Chapter 7 Routes of Drug Administration

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Oral (PO)

Oral administration will be covered in more detail in subsequent Chapters. Absorption after oral administration can be quite variable. Dosage form design may also be used modify the rate of absorption.

Advantages:

Convenient - portable, safe, no pain, easy to take.

Cheaper - compact, multi-dose bottles, automated machines produce tablets in large quantities.

Variety of dosage forms available - fast release tablets, capsules, enteric coated, layered tablets, slow release, suspensions, mixtures

Disadvantages:

Sometimes inefficient - high dose or low solubility drugs may suffer poor availability, only part of the dose may be absorbed. Griseofulvin was reformulated about 1970 to include the drug as a micronized powder. The recommended dose at that time was decreased by a factor of two because of the improved bioavailability.

Figure 7.2.1 First Pass Effect

First-pass effect - drugs absorbed orally are transported to the general circulation via the liver. Thus drugs which are extensively metabolized will be metabolized in the liver during absorption.

e.g. the propranolol oral dose is somewhat higher than the IV, the same is true for morphine. Both these drugs and many others are extensively metabolized in the liver.

Food - Food and G-I motility can effect drug 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, etc. However, for propranolol bioavailability is higher after food, and for griseofulvin absorption is higher after a fatty meal.

Local effect - Antibiotics may kill normal gut flora and allow overgrowth of fungal varieties. Thus, antifungal agent may be included with an antibiotic.

Unconscious patient - Patient must be able to swallow solid dosage forms. Liquids may be given by tube.

Figure 7.2.1 Typical Plot of Cp versus Time after Oral Administration Fast and Slow Release Dosage Forms

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