strep-toe-MYE-sin

Therapeutic Classification: anti-infectives

Pharmacologic Classification: aminoglycosides

• Active tuberculosis (in combination with other agents).
• Serious enterococcal or gram-negative infections (in combination with other agents).

• Inhibits protein synthesis in bacteria at level of 30S ribosome.

• Bactericidal action.

Spectrum:

• Notable for activity against.
• Enterococci (synergy with a penicillin is required).
• Also active against Mycobacterium.

Absorption: Well absorbed after IM administration. Negligible absorption when administered orally.

Distribution: Widely distributed throughout extracellular fluid. Poor penetration into CSF.

Metabolism/Excretion: Excretion is >90% renal.

Half-life: 2–4 hr (↑ in renal impairment).

(plasma concentrations†)

†All parenterally administered aminoglycosides.

Contraindicated in:

• Hypersensitivity
• Cross-sensitivity among aminoglycosides may occur.

Use Cautiously in:

• Renal impairment (dosage adjustments necessary; plasma concentrations monitoring useful in preventing ototoxicity and nephrotoxicity)
• Hearing impairment
• Mitochondrial DNA variants in the 12S rRNA gene (MTRNR1) or maternal history of ototoxicity (↑ risk of ototoxicity)
• Neuromuscular diseases such as myasthenia gravis
• Obese patients (dosage should be based on ideal body weight)
• OB: May ↑ risk of congenital deafness when used during pregnancy
• Lactation: Safety not established in breastfeeding
• Geri: ↑risk of ototoxicity and nephrotoxicity in older adults.

EENT: ototoxicity (vestibular and cochlear).

F and E: hypomagnesemia.

GU: nephrotoxicity.

MS: muscle paralysis (high parenteral doses).
Misc: hypersensitivity reactions.

Drug-Drug:

• Inactivated by penicillins and cephalosporins when coadministered to patients with renal impairment.
• Possible respiratory paralysis after inhalationanesthetics or neuromuscular blockers.
• ↑risk of ototoxicity with loop diuretics.
• ↑risk of nephrotoxicity with other nephrotoxic drugs.

• IM (Adults): Tuberculosis: 1 g/day initially, decreased to 1 g 2–3 times weekly;other infections: 250 mg–1 g every 6 hr or 500 mg–2 g every 12 hr.
• IM (Children): Tuberculosis: 20 mg/kg/day (not to exceed 1 g/day);other infections: 5–10 mg/kg every 6 hr or 10–20 mg/kg every 12 hr.

(Generic available)

• Lyophilized powder for injection: 1 g/vial;
• Solution for injection: 500 mg/mL;

• Assess patient for infection (vital signs, wound appearance, sputum, urine, stool, WBC) at beginning of and throughout therapy.
• Obtain specimens for culture and sensitivity before initiating therapy. First dose may be given before receiving results.
• Evaluate eighth cranial nerve function by audiometry before and throughout therapy. Hearing loss is usually in the high-frequency range. Prompt recognition and intervention are essential in preventing permanent damage. Also monitor for vestibular dysfunction (vertigo, ataxia, nausea, vomiting). Eighth cranial nerve dysfunction is associated with persistently elevated aminoglycoside levels. Aminoglycosides should be discontinued if tinnitus or subjective hearing loss occurs.
• Monitor intake and output and daily weight to assess hydration status and renal function.
• Assess patient for signs of superinfection (fever, upper respiratory infection, vaginal itching or discharge, increasing malaise, diarrhea). Report to physician or other health care professional.

• Monitor renal function by urinalysis, specific gravity, BUN, serum creatinine, and CCr before and throughout therapy.
  • May cause ↑ BUN, AST, ALT, serum alkaline phosphatase, bilirubin, serum creatinine, and LDH concentrations.
  • May cause ↓ serum calcium, magnesium, potassium, and sodium concentrations.
  • Plasma concentrations should be monitored periodically during therapy. Timing of plasma concentrations is important in interpreting results. Draw blood for peak levels 1 hr after IM injection completed. Trough levels should be drawn just before next dose. Peak level should be 20–35 mcg/mL (35–45 mcg/mL for mycobacterial diseases). Trough level should be <5 mcg/mL.

• Keep patient well hydrated (1500–2000 mL/day) during therapy.
• IM: IM administration should be deep into a well-developed muscle. Alternate injection sites.

• Instruct patient to report signs of hypersensitivity, tinnitus, vertigo, hearing loss, rash, dizziness, or difficulty urinating.
  • Advise patient of the importance of drinking plenty of liquids.
• Advise females of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding.

• Resolution of the signs and symptoms of infection. If no response is seen within 3–5 days, new cultures should be taken.