Question

pharmacology ; homework 1

Compare oral, sublingual, and rectal administration routes of drugs providing their advantages and disadvantages. Giving examples explain how the bioavailability of drugs would be affected by these administration routes.

Answer 1

Solving

Routes of Drug administration

1.Local routes

2.Systemic routes .

Systemic routes include Oral ,sublingual ,rectal,transdermal,nasal inhalational and other parenteral routes ( intravenous,intramuscular,intradermal,and subcutaneous )

1.Oral route --It is admiinitered through mouth .Drugs are given per oral .

Advantage --It is safer and economical

Diadvantage -- Several drugs are not effective by this route because of High first pass metabolism in Liver and intestinal wall (eg Nitrates ,Lignocaine ,Propranolol,pethidine )

2.Sublingual route --Drug is put into mouth under mouth and because of increased amount of blood vessels in tongue drug is absorbed through it .

Advantage -It avoids first pass metabolism ,can be used in emergencies can be self administered and also after getting the desired action ,rest of Drug can be spitted .

Drugs like Nitroglycerine ,Isosorbide dinitrate ,Nifedipine can be administered by Sublingual route .

Diadvantage - Excessive absorption leads to side effects .

3.Rectal route - Drugs administered in Rectum .It avoids first pass metabolism to 50 % extent .Diazepam is given by this route in children for Febrile seizures .

​​​Bioavailabilty --

1.It is the fraction of administered drug that reaches the systemic circulation in Unchanged form .

2.​​​When we administer drug orally ,first it is absorbed into portal circulation and reaches the Liver .Here some of Drug may be metabolised ( First pass metabolism or presytemic metabolism ) and rest of Drug reaches systemic circulation .Thus absorbtion and first pass metabolism are two important determinants of Bioavailability .

By intravenous route it is 100 % Bioavailability .

It can be calculated by comparing the AUC ( area under plamsa concentration curve ) for Intravenous route and for that particular route .It can be calculated by comparing the Excretion in urine .

1..AUC tells about the absorption of the drug .

2.Tmax tells about the time to reach maximum concentration ,rate of Absorption

3.Cmax is maximum concentration of drug that can be obtained .

Graph is plot between plasma concentration and Time to calculate Bioavailability .