Trimethoprim

SillyMangoX

Hello there, I hope this doesn't constitute as medical advice, it's just something that has struck my curiosity!
I was just wondering if anyone knows what class of antibiotics is trimethoprim in? I've tried googling it to no avail. The only results coming up is for trimethoprim combined with sulfonamine drugs (which would obviously class it as a sulfa drug), but I'm trying to find out what class it is in when it's on it's own! Thanks

partyatmygaff

It's not strictly speaking in a class of antibiotics in the same way that you have penicillin derivatives, macrolides and tetracyclines.

The only class I can think of giving it is antifolate. Technically, it's a dihydrofolate reductase inhibitor but that's akin to calling penicillin a "Peptidoglycan synthesis inhibitor". More of a description than a class.

SillyMangoX

partyatmygaff wrote: »

It's not strictly speaking in a class of antibiotics in the same way that you have penicillin derivatives, macrolides and tetracyclines.

The only class I can think of giving it is antifolate. Technically, it's a dihydrofolate reductase inhibitor but that's akin to calling penicillin a "Peptidoglycan synthesis inhibitor". More of a description than a class.

Yeah I get what you mean about the description, I wonder why is isn't part of a class though, is it the only type of antibiotic that inhibits the production of tetrahydrofolic acid?

partyatmygaff

Nope, the sulfonamides (and maybe a few others) inhibit folate synthesis.

SillyMangoX

So even though it does pretty much the same thing as the sulfonamides it still isn't classed as one? That's so confusing!

partyatmygaff

SillyMangoX wrote: »

So even though it does pretty much the same thing as the sulfonamides it still isn't classed as one? That's so confusing!

Well the thing is a lot of drugs have similar methods of action but aren't related to each other. Cisplatin and the nitrogen mustards have nearly the exact same method of action but are very different chemicals.

Sulfonamide antibiotics are called sulfonamides because they have a sulfonamide group in their structure.

Nonoperational

It and sulfonamides interfere with folate synthesis and utilisation... that's a broad classification there.

sillymoo

gpf101 wrote: »

It and sulfonamides interfere with folate synthesis and utilisation... that's a broad classification there.

Interesting. Now I realise why it is second line in UTIs in pregnancy any why you have to be careful with low folate status.

SillyMangoX

I find it so confusing that they both do the same thing and are classified as something different. So lets say hypothetically you had a reaction with sulfonamides or were resistant to sulfonamides, would the same thing happen with trimethoprim?

I thought I was so good at pharmacology till it came to all this antibiotic classification stuff!

Nonoperational

I wouldn't get too caught up with classifications. Sulfonamides are a class simply because they contain a specific chemical grouping. They're not limited to antibiotics.

For learning purposes with regard to antibiotics think of the class as sulfonamides with trimethoprim tagged on. Sulfonamides are mostly prescribed in combination with trimethoprim anyway (co-trimoxazole).

echo beach

sillymoo wrote: »

Interesting. Now I realise why it is second line in UTIs in pregnancy any why you have to be careful with low folate status.

It can't be used at all in the first trimester.