Factors Affecting Absorption of Drugs:
- Physico-chemical properties of drug:
- Physico-chemical properties which influence drug absorption are lipid solubility, pKa and molecular size of drug.
- Lipid soluble and unionized drugs are rapidly and efficiently absorbed into the blood circulation.
- Nature and type of dosage forms:
- Drugs given in aqueous solution are more rapidly absorbed than those given in oily, suspension, or solid form because solution mix more readily with aqueous phase at the absorptive site.
- Rate of drug absorption varies as solutions> emulsions> suspension> capsules> tablets> sustained release products.
- Concentration and volume:
- Drugs given in high concentration/doses or volume are absorbed more rapidly than those given in dilute concentration and small volume.
- High concentration and large volume develop high concentration gradient, an essential requirement for passive diffusion.
- Blood flow to site of administration:
- Better perfusion rate of the absorptive tissue enhances absorption of drugs. This is because blood circulation removes the drug from the site of absorption and maintains concentration gradient across the membrane.
- Area of absorbing surface:
- Drugs are absorbed more rapidly from the site having a larger surface area than that possessing small area.
- Ex: drugs are more rapidly absorbed from the intestine than from the stomach.
- Route of administration:
- Absorption of drugs in I.V is relatively rapid than I.M whereas I.M absorbed relatively rapid than SC. Similarly, SC absorbs faster than oral route.
- Absorption of lipid soluble drugs from pulmonary mucosa is very rapid because of its rich vascular and vast surface area.
- Disease states:
- Several disease states can influence the rate and extent of drug absorption. Ex; acid-base imbalance may alter body pH; infection may alter membrane permeability and cardiovascular disease may affect blood flow to its absorbing sites.