PARENTERALS I : Basics, route of administration, solvents used

Basics of parenteral dosage forms

Parenteral route: para- other, -enteral- intestine.

Parenteral dosage form: It can be defined as a sterile drug product, which is presented in the form of solution, suspension, emulsion or reconstituted lyophilised powder, suitable for administration by injection.

[Ref- https://www.sciencedirect.com/topics/medicine-and-dentistry/parenteral-drug-administration]

Routes of administration of parenterals:

1. Intravenous
2. Subcutaneous
3. Intramuscular
4. Intradermal
5. Intraspinal
6. Intrathecal
7. Intraarterial
8. Intraepidural
9. Intra-vitreous

• Maximum volume for single dose container: upto 1000 ml.
• Maximum volume for multi-dose container: up to 30 ml 
• Maximum volume for intradermal administration: 0.2 ml
• Maximum volume for subcutaneous administration: 1 ml
• Maximum volume for intramuscular administration: 2 ml/ 5 ml (for gluteal muscles).
• Maximum volume for intraarterial, intracardiac and intraspinal administration: 10 ml (without bactericide).
• Maximum volume for intravenous administration: 1000 ml ( 1 Liter).
• Maximum volume for intracorneal, sub-conjunctival and intravitreous administration: not exceeding 1 ml.

1. Volume not more than 20 ml should be administered by syringe.
2. Parenteral suspensions should not be given by intravenous route (blockage of small capillaries) and subcutaneous route (painful and irritating).
3. Mostly the vehicle for intravenous and intraspinal administration is aqueous in order to avoid damage to the brain capillaries.
4. In case of  intramuscular administration preparations can be aqueous or oil based.

VEHICLE USED FOR PARENTERAL PREPARATIONS

Mostly water is used in the parenteral formulations.

Depending on the stages at which water is used, it is divided into three categories:

1. Water for Injection (WFI): WFI is prepared by distillation or 2 stage reverse osmosis. It is used as a solvent for preparation of most of the injections. It should not contain more than 0.25 USP endotoxin units.
2. Sterile Water of Injection: Sterile WFI is prepared by sterilization of WFI. Limits for total solid content are slightly higher for Sterile WFI than WFI. This is the case because, WFI is packaged and then containers are sterilized (possibility of leaching of container material into water). Sterile water for injection is used only for dilution and reconstitution purposes with addition of isotonicity agent. It is supplied only as a single dose container.
3. Bacteriostatic Water for Injection: It is same as that of sterile water for injection and serves the same purpose. It is packaged as a single or multiple-dose container of volume not more than 30 ml. It is packaged along with bacteriostatic agents.

CO-SOLVENTS

• Co-solvents are the water miscible materials (liquids) used for solubilization of drug in the water.
• Examples- glycerin, ethyl alcohol, polyethylene glycol (PEG), propylene glycol, dimethyl acetamide, etc.

NON-AQUEOUS VEHICLES

• In oil- based and emulsion preparations certain fixed oils are used.
• Paraffin oil is never used in parenteral formulations.
• Sesame oil, cotton seed oil, isopropyl myristate, ethyl oleate.
• Sesame oil is having antioxidant properties.
• Commonly used non-aqueous solvents other than water are propylene glycol and polyethylene glycol.