Aluminium, magnesium and zinc phosphide are highly toxic inorganic phosphides commonly used in rodenticides, insecticides and fumigants by agricultural communities. Because of their low unit cost, they are widely used pesticides. This has contributed to a significant increase in its use for deliberate poisonings.
While aluminium phosphide poisoning is uncommon in our country in contrast to asian countries, Zinc phosphide poisoning is frequently encountered in Kenya possibly due to “unlimited and uncontrolled accessibility”.
Aluminum phosphide is marketed in Kenya under various trade names including Gastoxin, Detia Gas Ex, and Celphos. Zinc phosphide is locally available under trade names like Rat and Rat, Ratox BAIT, Fukokil, Kilrat, and Red Cat.
The major difference between superwarfarin rodenticides and inorganic phosphides is in their mexchanism of toxicity.
Unlike vitamin K antagonists including warfarin and superwafarins (bromadiolone, difenacoum, brodifacoum, difethialone and flocoumafen) which cause toxic effect through inhibition of the synthesis of some vitamin K-dependent clotting factors (Factors II, VII, IX and X), aluminium and zinc phosphides act via a toxic gas–hydrogen phosphide-that is liberated when the phosphides comes in contact with moist air, water and gastric acid and subsequently absorbed systemically.
The phosphine gas cause poisoning by irreversibly inhibitng repiratory enzyme cytochrome C oxidase, a result of which mitochondrial oxidative phosphorylation is inhibited (impedes cellular oxygen consumption and energy production). The blockade of cellular respiration is also associated with generation of free radicals-superoxide anion and highly reactive hydroxyl radicals–responsible for oxidative damage of cells primarily in the mitochondria of organs with high oxygen demand (brain, liver, heart, kidney, lungs).
From the foregoing, it is clear that administering a vitamin K antidote following ingestion or otherwise, as often done by care givers, of inorganic phosphide is injudicious and does not make pharmacological sense.
Management of inorganic phosphides, however, consists of supporting respiratory and cardiovascular functions, limiting further liberation of the toxic gas in the gut while enhancing its elimination through the lungs and kidneys.