Drug Administration

Drugs are administered by many different routes. The aim of drug administration is to achieve therapeutic levels of the drug at its site (or sites) of action. In general, this is achieved using the vascular compartment as the transport mechanism for redistribution. Drug administration is, therefore, designed to produce suitable drug levels within the blood. The choice of route for a particular drug takes into account physical properties, target site of action, consideration of possible toxic effects and the practicalities of administration. The routes are summarized in Figure PK.2 in a practical classification. The enteral and topical routes are most easily accessible, but require absorption across a barrier or membrane to establish their effect.

Absorption

Absorption is the process of taking the drug from the site of administration to the blood. This is necessary for all enteral and parenteral routes except for IV administration. Systemic absorption may occur from topically administered drugs but this is not the intended route. Absorption involves the crossing of barriers between administration site and vascular compartment with subsequent movement across the physical distance between the two. The distance within any local compartment is traversed by simple passive diffusion down the concentration gradient. Most barriers are made up of cells closely linked by tight junctions. The cell, thus, acts as both a filter and a device for active uptake so the drug must pass into and then out of the cell to cross the barrier. The main principles affecting absorption include:

INPUT Gn^rQ-inlesïrol MÏICI

Absorption

RECIFPTQR SI"F5 Î

Bojnd drLy

OUTPUT II. no

INPUT Gn^rQ-inlesïrol MÏICI

Absorption

RECIFPTQR SI"F5 Î

Bojnd drLy

Figure PK.1 Overview of pharmacokinetic processes

ROUTES OF DRUG ADMINISTRATION

Enteral

Oral

Buccal

Rectal

Parenteral

Intravenous

Intramuscular

Subcutaneous

Intradermal

Transdermal

Inhalational

Transtracheal

Topical

Skin

Eyes

Ears

Intranasal

Vaginal

Figure PK.2

• Simple passive diffusion

• Facilitated diffusion

• Active uptake

• Pinocytosis

The rate of diffusion is shown by the following formula: <,:av

where:

C = concentration difference either side of membrane A = area of membrane P = membrane permeability T = membrane thickness

The ability of a drug (or any molecule) to pass through a membrane is influenced by:

• Solubility in the membrane (lipid solubility)

• Degree of ionization

Was this article helpful?

0 0
Peripheral Neuropathy Natural Treatment Options

Peripheral Neuropathy Natural Treatment Options

This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.

Get My Free Ebook


Post a comment