Pharmacokinetic boosters are agents that are used to inhibit the metabolism of other substances, thereby increasing or prolonging the action of these substances. Ritonavir and its structural analogue cobicistat, being inhibitors of the CYP3A subfamily, are boosting agents that prolong the action of some antiretroviral medicines. Corticosteroids are mainly metabolised by the CYP3A enzyme group, particularly CYP3A4. Therefore, use of a CYP3A inhibitor with a corticosteroid is anticipated to increase systemic steroid levels.