I put the UK equivalents of Bonnie's list in brackets for you next to the products and some of the things each is used for - just for anyone who is interested.
1ml and 5ml Syringe
Vitamin C Tablets 100mg Chewables -
supplement if animal is ill/not eating normally
Vitrate Rehydration Fluids -
UK equivalent: Dioralyte or Lectade. Given to prevent/treat early dehydration. Useful in cases of diarrhea.
Acidophius Probiotic Powder -
Pro-C Probiotic, Bio-Lapis or Avipro Plus are the most common animal probiotics in UK. Given to balance/restore gut flora when animal ill/on medication/has diarrhea.
Critical Care Sachet -
Science Recovery or Nutripowder are UK alternatives. Mix up with water and syringe to guinea pigs who are not eating.
Betadine liquid -
Povidone Iodine. Dilute with water - 1 part Iodine to 10 parts water. Used as an antiseptic and occasionally used for skin complaints.
Malaseb -
antifungal shampoo, to treat fungal skin conditions. Malaseb is usually a Prescription-Only Medicine (POM); alternatives that you can buy in pharmacies include Nizoral and Alphosyl. Better yet, www.gorgeousguineas.com specialise in such shampoos.
Nail clippers
tweezers
scissors
External Mite Wash
Ivomec or Revolution for internal mites -
Can be given orally every 3 months as a "wormer" (and to treat/prevent internal parasites), alonside Panacur/Valbazen.
Disposable Gloves
Some herbal supplements that can be stored
Glucose - although alot of the rehydrate/electrlite replacements actually contain glucose which is handy as these store better ).
Disinfecting wipes or swabs
Cotton Buds
Ear Drops ( Surolan or other suitable )
Eye Drops
Painkillers ( metacam - only avail with vet appt )
this is all the stuff i am aiming to have in my first aid kit xxxxxxxxx
forgot to add some of this stuff isnt available in the uk or comes under a different name as this is an aussie list x
I have a varied first aid kit, but my absolute minimums are:
Painkillers (children's Nurofen, and Metacam)
Buscopan -
for treating minor bloat (I have two pigs prone to bloat/gas buildup)
Probiotic
Oxbow Vitamin C tablets
Oxbow Critical Care (Fine Grind) -
I prefer the Fine Grind as I don't need to butcher the syringes to syringe the feed! 
Bepanthen -
for topical skin problems/sores
Povidone Iodine
Ivomec
Panacur -
given at same time as Ivomec, once every three months.
Daktarin Oral Gel -
useful for all oral and dental trouble. My pigs had sore mouths before and after dental work, this gel helped hugely and got the pigs eating much quicker after having dental work done. My first port of call when a pig is having oral difficulties.
Sudafed Expectorant -
this is handy for my pigs who suffer from allergies, since it stops the raspy/grumbly breathing with just a one-off dose. Can also be used in conjunction with POMs in minor respiratory infections where coughing is troublesome.
I also have a stethoscope, disposable gloves, two types of nail clippers, dental rasps and buccal pad separators (
training is essential before using these!), a supply of 1ml syringes, a pill crusher (pestle and mortar), a Snugglesafe heatpad, tweezers, bowls and spoons (for making up syringe-feeds), a stack of towels and pillowcases (for wrapping/bathing) and of course...weighing scales!
Three years ago, I would never have dreamed of using most of the products in my kit, I was one of the most uptight people about what I put in my pigs. Circumstances, however, led me to having to try some of them and all of the above were extremely useful both in emergencies, and as complemetary medicines alongside veterinary treatments. I know what I'm doing with the meds, I know the safe doses, frequency, length of course etc. and I am training in rodentology - I never give anything I am remotely unsure about.
It must be said that a veterinary diagnosis and advice is extremely important, whether you use anything in your first aid kit or not. It's best that everyone views their first aid kit as just that -
first aid. Things that will help until you can get to a vet, and then you can discuss treatment with those "qualified" and if necessary continue with the same treatment. Do make sure you have a good vet though - don't wait until you actually
need the vet to find out whether s/he is experienced enough in guinea pig medical care!
Good luck today.
