Gentamicin
- Drugs List
- Therapeutic Indications
- Dosage
- Administration
- Contraindications
- Precautions and Warnings
- Pregnancy and Lactation
- Side Effects
- Monograph
Presentation
Chain of impregnated beads threaded on surgical wire.
Each bead contains 7.5mg gentamicin sulfate (equivalent to 4.5mg gentamicin base)
A chain of 10 beads contains 75mg gentamicin sulfate
A chain of 30 beads contains 225mg gentamicin sulfate
Drugs List
Therapeutic Indications
Uses
Short term or longer term treatment of bone infection, such as osteomyelitis, infected pseudarthroses or infected osteosynthesis.
Short term preventative of bone injury infection.
Short term prevention and treatment of soft tissue infection associated with abdominoperineal resections or operations on the small or large bowel. Other indication include bacterial peritonitis, cholecystectomies, infective fistulae, infected vascular grafts, soft tissue abscesses.
Dosage
Adults
The number of chains used depends on the size of the cavity and the clinical conditions at the site of infection. Usually 1 to 3 chains are used, but up to 5 chains have been inserted. The chains are laid in the cavity to allow easy removal. For smaller cavities the 10 bead chain (75mg implant) should be used.
Bone infection
Short term treatment
When implanting the chain, take into account the direction that the chain will be removed. The last bead on the chain should be visible above the skin through a separate stab incision and should be anchored in place by a loose suture. This allows the chain to be removed by careful traction, a few beads at a time daily.
The chains should normally be completely removed 10 to 14 days after insertion (preferably no more than 10 days after insertion). If local infection persists beyond 5 days after insertion, the chain should be removed, the cause of the infection should be determined before appropriate antibacterial therapy is initiated.
It is easier to remove chains and more comfortable for the patients if the chains do not become fixed to connective tissue.
If the beads are fixed to connective tissue to a great extent or if the traction of the beads is not adapted to the tissue conditions, there is a risk that one or more of the beads will become detached from the wire. In exceptional cases the wire may break during chain removal.
If any part of the chain becomes detached, an attempt should be made to remove the beads and wire within the cavity. If surgery is necessary to remove the chain, the risk of reoperating should be considered carefully. In high-risk patients it may be preferable to permanently leave the chain in situ.
To ensure all beads are removed from the cavity, it is important to count them as they are removed.
Longer term treatment
The chains may be implanted as for short term therapy, or they may be completed implanted in the cavity (i.e. no beads remaining above the skin) and removed surgically up to 3 months after insertion. The inserted chains will be entirely enclosed by primary wound closure.
The length of time the chains remain in situ depends on the orthopaedic procedure.
The control of local infection allows subsequent surgical procedures, such as cancellous bone grafting.
Soft tissue infection
Short term treatment
When implanting the chain, take into account the direction that the chain will be removed. The last bead on the chain should be visible above the skin through a separate stab incision and should be anchored in place by a loose suture. This allows the chain to be removed by careful traction, a few beads at a time daily.
The chains should be removed by the 6th day after insertion (by the 10th day at the latest). In most cases the chains should be withdrawn gradually, a few beads daily, from the second day after insertion.
Wound drainage
Excess drainage will dilute the gentamicin concentration at the site of infection. If possible primary wound closure should always be employed. However local condition and degree of inflammation should be considered.
An overflow drain may be used if considered absolutely necessary. Suction drainage may be used temporarily in cases of obstructed wound secretion flow.
Elderly
Children
Patients with Renal Impairment
In patients with moderate to severe renal impairment, renal function and serum gentamicin concentration should be monitored.
Administration
For implant into the cavity resulting from surgical removal of sequestrated bone or infected tissue.
The chains should not be implanted intraperitoneally.
Contraindications
None known
Precautions and Warnings
Pregnancy - see Pregnancy section
Toxic effects from the gentamicin chains are not anticipated as barely detectable gentamicin concentrations (no more than 0.5micrograms/ml) are found in the systemic circulation for up to 4 days after insertion.
Additional antibiotic therapy is required if the culture of the wound secretion contains anaerobic bacteria or organisms that are insensitive to gentamicin.
If gentamicin resistant organisms are found in the standard 10 microgram disc test, an MIC determination is recommended. Due to the high gentamicin concentrations at the infection site, organisms that are resistant to the standard 10 microgram disc screen may actually be sensitive. This test may therefore not give a true reflection of clinical efficacy.
The chains should not be implanted intraperitoneally.
There is no evidence to suggest that gentamicin chains have caused nephrotoxicity or ototoxicity in the young and elderly.
In patients with moderate to severe renal impairment, renal function and serum gentamicin concentration should be monitored.
Gentamicin chains should not be used concurrently with metal containing implants because of the theoretical possibility of surgical wire and implant corrosion. Remove gentamicin chains prior to implant of a metal prosthesis.
Pregnancy and Lactation
Pregnancy
Gentamicin chains are not recommended in pregnancy, however barely detectable gentamicin concentrations (no more than 0.5micrograms/ml) are found in the systemic maternal circulation for up to 4 days after insertion, so no ototoxic affects on the foetus are to be expected.
No problems in clinical use have positively been identified.
The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14-17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( www.toxbase.org ) or if this is unavailable at the backup site ( www.toxbasebackup.org ).
Lactation
Gentamicin is poorly excreted into breast milk. Newborn infants absorb small amounts of gentamicin which are unlikely to produce systemic effects if the mother is given typical three times daily dosage. Older infants would be expected to absorb even less gentamicin. Barely detectable gentamicin concentrations (no more than 0.5micrograms/ml) are found in the systemic maternal circulation for up to 4 days after insertion of the gentamicin chains.
Monitor the infant for possible effects indicative of disruption of the gastro-intestinal flora, especially those indicative of antibiotic-associated diarrhoea.
Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
Specialist advice is available from the UK Drugs in Lactation Advisory Service at https://www.midlandsmedicines.nhs.uk/content.asp?section=6&subsection=17&pageIdx=1
Side Effects
Hypersensitivity reactions
Overdosage
It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.
The following number will direct the caller to the relevant local centre (0844) 892 0111
Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( www.toxbase.org ) or if this is unavailable at the backup site ( www.toxbasebackup.org ).
Shelf Life and Storage
Store at room temperature.
Do not freeze.
Resterilisation should not be attempted under any circumstances.
Reference Sources
British National Formulary, 64th Edition (2012) Pharmaceutical Press, London.
BNF for Children (2012-2013) Pharmaceutical Press, London.
Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 2nd edition (2007) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.
Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 9th edition (2011) ed. Briggs, G., Freeman, R. and Yaffe, S. Lippincott Williams & Wilkins, Philadelphia.
Medications and Mothers' Milk, 14th Edition (2010) Hale, T. Hale Publishing, Amarillo, Texas.
Summary of Product Characteristics: Septopal Chains. Biomet Merck Ltd. Revised March 1999.
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