cbrsmurf Posted August 26, 2013 Share Posted August 26, 2013 Just curious (cause I'm tired of reading about NP vs PA vs AAPA vs PAFT vs everything), had a pharmacist tell me about it a while ago, but he couldn't explain it. Couldn't find the answer/pharmacologic explanation. Also, is the doxy shortage still going on? Link to comment Share on other sites More sharing options...
Guest JMPA Posted August 26, 2013 Share Posted August 26, 2013 Just curious (cause I'm tired of reading about NP vs PA vs AAPA vs PAFT vs everything), had a pharmacist tell me about it a while ago, but he couldn't explain it. Couldn't find the answer/pharmacologic explanation. Also, is the doxy shortage still going on? you just lazy, doxy decreases effects of augmentin through antagonism rendering the drug ineffective and no antibiotic coverage Link to comment Share on other sites More sharing options...
cbrsmurf Posted August 27, 2013 Author Share Posted August 27, 2013 Although my laziness IS very high, my stupidity is even higher. Please explain, preferably with pictures and monosyllable words, why they antagonize each other. Penicillins inhibit cell wall formation (inhibist one of the enzymes involved in cell wall formation, specifically) while tetracyclines target the mRNA-tRNA protein synthesis/translation. Why would they interfere rather than be synergystic? Link to comment Share on other sites More sharing options...
Moderator EMEDPA Posted August 27, 2013 Moderator Share Posted August 27, 2013 that combo would also likely give you vomiting and diarrhea....best of both worlds and at a premium price. Link to comment Share on other sites More sharing options...
Joelseff Posted August 27, 2013 Share Posted August 27, 2013 I remember that amoxicillin reduce the efficacy of Doxy. Or was it the other way around? It was never explained to me with graphs and charts (prob fell asleep during Pharmacology class on that one) but I remember not to prescribe together. I guess if I really have a gnawing need to know why, I could look it up...so could you. Lol. Sent from my myTouch_4G_Slide using Tapatalk 2 Link to comment Share on other sites More sharing options...
Moderator EMEDPA Posted August 27, 2013 Moderator Share Posted August 27, 2013 clinda covers pretty much everything that combo covers as monotherapy. gets your gram +, anaerobes, mrsa, etc doesn't cover some of the tropical med indications that doxy does but for those you would not need the augmentin either. come to think of it, who would need both? a pt with mrsa diverticulitis? augmentin + septra would work for that. Link to comment Share on other sites More sharing options...
medic25 Posted August 27, 2013 Share Posted August 27, 2013 clinda covers pretty much everything that combo covers as monotherapy. gets your gram +, anaerobes, mrsa, etc. Just make sure to check your local sensitivities. Some areas (such as mine) are seeing decent amounts of clindamycin resistance with MRSA. Link to comment Share on other sites More sharing options...
cbrsmurf Posted August 27, 2013 Author Share Posted August 27, 2013 that combo would also likely give you vomiting and diarrhea....best of both worlds and at a premium price. and a nice looking rash, just for looks Link to comment Share on other sites More sharing options...
cbrsmurf Posted August 27, 2013 Author Share Posted August 27, 2013 I remember that amoxicillin reduce the efficacy of Doxy. Or was it the other way around? It was never explained to me with graphs and charts (prob fell asleep during Pharmacology class on that one) but I remember not to prescribe together. I guess if I really have a gnawing need to know why, I could look it up...so could you. Lol. Sent from my myTouch_4G_Slide using Tapatalk 2 I've looked before, I haven't found a good answer to be honest. Link to comment Share on other sites More sharing options...
Joelseff Posted August 27, 2013 Share Posted August 27, 2013 I've looked before, I haven't found a good answer to be honest. I figure its one of those "because I said so" things that big daddy medicine throws at us. I'm sure our physician colleagues are in the same boat with this one. Sent from my myTouch_4G_Slide using Tapatalk 2 Link to comment Share on other sites More sharing options...
Acebecker Posted August 27, 2013 Share Posted August 27, 2013 Most likley a CYP450 interaction regarding the metabolism of the meds creating an antagonistic effect. Link to comment Share on other sites More sharing options...
Guest JMPA Posted August 27, 2013 Share Posted August 27, 2013 i would disagree, imho i dont think it is medication metabolism, its more of a competing/binding issue Link to comment Share on other sites More sharing options...
starseed22 Posted August 28, 2013 Share Posted August 28, 2013 I always thought that doxycycline would reduce the effectiveness of the penicillins because it will inhibit protein synthesis necessary for cell wall production. Without the necessary peptidoglycans in the cell wall there is no binding site for penicillin. Link to comment Share on other sites More sharing options...
cbrsmurf Posted August 28, 2013 Author Share Posted August 28, 2013 That logic does not really work if you think about it. I.e. If doxy reduces the peptidoglycan synthesis by 90%, the PCN would still work the same on the remaining 10%. The bacteria does not suddenly produce a new type of protein for cell wall synthesis (unless there's a mutation/plasmid transfer/or funky dormant secondary gene). Link to comment Share on other sites More sharing options...
cupojava Posted September 6, 2013 Share Posted September 6, 2013 Taking a shot at this: Tetracyclines are bacteriostatic while penicillins are bactericidal so they can never be given together because of drug inhibition. As you pointed out, the TCN works by stopping protein synthesis @ the ribosome (30S) while the PCN works at the cell wall. PCN attacks an active bacterium so it needs the bacterium to keep making protein to make the cell wall. If TCN stops the synthesis, there is no cell wall for the PCN to attack. Also, since TCN is bacteriostatic and will only stop new growth, it does not really kill the bacteria and it creates more chances for the bacteria to create efflux pumps contributing to Abx resistance. Because TCN is bacteriostatic, the effects on the ribosome is reversible so the effects are concentration dependent. This is different from using aminoglycosides with PCN. Although aminoglycosides can either be bactericidal or bacteriostatic and also attacks protein synthesis at the ribosomes, it is an irreversible binding to the ribosome. So if the PCN attacks the cell wall, the AMG gets inside the cell, first at the cell membrane then at the ribosomes resulting in bacterial death. That's why in H. pylori treatment, TCN + Amox combo does not work while Clarithro + Amox combo does and if you choose the TCN route, it must be for a longer time frame because the actions of the TCN are drug dose dependent. Link to comment Share on other sites More sharing options...
skyblu Posted September 11, 2013 Share Posted September 11, 2013 Taking a shot at this:Tetracyclines are bacteriostatic while penicillins are bactericidal so they can never be given together because of drug inhibition. As you pointed out, the TCN works by stopping protein synthesis @ the ribosome (30S) while the PCN works at the cell wall. PCN attacks an active bacterium so it needs the bacterium to keep making protein to make the cell wall. If TCN stops the synthesis, there is no cell wall for the PCN to attack. Also, since TCN is bacteriostatic and will only stop new growth, it does not really kill the bacteria and it creates more chances for the bacteria to create efflux pumps contributing to Abx resistance. Because TCN is bacteriostatic, the effects on the ribosome is reversible so the effects are concentration dependent. This is different from using aminoglycosides with PCN. Although aminoglycosides can either be bactericidal or bacteriostatic and also attacks protein synthesis at the ribosomes, it is an irreversible binding to the ribosome. So if the PCN attacks the cell wall, the AMG gets inside the cell, first at the cell membrane then at the ribosomes resulting in bacterial death. That's why in H. pylori treatment, TCN + Amox combo does not work while Clarithro + Amox combo does and if you choose the TCN route, it must be for a longer time frame because the actions of the TCN are drug dose dependent. This is correct. Link to comment Share on other sites More sharing options...
cbrsmurf Posted September 11, 2013 Author Share Posted September 11, 2013 Sounds good, thanks for the detailed explanation. I guess was wrong, sorry bout that starseed Link to comment Share on other sites More sharing options...
Joelseff Posted November 3, 2016 Share Posted November 3, 2016 Taking a shot at this: Tetracyclines are bacteriostatic while penicillins are bactericidal so they can never be given together because of drug inhibition. As you pointed out, the TCN works by stopping protein synthesis @ the ribosome (30S) while the PCN works at the cell wall. PCN attacks an active bacterium so it needs the bacterium to keep making protein to make the cell wall. If TCN stops the synthesis, there is no cell wall for the PCN to attack. Also, since TCN is bacteriostatic and will only stop new growth, it does not really kill the bacteria and it creates more chances for the bacteria to create efflux pumps contributing to Abx resistance. Because TCN is bacteriostatic, the effects on the ribosome is reversible so the effects are concentration dependent. This is different from using aminoglycosides with PCN. Although aminoglycosides can either be bactericidal or bacteriostatic and also attacks protein synthesis at the ribosomes, it is an irreversible binding to the ribosome. So if the PCN attacks the cell wall, the AMG gets inside the cell, first at the cell membrane then at the ribosomes resulting in bacterial death. That's why in H. pylori treatment, TCN + Amox combo does not work while Clarithro + Amox combo does and if you choose the TCN route, it must be for a longer time frame because the actions of the TCN are drug dose dependent. I was thinking about this (and decided to revive this thread lol) if the reason that Doxycycline and PCN are CI is TCN inhibits protein synthesis which reduces cell wall production, wouldn't Macrolide do the same thing since macrolide disrupts protein synthesis as well? (the post states aminoglycosides but cites clarithro as the example which is a macrolide) ???? Don't ask me why I remembered this 3 yr old post but I was reviewing for PANRE and thought of this post when I saw Doxycycline as a TX for CAP... Weird huh? Lol Sent from my SAMSUNG-SM-G870A using Tapatalk Link to comment Share on other sites More sharing options...
Moderator ventana Posted November 3, 2016 Moderator Share Posted November 3, 2016 Caution Advised amoxicillin + doxycycline caution advised if bactericidal action necessary: combo may decr. amoxicillin efficacy (tetracycline bacteriostatic effects may decr. penicillin bactericidal action) strangely enough this is only a "caution advised" from epocrates..... Link to comment Share on other sites More sharing options...
Joelseff Posted November 3, 2016 Share Posted November 3, 2016 Caution Advised amoxicillin + doxycycline caution advised if bactericidal action necessary: combo may decr. amoxicillin efficacy (tetracycline bacteriostatic effects may decr. penicillin bactericidal action)strangely enough this is only a "caution advised" from epocrates.....In Medscape both Doxy and Macrolide have a warning due to pharmacodynamic antagonistic action but Doxy has an "avoid" warning but macrolides have a "minor/significance unknown" warning. My question is why is macrolide less of a CI than Doxycycline when, if the above description is correct, they both inhibit protein synthesis. Is macrolide's inhibition of protein synthesis more selective in that it does not involve the cell wall allowing PCN to bind? Or is it like the explanation about the aminoglycosides as explained above? ????(the post cites clarithromycin as the example of why Aminoglycosides and PCN work together but clarithro is a mac and aminoglycosides also inhibit protein synthesis at 30s like TCN so more confusion) I asked my SP and he looked at me like "whuuuut?" lol Or am I just brain fried from reviewing? Lol Sent from my SAMSUNG-SM-G870A using Tapatalk Link to comment Share on other sites More sharing options...
Guest ERCat Posted November 3, 2016 Share Posted November 3, 2016 I feel 76% dumber after reading some of your responses. :-O How does anyone remember all these mechanism of actions? Looks like I have reading to do... Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.