Drug Delivery Systems: An Overview

Drug delivery systems (DDS) are an important component of drug development and therapeutics. The design of an effective delivery system requires a thorough understanding of the drug, the disease, and the target site. Various physicochemical product properties that influence the quality features of plasma clearance kinetics, tissue distribution, metabolism, and cellular interactions of a drug can often be controlled by using a delivery system.

This article focuses on what drug delivery systems are, characteristics of an ideal drug delivery system, classification of drug delivery systems as well as various drug delivery routes.

What is a drug delivery system?

Drug delivery systems (DDSs) are polymeric or lipid carrier systems that transport drugs to their targets or receptor sites in a manner that provides their maximum therapeutic activity, prevent their degradation or inactivation during transit to the target site(s) and protect the body from adverse reactions due to inappropriate disposition. It can be defined as a formulation or a device that enables the introduction of a therapeutic substance in the body and improves its efficacy and safety by controlling the rate, time, and place of release of drugs in the body.

The goal of an optimal DDS is to release the drug(s) to simultaneously provide maximal safety, effectiveness, and reliability.

Read Also: Understanding Pharmaceutical Dosage Forms

Ideal characteristics of drug delivery systems

1. It should increase the bioavailability of the drug.
2. It should transport the drug intact to the site of action while avoiding the non-diseased host tissue.
3. The product should be stable and delivery should be maintained under various physiological variables.
4. A high degree of drug dispersion.
5. The same method should be applicable to a wide range of drugs.
6. It should be easy to administer to the patient.
7. It should be safe and reliable.
8. It should be cost-effective.

Classification of drug delivery systems

Basically, the DDSs can be divided into two main types:

1. conventional DDSs and
2. novel DDSs.

Conventional drug delivery systems

Conventional DDSs are classical methods for delivery of a drug into the body. Generally, these systems are used more often when the goal is quickly absorption of a drug; therefore, a quick release of the drug is required. The conventional drug delivery forms include simple oral, topical, inhaled, or injection methods.

These methods cannot keep the drug concentration at a fixed and constant level for a given period of time (temporal delivery). One solution to overcome the problem of drug instability concentration is administration of multiple doses at regular intervals (repeated doses). However, this method has its own limitations. The concentration of the drug varies up and down irregularly in blood plasma and patient typically forgets to take the specific dose at its exact time. Due to the problems mentioned for conventional DDSs, the necessity of providing novel DDSs becomes more apparent.

Novel drug delivery systems

Novel drug delivery system (NDDS) sometimes called controlled DDS is a combination of advanced techniques and new dosage forms to introduce better drug potency, control drug release, provide greater safety, and target a drug specifically to a desired tissue. The term “controlled release” has a meaning that goes beyond the scope of only sustained release action. In other words, controlled release must have two properties such as predictability and reproducibility in the release kinetics.

NDDSs lead to efficient use of expensive drugs and excipients, and reduce in production cost. From the patient point of view, NDDS brings better therapy by improved comfort drug delivery devices which increase the standard of living.

NDDSs are divided into four categories including

1. rate-preprogrammed
2. activation-modulated
3. feedback-regulated
4. site-targeting DDSs

Drug delivery routes

Route of administration is the path taken by the drug to get into the body. Drugs may be introduced into the human body by various anatomical routes which are sometimes also the site of action, but most commonly transitory passages. They may be administered either systemic effects or targeted to various organs and diseases.

The choice of the route of administration depends on the disease, the effect desired, and the product available. Classification of various methods of systemic drug delivery by anatomical routes is shown below.

1. Gastrointestinal system
   • Oral
   • Rectal
2. Parenteral
   • Subcutaneous injection
   • Intramuscular injection
   • Intravenous injection
   • Intra-arterial injection
3. Transmucosal: buccal and through mucosa lining the rest of gastrointestinal tract
4. Transnasal
5. Pulmonary: drug delivery by inhalation
6. Transdermal drug delivery
7. Intraosseous infusion.

References

• Jain, K. (2020). Drug Delivery Systems (3^rd ed.). USA: Springer Science+Business Media, LLC.
• Mahato, R. and Narang, A. (2018). Pharmaceutical Dosage Forms and Drug Delivery (3^rd ed.). New York: Taylor & Francis Group, LLC.
• Rezaie, H., Esnaashary, M., Aref arjmand, A. and Öchsner, A. (2018). A Review of Biomaterials and Their Applications in Drug Delivery. Singapore: Springer Nature Singapore Pte Ltd.