Very pleased to hear you have more antibiotics but sorry the infection/symptoms havent been resolved yet.
0.5ml peadiatric (banana) septrin once daily may not be enough to shift a stubborn infection. If your piggies weigh 1kg or more, they can go up to 0;5ml twice daily (on the agreement of your vet) - so if there is little improvement over the next few days I suggest you ring them and discuss upping the dose. My exotics vet routinely prescribes the higher amount - (i.e. 1.0ml per day) be it split into two doses or just the one. So far he has prescribed it for UTI's, abcesses, RTI's, surgical wounds - all at the higher dose. Happy to talk to your vet if they have a problem with this suggestion.
Metacam can be given once or twice daily but there is a maximum dose...normally up to 0.2ml per kg (assuming you have the dog dose 1.5mg/ml) . This provides pain relief and is an anti inflammatory.
Please be aware that a lot of the dosages quoted on the forum assume that your piggie weighs approx 1kg (I have some very chunky piggies that weigh up to 1.5kg). Therefore any medication should always be calculated based upon the piggy's current weight, and the concentration of the medication checked. This applies to septrin also.
As well as the meds above and cranberry juice (latter alters the pH of the urine making it less favourable for bacteria and helps "flush" the system) - inflamed bladders do well (almost overnight!) on pearl barley gloop, which soothes the painful tissues and acts like an "internal emoluent" . Boil up a handful of pearl barley in water untill it is really squidgy - 40-60mins (keep topping up with water and don;t let the saucepan burn like I often do - the smell...and mess..... is disgusting!)
Once the barley is squidgy, sieve it and keep the liquid. (Personally I dilute this liquid 1:1 with concentrated cranberry extract from Holland & Barratt - it's in a small plastic bottle - to save all the extra syringing with normal cranberry juice) and keep in the fridge.
I dose twice a day with this mix 0.3ml-0.5ml per kg - this is the best remedy I have found for bladder problems - it not only stops the piggie squeaking on weeing but it stops the blood in the urine almost straight away. I've used it now four times on various pigs (sows and boars) and the results have been brilliant...and quick! Alll piggies have been on metacam and spetrin also - but it means their infections and symptoms are cleared up much faster.
I don;t tend to use cysitis remedies because they are full of potassium and sodium ions - many of my pigs have possible genetic heart condition and therefore these preparations, while being good for a UTI per se, may exacerbate either a heart or kidney problem.
Finally the "wash and disinfect everything" to avoid "secondary spread" is a good call by your vet. I suggest you invest in a medical disinfectant, Hibiscrub, (diluted as appropriate - normally 1:10) to clean the cages and other hard surfaces such as food bowls etc (it doesn;t have the lavender oils and other chemicals in it that Johnsons and other "pet shop disinfectants" etc do - which may cause problems for piggie respiration or irritate the skin. ) Hibiscrub is a medically-registered disinfectant proven to be active against the types of bacteria that would be causing the UTI and is also recomended by vets to syringe/flush abcesses and the like. As far as I am aware, (and from my own experiences) piggies can tolerate this with no problems. You can get Hibiscrub concentrated from most pharmacies (although some may have to order it in for you - go for the 500ml bottle as the most cost-effective)
As far as fleeces/bedding go - I suggest you soak in Vanish Oxi Extra Hygiene and wash in a non-bio washing powder (you can do both at once!) . Give a couple of extra rinses to get rid of all the chemicals befofe drying on the line and the ironing (the iron kills any residual bugs) . For the moment you are actually probably better of putting them on newspaper and changing it twice or thrice daily (I find that the cotton or other material threads from cloths used for bedding can potentially irritate their urethras in females and also the penises in males).
HTH - sorry it;s a long post but UTI's can frustratingly linger ....above is my experience on how to "bomb them"

. Antibiotics/metacam should at any rate be given for at at least 14 days to make sure "the little buggies" are annihilated - but with the suggestions above - hopefully you won;t be going beyond two weeks before your piggies are back to normal health
As i said before- very happy to talk to your vet if they want extra input so PM me for my phone number if required
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