AboutDr Alan Galbraith Expertise I can answer most questions on drugs, both medical and "recreational". Answers can be given in either technical or layperson terminology. My main areas of interest are psychiatric, gastrointestinal and cardiovascular drugs.
Experience I have been a university lecturer/head of department for almost thirty years, but am now retired. My research interests were alcohol, smoking and cardiovascular disease.
Organizations Institute of Biology, London.
Publications Principal author of "Fundamentals of Pharmacology" 4th Edition published in November 2003 by Pearson Education, Australia.
Question Why are there are number of different formulations of glyceryl trinitrate? Compare the onset and duration of action from a sublingual tablet and transdermal patch. (8marks) please be scientific.
Answer Dear Mahria
The two main preparations of GTN are for skin absorption (ointment and patches) and sublingual absorption (tablets and spray). If swallowed GTN is quickly degraded in the liver via the enterohepatic circulation and will have no therapeutic effect. As it is a very potent and highly lipophilic drug it is absorbed rapidly through the oral mucosa into the bloodstream where it fast action (within minutes) causes a venodilation to relieve the pain of angina pectoris. The use of the tablets or spray is a matter of patient preference but the tablets, once exposed to air rapidly degrade within a month or two. The spray being protected from the air has a much longer shelf life. The patch or ointment when applied to the skin release the GTN slowly by transdermal absorption (again because of its lipophilicity and potency ie mcg amounts). The skin being much thicker and impermeable therefore causes a slow release into the blood stream over a period of up to twelve hours. This route is good to prevent ischaemic events in cardiac muscle.
The injection for parenteral administration is good for its very facts venodilatory effect and is good for acute pulmonary hypertension.
The ointment is also good at helping anal fissures to heal by increasing the local perianal circulation.
I hope this is adequate for your purposes. There are other therapeutic uses too.
