Absorption - Pharmacokinetics

o   Active transport: highly specific – usually for transporting naturally occurring substances (e.g. amino acids)

o   Filtration through pores: absorbed via paracellular route in small intestine. E.g. frusemide, atenolol, digoxin

·        Factors affecting oral absorption:

o   Formulation: affects solubility and bioavailability.  Presence of other drugs (e.g. Fe, Ca)

o   Gastric emptying: ¯emptying ® ¯ absorption rate

o   Food: may slow gastric emptying, alter ionisation, decrease first pass metabolism. Affects different drugs differently

·        Alternative sites of absorption: 

o   Plasma concentration rises quickest for iv > im > sc (absorption similar to im but ¯ blood supply)

o   Intramuscular injection: affected by lipid solubility and blood flow

o   Rectal absorption: avoids GI irritation, good in vomiting, doesn‟t avoid 1^st pass metabolism

o   Pulmonary absorption: small particle size

o   Absorption from mouth: nitrates/buprenorphine

o   Absorption from nose: desmopressin & other peptides

o   Percutaneous: zero order absorption – for nicotine, nitrates, scopolamine