I know this response is late but hopefully it can be beneficial to someone else seeking the same advice.
I had a similar issue administering and figuring out the dosage of doxycycline after my Guinea pig developed a URI. After researching and speaking with a Vet, this is what I found.
Yes, creating suspension and administering it to your pet is doable when a vet isn’t feasible. Just answer.com/veterinarian was a great resource in figuring this out. This is a link to a Vet answering just that question.
https://www.justanswer.com/veterinary/b3fm6-crush-doxycycline-tabs-add-saline.html
My experience:
I have created a suspension and added it to food but if your piggy doesn’t eat ALL the food due to the taste the proper dosage may not be received and doxy is said to be bitter. So, straight syringe feeding works best.
With a 100mg pill I use a liquid suspension of 10ml to dissolve it in (Doxy will fully dissolve). 10ml is about 2 teaspoons. Let the pill sit for about 5 minutes for it to soften then smash it and mix it until it’s fully dissolve. This will create a suspension of 10mg/ml. With this suspension, a 1kg pig at 5mg/kg would need a syringe of .5cc. Guinea lynx has a great dosage calculator found here.
https://www.guinealynx.info/dose_calculator.html
For every 100mg pill add 10ml of liquid to maintain 10mg/ml. For the liquid you can use water but because it is bitter my vet suggested unsweetened apple juice to make it more palatable.
Since using doxycycline is necessary in a public health emergency i.e. anthrax, creating a doxy suspension is available via the FDA. Use this to guide you through the process just in case my explanation wasn’t clear. This websites dosage does not apply as it’s for humans.
https://www.fda.gov/media/75538/download
Now when using this suspension it only lasts about 24 hours. I have invested in a product called ORA-SWEET. This helps it to last for 7 days. I use this to compound meds for my kids who hate swallowing pills as well as my pets. I first soften and crush two 100mg pills in 10ml of water then add 10ml of the ORA-SWEET. That gives me 20ml of the 10mg/ml suspension for the week. You can buy this or a compounding product like it on Amazon.
A great resource for using this product and doxycycline suspension can be found here at the
University of Wisconsin – School of Veterinary Medicine
https://www.sheltermedicine.com/library/resources/?r=doxycycline-suspension
I hope this helps.