Pharmaceutical formulation is the process of combining various chemical substances with the active drug to form a final medicinal product, which is called a drug mixture or drug formulation.
A drug formulation can be given to the patient in various forms like solid, semisolid or liquid. The type of the formulation given depends upon the patient’s age, sex, and health condition and is specific for particular routes of administration.
Here we give a brief overview of the different forms of drug formulation development:
- Tablets – a tablet is disc-shaped and prepared by compressing a granulated powder in a die of suitable machinery. They are mostly coated with inert substances like starch to help them disintegrate in the digestive tract of the patient. A binding agent, lubricating material, and flavors are added to the tablets to make them palatable.
- Enteric Coated Tablets – are coated with a material that does not disintegrate in the acidic medium of the stomach but in the alkaline medium of the intestine. They can’t be chewed but consumed only by swallowing.
- Controlled Release Tablet – is designed to release the active ingredient of the drug in a specific amount over a specified period of time. Here, the amount of drug released is gradual over the day and doesn’t depend upon the pH of the digestive tract of the patient. Thus, a uniform amount of drug is released at a uniform rate.
- Sustained release preparations – release a fixed amount of drug over an extended period of time. Thus, they improve the treatment compliance by the patient.
- Capsules – can be hard or soft. Hard capsules contain the drug in solid form, which gets dissolved easily in water. Soft capsules have the drug in liquid or semi-solid form, which is non-soluble in water and soluble in propylene or glycol.
Liquid and Semi-Solid Formulations
They are more readily absorbed than the solid formulations and can be administered by various routes like:
- Oral preparations – Oral preparations are easier to swallow and administer medicines to children and old-age patients. Flavourings and sugar are added to some liquids to make them palatable. They are available as solutions, suspensions, or emulsions and must be shaken well before use.
- Topical Preparations – The application of a drug to an area of the body for direct treatment is called topical application. It includes:
- Eye drops
- Ear drops
- Nasal drops
- Nebulisers and inhalers
- Creams and ointments for skin application
- Gels and lotions
- Pessaries for vaginal administration of the drug
- Sublingual and Buccal Administration – It is useful for drugs which are active in very low concentration in the blood. Such drugs are administered as tablets under the tongue or between the cheek and the gum and allowed to dissolve. In this manner, the drug directly enters the bloodstream, bypassing the digestive tract and acts faster.
- Rectal Administration
- Suppositories: are used for drugs which are administered through the rectum. The drug is absorbed by the rectal mucosa and directly enters the bloodstream. The method is useful when a patient is unconscious, has nausea or difficulty in swallowing.
- Enemas: are liquid preparations for rectal administration. They can be used for topical or systemic treatment and also for a bowel movement.
- Parental Drug Administration – is drug administration outside the GI tract of the patient. Drugs can be inserted anywhere with the help of injections.
- Intradermal administration: where the drug is inserted into the dermis. g. Local Anaesthesia
- Subcutaneous injection: where the drug is inserted into the subcutaneous tissue or under the skin. It is mainly for the drugs that cannot be given through the mouth e.g. Insulin.
- Intramuscular injection: where the drug is inserted into the skeletal system or the muscle. The system is highly vascular, and hence, drugs with low molecular weight can easily pass through by direct diffusion into the bloodstream.
- Intravenous injection: is given directly in the vein and allows for a faster action of the drug.
However, to know whether to formulate a drug as a solid, liquid, or semi-solid formulation, a formulation scientist conducts a preformulation studies. Such studies help to evaluate the physical, chemical, and mechanical properties of the drug substance, its stability, and interaction with other chemical ingredients.
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