Stability Testing of Herbal Drugs

As per PCI Syllabus

(T. Y. B. Pharm  Sem –VI)  Unit- IV)

Stability testing of herbal drugs

Herbal drugs may be single active constituent or entire herb or combination of herbs consisting of mixture of constituents. Most of herbal drug products used are group of Constituents.

Stability testing of herbal products is a complicated issue because the entire herb or herbal product is regarded as the active substance, regardless of whether Constituents with defined therapeutic activity are known.
Trace metal contamination, leaching from the container, etc. & also Provide statistics for determination of shelf life.

The stability testing of herbal products include checking the quality which varies with the time under the influence of environmental factors, such as temperature, humidity, light, oxygen, moisture, other ingredient or excipients in the dosage form, particle size of drug, microbial contamination.

Therefore evaluation of the parameters based upon chemical, physical, microbiological, therapeutic and toxicological studies can serve as an important tool in stability studies.

Stability testing is required to determine the shelf life and assign expiry dates to medicines.

Problems related to the herbal product stability
Physical instability :

Natural medicines are usually prone to physical instability due to the presence of impurities and reaction with the container. Conditions like growth of the microorganisms and insect feeding affect the secondary metabolites and chemical composition of plants.

Volatile active components of natural medicine have the problem of volatility and decreasing activity during storage for a long time.

Environmental conditions
Environmental conditions such as rainfall, altitude, temperature, soil, storage conditions as well as different harvesting procedures, time and method of collection, manufacturing processes such as selecting, drying, purifying, extracting, and genetic variability can create substantial variability in the product quality, stability and in the concentration of plant constituents.

Light is also an important factor affecting phytomedicines by generating free radicals.

Chemical instability :

Herbal drugs are subjected to degradation during storage by oxidation, hydrolysis; crystallization, emulsion breakdown, enzymatic deterioration & chemical reactions with the additives & excipients. Temp. & moisture are the two major factors that affect quality & stability of a herbal product.

A chemical reaction increases by 2 to 3 fold for every 10°C rise in temp. Moisture absorbed on to the surface of solid drug often increases the rate of decomposition if it is susceptible to hydrolysis. Presence of enzymes in the product also increases the rate of chemical degradation.

Complex mixture variability  and inconsistency :

Herbal formulations are complex mixtures of different components obtained during extraction process. Each component has variable shelf life, activity, concentration and consistency. 
It creates a problem during storage condition determination as it is not easy to determine the stability of final herbal preparation based on the activity and stability profile of a single component.

Drug interactions deterioration decomposition and storage:

Moisture content above the critical value and mould growth in natural products can cause the interaction of the active components with the packaging material.

Also interactions of active component with the other ingredients of formulations used such as additives cause alteration in the novel drug activity.

Stability studies should be performed on at least three production batches of the herbal products for the proposed shelf life, which is normally denoted as long term stability and is performed under natural atmospheric conditions.

With the help of modern analytical techniques like spectrophotometry, HPLC, HPTLC and by employing proper guidelines it is possible to generate a sound stability data of herbal products and predict their shelf-life, which will help in improving global acceptability of herbal products.

Role of markers in determining the stability of herbal drugs:

Markers are chemically known compounds, which may or may not have therapeutic effect, they are used to calculate the quantity of herbal medicinal ingredients in herbal medicinal products.

It is important to isolate and structurally elucidate chemically defined substances in plants, drug and/ or drug preparations so that they can be used as markers that not only help to better understand the active principles of herbal drugs but also can enhance analytical quality control.

Analytical methods to determine stability of herbal products :
The analysis of herbal preparations is mostly done by modern chromatographic or Spectroscopic methods like HPLC, gas chromatography (GC), TLC, quantitative determinations by UV Visible spectroscopy or combinations of these. 

HPLC and GC methods can be used for identification and purity testing, as well as the detection of single compounds for assay, is possible during one analysis. LC and GC mass coupling are also the tools for determination.

Methods to deal with herbal drug instability 

Determination of the physical parameter :

Depending on type of preparation, sensory properties, physical constants, moisture, ash content, solvent residues & adulterations have to be checked to prove identity and purity Microbiological contamination and foreign materials such as heavy metals, pesticide residues,alfatoxins & radioactivity also need to be tested.

To prove the constant composition of herbal preparations, appropriate analytical methods have to be applied and different concepts have to be used in order to establish relevant criteria for uniformity. 

Determination of the impurity profile 
This technique helps in the identification of impurities that result from degradation of active constituents. The active constituents are subjected to a known degradation process and the degradation products are identified.

Degradation may be due to oxidation, reduction or hydrolysis hence we can have an idea of what could be the degradation products. 

These can be listed and kept as a reference library of degradation products. For routinely doing an impurity profile, this library can be referred and the nature and structure of the impurity can be traced.

Since impurities decrease the stability of the natural medicines, it is important to note the type of impurities.

It can be done by the analytical methods as HPLC, TLC, capillary electrophoresis,spectrophotometry, GC-MS etc.

Identification and quantification of all metabolites :

Non based identification and quantification of all metabolites in herbal or other natural products is vital to determine the status and stability of the complex mixtures.
IR spectroscopy in combination with chemometric data processing could provide total metabolic fingerprint profile of phyto formulations. 


Controlled storage conditions :

Control measure to protect against deterioration includes the use of airtight container made of materials that will not interact physically or chemically with the material being stored.  

Storage in ventilated cool, dry area and periodic spraying of the stored area with insecticide will help to prevent the spread of infestation. 

Influence of environmental factors such temperature, light, oxygen, moisture, other ingredient or excipients in the dosage form particle size of drug, microbial contamination, trace metal contamination, leaching from the container, etc.  should be established to recommend proper storage conditions.


 Thank you.