Antibiotics That Can Be Given IM

Beta-Lactams

Aminoglycosides

Others

When to Choose the IM Route

• IV access is not available or not feasible
• Outpatient/community treatment setting
• Long-acting/depot formulations needed (e.g., benzathine penicillin once every 3-4 weeks for RF prophylaxis)
• Single-dose treatment required (e.g., ceftriaxone 500 mg IM for uncomplicated gonorrhea)
• Oral route not possible (vomiting, unconscious patient)

Important Cautions

• Avoid IM in patients on anticoagulants (risk of hematoma)
• Repeated IM injections in infants can cause muscle contracture/fibrosis - especially with opioids and some antibiotics (noted in [Campbell's Operative Orthopaedics](Campbell's Operative Orthopaedics 15th Ed))
• Maximum volume per site: ~3-5 mL in adults (deltoid: max 2 mL)
• Always rotate injection sites for repeat dosing

Antibiotics That CANNOT Be Given IM

1. Vancomycin

• Only given IV (or orally for C. difficile colitis - oral not absorbed systemically)
• IM injection causes severe tissue necrosis and pain at the injection site
• IV must be given as a slow infusion (over 60 min) - rapid infusion itself causes "Red Man Syndrome" from histamine release
• Source: Goodman & Gilman's Pharmacological Basis of Therapeutics

2. Fluoroquinolones (Ciprofloxacin, Levofloxacin, Moxifloxacin)

• Available orally and IV only - no IM formulation
• Oral bioavailability is nearly 100%, so IV is used when oral not possible; IM is not a recognized route
• Highly irritating to muscle tissue

3. Linezolid (Oxazolidinone)

• Available orally and IV only
• Oral bioavailability is 100% (same as IV dosing), so IM offers no advantage
• No IM formulation exists
• Source: Goodman & Gilman's - "Linezolid is well absorbed after oral administration, with a bioavailability of 100%"

4. Macrolides

• Cause significant pain and local tissue irritation if given IM
• No IM formulations available clinically

5. Tetracyclines (Doxycycline, Tetracycline, Minocycline)

• Oral / IV only
• IM injection causes extreme pain and local necrosis due to low pH of the formulation
• Doxycycline IV is highly irritating even in veins; IM is never used

6. Carbapenems (Meropenem, Imipenem-Cilastatin, Ertapenem)

• Primarily IV only
• Exception: Ertapenem can be given IM (with lidocaine diluent) - but meropenem and imipenem are IV only

7. Colistin / Polymyxin B

• IV only (or inhaled/nebulized for pulmonary use)
• Causes severe local toxicity if given IM

8. Daptomycin

• IV only - no IM formulation
• Used for MRSA, VRE skin/soft tissue infections and bacteremia

9. Tigecycline

• IV only (a glycylcycline/tetracycline derivative)
• No oral or IM formulation

10. Trimethoprim-Sulfamethoxazole (Co-trimoxazole)

• Oral / IV only
• IM use not recommended due to local irritation and poor absorption

Quick Memory Aid

"VFLMTCCD T" = Vancomycin, Fluoroquinolones, Linezolid, Macrolides, Tetracyclines, Colistin, Carbapenems (most), Daptomycin, Tigecycline - all IV/oral only, never IM.

General Reasons an Antibiotic Cannot Be Given IM

1. Tissue necrosis/severe pain - e.g., vancomycin, tetracycline
2. No IM formulation manufactured - e.g., linezolid, fluoroquinolones
3. 100% oral bioavailability - makes IM redundant (linezolid, fluoroquinolones)
4. Erratic/unpredictable IM absorption for severe infections where reliable serum levels are needed
5. Anticoagulated patients - IM is generally avoided in anyone on anticoagulants due to hematoma risk (not antibiotic-specific)