Hamsters as a group are unusually sensitive to the potentially lethal effects of certain antibiotics, whether they are given orally or by injection. Potentially harmful antibiotics include ampicillin, penicillin, erythromycin, lincomycin and streptomycin.
The major way in which certain antibiotics cause reactions is by altering the normal microbial balance within the gastrointestinal tract. Once the normal intestinal microfloral balance has been upset, certain bacteria multiply to abnormally large numbers.
The multiplying bacteria produce harmful chemicals that can have lethal effects. Certain antibiotics are directly toxic and do not alter the normal microbial balance within the gastrointestinal tract; these antibiotics should never be used in hamsters.
Though injectable antibiotics can cause the problems described above, oral antibiotics are more often associated with them. Antibiotics should never be given to hamsters unless they are prescribed by your vet.
If your hamster is prescribed either oral or injectable antibiotics, try feeding it 1/2 cc (1/10 teaspoon) of plain, white yogurt orally morning and evening for the duration of the antibiotic treatment, and for an additional 5-7 days following treatment.
Yogurt helps replace those beneficial intestinal bacteria that often perish during antibiotic treatment.