Dosing and uses of G mycetin, Garamycin (gentamicin)
Adult dosage forms and strengths
injectable solution
- 10mg/mL
- 40mg/mL
Susceptible Infections
Conventional dosing
- 3-5 mg/kg/day IV/IM divided q8hr
Extended dosing interval (q24h+)
- Initial: 4-7 mg/kg/dose IV qDay
- Base dose on lean body weight
- Subsequent doses: Consult pharmacist
Surgical Infection
Prophylaxis
Oral/pharyngeal: 1.5 mg/kg IV PLUS clindamycin 600-900 mg IV
Ruptured viscus: 1.5 mg/kg IV q8hr PLUS clindamycin 600 mg IV q6hr
Endocarditis
Prophylaxis
GI, GU procedure: 1.5 mg/kg IV/IM <30 minutes before procedure PLUS ampicillin or vancomycin
Cystic Fibrosis
7.5-10.5 mg/kg/day IV/IM divided q8hr
Pelvic Inflammatory Disease (Off-label)
Loading dose: 2 mg/kg IV or Im
Maintenance dose: 1.5 mg/kg IV or IM q8hr
Mycobacterium Infection (Orphan)
Gentamicin liposome injection: For disseminated Mycobacterium avium-intracellulare infection
Orphan indication sponsor
- Liposome Company, Inc; One Research Way; Princeton, NJ 08540
Dosing Considerations
Gentamicin may be given IV/Im
Dosing regimens are numerous and are adjusted based on CrCl and changes in volume of distribution, as well as on the body space where distribution of the agent will occur
Monitor peak (4-12 mg/L) and trough (1-2 mg/L)
Monitor renal and auditory function
Each regimen must be followed by at least trough level drawn on third or fourth dose, 30 minutes before dosing
May draw peak level 30 minutes after 30-minute infusion
Use ideal body weight for mg/kg/dose; more accurate than total body weight
Gentamicin is usually a first-line aminoglycoside against infections with gram-negative organisms such as Pseudomonas aeruginosa, Proteus, Escherichia coli, Klebsiella, Enterobacter, Serratia, and Citrobacter, as well as against Staphylococcus (gram- positive)
Bacterial organisms causing usceptible infections
- Susceptible infections include the following:
- Pseudomonas aeruginosa
- Proteus species (indole-positive and indole-negative)
- Escherichia coli
- Klebsiella-Enterobacter-Serratia species
- Citrobacter species
- Staphylococcus species (coagulase-positive and coagulase-negative)
- Pseudomonas aeruginosa
- Proteus species (indole-positive and indole-negative)
- Escherichia coli
- Klebsiella-Enterobacter-Serratia species
- Citrobacter species
- Staphylococcus species (coagulase-positive and coagulase-negative)
Dosing Modifications
Renal impairment
- CrCl >90 mL/min and <60 years: q8hr
- CrCl 60-90 mL/min or ≥60 years: q12hr
- CrCl 25-60 mL/min: q24hr
- CrCl 10-25 mL/min: q48hr
- CrCl <10 mL/min: q72hr
- Following dialysis in ESRD
Pediatric dosage forms and strengths
injectable solution
- 10mg/mL
- 40mg/mL
Susceptible Infections
≥5 years: 2-2.5 mg/kg/dose IV/IM q8hr
<5 years: 2.5 mg/kg/dose IV/IM q8hr
<30 weeks' gestation
- 0-28 days: 2.5 mg/kg/day IV/IM
- >28 days: 3 mg/kg/day IV/IM
30-36 weeks' gestation
- 0-14 days: 3 mg/kg/day IV/IM
- >14 days: 5 mg/kg/day IV/IM divided q12hr
>36 weeks' gestation
- 0-7 days: 5 mg/kg/day IV/IM divided q12hr
- >7 days: 7.5 mg/kg/day IV/IM divided q8hr
Dosing Considerations
Monitor peak (4-12 mg/L) and trough (1-2 mg/L)
Monitor renal and auditory function
Individualization critical due to low therapeutic index
Use ideal body weight for mg/kg/dose, except in neonates (in whom actual body weight should be used)
Bacterial organisms causing susceptible infections
- Pseudomonas aeruginosa
- Proteus species (indole-positive and indole-negative)
- Escherichia coli
- Klebsiella-Enterobacter-Serratia species
- Citrobacter species
- Staphylococcus species (coagulase-positive and coagulase-negative)
G mycetin, Garamycin (gentamicin) adverse (side) effects
>10%
Neurotoxicity (vertigo, ataxia)
Gait instability
Ototoxicity (auditory, vestibular)
Nephrotoxicity (decreased CrCl)
Nephrotoxicity if trough >2 mg/L
1-10%
Edema
Rash
Reddening of skin
Itching
<1%
Drowsiness
Headache
Pseudomotor cerebri
Photosensitivity
Allergic reaction
Erythema
Anorexia
Nausea/vomiting
Weight loss
Increased salivation
Enterocolitis
Granulocytopenia
Agranulocytosis
Thrombocytopenia
Elevated LFTs
Burning
Stinging
Tremors
Muscle cramps
Weakness
Dyspnea
Warnings
Black box warnings
Neurotoxicity, manifested as bilateral auditory and vestibular ototoxicity, can occur in patients with preexisting renal damage and in patients with normal renal function treated at higher doses and/or for periods longer than those recommended; high-frequency deafness usually occurs first and can be detected only with audiometric testing
Aminoglycosides are potentially nephrotoxic; risk is greater in patients with impaired renal function and in those who receive high doses or prolonged therapy; rarely, nephrotoxicity may not become apparent until the first few days after cessation of therapy
Use with caution in premature infants and neonates because of renal immaturity and the resulting prolongation of serum half-life of the drug
Neuromuscular blockade and respiratory paralysis have been reported following parenteral injection, topical instillation (as in orthopedic and abdominal irrigation or in local treatment of empyema), and oral use of aminoglycosides, especially when given soon after anesthesia or muscle relaxants; if blockage occurs, calcium salts may reverse these phenomena, but mechanical respiratory assistance may be necessary
Avoid concurrent or sequential use of neurotoxic and/or nephrotoxic drugs, including other aminoglycosides (eg, amikacin, streptomycin, neomycin, kanamycin, paromomycin)
Cumulative listing of drugs to avoid from all aminoglycoside package inserts includes amphotericin B, bacitracin, cephaloridine, cisplatin, colistin, polymyxin B, vancomycin, and viomycin
Avoid potent diuretics (eg, ethacrynic acid, furosemide) because they increase risk of ototoxicity; when administered intravenously, diuretics may enhance aminoglycoside toxicity by altering antibiotic concentrations in serum and tissue
Contraindications
Prior aminoglycoside toxicity or hypersensitivity
Cautions
Risk of ototoxicity, neurotoxicity, nephrotoxicity
Narrow therapeutic index (not intended for long-term therapy)
Caution in renal failure (not on dialysis), myasthenia gravis, hypocalcemia, and conditions that depress neuromuscular transmission
Adjust dose in renal impairment
Endocarditis prophylaxis (GI, GU procedure): AHA Guidelines recommend only for high-risk patients
Pregnancy and lactation
Pregnancy category: d
Lactation: Enters breast milk; use with caution (AAP Committee states "compatible with nursing")
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of G mycetin, Garamycin (gentamicin)
Mechanism of action
Aminoglycoside antibiotic for coverage of gram-negative bacteria, including Pseudomonas species; synergistic with beta lactamase against enterococci; interferes with bacterial protein synthesis by binding to 30S and 50S ribosomal subunits
Absorption
Peak plasma time: IM (30-90 min); IV (30 min after 30-min infusion)
Distribution
Gentamicin crosses placenta; relative diffusion from blood into CSF is minimal even with inflammation
CSF-to-blood level ratio: Normal meninges (minimal); inflamed meninges (10-30%)
Protein bound: <30%
Vd: Neonates (0.4-0.6 L/kg); children: (0.3-0.35 L/kg); adults: (0.2-0.3 L/kg); Vd increased by edema, ascites, and fluid overload and decreased by dehydration
Elimination
Half-life: 2-3 hr (NRF)
Renal clearance: Directly related to renal function
Excretion: Urine (70% recovered as unchanged drug in patients with NRF)
Administration
IV Incompatibilities
Additive: Ampho B, ampicillin, cefazolin, dopamine, furosemide, heparin
Syringe: Ampicillin, heparin
Y-site: Furosemide, heparin
Not spec: Carbenicillin
IV Compatibilities
Additive: cimetidine, clindamycin, verapamiL
Syringe: clindamycin
Y-site: Amiodarone, esmolol, vitamins B/C
IV Preparation
Dilute single dose in 50-200 mL NS or D5W
IV Administration
Infuse over 30 min-2 hr
After infusion, flush line with NS or D5W
