Enteric Coating Flashcards
Enteric Coating Def
Polymer barrier that controls release location of drug. The polymer only dissolves at high pHs. This prevents dissolution in the stomach and only allows dissolution in stomach. When enteric coating is removed drug can be dissolved
Enteric Coating Function
Prevent dissolution in stomach. Prevents irritation of stomach, provides delayed release for optimal absorption, mask taste/smell and give aesthetic appearance
What types of materials can be enteric coated
Tablets, capsules (soft and hard), beads, granules and drug particles
3 Enteric Coating Polymer Categories
Methacrylate derivatives, cellulose derivatives and polyvinyl acetate derivatives
Enteric polymers characteristics
Contain acidic groups (eg carboxylic acid) and thus dissolve only at higher pH (acids are ionised at pHs above their pKas). Carboxylic acids only dissolve at pH >5 (ressistant to gastric conditions and soluble in intestine). Forms a continuous, non-toxic, low cost film
Eudragits Outline
2 types commercially L (organic solution or solid/aqueous dispersion) and S (organic solution/solid) . Formed by polymerisation of acrylic and methacrylic acids. Solubilises at pHs 5.5-7 (neutral/alkaline pHs, higher then stomach).
Cellulose Acetate Phthalate Outline
Enteric coating that dissolves at 6.2
Hydroxypropyl methylcellulose phthalate Outline
Enteric coating dissolves 4.5-5.5
Polyvinylacetal phthalate
Enteric coating. Dissolution ~5
Gastric pH
1.6-7.2
Esophageal pH
4-7
Duodenum pH
6-7
Jejenum pH
6-7.7
Ileum pH
6.5-8
Ascending Colon pH
5.5-7.5
Descending Colon pH
7-8
Rectal pH
6.8-7.9
Polymethacrate Properties
Catatonic (immediate release), anionic (delyed response) and neutral (sustained release)
Cellulose Derivatives
Cellulose Acetate Phthalate, hypromellose phthalate and polyvinyl acetate phthalate
Cellulose Acetate Phthalate Outline
Enteric coating. Powder, granuales and and flakes. Dissolves above pH 6. Insoluble in water and alcohol. Soluble in acetone and diethylene glycol
Hypromellose phthalate Outline
Enteric coating - cellulose derivative, disintegrate faster and more stable then cellulose acetate phthalate. Powder, granule and flake form. Dissolves above pH of 5 in duodenum. Hygrsocopic. Insoluble in water and dehydrated alcohol. Soluble in ethanol or acetone and methanol mix
Polyvinyl acetate phthalate
Polyvinyl acetate derivative. Enteric coating (equal stability as Hypromellose phthalate), viscosity enhancer and pellet core. Dissolves at pHs above 6. Hydrophobic, less prone to hydrolysis then other polymers
Benefits/merits of enteric polymers
pH-dependent release, protection of gastric mucosa, degradation prevention, allows for intestinal and colon targeting (gastric acid resistance)
Enteric Coating Drug Release
Polymer is ionised and dissolves at certain pH. Tablet core (drug matrix) swells and is diintegrated through ionisaton/decomposition by microbes
Coating Matrices Characteristics Outline
Hardness > 80 N, convex/spherical shape, low friability (<0.5%), sealant (core protection) and starting tablet weight
2 Methods of Enteric Coating
Fluid bed and pan coating
Pan Coating Outline
Tablets places in drum. Set tumbling (continuous movement). Coating is sprayed by sprayed gun (even spread distribution). Drying air also enters drum. Air exits drum through perforations. Improved air flow
Fluidised Bed Outline
Suspend solid enteric particles in upwards stream of air/gas. Substrate hetated to temp above melting point of enteric coating polymers by ovens/IR heaters/induction. Substrate is placed in fluidized enetric powder. Powder adheres to the surface and melts forming a coat
