Ten days assures the death of all strep bacteria which are the only bacteria which can cause the serious complication of rheumatic fever and rheumatic heart disease. Obviously this answer varies according to what kind of infection you have. In general, older, cheaper antibiotics such as amoxicillin, erythromycin or sulfa-based medicines still work very well for most illnesses. However, since these antibiotics are older and have been used for a longer period of time bacteria which are resistant to them do exist. Your clinician will help decide if a newer, more expensive antibiotic should be used.
Many antibiotics can irritate the stomach.
This is especially common with erythromycin, which should always be taken after eating. All antibiotics can cause an allergy. The usual sign of this is a skin rash. If this happens to you, stop taking the medication immediately and let your clinician know. Whether an antibiotic interacts with other medications depends on which antibiotic and which medications you are taking.