How do I make the prescribed ear drop, which contains Maxidex eye drops 5 ml and salicylic acid 1%?

Maxidex Eye Drops contains: 1 mg/ml dexamethasone and as excipients.   Benzalkonium Chloride 0.1 mg – Methyl hydroxypropylcellulose – anhydride disodium hydrogen phosphate – polysorbate 80 – Disodium residue Detaat – Potassium chloride – Monohydride citric acid and/or sodium hydroxide – purified water up to 1 ml.

salicylic acid is incompatible with Polysorbate 80.  

I suggest you use propylene glycol as a solvent. Chances are that both of these components resolve