Pharmacology
Infections
All of the following antibiotics are commonly implicated in causing C. difficile colitis EXCEPT for:
Answer:
Vancomycin is used to treat C. difficile colitis. Although any antibiotic is a potential risk factor for C. diff infection, the ones most commonly recognised are:- Clindamycin
- Fluoroquinolones e.g. ciprofloxacin
- Broad-spectrum penicillins e.g. co-amoxiclav
- Second- and third-generation cephalosporins e.g. ceftriaxone
Vancomycin
Pharmacology / Infections
Last Updated: 8th September 2021
Mechanism of Action
Vancomycin is a glycopeptide antibiotic which acts by inhibiting peptidoglycan formation and is active against aerobic and anaerobic Gram-positive bacteria including multi resistant staphylococci.
Vancomycin binds to the terminal end of the growing peptidoglycan to prevent further elongation and cross-linking due to inhibition of transglycosylase; this results in decreased cell membrane activity and increased cell lysis.
For systemic infection vancomycin must be given by intravenous injection as it is not absorbed orally. Penetration into cerebrospinal fluid is poor. It is given orally for pseudomembranous colitis caused by Clostridium difficile infection.
Indications
Indications include:
- C. difficile colitis
- Infections due to Gram-positive bacteria including endocarditis, osteomyelitis, septicaemia, pneumonia, septic arthritis and soft-tissue infection where MRSA is suspected/demonstrated
- Peritonitis associated with peritoneal dialysis
- Septicaemia related to vascular catheter
- Surgical prophylaxis (when high risk of MRSA)
Cautions
Vancomycin should be avoided if there is a history of deafness, and should be used with caution in the elderly. The dose should be reduced in renal impairment, and the plasma-vancomycin, renal function and auditory function monitored regularly.
Side Effects
Side effects include:
- Blood disorders including neutropenia
- Nephrotoxicity (acute interstitial nephritis)
- Ototoxicity (discontinue if tinnitus occurs)
- Rarely anaphylactoid reaction, cardiac arrest or 'red man' syndrome (flushing of the upper body) on rapid infusion
Monitoring
All patients require plasma-vancomycin measurement (after 3 or 4 doses if renal function normal, earlier if renal impairment).
All patients require blood counts, urinalysis, and renal function tests. Auditory function should be monitored in the elderly.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
