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59 Cards in this Set
- Front
- Back
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How do a dose of drug administered, the plasma concentration of that drug and volume of distribution relate to each other?
(Dose, Cp, Vd) |
Vd = Dose / Plasma concentration
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How is bioavailability measured (hint: AUC - area under the curve is involved)
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Bioavailability = AUC in PO* administration / AUC in IV administration * 100
AUC = area under a plot of drug plasma concentration over time PO or SL, however you administered the drug. The assumption is that IV is completely bioavailable, whereas other methods have to bypass liver or GI and are metabolized first. |
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How do you calculate the elimination constant from 1/2 life?
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Kel = .693 / t 1/2 (the half-life time)
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How do the elimination constant, total clearance and volume of distribution relate to each other?
(Kel, Cl-t, Vd) |
Cl-t = Kel * Vd
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How can you calculate 1/2 life from total clearance and volume of distribution?
(Cl-t, Vd) |
t 1/2 = (.693 / Cl-t) Vd
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What is the relationship between changes in total clearance and changes in plasma 1/2 life?
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As total clearance decreases, plasma 1/2 life increases
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How do you calculate renal clearance?
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Renal clearance = (urine flow rate * urine concentration) / plasma concentration
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How do you calculate a loading dose (single dose)?
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Loading Dose = Steady State Conc desired * Vd
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How do you calculate loading doses (multiple doses)?
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Loading doses (multiple doses) = Steady State Conc desire * Vd / # loading doses
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How would you adjust loading dose(s) in someone with renal disease?
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Trick! No change because the Vd is assumed to be unchanged.
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How do you approach maintenance doses of drug in someone with impaired renal clearance?
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Decrease maintenance doses, increase the interval, or both*
*More important for primarily renally cleared drugs |
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How do you adjust doses of renally excreted drugs in kidney disease?
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% decrease in GFR = % decrease in dose
Normal GFR = 100ml/min |
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How do you calculate infusion rate based on desired steady state concentration and clearance?
(Ko, Css, Cl-t) |
Ko = Css / Cl-t
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How do you calculate creatinine clearance?
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Clcr = Cr excretion / plasma concentration Cr*
But usually just use serum creatinine because it's more reliable than urine collection methods |
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What is the Welling and Craig nomogram used for?
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Indicates dose adjustment for renally vs. non-renally excreted drugs in chronic kidney disease patients. For non-renal (chloramphenicol), no adjustment needed. For 100% renal (tobramycin), big adjustment needed.
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What are two Phase I biotransformation enzyme inducers?
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Phenobarbitol and EtOH
- Warfarin and OCPs are affected |
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What is a Phase I biotransformation enzyme inhibitor?
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cimetidine
- warfarin is affected |
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What sorts of reactions take place in Phase I biotransformation?
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Redox and hydrolysis, via CYP 450 enzyme family
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What are Phase II biotransformation reactions?
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The coupling of the drug (or it's Phase I metabolite) to an endogenous substance, usually to something water soluble that allows for its excretion
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Which of the following statements about drug biotransformation is true:
They usually convert a drug to its more lipid-soluble form All involve complex multi-step chemical processes Their rates may be influenced by other drugs All occur in hepatic microsomal enzyme systems All of the above |
Their rates may be influenced by other drugs
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What may a drug be bound to that would make it not filterable?
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Proteins
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What will affect the secretion of an acid drug in the proximal tubule?
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The addition of another acid drug into the regimen (same goes for basic drugs).
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What would the consistency of urine have to be to encourage excretion of an acid drug?
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Alkaline
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Are Furosemide, thiazides and penicillins acidic or basic?
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Acidic
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Acid or base?
Amiloride, triamterine, dopamine |
Basic
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Drug Z, an organic acid with pKa of 3.0, has a renal clearance of 180 ml/min in a 70-kg male subject. One can conclude that the renal clearance of drug Z:
Approximates the renal plasma flow Indicates that drug Z is partially reabsorbed from the renal tubules Is likely to increase upon acidification of the urine May increase when another organic acid is administrated at the same time Indicates renal elimination partly by tubular secretion of drug Z |
Indicates that drug Z is partially reabsorbed from the renal tubules
(Clearance is normally 120ml/min for 70kg male) |
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10 mg of Drug X is injected intravenously
every 8 hours. The elimination half-life of drug X is 8 hr. What is the total amount of Drug X in the body after 3 days? |
20mg
If a drug is given every half-life, then the cumulative amount after steady state = 2xdose |
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In normal 70-kg subject's drug A has a half-life of 4 hours and a recommended infusion rate of 10 mg/min.
In a 70-kg patient with renal failure, the volume of distribution of drug A is like that found in normal subjects, but its total clearance is only half as large. An appropriate infusion rate of drug A for this patient would be: 2.5 mg/ml 5 mg/ml 10 mg/ml 20 mg/ml 40 mg/ml |
5mg/min
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What should you first recommend for someone with hypertension?
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Lifestyle changes
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What should recommend if lifestyle changes fail to achieve blood pressure targets?
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Thiazide or thiazide-like diuretics:
HCTZ Chlorthalidone Metolazone Indapamide |
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A 75 yo old pharmacist comes to the ER with complaints of CP and SOB. She has a history of HTN. She states that she takes an
aspirin daily and a diuretic that “acts at the distal tubule of the nephron.” She cannot remember the name of the diuretic. Considering her description, which of the following is the most likely diuretic? Furosemide Hydrochlorothiazide Mannitol Spironolactone |
HCTZ acts in DCT.
Furosemide is a loop diuretic, Mannitol is a proximal and loop diuretic, Spiro acts in CCD |
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What are thiazide diuretics AEs?
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Hypokalemia/natremia
HyperGLUC - glycemia, lipidemia, uremia and calcemia (only diuretic that increases reabsorption of calcium) |
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Who should NOT get a thiazide diuretic?
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Gout, sulfa allergies (thiazides are sulfas), people with Stage IV/V CKD (<30ml/min GFR)
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Which of the following diuretics can be used in a patient with a sulfa allergy (reaction is anaphylaxis)?
Acetazolamide Furosemide Hydrocholorthiazide Ethacrynic acid |
Ethacrynic acid - both loop diuretics. Thiazides are sulfas, and Furosemide may also cause a sulfa-like allergic reaction
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What are loop diuretics (like furosemide) AEs?
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OH DANG!
Ototox, HyperK, Dehydration, Allergy, Nephritis (interstitial), Gout |
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What is the relative strength of furosemide, torsemide, bumetanide?
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Torsemide = furosemide X2
Bumetanide = furosemide X40 |
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What are loop diuretics typically used for?
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Edema related to CHF (not typically for HTN)
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Which of the following blunts loop diuretics (like furosemide, torsemide, bumetanide and ethacrynic acid)?
Digoxin Aspirin Ibuprofen Warfarin |
Ibuprofen
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On a routine annual examination, a previously healthy 59 yo woman is found to have high BP. Her BP is confirmed on three subsequent visits. She tries to control it with diet and exercise, but 1 year later it is still elevated and so she is given a RX for a diuretic. She returns for a follow-up visit, and labs show an elevation of her potassium levels.
She was most likely prescribed which of the following diuretics? Acetazolamide Furosemide Hydrocholorthiazide Metolazone Triamterene |
Triamterene - a K sparing diuretic
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What are the K-sparing diuretics
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K-STAEs:
Spironolactone Triamterene Amiloride Eplerenone |
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Where do K-sparing diuretics act?
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CCD
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Which K-sparing diuretic can cause gynecomastia and anti-man effects?
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Spironolactone - it has a great affinity for aldosterone receptors
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What very common anti-hypertensive drugs should not be concurrently given to someone receiving a K-sparing diuretic?
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ACEIs/ARBs
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A 60-year-old hypertensive woman presents to her physician with visual changes. TIA is ruled out. She is then referred to an ophthalmologist, who prescribes a medication that subsequently causes drowsiness and tingling in her arms. Labs reveal hyperchloremic metabolic acidosis.
Which of the following drugs was most like prescribed? Furosemide Hydrochlorothiazide Acetazolamide Spironolactone |
Acetazolamide
Remember - ACIDazolamide causes acidosis, neuropathy Also don't give to sulfa allergic, and may increase risk of kidney stones |
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What drug is used for motion sickness, glaucoma, and illegally by meth users?
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Acetazolamide - makes meth stay in your body longer
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Mannitol is an osmotic diuretic that inhibits
sodium and water absorption in the kidneys. It would most likely be used for Pulmonary edema Congestive heart failure Acute cerebral edema Resistant hypertension |
Acute cerebral edema. Because it concentrates plasma, it encourages leakage of fluid from ICS to plasma and ISF
Don't give for CHF of edematous patients |
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How do ARBs drug names end?
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-artan (Losartan -Cozaar-is the only generic)
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TZ presents to your clinic in 2 months for a follow-up appointment and reports that he has a persistent dry cough which has been extremely bothersome. There have been no medication changes since you last saw him except for lisinopril 20mg once daily which you initiated at his previous discharge.
Which of the following would you recommend? Prescribe Robitussin AC 10 mL PO q 6hrs prn cough Discontinue the lisinopril Discontinue the lisinopril and start losartan 50mg once daily Nothing should change as the cough will subside on its own |
Discontinue lisinopril, start on 50mg of losartan
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What is ACEI MOA?
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Interferes with ACE which prevents ATII formation
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What is ARB MOA?
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Blocks angiotensin from binding with AT1 receptor
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What anatomical change should preclude prescribing ACEI?
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Bilateral RAS
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What HTN drug should all diabetics be on if possible?
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ACEI
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The PK properties of a new drug are being studied in normal volunteers during phase I clinical trials. The volume of distribution and clearance determined in the first subject are 80L and 4 L/hr, respectively.
The half-life of the drug in this subject is approximately 0.03 hours 14 hours 78 hours 139 hours 222 hours |
~14 hours
t1/2 = (.693/Cl)*Vd |
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A continuous IV infusion of lidocaine is given to a 70-kg patient with cardiac arrhythmias. The PK parameters for lidocaine are as follows: clearance (CL) = 9mL/min/kg, volume of distribution (Vd) = 70 L, half-life = 2 hours.
How long will it take for drug levels to reach 87.5% of steady state? 1.75 hours 3.5 hours 5.5 hours 6 hours 8 hours |
6 hours.
Only need to know the half-life. 2 = 50% steady state, 4 = 75% steady state, 6 = 8 |
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A new antibiotic is being tested in clinical trials. The following PK parameters have previously been determined:
Clearance = 100 mL/min Volume of distribution = 50 L Half-life = 3 hours Assuming that the drug is being administered IV, what loading dose should be given to a patient to quickly obtain a plasma concentration of 10mg/L? 5mg 25mg 100mg 500mg 1000mg |
500mg
LD = desired plasma concentration * Vd = 10 X 50 = 500mg |
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A pharmacy resident is trying to determine the plasma concentration of an experimental anti-arrhythmic agent (Drug X) at steady-state. A continuous IV infusion of the agent began 6 hours earlier at a rate of 3mg/min. Drug X has a half-life of 3 hours, a volume of distribution of 120L, and a clearance of 0.6L/min. If the rate of infusion remains constant, what will the plasma concentration be at steady-state?
0.005 mg/L 0.4 mg/L 2 mg/L 5 mg/L 40 mg/L |
5mg/L
Plasma concentration at SS = infusion rate / CL 3mg/min / .6L/min = 5mg/L Only need clearance and that it was constant IV infusion |
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A new antibiotic is being tested in phase II clinical trials. The following PK parameters had been determined in earlier trials:
Vd = 60 L, CL = 30 mL/min, t ½ = 23 hours F (bioavailability) = 50% This antibiotic is administered orally, and the target plasma concentration (Cp) is 2mg/L. What is the appropriate loading dose for this drug? 15mg 30mg 60mg 120mg 240mg |
240mg
LD = Cp X Vd / bioavailability 2mg/L x 60L / .5 = 240mg Need Vd, desired plasma conc and bioavailability |
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A patient with CHF, HTN, DM, and glaucoma is on several medications. During a routine urine and blood sample analysis, the following electrolyte disturbances are noted:
↓ sodium, ↑ chloride, and ↓ potassium in the blood, ↑ calcium phosphate and bicarbonate in the urine Which of the following drugs most likely caused these electrolyte disturbances? Captopril Furosemide Acetazolamide Spironolactone Hydrocholorthiazide |
Acetazolamide - note crystals in urine (kidney stones) and glaucoma on history, also spilling bicarb which makes sense because it's a carbonic anhydrase inhibitor and patient is unable to reabsorb bicarb
This is why they can become acidotic |
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A patient with essential HTN is starting diuretic therapy. He has a history of calcium oxalate renal stones.
Which of the following diuretics would be most appropriate for this patient? Acetazolamide Furosemide Hydrocholorthiazide Spironolactone Triamterene |
HCTZ - great for stones
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