Competitive vs. noncompetitive antagonist Competitive shifts agonist curve to the right characteristics resembles substrate [S] blocks active site and can be overcome by ↑ [S] ↓ potency, ↑ Km, and Vmax is unchanged Noncompetitive antagonist shifts agonist curve downward characteristics does not resemble [S] does not block active site, therefore no ↑ [S] can overcome effect ↓ efficacy and potency, ↓ Vmax, and Km is unchanged ↑ EC50 of agonist (half maximally effective concentration for producing a given effect) Agonist vs. partial agonist Agonist acts on the receptor and triggers a full response (100% effect) Partial agonist acts on the same receptor as the full agonist ↓ efficacy, independent of dose may be more potent, less potent, or equally potent potency is an independent factor can compete with full agonist to inhibit some of the response of the full agonist Synergism & Potentiation Synergism the combined action of two drugs is greater than the activity of either alone (in total) for example: monobactams and aminoglycosides Potentiation drug A is required for the full effect of drug B to occur, but drug A itself does not have much of an effect (unlike synergism)