When it comes to infants and young children, they are typically administered smaller doses of medication in comparison to adults. This is primarily because their organ functions still need to fully develop, meaning their bodies are not as efficient at metabolizing or eliminating drugs. Additionally, their blood-brain barrier is more permeable than in adults. As a result, high concentrations of drugs can easily penetrate the central nervous system (CNS), potentially leading to neurological damage.

Elderly patients are also usually given smaller doses of medication. This is because aging can significantly affect drug disposition. Moreover, if an elderly patient has multiple chronic diseases and takes numerous drugs, this could result in a range of adverse reactions.

Pregnant women present another unique case because drugs can cross the placenta, which could lead to teratogenic effects, causing fetal developmental abnormalities.

Patients with liver disease are usually advised to take smaller doses of drugs over extended periods. This recommendation stems from the fact that a damaged liver is less efficient at metabolizing and detoxifying drugs.

Intravenous administration of drugs allows these substances to enter the bloodstream directly, bypassing the gastrointestinal (GI)tract and hepatic metabolism, resulting in a quick response to the drug. In contrast, orally administered drugs need to pass through the GI tract and are subject to hepatic metabolism before they enter the systemic circulation, which generally results in a slower response