Creams are defined as Semi-solid preparations for cutaneous application, intended for local or transdermal delivery of active substances, or for their emollient or protective action. They are of homogeneous appearance. Creams are topical semi-solid dosage form, contain one or more active ingredients uniformly dispersed or completely dissolved in a
specific base and suitable specific excipients such as, viscosity-enhancer agent, emulsifiers, antimicrobial agents, stabilizing agents and antioxidants.
Use of antimicrobial agent is quiet necessary in preparations that are more susceptible to the growth of microorganisms or unless product have itself some antimicrobial properties. Assurance must be provided through product sufficient preformulation studies that excipients do not interfere with availability of the active ingredient(s) and indicate
suitable compatibility with other excipients of the dosage form.
Stability of a pharmaceutical product may be defined as the proficiency of any dosage form in a specific container/closure system to persist its physical, chemical, toxicological, microbiological specifications. Stability of pharmaceutical preparations can also be affected due to microbiological changes like growth of microorganisms in non-sterile products and changes occurs in preservative efficacy. Stability studies are useful in
providing sufficient information that must be required in selection of acceptable formulations, excipients and packing material for under development product and to evaluate its shelf life and storage conditions.
According to WHO, environment factors effects the stability of finished pharmaceutical products which include temperature, light, humidity .On the other hand nature and physicochemical properties of active ingredients and excipients also influence the stability of product. Manufacturing procedure, closure, container and packing material nature play an important role in maintaining the stability of preparations.
Types of Degradation in Creams
• Degradation by heat
• Degradation by change in pH
• Degradation by microbial contamination
• Degradation by formulation ingredients
Evidence of degradation
Visible change in consistency or appearance in dosage form like excessive “bleeding” (separation of excessive amounts of liquid) or formulation forms grittiness and agglomerates. Other noticeable changes are:
• Change in color or discoloration
• Emulsion breakdown; Crystal formation
• Preparation shrinked due to evaporation of water
• Evidence of presence of microbial growth
• Change in odor is also a sign of instability
• Avoid to form dilutions of topical semi solid dosage form until and unless it must require and care should be taken to use base of same type to obtain homogenous mixture.
• Creams should be of uniform consistency. No solid components should be observed when a cream is rubbed on the back of the hand.
• The container material must not interfere with product and affect the quality of the preparation or allow contamination of any type across the material of the container into the preparation. The closure must be well fitted to container and is equipped in such a way that tells whether the container has ever been opened or not.
• Packaging must be adequate to protect Topical semi-solid dosage forms, must be packed that it is prevented from light, humidity, and loss during handling and transportation. Mostly flexible metal tubes are used. Nasal, aural, vaginal, or rectal creams should be delivered in containers modified for suitable delivery of the product to the site of application, or along with proper applicator.
Stability Testing Methods
Stability testing is performed to determine the quantitative decrease in the amount of active ingredient in any dosage form due to degradation. Stability indicating methods are used to measure concentration of active ingredient accurately regardless of presence of impurities and interaction of excipients or degradation products. Following are types of
Real-time stability testing
To get significant degradation in product under recommended storage conditions, real time stability test is performed; it is done for long period of time to achieve required degradation.
Accelerated stability testing
In accelerated stability testing, a product is subjected to different raised temperatures, warmer and ambient to accelerate degradation. Amount of heat that is supplied to make conditions required for product failure is than calculated.
Retained sample stability testing
In this testing one batch products are retained for at least 1 year and performed stability testing .This practice is required for usually every marketed product.
Cyclic temperature stress testing
In cyclic temperature stress testing, product being subjected to cyclic temperature stress on the basis of knowledge of product in order to create likely market place storage conditions. The cycle time is set as 24 hours according to diurnal rhythm on earth i.e. 24 hour. This testing is not considered as routine testing for marketed products but mostly products experienced such conditions during storage in market.
Microbiological Spoilage in Pharmaceutical Creams and Cosmetics
Major cause of microbiological spoilage in cream are bacteria, yeast or fungi which enormously affect their metabolic activities by making behavioral changes due to genetic alterations which lead to adaptations of wide range of environment conditions .Genetic mutation is also another cause of microbiological spoilage.
Toiletry products, complex cosmetics of either usual ingredients or natural products including vitamins and animal proteins, come under this heading. These materials are highly susceptible to microbial growth because of reason these provides sufficient nutrients to micro-organism, destroy activity of preservatives added and lead to contamination. Example of Klebsiella species was quoted in this article that this organism frequently produces gas in prolonged preserved products when subjected to use in cream and lotions.
Topical preparations may contain some level of microbial presence in which Staphylococci and other gram-positive cocci are more preeminent. These topical products have less capability of suppressing bacterial growth during usage and usually do not meet the microbial limits stated in official monographs. Microbial contamination adversely affects the stability of product.
Following are some significant changes occur in pharmaceutical creams and lotions due to microbial contamination.
• Altered activity
• Visible growth
• Gas production
• Color changes
• Change in texture and taste
• Olfactory effect