Monoclonal antibodies (MAbs) exhibit complex pharmacokinetics (PK) and pharmacodynamics (PD, response) against tumor necrosis factor (TNF). Many factors impact anti-TNF MAb PK, altering MAb clearance and therefore the half-life: albumin, weight (particularly, obesity), disease (severity, stage and co-morbidities) and concomitant administration of immunosuppressants (e.g. methotrexate). These factors can alter MAb exposure, impacting on the likelihood of clinical response. Formation of anti-drug antibodies (ADAs) is another potential factor that can affect MAb PK. Factors impacting the likelihood of developing ADA are classified as patient-related (concomitant immunosuppressants, prior ADA against other anti-TNF MAb) or product-related (structure, manufacturing process, aggregate formation, route of administration and dosing regimen). Repeated episodic exposure can induce ADAs, shortening the effective treatment interval. Avoiding intervals where anti-TNF MAbs are non-measurable is important for efficacy and may delay onset of ADAs. Thus, patients whose factors predispose them to having faster clearance (or short half-life) such as severe disease, low albumin or high body weight may need shorter dose intervals to reduce the likelihood of intermittent exposure. ADAs can have no effect or can impact efficacy through MAb binding, thus inhibiting its function or potentially causing hypersensitivity reactions (PD). ADA can also increase MAb clearance (PK). Because of their impact on MAb clearance, ADAs have been linked to lower serum drug concentrations, potentially negatively impacting clinical response. ADAs have been reported for biologics in most therapeutic areas. ADAs are well documented in clinical studies due to the Food and Drug Administration and the European Medicines Agency recommendations regarding testing and impact of immunogenicity. Lastly, the dose metrics (e.g. mg vs. mg/kg) can cause issues as well. MAbs such as infliximab are dosed on a mg/kg basis, which commonly results in low concentrations in patients with low body weight. Conversely MAbs such as adalimumab are administered as a flat (mg) dose, which can result in low concentrations in high weight patients.