Aminoglycosides

Aminoglycosides are powerful antibiotics used in hospitals for serious infections. As a pharmacist, you'll often see them in IV forms, especially for critically ill patients. Understanding their pharmacology, administration, and toxicity risks is essential to support safe use.

General Principles of Link:

Anti-Infectives

Medicine Link

Gentamicin

Amikacin

Tobramycin

What Are Aminoglycosides?

Aminoglycosides are concentration-dependent, bactericidal antibiotics that:

• Inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit

• Cause cell membrane damage

• Are effective mostly against aerobic Gram-negative bacteria, including Pseudomonas aeruginosa

📌 Examples:

• IV/IM: Gentamicin, Amikacin, Streptomycin, Tobramycin

• Oral (non-absorbed): Paromomycin – mainly used for intestinal infections

  
  

Core Medicines

1. Gentamicin

Gentamicin

✅ Use:

• Empiric therapy for serious Gram-negative infections (up to 48 hrs)

• Pseudomonas aeruginosa, enterococcal endocarditis (with beta-lactam), brucellosis

• Surgical prophylaxis

💊 Dose:

• Once-daily IV/IM:

  • 60 mL/min CrCl: 5–7 mg/kg

  • 30–60 mL/min: 4–5 mg/kg

  • <30 mL/min: Specialist advice

• Endocarditis: 1 mg/kg every 8 hrs (TDM required)

⚠️ Caution:

• Renal/hearing impairment, elderly, neuromuscular disorders

• Avoid in previous aminoglycoside ototoxicity

• Use adjusted body weight if BMI >35

📋 Instructions:

• Infuse IV over 15–30 minutes

• Don’t mix with penicillins in same IV line — flush in between

  
  

2. Amikacin

Amikacin

✅ Use:

• Resistant Gram-negative infections

• Mycobacterial infections (e.g., TB, NTM)

💊 Dose:

• 15–20 mg/kg IV/IM once daily

• NTM: 10–15 mg/kg daily or 15–25 mg/kg 3x/week

• Adjust based on renal function and therapeutic drug monitoring

⚠️ Caution:

• Similar to gentamicin — especially in elderly, renal impairment, CF, burns, or ICU patients

• Screen family history for mitochondrial mutations (A1555G) if history of aminoglycoside-induced deafness

📋 Instructions:

• IV infusion over 15–30 mins or slow IV push (3–5 mins if <500 mg)

  
  

3. Tobramycin

Tobramycin

✅ Use:

• Gram-negative infections, P. aeruginosa, cystic fibrosis

• Systemic use and inhaled formulations

💊 Dose:

• IV: 5–7 mg/kg once daily

• CrCl 30–60 mL/min: 4–5 mg/kg

• CF: 10 mg/kg IV (max 660 mg), adjust via TDM

• Inhaled: 300 mg twice daily for 28 days (cycle), or DPI 112 mg twice daily

⚠️ Caution:

• Monitor renal function and serum levels

• Inhaled use may cause cough, bronchospasm, or taste changes

• Avoid mixing inhalation drug with other nebulised solutions

📋 Instructions:

• Nebulised via PARI nebuliser over 15 minutes

• Always administer bronchodilator first

  
  

Monitoring & Therapeutic Drug Levels

Situation	Monitoring Needed?	Notes
<48 hrs use	No (if stable renal function)	Empiric use only
>48 hrs use	Yes	TDM required
Method	AUC-based (preferred)	2 levels: 30 min & 6–14 hrs post-dose
Multiple doses/day	Trough level <1 mg/L	Especially for endocarditis
Renal Function	Daily creatinine if unstable	Or every 3–5 days if stable

AUC Target: Approx. 100 mg·h/L

⚠️ Side Effects

Effect	Description
Nephrotoxicity	Reversible. Risk ↑ with long treatment, dehydration, high dose
Ototoxicity	May be irreversible. Symptoms: tinnitus, hearing loss, vertigo
Neuromuscular blockade	Rare. Can cause respiratory depression. Reversed with IV calcium gluconate
Others (Rare)	Anaphylaxis, bronchospasm, peripheral neuropathy

👂 If hearing or balance symptoms occur, stop drug and refer.

Practice Points

• Use empirically only for ≤48 hours → then de-escalate based on culture

• Always check baseline renal function (CrCl) before starting

• Hydration is key to reduce nephrotoxicity risk

• Monitor for:

  • Vestibular symptoms: nausea, gait disturbance

  • Cochlear symptoms: hearing loss, tinnitus

• If renal function worsens early (<5 days), it’s often the illness—not yet drug toxicity

  
  

Counselling Points

Here’s how you can explain it to patients on longer courses:

“This antibiotic is strong and effective, but may sometimes affect your kidneys or hearing. Please let your doctor know if you feel dizzy, notice ringing in your ears, or have any hearing changes. You’ll likely have regular blood tests during treatment.”

For inhaled tobramycin:

“Use your reliever inhaler first, then wait 15 minutes before using this nebuliser. Rinse your mouth afterward and watch for hoarseness or cough.”

Lifestyle Tips for Patients

Tip	Reason
Stay well hydrated	Prevents nephrotoxicity
Report hearing/balance issues early	May indicate early ototoxicity
Take care with balance if dizzy	Reduce fall risk from vestibular effects
Attend all blood tests	To monitor drug levels and kidney function
Use bronchodilator before inhaled tobramycin	Reduces bronchospasm risk

✅ Summary for Pharmacists

Key Point	Takeaway
Main use	Serious Gram-negative infections (IV only)
Preferred dosing	Once daily (unless endocarditis)
Monitoring	TDM if >48 hrs or impaired renal function
Toxicity signs	Hearing changes, dizziness, rising creatinine
Practical tip	Use ideal/adjusted weight for dosing; don’t mix with penicillins