Pharmacokinetics is the field dedicated to investigating the absorption, distribution, metabolism and excretion of drugs. Absorption of drugs is affected when they are taken together with a meal. Depending on the drug, the area under the concentration curve is affected by whether a medication is taken before or after a meal. Combined use of drugs with a high plasma protein binding fraction may be dangerous, since drug efficacy is impacted by efficiency, which in turn is affected by the degree to which it binds to proteins. Even more significant is the issue of "drug/drug" interactions that arise due to inhibition of the cytochrome P450 (CYP) hepatic microsomal enzyme system. Some antidepressants, such as paroxetine and fluvoxamine, are strong inhibitors of the CYP system. In the case of a medication that depends on renal clearance for elimination, caution is required when taking such a drug if it influences renal function. When a medicinal effect changes, pharmacodynamic changes must also be considered.
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