implant

An implant is a small solid object, often no bigger than a grain of rice or a thin rod, that is placed into the body, usually just under the skin, and slowly releases its drug over weeks, months, or even years. It is like burying a slow-leaking reservoir at the site where steady supply is wanted.

Implants are made from polymers or other solid materials that either let the drug diffuse out gradually, or erode away to release it, or sometimes both. Some are biodegradable and dissolve once the drug is spent, others are non-degradable and must be removed at the end. Familiar examples include contraceptive rods placed under the skin of the arm that work for several years, and small implants placed in the eye to treat chronic eye disease.

The great advantage is very long, steady delivery without the patient having to remember anything, which is excellent for adherence. The drawbacks are that insertion (and sometimes removal) is a minor surgical procedure, the dose cannot easily be adjusted or stopped once in place, and there can be irritation or scarring at the site. Implants suit potent drugs needed at a low, constant rate for a long time.