SPECIAL DRUG DELIVERY SYSTEMS
In order to improve drug delivery, to prolong the duration of action and thereby improve patient compliance, special drug delivery systems are being tried. Drug targeting, i.e. to deliver drugs at the site where it is required to act is also being aimed at, especially for anticancer drugs. Some such systems are ocusert, progestasert, transdermal adhesive units, prodrugs, osmotic pumps. Computerized pumps and methods using monoclonal antibodies and liposomes as carriers.
Ocusert : Ocusert systems are thin elliptical units that contain the drug in a reservoir which slowly releases the drug through a membrane by diffusion at a steady rate, e.g. pilocarpine ocusert used in glaucoma is placed under the lid and can deliver pilocarpine for 7 days.
Progestasert is inserted into the uterus where it delivers progesterone constantly for over 1 year.
Transdermal adhesive units:
Prodrug is an inactive form of a drug which gets metabolized to the active derivative in the body. A prodrug may overcome some of the disadvantages of the conventional forms of drug administration, e.g. dopamine does not cross the BBB; levodopa, a prodrug crosses the BBB and is then converted to dopamine in the CNS. Prodrugs may also be used to have a longer duration of action, e.g, Bacampicillin (a prodrug of ampicilin) is longer acting.
Osmotic pumps are small tablet-shaped units containing the drug and an osmotic substance in two different chambers. The tablet is coated with a semipermeable membrane in which a minute laser-drilled hole is made. When the tablet is swallowed and reaches the gut, water enters into the tablet through the semipermeable membrane. The osmotic layer swells and pushes the drug slowly out of the laser-drilled orifice.
This allows slow and constant delivery of the drug over a long period of time. It is also called gastrointestinal therapeutic system (GITS). Some drugs available in this formulation are iron and prazosin.
Computerized miniature pumps: These are programmed to release drugs at a definite rate either continuously as in case of insulin or intermittently in pulses as in case of GnRH. Various methods of drug targeting are tried especially for anticancer drugs to reduce toxicity.
Monoclonal antibodies are antibodies against the tumor specific antigens are used to deliver anticancer drugs to specific tumor cells.
Liposomes are phospholipids suspended in aqueous vehicles to form minute vesicles. Drugs encapsulated in liposomes are taken up mainly by the reticuloendothelial cells of the liver and are also concentrated in malignant tumors. Thus site-specific delivery of drugs may be possible with the help of liposomes.
- Ensure that the correct drug is administered by the right route and in the right dose.
- History of allergy should be taken particularly before parenteral administration of drugs
- Monitor the adverse effects
- Drugs should be kept in a safe place
- Check the prescription, drug label and the patient’s name before the administration of drugs.