First Aid Pharmacology Principles

Front 1

What is Km? Define and formula

Back 1

Km is the affinity of an enzyme for its substrate. It is the concentration of solute at 1/2 Vmax. Decreased Km is increased affinity. (Km is inversely proportional to affinity).

Front 2

Volume of distribution, Vd

Back 2

Vd = (amount of drug in the body) / (plasma drug concentration)

Front 3

Clearance, CL

Back 3

CL = (rate of elimination of drug) / (plasma drug concentration) = Vd*Ke. It represents the volume of plasma that is cleared of drug per unit time.

Front 4

Half life, t1/2

Back 4

t1/2 = (0.7*Vd) / (CL) Property of first order elimination. Drug infused at a constant rate takes 4-5 half lives to reach steady state.

Front 5

Bioavailability, F

Back 5

Fraction of drug administered that reaches circulation. IV F=100%.

Front 6

Loading Dose

Back 6

Loading Dose = Cp * Vd/F

where Cp is the target plasma concentration, Vd is vol of distribution, and F is bioavailability.

Front 7

Maintenance Dose

Back 7

Maintenance dose = Cp * CL/F

where Cp is the target plasma concentration, CL is clearance, and F is bioavailability.

Front 8

Potency

Back 8

Potency is the amount of drug needed for a given effect. Increased potency is increased affinity for receptor. Highly potent drug classes include chemotherapeutics, antihypertensives, and antilipid drugs.

Front 9

Efficacy

Back 9

Efficacy is the maximal effect a drug can produce. High efficacy drugs include analgesics, antibiotics, antihistamines, and decongestants.

Front 10

Zero-Order Elimination. Define and three examples

Back 10

Zero Order Elimination:
Rate of elimination is constant, regardless of Cp (Constant amount of drug eliminated per unit time, and Cp decreases linearly with time). Phenytoin, Ethanol, ASA (Aspirin).

Front 11

First Order Elimination (define)

Back 11

Rate of elimination is proportional to the drug concentration (a constant fraction of the drug is eliminated per unit time). Cp decreases exponentially over time.

Front 12

Weak acid drugs: examples and how they are trapped. OD tx. Formula (lipid sol <--->trapped)

Back 12

Phenobarbitol, methotrexate, aspirin.

Trapped in basic environments (basic urine).

OD tx = bicarbonate

RCOOH <-----> RCOO- + H+

Front 13

Weak base drugs: examples and how they are trapped. OD tx. Formula (lipid sol <--->trapped)

Back 13

Amphetamines.

Trapped in acidic environments (acidic urine).

OD tx: ammonium chloride.

RNH2 + H+ <------> RNH3+

Front 14

Phase 1 metabolism

Back 14

Reduction, oxidation, hydrolysis. Usually yields slightly polar, water-soluble metabolites (often still active). Cytochrome P450

Front 15

Phase II Metabolism

Back 15

Geriatric pts lose Phase 1 first, and thus "have GAS". Glucuronidation, Acetylation, Sulfation. Usually yields very polar, inactive metabolitites which are renally excreted. Patients who are SLOW acetylators have greater side effects from certain drugs because of decreased rate of metabolism.

Front 16

Pharmacodynamics of Competitive Antagonist, plus examples.

Back 16

Shifts curve to the right... decreased potency but no change in efficacy. Diazepam and flumazenil on GABA receptor.

Front 17

Pharmacodynamics of a noncompetitive antagonist.

Back 17

Shifts curve downwards. Decreased efficacy. NE and phenoxybenzamine on alpha-receptors.

Front 18

Pharmacodynamics of a Partial Agonist

Back 18

Acts at the same site as a full agonist, but with reduced max effect. Decreased efficacy. Potency can be increased OR decreased. Morphine and buprenorphine at opiod mu receptor.

Front 19

Therapeutic Index: what does it tell you and how do you calculate it.

Back 19

Measurement of drug safety. Safer drugs have higher TI values.

TILE: TI = LD50/ED50

Where LD50 is the median lethal dose, and ED50 is the median effective dose.