Toxicity refers to a drug’s potential to cause harm to a patient. While highly toxic drugs are rarely approved for use, analyzing a drug’s safety is more complicated than determining whether or not it has any harmful side effects. Regulators must decide whether a drug’s benefits outweigh its potential harms. If a mild painkiller has the potential to cause liver damage, for example, that would likely be deemed an unreasonable risk. On the other hand, a third-line cancer drug with the same potential side effect might be considered reasonably safe, due to the severity of the condition being treated.

To ensure patients receive effective drugs without unnecessary toxicities, sponsors evaluate various dosages (i.e., the frequency and amount of a drug administered), and include a recommended dosage in the drug’s label. In oncology the standard approach to dosing evaluations has been assessing the maximum tolerated dose (MTD). The MTD approach works well for chemotherapies as effectiveness generally increases with a higher dose; however, for newer targeted therapies a lower dose may be equally as effective and more tolerable than a higher dose.

The tolerability of a dose is the degree to which symptomatic and non-symptomatic adverse events associated with the product’s administration affect the ability or desire of the patient to adhere to the dose or intensity of therapy. Using patient-reported outcomes (PRO) to assess tolerability is one approach that helps characterize the optimal dosage, offering a more patient-centered approach to dosing evaluations, which can provide insights into safety and efficacy of a drug and fosters the development of more patient-centered care. Read more about Friends’ Tolerability & Dosing efforts here and how we work to incorporate patient perspectives in assessments of tolerability.