Humans maintain body temperature within a narrow range. Drug administration can upset the usual balance and cause a fever. The drug may interfere with heat dissipation peripherally, increase the rate of metabolism, evoke a cellular or humoral immune response, mimic endogenous pyrogen, or damage tissues. The fever may be a result of the pharmacological action of the drug or some other unrelated effect. Drug-induced fever is most commonly the result of a hypersensitivity reaction and its characteristics resemble those of an allergic reaction. The fever most commonly occurs after 7 to 10 days of drug administration, persists as long as the drug is continued, disappears soon after stopping the drug, and will rapidly reappear if the drug is restarted. The agents most commonly associated with causing fever include the penicillins, cephalosporins, antituberculars, quinidine, procainamide, methyldopa, and phenytoin.