Ayurveda and herbal or botanical ingredients most commonly are powders of the plant parts or their extracts or oils. Most of these can be administered as oral dosage forms such as capsules or tablets. Hard capsules offer some advantages over tablets as illustrated below.
Light, fluffy powders
Most of the Ayurveda and herbal powders are light, flappy and fibrous with bulk density less than 0.5 g/ml. These are difficult to compress as such in tablet form and will need granulation or roller compaction with binder and may often need diluent. Granulation can increase disintegration time or reduce dissolution requiring disintegrant. It is possible to fill such powders in capsules with minimum excipients.
Extracts are used to reduce the dose so that these can be formulated as capsules or tablets. Extracts can be hard or sticky or waxy and will need diluent to impart tableting. For example, Ashwagandha 250 mg extract needs almost equal quantity of excipients that makes a tablet 500 mg in weight. Corresponding capsule weighs about 400 mg.
Some of the ayurvedic and herbal products are too bitter and may need additional step of coating. Capsules offer good protection against the bitter taste.
Some Ayurveda and herbal products in powder or tablet form may have characteristic odour. Capsules can effectively block such odours.
Oils, oily extracts and essential oils as Liquid Filled Hard Capsules
Liquid Fill Hard Capsules (LFHC) technology enables filling of liquids in hard capsules and band sealing these capsules. Other options are to absorb these oils on absorbents such as silicon dioxide and filling these powders in capsules or compressing as tablets after addition of diluents. Piascledine 300 (Expanscience Laboratories, France) is composed of a mixture of soybean oil and avocado oil. It was initially marketed as a tablet that required five manufacturing steps. The product has been changed to a liquid filled hard capsule that requires only mixing and filling and is also much smaller than original tablet. Some LFHC products are MCT oil, Flaxseed oil, Neem extract, Black seed oil, Brahmi, Moring leaf extract, Curcumin, Astaxanthin, Sea buckthorn, colostrum etc.
Liquid Filled Combination Capsules
Besides liquids, it is also possible to fill suspensions, semi-solids, pastes, hot melts (up to 70°C) and combination fills. Combination fills (Fig. 1) include pellets, mini/micro tablets or another capsule (capsule in capsule) in addition to the liquid. Contents of the capsule can be seen using transparent capsules. Liquids could be oils or non-aqueous systems. Even acidic aqueous systems can be filled in enteric capsules. Liquid filled capsules help to improve dissolution and bioavailability.
Fig. 1 – Capsules containing liquid plus tablet or another capsule
A combination product may consist of an outer hard capsule that contains both plant oils and a smaller enteric-coated capsule filled with probiotic bacteria. The coated inner capsule would create an effective moisture barrier for the probiotic bacteria in the stomach, allowing these otherwise incompatible ingredients to be administered together in a single dosage form.
Gelatin or HPMC capsules
There is choice to use either gelatin capsules or HPMC (Hydroxy Propyl Methyl Cellulose) capsules. HPMC is the vegetarian source and has lower moisture content of three to eight per cent as compared to 13-16 per cent for gelatin capsules.
Hygroscopic and moisture-sensitive formulations
Some of the herbal powders or extracts are hygroscopic for which HPMC capsules may be preferred. Gelatin capsules might turn brittle for such products and stability might get affected.
Saving on the packaging materials cost
Some tablets may require Alu-Alu foil packaging for better stability and protection from moisture. These tablets, if reformulated as capsule, may show better stability even in blister pack, which is more compact and more economical.
Delayed release capsules
Such capsules delay release of formulation by 60 minutes or when the capsule is exposed to intestinal pH. This is required for acid-sensitive products that require acid protection e.g. probiotics and enzymes, avoids acid reflux, ex- garlic, mint.
Some people such as small children and very old people may have difficulty in swallowing capsules or tables. Sprinkle capsules are designed to open easily and contents can be sprinkled or poured on soft food for easy swallowing.
Choice of colours
Body and cap of the capsules may be transparent or may have same or different colours. Large variety of colour shades are available. This can help to identify and differentiate products from one another.
Printing on capsules
Printing directly on the product to be administered can avoid mix-ups and wrong administration. Brandshield 360° technology enables having capsules printed with two colours, around the circumference, one on the cap and another colour on the body of the capsule. Brandshield 4C (Fig. 2) is the four-colour circular-oriented printing to differentiate the product, increase customer recall and protect against counterfeiting. Thus, product name or code, company name or logo, message, etc. can be pre-printed on the capsule to enhance the product value.
Fig. 2 – Brandshield 4C pre-printed empty capsules
Enteric coating or enteric pre-coated capsules
Enteric coating helps to protect the contents from acidity of the stomach and allows delayed or targetted release of the active ingredients. For example, Colpermin capsules, manufactured by Tillots Pharma, contains 0.2 ml peppermint oil in enteric-coated hard capsule for the treatment of irritable bowel syndrome. These capsules are coated after filling and band sealing. Band sealing of the capsule shell protects the contents from the coating material and also smooths the edge between the capsule body and cap. Now, pre-coated enteric capsules are available that will eliminate lengthy enteric coating process in the plant for capsules or tablets.
Capsules are tasteless, odourless and easy-to-swallow. Consumer perception is that capsules are of higher value and more effective.
It is beneficial to use hard capsules for filling ayurvedic and herbal products in many different ways such as easy processing, bitter taste and odour masking, filling liquid systems, combination filling, option of vegetarian capsules, moisture protection, delayed or enteric release, counterfeiting and branding through colour printing, consumer preference, etc.