment with naltrexone should be given as part of a support programme to help the person manage their opioid dependence.

• There is no consensus about the management of patients if body packing of opioids is confirmed:

  • Options include watchful waiting, with or without the use of laxatives, whole bowel irrigation, endoscopic removal or surgery. A risk-benefit analysis should be performed, taking into consideration whether the patient is symptomatic or asymptomatic and whether the treatment is likely to increase or decrease the risk of package rupture.

  • Most patients can be managed by watchful waiting and discharged from hospital as soon as the package has been evacuated with a normal bowel movement.¹⁶

  • Surgery should only be performed in body packers with signs of intoxication or ileus.¹⁷

For further care for Opioid Misuse and Dependence, see also the articles on Opioid Detoxification and Substitute Prescribing for Opioid Dependence.

Prognosis

The development of noncardiogenic pulmonary oedema (also known as acute lung injury) carries a poor prognosis (it is not naloxone-reversible). Multiple drug ingestion and comorbidity (eg, cardiac or renal conditions) also increase the risk of death.¹⁸

Opiate poisoning prevention¹⁹

Drug misusers must be educated about the risks they face. They must understand loss of tolerance after reduction therapy or enforced abstinence as in prison. They must understand the enhanced risk with benzodiazepine use too. They are much less likely to have a serious overdose if they inhale rather than inject.

Daily dispensing of methadone with supervised consumption has greatly reduced the risks.²⁰

Take-home naloxone schemes are effective but pragmatic difficulties such as avoiding misuse and ensuring adequate supplies may need to be overcome.²¹