It acts by binding free IgE at the same site that IgE would bind to its high-affinity receptor (FcεRI) on mast cells, thereby reducing free IgE in the serum

Immunosuppression
Doctors will sometimes prescribe immunosuppressive drugs such as prednisolone and ciclosporin if the patient has an intense form of solar urticaria. However, the side effects of these medicines can be severe which is why they are reserved for the most extreme of cases. Plasmapheresis
In more extreme cases, plasmapheresis can be considered. This technique is used to remove the blood plasma or fluid in the red blood cells and then return the cells to the body. It "removes a circulating factor from the blood that may be involved in causing the urticaria," but is still being tested and is not always effective. When the treatment is a success, the patients photosensitivity is decreased to the degree that they can undergo PUVA which can result in the relief of the urticarial outbreaks for an extended period of time. The major setback to this treatment is that the side effects can be severe and may include anaphylactoid reactions. Epidemiology
In the United States, only about 4% of patients with photosensitive disorders are reported to have been diagnosed with solar urticaria. Internationally, the number is slightly larger at 5.3%.
Tobramycin passes the placenta: in the fetus, 20% of the mothers concentrations have been measured.The substance is neither bound to plasma proteins, nor is it metabolized. It is excreted in unchanged form via the kidneys with a biological half-life of about 2 to 3 hours. Elimination from deep compartments such as the renal cortex follows after 8 to 12 hours. In newborns the half-life is 4.6 hours on average; in those with a low birth weight it is as long as 8.7 hours on average. People with reduced kidney function also have a longer half-life for tobramycin, while in those with severe burns it can be shorter. References
Further reading
Davis BD (September 1987). "Mechanism of bactericidal action of aminoglycosides". Microbiological Reviews. 51 (3): 341–50. doi:10.1128/MMBR.51.3.341-350.1987. PMC 373115. PMID 3312985. External links
"Tobramycin". Drug Information Portal. U.S. National Library of Medicine.