Changes

In man, 60-90% of an oral does of primidone is absorbed from the gastointestinal tract, with serum levels peaking about three hours following administration. Absorption is thought to be similar in animals, but primidone is metabolised once absorbed. Oxidation at carbon 2 results in the formation of phenobarbital, and cleavage at the same site gives PEMA. Primidone, phenobarbital and PEMA all possess anticonvulsant activity, but 85% primidone's activity in dogs is due to the phenobarbital it forms. This is because the potentcy of primidone and PEMA is one-thirtieth that of phenobarbital, and phenobarbital accumulates to the highest concentrations since it is the compound with the longest half-life.  

In man, 60-90% of an oral does of primidone is absorbed from the gastointestinal tract, with serum levels peaking about three hours following administration. Absorption is thought to be similar in animals, but primidone is metabolised once absorbed. Oxidation at carbon 2 results in the formation of phenobarbital, and cleavage at the same site gives PEMA. Primidone, phenobarbital and PEMA all possess anticonvulsant activity, but 85% primidone's activity in dogs is due to the phenobarbital it forms. This is because the potentcy of primidone and PEMA is one-thirtieth that of phenobarbital, and phenobarbital accumulates to the highest concentrations since it is the compound with the longest half-life.  

Some vets use primidone continues in patients which have proven refractory to phenobarbital, even at maximum doses. at the maximum therapeutic drug concentration. Note that its efficacy in the scenario has not been proven. efficacy may simply reflect improced conversion to phenobarbital (i.e. animals that are induced may metabolise the drug to greater concentrations of phenobarbital that those generated from administration of phenobarbital alone). There is no advantage in useing primisone rather than phenobarbital for control of epilepsy in most dogs.

Some vets use primidone continues in patients which are refractory to phenobarbital, even at maximum doses. at the maximum therapeutic drug concentration. The efficacy of primidone in this capacity has not been proven, and mau simply be due to animals receiving primidone metabolising the drug to greater concentrations of phenobarbital that those generated from administration of straight phenobarbital. In most dogs, however, there is no advantage in using primidone over phenobarbital for seizure control, and there are added side effects. Primidone is also more expensive than phenobarbital, but in some countries may be subject to lesser degrees of control and record keeping.

 

Cats metabolise primidone to phenobarbital to a lesser extent than dogs, so it follows that the drug may be less effective and more toxic. Primidone is not recommended for use in cats.

Although seizures can be controlled with primidone in dogs, primidone has little advantage over phenobarbital in dogs. Control of seizures ion dogs is correlated with the plasma concentration of phenobarbital rather than primidone. In a comparison between primidone and phenobarbital. there was no significant difference between phenobarbital and primidone with respect to seizure control, and primidone appeared more likely to induce liver injury than phenobarbital. The authors conluded that phenobarbital, rather than primidone, should be the drug of first choice for treatment of canine epilepsy. However, there may be rare cases that respons to primodone when phenobarbital alone has not been effective (1 out f 15). primodone is more expensive than phenobarbital but is not classifies as a controlled drug in the US and therefore does not require the same degree of record keeping.

 

Primidone is more toxin in cats and rabis. cats metabolise primidone to phenobarbital to a lesser extent than dogs - less effective, more toxic.

==Dosage==

==Dosage==