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USMLE pharm
Pharm general principles/equations etc.
| Question | Answer |
|---|---|
| high Km = High/low affinity | High Km = low affinity |
| Changing substrate concentrations changes Km T/F | False. Km will not change with a change in substrate concentrations |
| In Lineweaver burk plot: Increasing Vmax has what effect? | Increasing Vmax = decrease in y intercept |
| In Lineweaver burk plot, increasing Km (decreasing ___) will have what effect? | Decrease affinity; will cause the X-intercept to move to teh right |
| Vd | Amount of drug in body compared to the plasma concentration. (Amt drug/plasma conc) or Dose/Co. |
| Low Vd, Medium Vd, High Vd. | Low vd = 4-8 L, Medium = (body water), High Vd = > body weight; distributes in tissue |
| Clearance (CL) | Relates teh rate of elimination to the plasma concentration. (Rate of elimination/plasma concentration) OR Vdx Ke, where Ke = elimination constant |
| Half life | Time required to change the amount of drug in the body by 1/2 during elimination. t = 0.7x Vd/Cl= 0.7/Ke |
| Loading dose | (Cp x Vd)/F where Cp (target plasma concentration), F = bioavailability |
| Maintenance dose | (Cp x CL)/F, where CP = target plasma concentration |
| How do liver/kidney disease affect pharmacology | 1. Can change the volume of distribution, 2. Maintenance dose will decrease, but loading dose will remain the same |
| How does infusion concentration affect steady state | 1. will not affect time to reach steady state but can affect concentration at steady state |
| Drugs that exhibit zero-order elimination | PEA Phenytoin, Ethanol, Aspirin (will decrease at a constant amount/unit time) |
| Maximal effect a drug can have | Efficacy |
| Amount of drug needed for a given effect | Potency |
| How do competitive agonists affect potency/efficacy? | Cause a decrease in potency |
| How do non-competitive agonists affect potency/efficacy? | Decrease efficacy |