Poisons and Antidotes Flashcards
What are strategies to counteract poisons?
Can use pharmacokinetic and pharmacodynamic approaches:
- decrease absoprtion
- Neutralise the chemical or metabolite so it can’t react
- Enhance elimination
- Replace the activity
- Antagonise the effect
What drugs are used to decrease absorption?
Ipecac
Activated charcoal
How does Ipecac decrease absorption?
It has cephaeline in it that stimulates the central vomiting centre, as well as emetine, that activates sensory receptors in the proximal small intestine.
It will effect the absorption of other antidotes (N-acetyl cysteine and activated charcoal)
How does activated charcoal decrease absorption?
Drug can absorb into the charcoal. It can create a concentration gradient across mesenteric vasculature so that the drug can be eliminated faster.
What is the usual dose of activated charcoal and what route can it go through?
1-2g/kg orally or naso-gastric tube
In which ways can a chemical be ‘neutralised’?
- Iron by Deferoxamine
2. Paracetamol by N-acetyl cysteine
How does deferoxamine neutralise iron?
Ingestion of a lot of iron overwhelms the gastrointestinal regulatory mechanisms resulting in a lot of iron absorption. Iron causes toxicity by injuring the intestinal mucosa and generating oxygen free radicals.
Deferoxamine mesylate chelates the free iron to form feroxamine, but doesn’t remove iron from proteins like haemoglobin.
Feroxamine is excreted through urine.
How does N-acetyl cysteine neutralise paracetamol?
Paracetamol –> Quinoneimine (that reacts with sulfhydryl groups, such as that in N-acetyl cysteine).
It acts as a precursor for glutathione synthesis and so boosts the resynthesis of this vital intracellular agent and thus prevents liver damage.
Can act as an anti-oxidant, blocking ROS cell death.
How does urinary alkylisation enhance elimination of salicylate?
Sodium bicarbonate is used to raise the urinary pH >7.5. Weak acids under pKa of 7 become trapped in the kidney tubular fluid.
If poorly monitored, may produce too high a pH, impairing cardiac contrility and fluid overload could occur.
What is the original trade name for Heroin?
Diacetylmorphine.
How does Naloxone provide a pharmacodynamic intervention for Heroin?
It acts as an antagonist at the u, l and delta opiod receptors.
It has a shorter half life than heroin so relapse can occur. It can also precipitate Heroin withdrawal.
What happens when you overdose on Warfarin?
Appearance of blood in stools, excessive menstrual bleeding, excessive bruising, etc.
Necrosis and/or gangrene of skin and other tissues.
Death.
What does Vitamin K do to the activity of Warfarin?
Replaces its activity.
What is the initial dose of Vitamin K in replacing the activity of Warfarin?
25-100mg/day.
At higher concentrations, what is Vit. K reduced to?
Hydroquinone by another warfarin-sensitive liver reductase.
