A 42–year–old man comes to the emergency department because of sudden-onset diarrhea and nausea directly following a fish barbeque at the beach. The next day, he cannot lift his left hand. Examination shows a wrist drop in the left hand. His pulse is 56/mm. However, his pupils are normal and there is no difficulty in eating. 

Which of the following is the treatment for this condition?
Antihistamines
Conservative only
Gastric lavage
Suitable antibiotics