Give 1mg of Benadryl per pound such that if your dog weighs 30 pounds, you should give it 30 mg of Benadryl. Talk your veterinarian - while antihistamines are generally safe, there are the potential for side effects particularly if your dog has chronic organ failure (renal failure, liver failure, congestive heart failure, etc.).
1 Encephalitis is inflammation of the brain.  Meningitis is inflammation of the membranes (called meninges) that surround the brain and spinal cord.
Must Read Articles Related to Brain Infection. Encephalitis Encephalitis is an acute infection and infla...learn more >>. Meningitis in Adults Meningitis is an infection of the la...learn more >>. Meningitis in Children Meningitis is an inflammation of the membranes that surround the spinal cord or brain.