Page 123 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

include:
1. The use of tetracyclines derivatives (Minocycline, Doxycycline and

Methacycline)

They are all highly lipophilic in nature with a partition coeffecient values which are

(20-30) times greater than the original normal tetracycline. Hence they are highly

absorbed compared to tetracycline

They are taken in small doses compared to normal tetracycline, for example

doxycycline is taken as 100 mg dose twice daily, while tetracycline is taken as 250

mg 4 times a day

2. The use of Ampicillin ester derivatives (Pivampicillin and Bacampicillin)

These esters exhibit higher partition coefficient and hence higher absorption and

bioavailability compared to normal original ampicillin.

These prodrugs after being absorbed will then hydrolyze in the blood by the action

of esterase enzymes to release the free form of ampicillin.

Formulation Factors Affecting Drug Absorption

i) Influence of excipients of dosage form on drug absorption

1. Diluents

 For example, phenytoin intoxication which occurred in epileptic patients as a

consequence of changing the diluents from calcium sulphate dehydrate to lactose

although the quantity of phenytoin in both formulations was the same.

 The excipient calcium sulphate dehydrate had been responsible for decreasing the GIT

absorption of phenytoin possibly due to the formation of insoluble complex.

 When the calcium sulphate dehydrate was replaced by lactose,

 Bioavailability was improved and
 Resulted in higher plasma levels of phenytoin
 Producing toxic side effects of phenytoin.

122