1. Non-competitive antagonism
can be confused with insurmountable competitive antagonism
differs in that antagonist and agonist are not competing for the same site
eg Ca channel blocker - VERAPAMIL
could be PHYSIOLOGICAL antagonists
ie have opposing effects eg on blood pressure HISTAMINE & NORADRENALINE

2. Other forms of antagonism
PARTIAL AGONISTS
Since partial agonists cannot produce a maximum response
They inhibit a full agonist from doing so
PHYSIOLOGICAL ANTAGONISTS
ie have opposing effects eg on blood pressure HISTAMINE & NORADRENALINE

3. Other forms of antagonism II
CHEMICAL
uncommon
a substance which combines with the agonist in solution
PHARMACOKINETIC
antagonist “reduces” the amount of drug
eg WARFARIN & BARBITURATES
barbiturates induce hepatic metabolism
hence warfarin broken down more quickly than expected

4. Recommended Reading Antagonism
Medical Pharmacology at a Glance, 5th Ed: Page 11
Pharmacology, 5th Ed: Pages & 18-19
Basic and Clinical Pharmacology Online Book: Section I, Chapter 2, Relation between drug concentration and response, other mechanisms of drug antagonism