I would not use Loratadine but you can definetely try to use Diphenhydramine. This is better known as Benadryl . Make sure that you use plain Benadryl and not the cold or flu version.
The dosage at which it is usually given is 1 mg per pound of dog every 8-12 hours. However as with any medication there may be side effects and it is always highly recommended to discuss with your vet first. Avoid giving it to your dog if he has certain health condition like glaucoma, prostatic disease, cardiovascular disease or hyperthyroidism.
You can read more about Benadryl in the reference link below:
While plain Claritin (loratadine) has been shown to be succesful in humans it has proved quite ineffective in canines, this is why it is not recommended. It has not been used much in canines therefore no dosage instructions or general info have ever appeared. Veterinarians instead are much more familiar with Benadryl and have been using it for quite a while. Other common allergy medications used in veterinary care are:Hydroxyzine (atarax), Chlorpheniramine (Chlor-Trimeton) and Atopica. You can read more about Claritin and more about allergies in the reference link below:
Claritn D should be strictly avoided as this contains Pseudoephedrine which can be pretty toxic.
I hope this info has helped you, let me know if I can be of any further assistance. My best wishes!