A drug carrier or drug vehicle is a substrate used in the process of
drug delivery
Drug delivery refers to approaches, formulations, manufacturing techniques, storage systems, and technologies involved in transporting a pharmaceutical compound to its target site to achieve a desired therapeutic effect. Principles related to d ...
which serves to improve the selectivity, effectiveness, and/or safety of
drug administration
A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and rel ...
. Drug carriers are primarily used to control the release of
drugs
A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via inhalat ...
into systemic circulation. This can be accomplished either by slow release of a particular drug over a long period of time (typically
diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
) or by triggered release at the drug's target by some stimulus, such as changes in pH, application of heat, and activation by light. Drug carriers are also used to improve the
pharmacokinetic
Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to determining the fate of substances administered ...
properties, specifically the
bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.
By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...
, of many drugs with poor water solubility and/or membrane permeability.
A wide variety of drug carrier systems have been developed and studied, each of which has unique advantages and disadvantages. Some of the more popular types of drug carriers include
liposome
A liposome is a small artificial vesicle, spherical in shape, having at least one lipid bilayer. Due to their hydrophobicity and/or hydrophilicity, biocompatibility, particle size and many other properties, liposomes can be used as drug deliver ...
s, polymeric
micelle
A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated collo ...
s,
microspheres
Microparticles are particles between 0.1 and 100 μm in size. Commercially available microparticles are available in a wide variety of materials, including ceramics, glass, polymers, and metals. Microparticles encountered in daily life includ ...
, and
nanoparticles
A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...
.
Different methods of attaching the drug to the carrier have been implemented, including
adsorption
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
, integration into the bulk structure,
encapsulation, and
covalent bond
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
ing. Different types of drug carrier utilize different methods of attachment, and some carriers can even implement a variety of attachment methods.
Carrier types
Liposomes
Liposomes are structures which consist of at least one
lipid bilayer
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...
surrounding an aqueous core. This hydrophobic/hydrophilic composition is particularly useful for drug delivery as these carriers can accommodate a number of drugs of varying
lipophilicity
Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipop ...
. Disadvantages associated with using liposomes as drug carriers involve poor control over drug release. Drugs which have high membrane-permeability can readily 'leak' from the carrier, while optimization of ''in vivo'' stability can cause drug release by diffusion to be a slow and inefficient process.
Much of the current research involving liposomes is focused on improving the delivery of anticancer drugs such as
doxorubicin
Doxorubicin, sold under the brand name Adriamycin among others, is a chemotherapy medication used to treat cancer. This includes breast cancer, bladder cancer, Kaposi's sarcoma, lymphoma, and acute lymphocytic leukemia. It is often used togeth ...
and
paclitaxel
Paclitaxel (PTX), sold under the brand name Taxol among others, is a chemotherapy medication used to treat a number of types of cancer. This includes ovarian cancer, esophageal cancer, breast cancer, lung cancer, Kaposi's sarcoma, cervical cancer ...
.
Polymeric micelles
Polymeric micelles are drug carriers formed by the aggregation of some
amphiphilic
An amphiphile (from the Greek αμφις amphis, both, and φιλíα philia, love, friendship), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'') properties. Such a compoun ...
molecule with an amphiphilic
block copolymer
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
. These carriers form at some high concentration specific to the compounds used, called the
critical micelle concentration
In colloidal and surface chemistry, the critical micelle concentration (CMC) is defined as the concentration of surfactants above which micelles form and all additional surfactants added to the system will form micelles.
The CMC is an important ch ...
. The addition of an amphiphilic block copolymer effectively lowers this critical micelle concentration by shifting the monomer exchange equilibrium.
These carriers are comparable to liposomes, however the lack of an aqueous core makes polymeric micelles less accommodating to a wide variety of drugs.
Microspheres
Microspheres are hollow, micron-sized carriers often formed via self-assembly of polymeric compounds which are most often used to encapsulate the active drug for delivery. Drug release is often achieved by diffusion through pores in the microsphere structure or by degradation of the microsphere shell. Some of the research currently being done uses advanced assembly techniques, such as precision particle fabrication (PPF), to create microspheres capable of sustained control over drug release.
Nanostructures
Nanodiamonds
Nanodiamond
Nanodiamonds, or diamond nanoparticles, are diamonds with a size below 100 nanometers. They can be produced by impact events such as an explosion or meteoritic impacts. Because of their inexpensive, large-scale synthesis, potential for surfa ...
s (NDs) are carbon nanoparticles which can vary from ~4-100 nm in diameter. NDs are typically formed in two ways: from micron-sized diamond particles under high-pressure high-temperature conditions, called high-pressure high-temperature nanodiamonds (HPHT NDs) and by shock-wave compression, called detonation nanodiamonds (DNDs). The surfaces of these NDs can be modified by processes such as oxidation and aminification to alter adsorption properties.
Nanofibers
Protein-DNA complexes
Protein-drug conjugates
Erythrocytes
Virosomes
Dendrimers
Resources
''The following research papers from
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
are in pdf format'':
Biodegradable hydrogels for bone regeneration through growth factor releaseDevelopment of acid-sensitive copolymer micelles for drug delivery
References
{{reflist
External links
at
PhysOrg.com
Phys.org is an online science, research and technology news aggregator offering briefs from press releases and reports from news agencies (a form of journalism sometimes pejoratively called churnalism). The website also produces its own science ...
Designing Better Cancer Drugs Insight into Carrier Molecules' Functionality which may yield Safer Cancer Treatmentsat MIT magazine
TechnologyReview.com
Medicinal chemistry