Antihistamines, such as Benadryl, are effective medications for an itchy dog.  Dogs with allergies develop itchy skin, and just like humans antihistamines can help reduce those symptoms.  Many antihistamines are safe, but dose and duration are different for dogs.  Antihistamines often cause drowsiness in dogs, which also make them an effective sedative for car trips.  Some dogs have rare excitable side effects instead which can make them undesirable.  The following list can help you dose your dog appropriately.  If the itchiness persists or if you have any questions be sure to contact your dog's veterinarian at Mission Viejo Veterinary Hospital.

Benadryl (diphenhydramine)
1 to 10 lbs: 1/2 to 1 tsp of Children's Benadryl twice daily
10 to 22 lbs: 1/2 to 1 25 mg tablet twice daily
22 to 33 lbs: 1 25 mg tablet or capsule twice daily
33 to 55 lbs: 1 to 2 25 mg tablets or capsules twice daily
55 to 75 lbs: 2 to 3 25 mg tablets or capsules twice daily
> 75 lbs: 2 to 4 25 mg tablets or capsules twice daily