Absorption rate is a measures of how quickly a drug or other substance is absorbed into the bloodstream. The faster the absorption, the more rapidly the substance will take effect. The absorption rate is affected by many factors, including the route of administration (e.g., oral, intravenous), the type of formulation (e.g., tablet, suspension), and individual differences in physiology (e.g., body weight, gut motility). Generally speaking, substances that are injected directly into the blood stream will have a more rapid absorption than those taken orally. Likewise, substances that are in a gel or liquid form will be absorbed more quickly than those in a solid form. Factors that can decrease absorption rate include food in the stomach (which can bind to and slow the release of a drug from its tablet formulation), and certain medical conditions such as diabetes (which can delay gastric emptying).
There are several methods for assessing absorption rate. The most common is measuring the concentration of the substance in the blood over time. This can be done through periodic blood draws or, more commonly, continuous monitoring via an intravenous catheter. Other methods include measuring the amount of drug excreted in urine or sweat, or changes in heart rate or other physiological parameters that occur after administration of the drug.
Absorption rate is an important consideration in drug development and therapeutic use. Drugs that are absorbed too slowly may not reach therapeutic levels in the body, while those that are absorbed too quickly may cause side effects. Therefore, optimizing absorption rate is a key goal in the design of new drugs and formulations.