What agent may be used to treat a cat with early onset of rear leg paralysis and tachycardia?

In the context of treating a cat with early onset rear leg paralysis and tachycardia, a fibrinolytic agent is the most suitable choice. This is because rear leg paralysis in cats can often be associated with thrombosis, particularly aortic thromboembolism (ATE), which is a common condition where a blood clot obstructs blood flow to the hind limbs. This can lead to symptoms like paralysis and rapid heart rate (tachycardia) as the body struggles to maintain circulation and respond to the stress of the clot.

Fibrinolytic agents work by dissolving blood clots, thus aiding in the restoration of blood flow to the affected areas. In the case of the cat experiencing paralysis, using a fibrinolytic agent can potentially improve limb viability and alleviate the acute symptoms caused by the clot.

In regard to the other options, while antibiotics are vital in treating infections, they would not address the acute circulatory issue present in this scenario. Antihistamines are primarily used for allergic reactions and would not be relevant in treating paralysis or tachycardia. Analgesics provide pain relief but again do not resolve the underlying issue of a possible clot causing the paralysis. Thus, a fibrinolytic agent is the most appropriate choice