Compared to adults, infants and young children are given smaller drug doses as their organ functions are not fully developed, and the drugs are not efficiently metabolized or eliminated. Also, their blood-brain barrier is more permeable and high concentrations of drugs in the CNS can cause neurological damage. Elderly patients are given smaller drug doses as aging influences drug disposition. If an elderly patient with several chronic diseases takes multiple drugs, it can lead to different adverse reactions. In pregnant women, drugs can pass through the placenta, resulting in teratogenic effects in the developing fetus. In patients with liver disease, lower doses of the drug over longer intervals are recommended because an impaired liver cannot metabolize or detoxify the drug efficiently. Drugs given intravenously directly enter the bloodstream, bypassing the GI tract and hepatic metabolism, so the drug response is quick. In contrast, drugs taken orally pass through the GI tract and undergo hepatic metabolism before entering the systemic circulation. Such drugs show a slow response.