The penicillins.

The penicillins as a group are the most frequently and widely used of the antimicrobial agents because they are effective, low in toxicity, and relatively inexpensive. Effectiveness is due to the bactericidal action, the excellent distribution throughout the body spaces, and the wide spectrum of activity. Knowledge of the variation in spectrum of activity of the various types of penicillins is needed for effective use of the appropriate drug against individual infections. Allergenicity is the most frequent and serious problem associated with the use of penicillins. Individual penicillins, however, do have different side effects. The older penicillins are so inexpensive that the cost of their use need hardly be considered, whereas the newer penicillins are expensive and should be used only when they are clearly more effective for treatment than are drugs such as penicillin G.