Pharm K equations

Question 1

Volume of distribution

Answer 1

Amt of drug in body / C (amount of drug in plasma)

Question 2

CL

Answer 2

Vd *Ke (elimination constant)
Rate of elimination of drug / plasma concentration of drug
ml/min

Question 3

Half Life

Answer 3

0.693*Vd / Cl
4-5 half lives to clear
3.3 half lives to reach 90% steady state
Time to steady state depends on half life

Question 4

Loading Dose

Answer 4

Cp *Vd / F
Cp = target plasma concentration
Vd = volume of distribution
F = bioavailability
How much drug do you need to reach Cp as quickly as possible

Question 5

Maintenance Dose

Answer 5

Cp * CL * t (time between doses)/ F

Amount drug needed to keep patient at target plasma levels

Question 6

Phase 1 metabolism

Answer 6

Reduction, Oxidation, Hydrolysis- P450, liver ER and mito
Older people loose this
Drug retains some bioactivity

Question 7

Phase 2 metabolism

Answer 7

Glucuronidation, Acetylation, Sulfation
Old people retain this
Drug looses activity and usually renally excreted

Question 8

Weakly acidic drugs

Answer 8

TCA; phenobarbital, methotrexate, aspirin

“when you take acid you get “AMPT”

Question 9

How do you treat an overdose with a weakly acidic drug?

Answer 9

bicarbonate

Question 10

Weakly basic drug(s)

Answer 10

amphetamines (Aderall)

Question 11

How do you treat overdose with weakly basic drugs?

Answer 11

ammonium chloride

Question 12

What drugs are zero order elimination

Answer 12

Phenytoin, Aspirin, Ethanol

PEA

Question 13

Drugs with small therapeutic index?

Answer 13

Digoxin, lithium, theophylline, warfarin

Question 14

Therapeutic index?

Answer 14

Median Toxic Dose TD50/ Median effective dose ED50

Question 15

Example of a competitive anatgonist

Answer 15

Flumazenil (anatagonists GABA receptors that are stimulated by a benzodiazapine drug like diazepam)
Flumazenil is a drug given for a diazepam overdose
Decreases the potency of the drug

Question 16

Example of a non competitive anatgonist

Answer 16

Phenoxybenzamine for NE on alpha receptors

Used to treat a pheo

Question 17

Example of a partial agnoist

Answer 17

Buprenorphine for u opioid receptors (fully agonized by morphine)
People will have opposite rxn to buprenorphine depending on their morphine baseline (heroin addicts will get withdrawl while morphine naive people will feel the effects of morphine)

Question 18

CYP450 Inducers

Answer 18

Chronic alcoholics Steal Phen-Phen, and Never Refuse Greasy Carbs

• Chronic alcohol use
• St. Johns wort
• Phenytoin
• Phenobarbital
• Nevirapine
• Rifampin
• Griseofulvin
• Carbamazepine (auto inducer, induces CYP450 that metbolizes the drug)

Question 19

CYP450 Inhibitors

Answer 19

AAA RACKS IN GQ Magazine

• Acute alcohol abuse
• Ritonavir
• Amiodarone
• Cimentidine
• Ketoconazole (and other azoles)
• Sulfonamides
• INH (Isonaizid)
• Grafruit Juice
• Quinidine
• Macrolides (except azithromycin)

Question 20

CYP450 Substrates

Answer 20

Always Think When Outdoors

• Anti-epileptics
• Theophylline
• Warfarin
• OCPs

Question 21

Drugs that differ based on slow v fast acetylation

Answer 21

Hydralazine
INH
Procainamide

Question 22

Probenecid

Answer 22

Substrate OATs

Question 23

OAT secretion in the PCT

Answer 23

FIMP

furosemide, indomethacin, methotrexate, penicillin

Question 24

OCT secretion in the PCT

Answer 24

dopamine, histamine, cimetidine, atropine, and chlorpromazine

Question 25

Therapeutic window

Answer 25

Median toxic - median therapeutic

Question 26

Peak concentration of the drug (bolus)

Answer 26

dose/ Vd

Question 27

Drug concentration in steady state

Answer 27

Cp = rate in/ Cl

Question 28

Max concentration

Answer 28

Steady state + 0.5(bolus)