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Intra-ocular concentration-time relationships of subconjunctivally administered gentamicin
M M van Rooyen1, J F Coetzee, D F du Toit
1Department of Ophthalmology, University of Stellenbosch and Tygerberg Hospital, Parowvallei, CP.
South African Medical Journal = Suid-Afrikaanse Tydskrif Vir Geneeskunde
|September 7, 1991
Summary
This study determined optimal gentamicin dosing for cataract surgery. A pharmacokinetic model and nomogram were developed to guide pre-operative subconjunctival gentamicin administration, ensuring effective intraocular drug concentrations.
Area of Science:
- Ophthalmology
- Pharmacokinetics
- Drug Dosing
Background:
- Prophylactic antibiotics are crucial in ophthalmic surgery to prevent infections.
- Gentamicin is commonly used, but optimal pre-operative dosing requires understanding its intraocular pharmacokinetics.
- Accurate dosing ensures therapeutic levels while minimizing systemic exposure.
Purpose of the Study:
- To establish a pharmacokinetic model for subconjunctival gentamicin in patients undergoing cataract surgery.
- To develop a dosing strategy and a practical tool (nomogram) for pre-operative gentamicin administration.
- To achieve target intraocular gentamicin concentrations for effective prophylaxis.
Main Methods:
- Eighty-nine patients received varying doses (5, 10, or 20 mg) of subconjunctival gentamicin pre-operatively.
- Aqueous humor samples were collected during surgery to measure gentamicin concentration.
- Non-linear regression analysis was used to fit an open one-compartment pharmacokinetic model with first-order kinetics.
Main Results:
- A statistically acceptable pharmacokinetic model was successfully fitted to the data.
- The model allowed simulation of multiple-dose kinetics and calculation of required doses.
- A simple linear nomogram was constructed for practical dose determination.
Conclusions:
- The developed pharmacokinetic model accurately describes gentamicin behavior in the aqueous humor.
- The linear nomogram provides a straightforward method for clinicians to determine optimal pre-operative gentamicin doses.
- This approach facilitates effective antibiotic prophylaxis in cataract surgery.