How can I differentiate between common types of overdose in a primary care setting?

Differentiating between common types of overdose in a primary care setting primarily involves a systematic assessment, detailed history taking, and clinical examination, with a focus on specific signs and symptoms (toxidromes) associated with different substances ¹.

• Initial Assessment and Emergency Transfer: Regardless of the suspected substance, immediately assess the person using the ABCDE approach (Airway, Breathing, Circulation, Disability, Exposure) ¹. If the person is unconscious, has a reduced level of consciousness, reduced respiratory rate or oxygen saturation, hypotension, significant heart rate abnormalities (tachycardia, bradycardia, irregular pulse), hypothermia or hyperthermia, or has had a seizure, arrange emergency transfer to hospital immediately ¹. Investigations are generally not routinely necessary or appropriate in primary care for those who do not need emergency referral to hospital ¹.
• History Taking: If emergency transfer is not required, gather a detailed history from the person, friends, or family ¹:
  • Substance Taken: Identify the specific substance(s), the amount, and if any other medicines or alcohol were involved ¹. Prompt for quantities in terms of strips or packets, as initial accounts may be unreliable ¹.
  • Timing: Establish the exact timing of ingestion, especially for substances like paracetamol ¹.
  • Route of Administration: Determine if it was by mouth, inhalation, or injection ¹.
  • Intent: Ascertain if it was accidental, deliberate, or a therapeutic error ¹.
  • Other Details: Gather information on age, weight, sex, medical history (including psychiatric history and self-harm), current medications, and factors affecting metabolism or excretion (e.g., renal or hepatic impairment) ¹.
• Clinical Examination and Toxidromes: Perform an examination to look for signs consistent with specific poisons or drug classes ¹:
  • General Observations: Look for track marks (intravenous drug misuse), alcohol or solvents on breath, stigmata of liver disease (alcohol dependence), atypical bruising, or skin blisters ¹.
  • Neurological Examination: This is crucial for differentiation ¹.
    • Pupil Size and Reaction: Widely dilated pupils that react poorly to light can indicate agents with anticholinergic activity (e.g., tricyclic antidepressants) or sympathomimetic activity (e.g., amphetamines) ¹. Pinpoint pupils (miosis) suggest exposure to opioids or agents with cholinergic activity (e.g., pesticides) ¹.
    • Eye Movements: Strabismus, internuclear ophthalmoplegia, dysconjugate roving eye movements, and total external ophthalmoplegia may be seen with poisoning from tricyclic antidepressants, barbiturates, phenothiazines, and anticonvulsants (e.g., phenytoin, carbamazepine) ¹.
    • Abnormal Movements: Assess for acute dystonic movements (antidopaminergics like antipsychotics), hypertonia, hyperreflexia, and extensor plantar response (tricyclic antidepressant poisoning) ¹.
    • Visual Changes: Blurring, loss of vision, or tunnel vision can occur with some drugs, such as quinine ¹.
  • Toxidromes: Compare the person's symptoms and examination findings to commonly associated toxidromes to help identify the unknown poison ¹.
• Information Sources: Consult the poisons information database TOXBASE for specific poison information and management guidance ¹. If poisoning is severe or complex, the poison is unknown, or there are significant comorbidities or uncertainties, telephone the National Poisons Information Service (NPIS) for advice ¹. For pregnant individuals, contact the UK Teratology Information Service (UKTIS) ¹.
• Safeguarding: Consider child maltreatment if there are repeated presentations of accidental ingestion of poisons in a child, or if the explanation for the poisoning is absent or unsuitable ¹,².