PHARMACOLOGY

 PHARMACOKINETIC DRUG INTERACTIONS ::

Drugs may alter the absorption distribution metabolism or excretion of other drugs Such interactions are termed as pharmacokinetic drug -interactions 

        Following are various mechanisms of pharmacokinetic drug interactions ::

1.Modification of absorption of drugs ::

Absorption of drugs from g.i. tract is modified whenever any drug interaction alter (a) the functions of the gastrointestinal (g.i.) tract (b) the physico-chemical characteristics of the contents of the tract which affect oral dosage forms (c) the condition of mucosa and (d) active and passive transport mechanisms that move the drugs from the tract through its lining of the body fluids 

(A) Alteration of g.i. tract functions ::

Motility ::

Emptying time of the stomach varies with the intensity of the gastric motility The length of time a drug remains in the intestinal tract before it is excreted varies with the intensity of intestinal peristalsis The total amount of incompletely absorbed drugs like digoxin and tetracyclines that cross the g.i. epithelium varies markedly with g.i. motility Faster a drug passes through the stomach and intestine smaller is the amount of drug absorbed Thus cathartics which increase g.i. motility tend to reduce the absorption of any given medication Propantheline or atropine decreases g.i. motility and hence increase absorption of drugs 

Bacterial flora ::

Modifying or eliminating the intestinal flora with antimicrobials may alter the susceptibility of patients to a drug oral anticoag ulants may cause bleeding if they are administered after vitamin -K synthesizing microflora have been destroyed