Since your post about your cat's weird reaction to diazepan was dated some time ago, by now you've seen that the symptoms have disappeared. However, a LOT of people give tranquilizers to pets without consulting a vet about the proper dose, possible reactions, etc. Many people aren't even aware that 500-100mg of acetaminophen (Tylenol®), which is a normal human dose, if given to a cat proves fatal in 85% (or more) instances. I am posting this in the hopes that it will give cat lovers some guidelines about diazepam and related drugs. I am not a veterinarian, but I AM a R.Ph. (Registered Pharmacist) and fill scripts for animals and compound special meds for them quite frequently.
First off, there is a group of drugs that first appeared in 1960 called "benzodiazepines," or "benzos" in med-speak. They are all minor modifications of the original benzo, chlordiazepoxide (Librium®), and all have the essentialy identical effects and side effects. Where they differ is in times for onset of desired effects, duration of effects, and clearance from the body. The benzos are used very frequently in animals as well as humans, mainly because (over a short period, four months at most) they are VERY effective and safe; it's almost impossible to overdose on benzos unless they are mixed with alcohol or sedating narcotics.
The main benzos in use today in animals are chlordiazepoxide (Librium®), diazepam (Valium®), and lorazepam (Ativan®). Occasionally a vet will use alprazolam (Xanax®) or clorazepate (Tranxene®), but clorazepate is rarely used even in humans today, and alprazolam (Xanax®) should have been taken off the market by the FDA years ago because of its high abuse/dependence risks (more on this later).
Among the three benzos used by vets, lorazepam is prescribed at least ten times more often than the other two. Chlordiazepoxide is VERY slow (4 hours or more) to take effect orally and is actually converted to diazepam and several other active chemicals in the liver. Oral lorazepam typically takes about 2 hours to reach maximal effects, but it has a very short "half-life" and no active metabolites; its effects disappear 8-12 hours after a single dose. Diazepam is VERY fast acting orally; effects begin in about 15-20 minutes and reach their peak within an hour. However, due to its chemistry (way too involved to go into here), a SINGLE dose typically "wears off" in 3-4 hours. However, it has several active metabolites (chemicals which have the same effect as the parent drug, sometimes even stronger) that persist in the system for 100-150 hours. This is why a person taking diazepam daily will notice it seems to work a little better each day until it reaches "steady-state" in 7-10 days. It is used when very quick, brief sedation is desired (pre-op, dental procedures, etc.) However, because it does remain in the system a long time, if a subject (human or cat) has some unexpected bad reaction to it, it may take several days to clear up completely.
ALL BENZOS, IN HUMANS AND ANIMALS, HAVE THE POTENTIAL TO CAUSE A PARADOXICAL EFFECT. THE SUBJECT BECOMES AGITATED, "HYPER," AND OFTEN ASSAULTIVE ("VICIOUS" IN CATS), AS IF THE SUBJECT HAD TAKEN A LARGE OVERDOSE OF AMPHETAMINES (Adderall®, Vyvanse® & others) OR METHYLPHENIDATE (Ritalin®, Concerta® & others). This is actually quite rare, occurring in about 1-2% of humans (not sure about cats). Also, all benzos increase appetite (moreso in cats than people), so you may notice Garfield emptying his food dish much quicker and still wanting more. For this reason, chlordiazepoxide is often given to malnourished or emaciated cats like those found where there are 20 or 30 in a single house, basically neglected.
For diazepam, the typical dose for cats is 0.5 to 1mg for every pound the cat weighs. (My Maine Coon weighs 22 lbs. and would need a 10mg tablet.) Benzos should NEVER be given to a cat younger than one year or older than 10-12. Standard dosage for lorazepam is 0.1 to 0.25mg per pound of weight; chlordiazepoxide is usually prescribed at 2-4mg per pound.
Again, these are drugs which have been in use since the early 60s and are still very frequently used because they ARE effective with few adverse effects (compared to, say, barbiturates). The exception is alprazolam (Xanax®), which is active for such a short time (3-5 hours, 6 at most) that multiple doses are required daily, and patients using the drug for extended periods of time or at the dosages recommended for "panic attacks" very often suffer a "withdrawal" effect between doses, and start taking it more often than prescribed or increasing the dosage, and become seriously dependent, psychologically AND physically. In short, what we used to call "addicted." (Suddenly stopping ANY benzo that's been taken for 7-8 months or longer, especially at high dosages, CAN BE FATAL IN HUMANS. A slow detox over many months is required.)
Your cat's reactions are not uncommon, nor serious or permanent (but very frightening to the owner!). Make certain your vet knows the cat's response; chances are lorazepam will be a much better choice.
I realize this is a LONG post, but I hope it will provide some basic facts and guidelines for cat lovers, because the benzos ARE used very frequently in domestic mammals.