This Publication Is Searchable The Merck Manual of Diagnosis and Therapy Section 22. Clinical Pharmacology Chapter 302. For each clinical situation and patient, risks must be weighed against benefits by considering the qualitative and quantitative effects of using a drug and the likely outcome if the drug is withheld.
Drug therapy is justified only if the possible benefits outweigh risks.
The decision depends on adequate knowledge of the patient, of the disease and its natural history, and of the drug and its potential adverse effects. Each patient reacts differently to drugs and chemicals. Patient-related factors include age, sex, pregnancy status, occupation, social circumstances, and genetic traits. Any factor alone or in combination may influence the course and severity of the disease or the response to a drug. For example, penicillin anaphylaxis, which is rare but potentially fatal, may be avoided by obtaining an adequate history and performing appropriate skin tests.