7.5 Forensic Toxicology & Poisoning: Diagnosis, Evidence, Antidotes & Philippine Laws

Why this area matters

Poisoning is a common reason for emergency consultation in the Philippines: pesticides in farming households, kerosene and household chemicals in children, alcohol and methanol-tainted lambanog, and drug overdoses. Every suspected poisoning is potentially medicolegal (suicide, homicide or accident). The physician must treat the patient and preserve the evidence at the same time.

Classification of poisons

Toxicity depends on dose, route, rate, form, tolerance and the person's health. As Paracelsus put it, "the dose makes the poison".

Proving a poisoning

1. Circumstantial evidence: the suspected source, such as empty containers, a suicide note, a dispute or a purchase of poison.
2. Clinical evidence: sudden onset after food or drink in a previously healthy person, a toxidrome (cholinergic, anticholinergic, sympathomimetic, opioid, sedative), and several people falling ill together.
3. Chemical evidence: detection and quantification of the poison in body fluids, vomitus or the suspected source. This is the most convincing proof.
4. Autopsy evidence: corrosion, odors (bitter almond with cyanide, garlic with arsenic or organophosphates), cherry-red livor (carbon monoxide or cyanide), congestion and organ damage.
5. Experimental evidence: rarely, testing the suspected material on animals.

Specimens and preservation

• Living patient: the first gastric aspirate or lavage fluid, vomitus, blood (with and without preservative) and urine. Collect them before antidotes or large volumes of fluid when possible.
• Autopsy:
  • stomach and contents, a portion of the liver, a kidney, urine, heart blood and vitreous humor;
  • for chronic metal poisoning, hair and nails, because arsenic deposits in keratin;
  • in exhumed bodies, also the soil around the coffin.
• Use clean glass or approved containers, one per specimen. Seal, label (name, date, time, collector) and refrigerate. Document the chain of custody from collection to laboratory.

Duties of the treating physician

• Treat first: airway, breathing, circulation, decontamination, antidote.
• Preserve evidence and record the history verbatim.
• Report suspected homicidal or suicidal poisoning to the authorities. PD 856 Sec. 91(f) requires notification when a certified death may be due to crime.
• Consult a poison center. The UP-PGH National Poison Management and Control Center gives 24-hour advice.

Poisonings common in Philippine practice

Decontamination. Activated charcoal (about 1 g/kg) is useful within about 1 hour for poisons it binds. It does not bind iron, lithium, alcohols, acids or alkalis. Gastric lavage is reserved for selected early, life-threatening ingestions with a protected airway. Ipecac is no longer used.

Alcohol and dangerous drugs

• Ethanol causes progressive effects: disinhibition, then incoordination, stupor, coma and respiratory depression. Its legal relevance includes intoxication as an alternative circumstance (RPC Art. 15) and drunk driving.
• The Anti-Drunk and Drugged Driving Act (RA 10586, 2013) lets officers use field sobriety tests and breath analyzers. Under its implementing rules, a BAC of 0.05% or more is conclusive proof of driving under the influence of alcohol. Drivers of trucks, buses, motorcycles and public utility vehicles are held to a stricter threshold, where any measurable alcohol counts. Drugged driving is established by a confirmatory drug test under RA 9165.
• The Comprehensive Dangerous Drugs Act (RA 9165) governs:
  • drug testing: a positive screening test must be confirmed (for example by GC-MS) to be valid in court;
  • prescribing: S-2 license and the special prescription form;
  • chain of custody (Sec. 21, as amended by RA 10640). Seized drugs must be physically inventoried and photographed immediately after seizure in the presence of the accused or counsel, an elected public official, and a representative of the National Prosecution Service or the media. Unjustified lapses can lead to acquittal.