Drug carriers are substances that serve as mechanisms to improve the delivery and the effectiveness of drugs. Drug carriers are used in sundry drug delivery systems such as:
- controlled-release technology to prolong in vivo drug actions;
- decrease drug metabolism, and
- reduce drug toxicity.
Carriers are also used in designs to increase the effectiveness of drug delivery to the target sites of pharmacological actions.
Carriers which are able to biodegrade include:
- Microspheres made of the biodegradable polymer poly(lactic-co-glycolic) acid
- albumin microspheres;
- synthetic polymers (soluble);
- Protein-DNA complexes;
- protein conjugates;
See also 
The following research papers from IUPAC are in pdf format:
- Biodegradable hydrogels for bone regeneration through growth factor release
- Development of acid-sensitive copolymer micelles for drug delivery
- Weighting cancer drugs to make them hit tumors harder PhysOrg.com article
- Designing Better Cancer Drugs Provides insight into carrier molecules' functionality which may yield safer cancer treatments.