Side effects of phenoxymethylpenicillin

explosive diarrhoea

Feeling really naueaseas and availability to eat well or at all. Just drink a lot of sweet drinks like squash. Personal experience...

[On and off-target are not proper terms in pharmacology]

I assume that by "on-target" you mean the intended pharmacodynamic effects, and by "off-target" side effects.

The intended effect of the penicillins is inhibition of synthesis of peptidoglycan [they], which is the major component of bacterial cell walls. The failure to make a cell wall leads to the blighters bursting = dying!! - this helps treat the infection.

Diarrhoea as a side effect [could be called "off-target", I suppose] is due to destruction by the same mechanism as above of the bacterial flora of the intestines, which play a part normally in digestion of cellulose [we humans, unlike cows [and other ruminants], cannot synthesize cellulase [mainly cos very few people eat grass lol]].

A serious side effect is, of course, an allergic reaction [although unusual] in the form of anaphylactic shock, which can be fatal, so every prescription should be preceded by a question to the patient about any previous such reaction.

Penicillin V [phenoxymethylpenicillin], being acid-resistant is given orally [unlike penicillin G [benzylpenicillin, which needs to be given IM.

Although both these penicillins are effective against gram-positive bacteria, their use now is limited due to the development of bacterial resistance, and the appearance on the market of numerous 2nd and 3rd generation penicillins e.g. ampicillin, methicillin. cloxacillin.

You got a great answer above, but this is really something that would have been extremely easy to Google.

It’s really not. I searched it and plenty of side effects came up but nothing specified which were on/off-target.