What is it ?

Lasix. oral + IV forms.
loop diuretic. selectively inhibit NaCl reabsorption in the Thick Ascending Loop (TAL)

PHARMACODYNAMICS

Thick ascending loop of Loop of Henle

inhibit NKCC2, the luminal Na+/K+/2CL-transporter in the TAL of Henle’s loop.
hence :
a. REDUCING the reabsorption of NaCl
b. also diminish the lumen-positive potential that comes from K+ recycling >>>> increase in M+ and Ca2+ excretion

induce expression of cyclooxygenases (COX-2) >>>more synthesis of PG from AA

increases renal blood flow via PG actions on kidney vasculature

PHARMACOKINETICS

rapid absorption.
eliminated via glomerular filtration + tubular secretion.
duration of effect ~2-3 hours.

CLINICAL INDICATIONS

Acute pulmonary oedema

Acute hypercalcemia.

Hyperkalaemia

Acute Renal Failure

Anion OVerdose

TOXICITY

Hypoklaemic Metabolic Alkalosis

Ototoxicity

Hyperuricemia

Hypomagnesemia

Allergic reactions

MCQ questions :

3. which is NOT true of diuretics?

a. Loop diuretics can be used to treat hypercalcaemia

b. Frusemide is used in the prophylaxis of acute mountain sickness

c. Cirrhotic oedema responds to spironolactone

d. They may enhance the efficiency of ACE inhibitors

e. Hydrochlorothiazide is useful in diabetes insipidus

ANSWER : B

Viva questions : http://lifeinthefastlane.com/exams/facem-primary/pharmacology-viva/pharm20100212/

Apologies for the long hiatus —-had bouts of personal problems including a mishap involving a loved one.

I do have a few cases to dissect. My original aims for this blog was to try and do something like what this fella Chris Partyka  (an EM registrar in NSW i think) does i.e. his blog : http://thebluntdissection.com/ 

However before that I have my primaries coming up and its daunting. Only 78 days to go !

I thought i’ll do something different….while am trying to compile cases and lessons I learnt I’ll also revise my drugs so….

…………….presenting ONE DRUG A DAY.

Today’s drug—–drumroll please

ACETAZOLAMIDE

with every drug the format will be

1. WHAT IS IT

2. PHARMACODYNAMICS

3. PHARMACOKINETICS

4. CLINICAL INDICATIONs

5. SIDE EFFECTs

• What is it ?

diuretic. sold under trade name Diamox. Carbonic anhydrase inhibitor.

• PHARMACODYNAMICS ?

inhibits carbonic anhydrase (CA) blocking NaHCO3 reabsorption,
where >>> at the Proximal convoluted tubule PCT

What is CA used for ?
see diagram below (photo taken from Katzung)

CA does 2 things :

a. Carbonic acid (H2CO3) is rapidly dehydrated by CA to carbon dioxide and water within the lumen
b. the same carbon dioxide and water (within the PCT) is rehydrated by CA to become carbonic acid again

• PHARMACOKINETICS
  well absorbed orally. Excretion by secretion in proximal tubule S2 segment.

• CLINICAL INDICATIONS

1. Glaucoma-via reduction in aqueous humor formation
2. Urinary Alkalinization -increasing urine pH for hyperuricia/cystinueia
3. Metabolic Alkalosis- esp in CHF patients
   
4. Acute Mountain Sickness-decreasing CSF and decreasing pH of CSF/brain : increases ventilation
5. Others – adjuvants in epilepsy/hypokalaemic periodic paralysis/CSF leak

• SIDE EFFECTS

1. Hyperchloremic MEtabolic Acidosis
2. Renal stones
3. Renal Potassium Wasting
4. Drowsiness + parasthesia

Worth watching this :

Youtube video on brief physiology : http://youtu.be/FmKv2qPuB4k

Lifeinthefastlane.com’s critical care manual book by Dr Paul Young : http://lifeinthefastlane.com/book/critical-care-drugs/acetazolamide/