Immunology Smarties

[Elfin]

I was wondering if someone clever could please explain to me (in layman's terms), the science behind why a 1kg Chihuahua pup gets exactly the same dose of vaccination as a 70kg Neapolitan Mastiff.

Subsequently, could a "normal" single vaccination dose elicit the same immune response if divided in half, and each half given to two 25kg dogs?

[Rappie]

Each dose of vaccine contains a sufficient number of 'particles' to an induce an adequate immune response in an average animal with an average immune system - hence the "per dog" and "per cat" (and even "per horse") dose. Giving half a dose might stimulate a response, but it might not. The immune system itself isn't really size dependent (though other size related factors may influence the immune system).

When we dose with other drugs we are trying to get a particular concentration of drug in tissues, or have the drug level in tissues be at a particular point for a particular length of time. Both of these results depend on the size of dog and the amount of drug given but the dose rate is the same regardless of the size of the patient (eg 0.5mg/kg, or 1mg/kg).