Overview of parenteral or injectable dosage forms & more on leading CDMOs offering injectable / parenteral formulation development services.
Q1. What are the injectable formulations and what benefits do they offer over other dosage forms?
Injectable formulations are sterile preparations intended to be administered directly into the systemic circulation system in humans or animals. Intravenous, subcutaneous, and intramuscular injection of parenteral formulations are important and critical routes of administration when oral ingestion of drugs is contraindicated.
Injectable formulations, also known as parenteral formulations, include injectable solutions, injectable suspensions, or injectable emulsions, powders for injection or infusion, and implants.
Injectable forms are thus drugs that are administered directly into veins, muscles or under the skin, or more specialized tissues such as the spinal cord. In order to achieve delivery via such routes, parenteral dosage forms need to be stable, sterile, isotonic, chemically pure and free from pyrogens, toxins and foreign particles.
Some Advantages of Parenteral Preparations or Injectable Forms:
- Parenteral products or injectable drug products are useful for patients who cannot take drugs orally or those that are destroyed by digestive secretions such as insulin, other hormones and antibiotics.
- Parenteral preparations can be injected directly into tissues for targeted drug delivery which can elicit an immediate drug response.
- Parenteral products could be used on unconscious, uncooperative, and vomiting patients or under circumstances that require rapid onset of action.
- Parenteral preparations are free from pyrogens and have low toxicity as compared to solid dosage forms.
Complex parenteral formulations or injectable formulations are widely used for treating cancer and intravenous administration is the most frequently used route for parenteral chemotherapy. In addition, the rising prevalence of rheumatoid arthritis is expected to aid business development of injectable cytotoxic drugs (cytotoxic medications).
Furthermore, as per a report published by Fortune Business Insights ‘the global injectable cytotoxic drugs market size was USD 15.81 billion in 2019. The global impact of COVID-19 has been unprecedented and staggering, with injectable cytotoxic drugs (cytotoxic medications) witnessing a positive demand shock across all regions amid the pandemic’.
Q2. What are the different components involved in the development of injectables?
The different types of parenteral drug products include sterile solutions, injectable suspensions, injectable emulsions, etc. The components which constitute parenteral finished products include active ingredients, formulation additives, vehicles, and primary container and closure systems. These injectable drug product components are explored in detail below.
Active Pharmaceutical Ingredients (APIs)
The active pharmaceutical ingredient (API) is the ingredient of the medicine that allows the medicine to have a therapeutic effect in the body. Examples of active ingredients include paracetamol, ibuprofen and insulin.
Formulation Additives
Formulation additives or added substances may include preservatives, water-soluble or oil-soluble antioxidants, buffer systems, etc. These substances usually play a role in safeguarding the purity of a formulation.
Excipients are added to injectable forms to enhance or maintain active ingredient solubility (solubilizers) and/or stability (buffers, antioxidants, chelating agents, cryo- and lyoprotectants). Added substances are also involved in maintaining sterility, minimizing pain and tissue irritation, maintaining and controlling solubility and functioning as bulking agents, viscosity imparting agents, etc.
Formulation Vehicles
Water is the most commonly used vehicle for parenteral preparations and is the most suitable since aqueous preparations are well tolerated by the body and are the safest to be used. Highly purified water, bacteriostatic water, or sterile water for injection may be used.
In addition to the type of aqueous vehicle selected, water miscible solvents are used to make a portion of the vehicle. They primarily affect the solubility of drugs and reduce hydrolysis. Alternatively non-aqueous vehicles like oils and oleates may be used to constitute the vehicle for a parenteral dosage form.
Primary Container and Closure Systems
Once the finished parenteral products are prepared they are packaged in primary containers and closed with closure systems. Finished parenteral products are usually packed in glass ampoules, bottles or vials, in plastic bottles or bags, or in pre-filled syringes. Desirable features of an injection container include no interactions with the container contents, withstanding high temperatures, protection against light, etc.
Next the ampoules, vials, pre-filled syringes, etc. are fitted with container closure systems which include natural and synthetic rubber among other materials. Closures, also known as stoppers, are an important part of the final packaging of pharmaceutical preparations, particularly those that are intended to be sterile. Finished parenteral products are sterile preparations which are sealed using container closure systems.
Q3. What are the biggest challenges associated with parenteral drug formulations?
Some challenges associated with parenteral drug formulations and injectable drug development are explored below.
- The main challenge with parenteral dosage forms is achieving drug substance and excipient compatibility as well as avoiding leaching or adsorption issues between the preparation and the primary container.
- When novel added substances are used in the development of parenteral drug products, new excipient approvals are required. To achieve a new excipient approval, one has to ensure that there is enough safety data available, and that the toxicity studies have been done.
- Manufacturing sterile APIs for the development of injectable drug products has its own set of challenges including manufacturing issues related to sterilization, validation, lyophilization, GMP compliance and stability.
- Various measures need to be reviewed for container closure systems during the development of parenteral drug products including suitability, integrity and coring studies for multidose containers to ensure that a container closure system (CCS) is compatible with the given parenteral preparation.
- Another major issue associated with the development of injectable products is poor solubility which consequently results in lower drug absorption. Various solubility enhancing techniques can be used to increase the solubility of a parenteral product.
- Some other limitations associated with the formulation development of parenteral products include