The dose you use of Optimmune is supposed to be controlled by the length of the line you squeeze onto the eye. This then governs also how long the tube lasts. On average you will get about 1 month from a tube if you are careful about not wasting any and apply a small amount (a quarter of a cm is the minimum recommended dose, twice daily. Theoretically the shelf life is supposed to be 1 month after opening, due to the potential for contamination etc. You are advised to not use any left over after 1 month, though many people do not stick to this.
PRECAUTIONS : Identification of infecting organisms should be made either by microscopic roll smear evaluation or by culture as appropriate. Antibiotic susceptibility of the pathogenic organism(s) should be determined prior to use of this preparation.
If overgrowth of nonsusceptible bacteria, fungi, or yeasts occur, or if hypersensitivity develops, treatment should be discontinued and appropriate therapy instituted.
Administration of recommended doses of gentamicin-betamethasone-clotrimazole ointment beyond 7 days may result in delayed wound-healing.
Avoid ingestion. Adverse systemic reactions have been observed following the oral ingestion of some topical corticosteroid preparations. Patients should be closely observed for the usual signs of adrenocorticoid overdosage which include sodium retention, potassium loss, fluid retention, weight gain, polydipsia, and/or polyuria. Prolonged use or overdosage may produce adverse immunosuppressive effects.
Use of corticosteroids, depending on dose, duration, and specific steroid, may result in endogenous steroid production inhibition following drug withdrawal. In patients presently receiving or recently withdrawn from corticosteroid treatments, therapy with a rapidly acting corticosteroid should be considered in especially stressful situations.
Before instilling any medication into the ear, examine the external ear canal thoroughly to be certain the tympanic membrane is not ruptured in order to avoid the possibility of transmitting infection to the middle ear as well as damaging the cochlea or vestibular apparatus from prolonged contact.
A hot spot, or what veterinarians term "acute moist dermatitis," is a painful and inflamed area of the skin that is often accompanied by discharge and a bad odor. Hot spots occur via allergic reactions to bacterial skin infections often caused by a lesion or wound. Skin breaks, lesions, and wounds can have a variety of causes, including flea bites, scratches, scrapes or nicks, anal gland problems, and underlying allergies. Dogs often itch and scratch skin breaks and wounds to such an extent that wet scabs form on the fur.  Hot spots can be painful for dogs and can become very large quite quickly. It is important to seek prompt and adequate treatment if you notice a hot spot on your dog.