Ribosomal resistance to streptomycin develops readily, limiting its role as a single agent.
A. Mycobacterial Infections
Streptomycin is mainly used as a second-line agent for treatment of tuberculosis. The dosage is 15 mg/kg/d with a maximum of 1 g/d (20–40 mg/kg/d for children), and it may be given intramuscularly or intravenously. It should be used only in combination with other agents to prevent emergence of resistance. See Chapter 47 for additional information regarding the use of streptomycin in mycobacterial infections.
B. Nontuberculous Infections
In plague, tularemia, and sometimes, brucellosis, streptomycin, 1 g twice daily (15 mg/kg twice daily for children), is given intramuscularly in combination with an oral tetracycline.
Penicillin plus streptomycin is effective for enterococcal endocarditis and 2-week therapy of viridans streptococcal endocarditis; however, for susceptible strains, gentamicin is used more commonly when an aminoglycoside is selected as adjunct therapy. Streptomycin remains a useful agent for treating gentamicin non-susceptible enterococcal infections, as some isolates that are resistant to gentamicin (and therefore resistant to netilmicin, tobramycin, and amikacin) will remain susceptible to streptomycin.
Fever, skin rashes, and other allergic manifestations may result from hypersensitivity to streptomycin. This occurs most frequently with a prolonged course of treatment (eg, for tuberculosis).
Pain at the injection site is common but usually not severe. The most serious toxic effect with streptomycin is disturbance of vestibular function—vertigo and loss of balance. The frequency and severity of this disturbance are in proportion to the age of the patient, the blood levels of the drug, and the duration of administration. Vestibular dysfunction may follow a few weeks of unusually high blood levels (eg, in individuals with impaired renal function) or months of relatively low blood levels. Vestibular toxicity tends to be irreversible. Streptomycin given during pregnancy can cause deafness in the newborn.
Gentamicin is a mixture of three closely related constituents, C1, C1A, and C2 (Figure 45–2) isolated from Micromonospora purpurea. It is effective against both Gram-positive and Gram-negative organisms, and many of its properties resemble those of other aminoglycosides.
Gentamicin sulfate, 2–10 mcg/mL, inhibits in vitro many strains of staphylococci and Gram-negative bacteria, including
P. aeruginosa and Enterobacteriaceae. Like all aminoglycosides, it has no activity against anaerobes.