Wednesday, February 18, 2015

Study group discussion: Sulfonamides, Trimethoprim Sulfamethoxazole and other sulfa drugs

One extra review question session for today!

Give one example of longest acting sulphonamides.

Sulfadoxine!

Which are the other drugs with a sulfa structure?

Diuretics - Loop, thiazide and also acetazolamide. Except ethacrynic acid.

So any more drugs?

Hint- one anti-leprosy, anti-hypertension, and another one anti-diabetic.

Dapsone.

Correct!

Umm Sulfonylureas.

The hint was in the name! Correct!

Which anti hypertensive though? :O

Diazoxide :)

Ahh!

Side effects of diazoxide?

Ahh..Steven Johnson syndrome?

I'm looking for the very unique side effect which helps in treating a tumor.

Diazoxide has an anti-insulin effect.. It's used in insulinomas.

Ooh.

And what's the unique side effect of Minoxidil?

Minoxidil was used as an antihypertensive, but it caused hair growth. So they used it topically for hair loss!

If the dose of sulfamethoxazole in cotrimoxazole is 100 mg. What is the dose of trimethoprim

It's always given in the ration of 1:5
One part trimethoprim to 5 parts sulfamethoxazole

Ohh so 20 mg trimethoprim

Yup.

What is fixed drug eruptions?

Every time you eat the drug..you get a specific skin reaction at the same place every single time.

Name the site of action of smx and tm. How do they produce the sequential blockade?

Folate synthase SMX and TMP DHFRase

Sulfo doesn't inhibit the enzyme..its not the main action

Prevents formation of dihydrofolate?  Folate synthase right?

No. It's an antimetabolite. Structure similar to PABA. It attaches itself in place of PABA ..hence the mechanism of action!

One last question. Name other drugs which inhibit dihydrofolate reductase ?

Methotrexate.

Hint-  anti- epileptic drugs and one anti malarial.

Oh yes. Anti malarial! Pyrimethamine!

Correct!

Is it phenytoin?

Yes!

That's why these drugs are not given in pregnancy!

I guessed because of the megaloblastic anemia side effect!

High chances of NTD due to folic acid deficiency.

Oh well IkaN..It's all inter related :)

Totally! Medicine <3

Nice session!

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