The efficacy and toxicity of several drugs is circadian-rhythm dependent, and this can be exploited as a guide to ameliorate such drug toxicity. Gentamicin is an aminoglycoside antibiotic used in treatment of a variety of infections. Its use is however limited by its associated nephrotoxicity. This nephrotoxicity is ameliorated by reduction in dosing frequency to once a day dosing, use of antioxidants and exploration of circadian variation in gentamicin nephrotoxicity. Temporal variation in gentamicin nephrotoxicity and the use of antioxidants at the time of highest nephrotoxicity are alternative ameliorative strategies for this established toxicity. This study compares the effect of concurrent administration of vitamin B complex and gentamicin based on its temporal variation in nephrotoxicity, with alternative approaches of use of a single strategy alone. Young wistar rats of both sexes were used in this study. A nephrotoxic dose of gentamicin was determined from a ten day study with 80, 100 and 120 mg/kg intraperitoneal gentamicin administration using selected biomarkers as indices. Nephrotoxicity was accessed by elevation of serum urea and serum creatinine which are biomarkers of nephrotoxicity and histological changes of the kidney. Administration of 100 mg/kg of gentamicin at 0800, 1200, 2000 and 0000 hours resulted in nephrotoxicity with maximal toxicity observed at 1200 hours where the level of serum urea and creatinine differed significantly (p≤0.05) from the normal saline control and minimal toxicity was seen at the 0000 hour. Histology of the kidneys showed lymphocyte hyperplasia, interstitial haemorrhages, tubular and glomerular necrosis in the 1200 hour group which was observed to be mild in the 0000 hour group. No significant change was seen in the levels of serum electrolytes (Na+, K+, Cl+, Ca2+) and liver function enzymes (ALT, AST and ALP) irrespective of time of treatment. Concurrent administration of gentamicin and vitamin B complex at 1200 and 0000 hours resulted in amelioration of gentamicin nephrotoxicity. However, the amelioration produced by the administration of gentamicin alone at the time of minimal toxicity (0000 hour) was greater than that produced by concurrent administration of gentamicin and vitamin B complex at this time point. The administration of gentamicin based on its temporal variation in nephrotoxicity offers better amelioration of nephrotoxicity than concurrent administration of gentamicin at the time of highest toxicity with vitamin B complex in wistar rats.



1.1 Background

Gentamicin an aminoglycoside antibiotic is widely used in the treatment of a variety of infections, especially infections caused by gram negative bacteria (Buabong et al., 1999; Martin et al., 2012). Gentamicin remains a first line antibiotic for many infections because, in addition to its clinical effectiveness, the rate of resistance is very low and it is inexpensive (Pavle et al., 2012). The major limitation to the routine use of gentamicin and other aminoglycoside antibiotics is their potential nephrotoxicity, which can develop even with normal therapeutic doses (Randall and Terrell, 1987). Approximately 8 to 26% of hospitalized patients receiving gentamicin will develop renal impairments (Kahlmeter and Dahlager, 1984; Badreldin et al., 2011).

Various strategies have been elucidated for the amelioration of gentamicin nephrotoxicity. The goal of reducing or protecting against its nephrotoxicity has attracted much effort and attention because gentamicin nephrotoxicity constitutes a major drawback to its use in clinical settings (Ali, 2003; Yasin et al., 2003; Bello and Chika, 2009; Khan et al., 2009). Research aimed at obtaining intrinsically less toxic compounds has met with only modest success, and only few of the approaches proposed to reduce the toxicity of gentamicin have reached practical clinical applications (Mingeot-Leclerq and Tulkens, 1999). It is therefore important to develop newer, simpler and effective strategies that will effectively ameliorate or eliminate the nephrotoxicity of gentamicin in experimental animals, and be clinically applicable. The need for newer and more effective strategies for ameliorating the nephrotoxicity of gentamicin has led scientists and clinicians to the science of chronobiology.

Chronobiology is the study of mechanisms and alterations of each organism’s temporal structure under various situations (Halberg and Carandante, 1997). Biological systems possess a very prominent temporal structure. The most important rhythm in chronobiology is the circadian rhythm. Circadian rhythm is a biological process that displays an endogenous, entrainable oscillation of about twenty four hours. Circadian rhythms in the effects of various chemical agents have been documented (Koppisetti et al., 2010). A temporal variation in the renal toxicity of gentamicin has been reported in experimental animals and man (Prins et al., 1997; Lebrun et al., 1999).

Chronobiological observations have led to the development of the scientific discipline of chronopharmacology. Chronopharmacology is concerned with the activity, toxicity and kinetics of drugs as a function of time of administration, in relation to synchronization of the organism, and investigates alterations of the temporal structure of the organism receiving the drug (Reinberg and Smolensky, 1983). Nearly all functions of the body, including those influencing pharmacokinetic parameters, such as drug absorption, drug metabolism and renal elimination, display significant daily variations and the effectiveness and toxicity of many drugs vary depending on dosing time. These observations call for a circadian time-specified drug treatment (Lemmer, 2000). Several risk factors for aminoglycoside associated nephrotoxicity have been identified. These risk factors include; the presence of co-morbidities, volume depletion, liver dysfunction, sepsis, renal dysfunction, hypokalemia and hypomagnesemia (Paterson et al., 1998; Raveh et al., 2002). Other risk factors are prolonged therapy, frequency of aminoglycoside dosing, an elevated serum aminoglycoside concentration, the timing of aminoglycoside administration and simultaneous interaction with other nephrotoxic drugs (Mingeot-leclerq and Tulkens, 1999).

Studies have shown that renal damage due to gentamicin is associated with oxidative stress, and demonstrated that reactive oxygen species including free radicals, superoxide, hydroxyl radical anion and hydrogen peroxide are important mediators of tissue injury (Fanton and Ward, 1982). Co-administration of antioxidants along with gentamicin has been shown to significantly ameliorate nephrotoxicity associated with gentamicin (Pedraza-chaverri et al., 2000; Ali, 2003; Badreldin et al., 2011; Chetankumar et al., 2013).

Gentamicin is excreted by glomerular filtration and is partially reabsorbed by renal proximal tubules, the tubules also accumulate the antibiotic, and are the primary sites of nephrotoxicity. The intra-cortical accumulation of gentamicin enhances its nephrotoxicity and limits its use (Gomes et al., 2002). Serum creatinine and serum urea, are potent indicators of renal dysfunction (Polat et al., 2006; Saleemi et al., 2009). Increase in serum creatinine and serum urea in renal dysfunction results from reduction in renal functions, accompanied by impairment in glomerular functions (Karahan et al., 2005). Body weight is also an important indicator of nephrotoxicity. Increased catabolism seen in acute renal failure, results in acidosis which is accompanied by anorexia, hence food intake decreases and a significant decrease in body weight is observed (Erdem et al., 2000). Histopathological examination of the kidney shows morphological changes in renal cortex due to nephrotoxicity (Derakhshanfar et al., 2007). Electrolyte abnormalities are also observed in gentamicin induced nephrotoxic models and patients (Fukuda et al., 1991).

1.2 Statement of Research Problem

Gentamicin is widely prescribed in clinical practice because of its role in the treatment of severe gram negative infections, concentration dependent killing, significant post antibiotic effect and its low cost (Lucena et al., 1995; Pedraza-Chaverri et al., 2000). Its use is however limited by its potentially serious adverse effects, most notably its nephrotoxicity (Oliveira et al., 2009). There is need to devise new strategies that will preserve the antimicrobial activity and reduce or eliminate the nephrotoxicity associated with gentamicin therapy.

Temporal variations in the nephrotoxicity of gentamicin has been observed in experimental animals as well as in humans (Prins et al., 1997; Lebrun et al., 1999). Antioxidants have been used as protective agents for gentamicin nephrotoxicity (Yasin et al., 2003; Badreldin et al., 2011). These two strategies of ameliorating gentamicin nephrotoxicity need to be investigated to determine if one is superior to the other in ameliorating gentamicin nephrotoxicity, or if the two strategies combined, offer better nephroprotection than either strategy alone, so as to develop newer, simpler and more cost effective protocols for ameliorating gentamicin nephrotoxicity.

1.3 Justification

Since the effectiveness and toxicity of many drugs depend on dosing time associated with twenty four hours rhythm of biochemical, physiological and behavioral processes under the control of the circadian clock, a dependence of a drug on circadian rhythm can be used as a guide to ameliorate the toxicity of that drug (Paranjpe and Sharma, 2005). Several strategies have been proposed for ameliorating the nephrotoxicity associated with gentamicin (Beauchamp et al., 1996). There is need for scientists as well as clinicians to explore these strategies, for ameliorating the nephrotoxicity of gentamicin in comparison with the amelioration offered by temporal variation of gentamicin. Results from experimental and clinical studies, can be used for optimizing therapy, in order to maximize the antimicrobial effects and ameliorate the nephrotoxicity of this drug.

Strategies for ameliorating the nephrotoxicity of gentamicin in experimental animals may be used to optimize therapy in humans. It is expected that at the end of this study new insights into the temporal variation of gentamicin in comparison with the use of antioxidants will be demonstrated and strategies that will preserve the antimicrobial activity, and reduce or eliminate the nephrotoxicity of gentamicin might be developed.

1.4 Aim and Objectives of the Study

1.4.1 Aim of the Study

The aim of this study is to investigate the effect of temporal variation and vitamin B complex administration on gentamicin nephrotoxicity in wistar rats.

1.4.2 Specific Objectives

1. To establish a time of administration for gentamicin, that offers significant amelioration of its nephrotoxicity in wistar rats.

2. To determine if the employment of both time of gentamicin administration based on its temporal variation in toxicity, with concurrent use of vitamin B complex for nephroprotection, offers superior amelioration of nephrotoxicity than either protocol.

1.5 Research Hypothesis

Time of administration of gentamicin based on its temporal variation offers superior amelioration against gentamicin associated nephrotoxicity, than concurrent use of vitamin B complex with gentamicin at the time of least toxicity in wistar rats.