Factors influencing oral absorption

Factors influencing oral absorption

Often patient instructions include a direction to take with food or take on an empty stomach. Absorption is slower with food for tetracyclines and penicillins, but for propranolol bioavailability is higher after food.

The most common change to absorption comes from alterations in gastric emptying. Most drugs begin to be absorbed after 30 minutes, but a delay in gastric emptying can cause this to be 90 minutes. Drugs are usually still fully absorbed, just the effect is flattened out. The following accelerate gastric emptying: glass cold water and metoclopramide; and these retard gastric emptying:

fatty meal, acidic drinks, anticholinergic drugs and increasing age.

Sometimes the pH at absorption site is changed due to disease or more commonly, other drugs. Since many drugs need to have an acidic environment, drugs such as omeprazole, antacids, and ketoconazole can decrease absorption of other drugs.

Lastly there may be alterations in the function of the gastric and metabolic enzymes. These alterations can be very significant (see first-pass effect) and are more likely to be due to drug interactions than any sort of disease state.