PHARMACOLOGY

 FACTORS AFFECTING BIOAVAILABILITY AND ACTION OF DRUGS ::

There are number of factors that affect bioavailability of drugs These are mainly the factors affecting absorption distribution metabolism and excretion of drugs Since some of them have already been dealt with individually in only the main points will be mentioned here 

Age ::

Children and old people need lesser amount of drug than the standard adult dose Children need smaller doses in proportion to their age Infants are also found intolerant to certain drugs (opium) and tolerant to others (belladonna) following are the reasons why neonates need different doses as compared to adults 

1.Compared to the adult water content in neonates is higher (75%) 

2.Membrane permeability and blood brain barrier permeability is greater neonates as compared to adults 

3.Protein binding is considerably less in the neonates as compared to adults 

4.Hydroxylation and glucuronidation are very slow to develop while sulfate conjugation is much faster in neonates 

5.Glomerular filtration at birth is 30-40% that of the adult and it increases to about 50% after 5 days it reaches adult rate at about 5 months of age 

Similarly transition from middle to old age is accompanied by substantial changes ::

1.Age related changes in upper gastrointestinal functions (achlorhydria changes in motility or diminished blood (flow) 

2.