Pharmacodynamics interactions can be discussedunder the headings of DRUG RECEPTORinteractions .. !It can be> Ion channels linked interaction> G coupled linked interaction> Enzyme receptor linked interaction> Intracellular receptor linked interactions> Other misc. interactionsIt is the effect of the drug on the body .. !
Pharmacodynamics includes the concepts of AFFINITY of thedrug for receptor, INTRINSIC ACTIVITY caused by that drug..On the basis of intrinsic activity , a drug can be an AGONIST orANTAGONIST .. !Agonism can be complete or partial .. This is when a drug hasaffinity and shows complete intrinsic activity at its therapeuticdose then it is complete agonism .. Where as on maximumtherapeutic dose, if an agonist is unable to show completeintrinsic activity then we call it as partial agonist .. !Examples: Bethanicol (on M receptors), Pilocarpine, etc.
Antagonism can be CHEMICAL, PHYSIOLOGICAL andPHARMACOLOGICAL>* Chemical is when receptor is not involved .. 2 or more drugscombine 2gether to inactivate each other.e.g: Protamine inactivates heparin>* Physiological is when opposite effects are produced byacting on different receptors. e.g: insulin and glucagon,norepinephrine and acetylcholine>* Pharmacological is when one drug binds with the samereceptor of the agonist and prevents it responsee.g: atropine at muscuranic receptors, propranolol at betareceptors..
Other interactions between the drugs can be>* Addition : 1+1 = 2e.g: combined therapy of ephedrine and aminophylline inasthma>* Synergism : 1+1 =>2e.g: Sulphonamides with trimethoprim used as antibacterialdrugs ..>* Potentiation : 0+1=>1e.g: Carbidopa and levodopa in treatment of Parkinsonism ,, !
Pharmaceutical interactions includeinteractions between the drugs ..It is mainly the interaction before the drugs have systemiceffect,for example 2 incompatible drugs when given intravenously ..(it may show precipitation or not)e.g: Promethazine hydrochloride 50 mg/2 mL is incompatiblewhen given with dexamethasone sodium phosphate,frusemide, morphine, phenytoin, sodium bicarbonate insyringe !
Adverse Drug Reactions !!!Drugs, which are used together to treat multiple problems , cancause more adverse drugs reactions, for example;> Antihistamines (e.g benadryl, actifid,etc) used for treatingallergy can adversely cause Sedation !> NSAIDs (e.g Aspirin, Ibrufen, Mefenamic acid, etc) used asanalgesics and anti- pyretics can adversely cause irritation of GITleading to dyspepsia, diarrhea, ulceration, etc ..> Opoids (e.g Morphine, paracetamol, etc) used as painkillers canadversely cause nausea, vomiting, drowsiness, constipation, etc !