Pharmacotherapy can be defined as the treatment and prevention of illness and disease by means of drugs of chemical or biological origin. It ranks among the most important methods of medical treatment, together with surgery, physical treatment, radiation and psychotherapy. Although it is almost impossible to estimate the exact extent of the impact of pharmacotherapy on human health, there can be no doubt that pharmacotherapy, together with improved sanitation, better diet and better housing, has improved people’s health, life expectancy and quality of life.
Unprecedented developments in genomics and molecular biology today offer a plethora of new drug targets. The use of modern chemical synthetic methods (such as combinatorial chemistry) enables the synthesis of a large number of new drug candidates in shorter times than ever before. At the same time, a better understanding of the immune system and rapid progress in molecular biology, cell biology and microbiology allow the development of modern vaccines against old and new challenges.
However, for all these exciting new drug and vaccine candidates, it is necessary to develop suitable dosage forms or drug delivery systems to allow the effective, safe and reliable application of these bioactive compounds to the patient. It is important to realize that the active ingredient is just one part of the medicine administered to the patient and it is the formulation of the drug into a dosage form or drug delivery system that translates drug discovery and pharmacological research into clinical practice.
Indeed the drug delivery system employed plays a vital role in controlling the pharmacological effect of the drug as it can influence the pharmacokinetic profile of the drug, the rate of drug release, the site and duration of drug action and subsequently the side-effect profile. An optimal drug delivery system ensures that the active drug is available at the site of action for the correct time and duration.
Drug delivery systems
Drug delivery refers to approaches, formulations, technologies, and systems for transporting a pharmaceutical compound in the body as needed to safely achieve its desired therapeutic effect.
· Drug delivery systems according to the physical state
Based on physical state, drug delivery systems may be:
– Gaseous (e.g. anaesthetics),
– Liquid (e.g. solutions, emulsions, suspensions),
– Semisolid (e.g. creams, ointments, gels and pastes) and
– Solid dosage forms (e.g. powders, granules, tablets and capsules).
· Drug delivery systems according to route of administration
Another way of differentiating dosage forms is according to their site or route of administration.
– Parenteral drug delivery: Drugs can be administered directly into the body, through injection or infusion. Depending on the site of administration into the body it can be differentiated into:
a) Subcutaneous injection
b) Intramuscular injection
c) Intravenous injection
d) Intradermal injection
e) Intraperitoneal injection
– Oral drug delivery: The oral route is the most popular route to administer drugs. Suspensions, tablets, capsules,etc are administered through this route.
– Topical drug delivery: Drugs can also be administered on to the skin to enter into the body. Mostly semisolid dosage forms are used for this, including creams, ointments, gels and pastes. However, liquid dosage forms, such as emulsions, or solid dosage forms, such as transdermal controlled drug delivery systems (patches), can also be used.
– Transmucosal: In this drugs are administered hrough nasal, buccal/sublingual, vaginal, ocular and rectal routes.
· Drug delivery systems according to mechanism of drug release
Another system that can be used to differentiate drug delivery systems is according to the way the drug is released. It can be differentiated as:
– Immediate release – drug is released immediately after administration.
– Modified release – drug release only occurs sometime after the administration or for a prolonged period of time or to a specific target in the body. Modified-release systems can be further classified as:
a) Delayed release: drug is released only at some point after the initial administration.
b) Extended release: prolongs the release to reduce dosing frequency
– Sustained release: These systems maintain the rate of drug release over a sustained period of time.
– Controlled release: Controlled-release systems also offer a sustained-release profile but, in contrast to sustained-release forms, controlled-release systems are designed to lead to predictably constant plasma concentrations, independently of the biological environment of the application site. This means that they are actually controlling the drug concentration in the body, not just the release of the drug from the dosage form, as is the case in a sustained-release system.
– Targeted drug delivery (smart drug delivery): It is a method of delivering medication to a patient in a manner that increases the concentration of the medication in some parts of the body relative to others. The goal of a targeted drug delivery system is to prolong, localize, target and have a protected drug interaction with the diseased tissue.