1. Factors Affecting Drug Absorption (Pharmaceutical factor)
SALMAN BIN ABDUL AZIZ UNIVERSITY
COLLEGE OF PHARMACY
Factors Affecting Drug Absorption (Pharmaceutical factor)
PHARMACEUTICS- IV
(PHT 414 )
Dr. Mohammad Khalid Anwer
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2. Pharmaceutical Factors
Nature and type of dosage forms:-
Solutions Suspensions
Tablets Capsules
Coated tab Enteric coated tab
Excipients and adjuvant
Product age and storage conditions.
Disintegration test
Dissolution test
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3. MEANS Absorption rate depends on the dosage
NATURE AND TYPE OF DOSAGE FORM
MEANS Absorption rate depends on the dosage
Form which is administered, ingredients used, procedures
Used in formulation of dosage forms.
The availability of the drug for absorption from the
dosage forms is in order.
Solutions > Suspensions > capsules > Compressed
Tablets > Coated tablets.
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4. SOLUTIONS Shows maximum bioavailability and factors affecting
Absorption from solution are as follows
Chemical stability of drug
Complexation: between drug and exipients of formulation
to increase the solubility, stability.
3. Solubilization: incorporation of drug into micelles to increase the solubility of drugs.
4. Viscosity
5. Type of solution: Whether aqueous or oily solution.
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5. It comes next after solutions with respect to bioavailability
SUSPENSIONS:
It comes next after solutions with respect to bioavailability
Factors that affects absorption from suspensions are
Particle size and effective surface area of dispersed phase
2. Crystal form of drug: some drug can change their crystal
structure.
Eg. Sulfathiazole can change its polymorphic form, it can be
overcome by addition by adding PVP.
3. Complexation: Formation of nonabsorbable complex between
drug and other ingredients.
Eg. Promazine forms a complex with attapulgite.
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6. 4. Inclusion of surfactant
Eg. The absorption of phenacitin from suspension is increased in
presence of tween 80.
5. Viscosity of suspension
Eg. Methyl cellulose reduces the rate and absorption of
nitrofurantoin
6. Inclusion of colourants:
Eg. Brilliant blue in phenobarbitone suspension.
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7. CAPSULES Two types of capsule Hard gelatin capsule
2. Soft gelatin capsule
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8. Capsules
For hard gelatin capsules the shell should disrupt quickly and expose the contents to the GI fluids.
Factors influencing are particle size, density, crystal form of the drug, selection of diluents.
For hydrophobic drugs with a fine particle size in capsule results in decrease in porosity of the powdered drug and thus decreased penetrability by the solvent which results clumping of particle.
soft elastic capsule dissolve faster than hard gelatin capsule & tablets. Which shows better bioavailability from oily solutions, emulsions, or suspensions.
The problem with SGC is high water content of shell, moisture migrate in to the shell causes crystallization of the drug results in altered dissolution characteristics .
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9. The rate of absorption of drugs from capsule is function
HARD GELATIN CAPSULE
The rate of absorption of drugs from capsule is function
Of some factors.
1.Dissolution rate of gelatin shell.
2.The rate of penetration of GI fluids into encapsulated mass
3.The rate at which the mass disaggregates in the GI fluid
4. The rate of dissolution.
5. Effect of excipients;
a).Diluents
b).Lubricants
c). Wetting characteristics of drug
d).Packing density
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10. SGS may used to contain non aqueous solution or liquid or semi solid.
SOFT GELATIN CAPSULE
SGS has a gelatin shell thicker than HGS, but shell is plasticized by adding glycerin, sorbitol.
SGS may used to contain non aqueous solution or liquid or semi solid.
SGC have a better bioavailability than powder filled HGC and are equivalent to emulsions.
Eg. Quinine derivative was better absorbed from SGC containing drug base compared with HGC containing HCl salts.
Grieseoflavin exhibited 88% absorption from Soft Gelatin Capsules compared to HGC(30%)
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11. TABLETS
1.Compressed tablets
2. Coated tablets
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12. Compressed Tablets This is the most widely used dosage form.
Problem with this arises from reduction in the effective surface area due to granulation & subsequent compression in to dosage form.
Tab disintegration and granule disaggregation are the imp steps in absorption process.
Compression force also may be an important factor.
Disintegration is the rate limiting step for this.
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13. Bioavailability are more due to large reduction in surface area.
Compressed tablets
Bioavailability are more due to large reduction in surface area. A B
Intact tablets a granules primary drug particles K2 K1 K3
Drug in GI fluid K4
Drug absorbed in body
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14. The rate constants decrease in the following order.
K3>>K2>>K1
The overall dissolution rate and bioavailability of a poor
Soluble drugs is influenced by
1.The physicochemical properties of liberated particles.
2. The nature and quantity of additives.
3. The compaction pressure and speed of compression.
4. The storage and age of tablet
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15. Na Salicylates + starch = Faster dissolution
1.Effect of diluents :
Na Salicylates + starch = Faster dissolution
Na salicylates + lactose=Poor dissolution.
2.Effect of Granulating agent:
Phenobarbital + Gelatin solution=Faster dissolution
Phenobarbital+PEG 6000= poor dissolution.
3.Effect of lubricants:
Magnesium stearate will retard the dissolution of aspirin tablet
Whereas SLS enhance the dissolution.
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16. 4.Effect of disintegrants:
Starch tend to swell with wetting and break apart the dosage
form. It is reported that 325mg of salicylic acid tablet were
prepared by using different concentrations (5%,10%,20%) and
max. dissolution was achieved With 20% starch.
5. Effect of colorants:
6.Effect of Compression force:
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17. Coated tablets
Coat is generally used to mask unpleasant taste & odor & to protect the ingredients from decomposition during storage.
This adds an additional barrier between GIT & drug. It should get dissolve before tablet disintegration & dissolution.
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18. COATED TABLETS Cont……………..: There are three types of coating
Sugar coating
Film coating
Enteric coating
Sugar coating will take more time than film coating.
Care should be taken while selecting the coating material
Ex: methyl cellulose which retards the dissolution
SUGAR COATING:
Sugar,Shellac,fatty glycerides, bees wax, silicone resin
Sub coating agent: Talc,acacia,starch.
FILM COATING:
Polymers, dispersible cellulose derivatives like HPMC
CMC.
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19. Enteric coated tablets
It is a special film coated design to restricts the gastric fluids & to dissolve in small intestine.
Protect the drug from the degradation in the stomach Ex: erythromycin.
Minimize the gastric distress caused by some drugs. Ex: aspirin.
These tablets must empty the stomach before the drug absorption can begin.
The polymers with pKa values ranging from 4-7 have been found to use.
Shellac, cellulose acetate phthalate etc.
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