Aminoglycoside toxicity: daily versus thrice-weekly dosing for treatment of mycobacterial diseases

Aminoglycoside use is limited by ototoxicity and nephrotoxicity. This study compared the incidences of toxicities associated with 2 recommended dosing regimens. Eighty-seven patients with tuberculosis or nontuberculous mycobacterial infections were prospectively randomized by drug to receive 15 mg/kg per day or 25 mg/kg 3 times per week of intravenous streptomycin, kanamycin, or amikacin. Doses were adjusted to achieve target serum concentrations. The size of the dosage and the frequency of administration were not associated with the incidences of ototoxicity (hearing loss determined by audiogram), vestibular toxicity (determined by the findings of a physical examination), or nephrotoxicity (determined by elevated serum creatinine levels). Risk of ototoxicity (found in 32 [37%] of the patients) was associated with older age and with a larger cumulative dose received. Vestibular toxicity (found in 8 [9%] of the patients) usually resolved, and nephrotoxicity (found in 13 [15%] of the patients) was mild and reversible in all cases. Subjective changes in hearing or balance did not correlate with objective findings. Streptomycin, kanamycin, and amikacin can be administered either daily or 3 times weekly without affecting the likelihood of toxicity.

Tuberculosis drugs' distribution and emergence of resistance in patient's lung lesions: A mechanistic model and tool for regimen and dose optimization

BACKGROUND

The sites of mycobacterial infection in the lungs of tuberculosis (TB) patients have complex structures and poor vascularization, which obstructs drug distribution to these hard-to-reach and hard-to-treat disease sites, further leading to suboptimal drug concentrations, resulting in compromised TB treatment response and resistance development. Quantifying lesion-specific drug uptake and pharmacokinetics (PKs) in TB patients is necessary to optimize treatment regimens at all infection sites, to identify patients at risk, to improve existing regimens, and to advance development of novel regimens. Using drug-level data in plasma and from 9 distinct pulmonary lesion types (vascular, avascular, and mixed) obtained from 15 hard-to-treat TB patients who failed TB treatments and therefore underwent lung resection surgery, we quantified the distribution and the penetration of 7 major TB drugs at these sites, and we provide novel tools for treatment optimization.

METHODS AND FINDINGS

A total of 329 plasma- and 1,362 tissue-specific drug concentrations from 9 distinct lung lesion types were obtained according to optimal PK sampling schema from 15 patients (10 men, 5 women, aged 23 to 58) undergoing lung resection surgery (clinical study NCT00816426 performed in South Korea between 9 June 2010 and 24 June 2014). Seven major TB drugs (rifampin [RIF], isoniazid [INH], linezolid [LZD], moxifloxacin [MFX], clofazimine [CFZ], pyrazinamide [PZA], and kanamycin [KAN]) were quantified. We developed and evaluated a site-of-action mechanistic PK model using nonlinear mixed effects methodology. We quantified population- and patient-specific lesion/plasma ratios (RPLs), dynamics, and variability of drug uptake into each lesion for each drug. CFZ and MFX had higher drug exposures in lesions compared to plasma (median RPL 2.37, range across lesions 1.26-22.03); RIF, PZA, and LZD showed moderate yet suboptimal lesion penetration (median RPL 0.61, range 0.21-2.4), while INH and KAN showed poor tissue penetration (median RPL 0.4, range 0.03-0.73). Stochastic PK/pharmacodynamic (PD) simulations were carried out to evaluate current regimen combinations and dosing guidelines in distinct patient strata. Patients receiving standard doses of RIF and INH, who are of the lower range of exposure distribution, spent substantial periods (>12 h/d) below effective concentrations in hard-to-treat lesions, such as caseous lesions and cavities. Standard doses of INH (300 mg) and KAN (1,000 mg) did not reach therapeutic thresholds in most lesions for a majority of the population. Drugs and doses that did reach target exposure in most subjects include 400 mg MFX and 100 mg CFZ. Patients with cavitary lesions, irrespective of drug choice, have an increased likelihood of subtherapeutic concentrations, leading to a higher risk of resistance acquisition while on treatment. A limitation of this study was the small sample size of 15 patients, performed in a unique study population of TB patients who failed treatment and underwent lung resection surgery. These results still need further exploration and validation in larger and more diverse cohorts.

CONCLUSIONS

Our results suggest that the ability to reach and maintain therapeutic concentrations is both lesion and drug specific, indicating that stratifying patients based on disease extent, lesion types, and individual drug-susceptibility profiles may eventually be useful for guiding the selection of patient-tailored drug regimens and may lead to improved TB treatment outcomes. We provide a web-based tool to further explore this model and results at http://saviclab.org/tb-lesion/.

Comparison between systemic and oral antimicrobial prophylaxis in colorectal surgery

In a prospective randomised trial in which 93 patients undergoing elective colorectal operations were given a short prophylactic course of metronidazole and kanamycin orally or systemically, postoperative sepsis occurred in only 3 (6.5%) of those given antimicrobials systemically, compared with 17 (36%) of those given oral prophylaxis (P less than 0.01). 15 of the 17 infections in patients who received antimicrobials orally were due to kanamycin-resistant bacteria present in the colon at operation. Bacterial overgrowth of Staphylococcus aureus was recorded in 6 of the patients who received oral therapy. Antibiotic-associated pseudomembranous colitis occurred in 7 patients, 6 of whom had received prophylaxis orally. These results indicate that oral administration of prophylactic antimicrobials in colon surgery should be avoided because of the risks of bacterial resistance, superinfection, and antibiotic-associated pseudomembranous colitis. Systemic per-operative antimicrobial prophylaxis is safer and more effective.

Prophylactic oral antimicrobial agents in elective colonic surgery. A controlled trial

A controlled trial has been carried out in 50 patients undergoing elective colonic surgery to assess the efficacy of prophylactic oral metronidazole specifically directed against anaerobic colonic microflora in combination with kanamycin to reduce the aerobic flora. A control group received dietary and mechanical preparation alone. A significant reduction of both aerobic and anaerobic colonic microflora was achieved in the group receiving prophylactic antimicrobial agents, and this was reflected in a significant reduction in postoperative wound infections. 1 control patient died from Bacteroides septicaemia. No toxic or other side-effects from this prophylactic regimen occurred in this trial.

Intra-cochlear administration of dexamethasone attenuates aminoglycoside ototoxicity in the guinea pig

This study demonstrates the attenuation of aminoglycoside ototoxicity by cochlear infusion of dexamethasone (Dex) using a microcannulation-osmotic pump delivery system. The results indicate that treating the cochlea with Dex both before and after kanamycin administration was more effective in preventing ototoxicity than Dex treatment only after kanamycin administration. A concentration of 1 ng/ml Dex showed the greatest protective effect on both kanamycin-induced threshold shift of the auditory brainstem response and outer hair cell survival. These results show that the Dex treatment attenuates both functional and structural damage of the inner ear from aminoglycoside toxicity.

Evaluation of a standardized treatment regimen of anti-tuberculosis drugs for patients with multi-drug-resistant tuberculosis (STREAM): study protocol for a randomized controlled trial

BACKGROUND

In contrast to drug-sensitive tuberculosis, the guidelines for the treatment of multi-drug-resistant tuberculosis (MDR-TB) have a very poor evidence base; current recommendations, based on expert opinion, are that patients should be treated for a minimum of 20 months. A series of cohort studies conducted in Bangladesh identified a nine-month regimen with very promising results. There is a need to evaluate this regimen in comparison with the currently recommended regimen in a randomized controlled trial in a variety of settings, including patients with HIV-coinfection.

METHODS/DESIGN

STREAM is a multi-centre randomized trial of non-inferiority design comparing a nine-month regimen to the treatment currently recommended by the World Health Organization in patients with MDR pulmonary TB with no evidence on line probe assay of fluoroquinolone or kanamycin resistance. The nine-month regimen includes clofazimine and high-dose moxifloxacin and can be extended to 11 months in the event of delay in smear conversion. The primary outcome is based on the bacteriological status of the patients at 27 months post-randomization. Based on the assumption that the nine-month regimen will be slightly more effective than the control regimen and, given a 10% margin of non-inferiority, a total of 400 patients are required to be enrolled. Health economics data are being collected on all patients in selected sites.

DISCUSSION

The results from the study in Bangladesh and cohorts in progress elsewhere are encouraging, but for this regimen to be recommended more widely than in a research setting, robust evidence is needed from a randomized clinical trial. Results from the STREAM trial together with data from ongoing cohorts should provide the evidence necessary to revise current recommendations for the treatment for MDR-TB.

TRIAL REGISTRATION

This trial was registered with clincaltrials.gov (registration number: ISRCTN78372190) on 14 October 2010.

Treatment with antibiotics reduces plasma equol concentration in cynomolgus monkeys (Macaca fascicularis)

To explore the importance of equol on health outcomes in future studies, it was necessary to develop a method to reduce equol production. Female monkeys (n = 22) fed a soy diet were treated twice daily with vehicle (control; n = 4), doxycycline (2.5 mg/kg; n = 4), metronidazole (125 mg/d; n = 3), kanamycin (1000 mg/d; n = 4), vancomycin (100 mg/d; n = 3) or kanamycin+vancomycin (n = 4). Plasma samples were collected 4 h postfeeding at baseline, after 4 wk of treatment and 8 wk after the end of treatment and analyzed for isoflavonoid concentrations. Fecal swabs were collected at baseline and at the end of antibiotic treatment for analysis of Gram(+) and Gram(-) bacterial growth. Equol concentrations were reduced (P < 0.05) compared with baseline by 80, 93, 98 and 99% after treatment with metronidazole (955 +/- 164 vs. 193 +/- 53 nmol/L), kanamycin (545 +/- 211 vs. 37.1 +/- 17.6 nmol/L), vancomycin (607 +/- 163 vs. 8.9 +/- 8.2 nmol/L) and kanamycin+vancomycin (721 +/- 169 vs. 17.4 +/- 17.3 nmol/L), respectively. Daidzein concentrations were increased (P < 0.05) compared with baseline by treatment with doxycycline (336 +/- 87 vs. 576 +/- 76 nmol/L), kanamycin (168 +/- 67 vs. 374 +/- 15 nmol/L), and kanamycin+vancomycin (166 +/- 35 vs. 384 +/- 78 nmol/L). Similar increases (P < 0.05) in dihydrodaidzein were observed after treatment with kanamycin (31.2 +/- 6.2 vs. 479 +/- 188 nmol/L) and metronidazole (56.0 +/- 27.9 vs. 414 +/- 212 nmol/L). Isoflavonoid concentrations returned to baseline values after antibiotic treatment was terminated. Gram(+) bacterial growth was reduced by all treatments, including Control, compared with baseline. In conclusion, treatment with antibiotics resulted in a marked reduction in plasma equol concentrations and altered plasma isoflavonoid patterns in cynomolgus monkeys.

Improved penetration of aminoglycosides and fluorozuinolones into the aqueous humour of patients by means of Acuvue contact lenses

OBJECTIVES

In order to improve the penetration of topically applied drugs in ophthalmology, the suitability of hydrophilic contact lenses (Acuvue, Vistacon, power -1.0 D) as a drug delivery system for antibiotics was tested. A prospective study was undertaken to determine the transcorneal penetration of five topically applied aminoglycosides and fluoroquinolones into the aqueous humour of patients.

METHODS

Two hundred and sixty-five patients undergoing cataract extraction received 0.3% gentamicin, kanamycin, tobramycin, ciprofloxacin or ofloxacin solution by two different modes of administration: either as eye drops (nine drops every 15 min, starting 2 h prior to surgery) or by means of a drug delivery system (Acuvue contact lenses soaked for 1 h in eye drop solution without preservatives, 15 h prior to surgery). At the beginning of cataract extraction, 50-100 microl aqueous fluid was aspirated from the anterior chamber and immediately stored at -80 degrees C. Antibiotic concentrations were measured using fluorescence polarisation immunoassays (aminoglycosides) or high-performance liquid chromatography (fluoroquinolones).

RESULTS

After soaking for 1h in 0.3% eye drop solutions, Acuvue contact lenses released about 190-250 microg aminoglycoside and ofloxacin and 1000 microg ciprofloxacin. These amounts are considerably lower or in the same order of magnitude than obtained with application of eye drops (1350 microg). From the aminoglycosides tested, only gentamicin and tobramycin, but not kanamycin, were able to penetrate into the aqueous humour of patients. After the wearing of antibiotic-soaked lenses, mean aqueous humour concentrations were higher than after the use of eye drops. This difference reached significance in tobramycin (1.09 (1.30) microg x ml(-1) vs 0.49 (0.79) microg x ml(-1)), ciprofloxacin (1.23 (0.60) microg x ml(-1) vs 0.38 (0.33) microg x ml(-1)) and ofloxacin (5.55 (2.53) microg x ml(-1) vs 0.56 (0.37) microg x ml(-1)). The percentage of patients with aqueous humour concentration above the MIC90 of Staphylococcus epidermidis, the most common cause of postoperative endophthalmitis, was 92% and 100% after wearing ciprofloxacin- or ofloxacin-soaked lenses, respectively.

CONCLUSION

Gentamicin and tobramycin penetrated into the aqueous humour of patients, whereas kanamycin was not able to overcome the corneal barrier. Acuvue contact lenses soaked in 0.3% eye drop solutions can release sufficient amounts of gentamicin, ciprofloxacin and ofloxacin to produce bacteriostatic concentrations in the humor aquosus. Acuvue contact lenses can be recommended as a drug delivery system for fluoroquinolones.

Hair cell regeneration in the European starling (Sturnus vulgaris): recovery of pure-tone detection thresholds

Behavioral detection thresholds were obtained from four starlings before, during, and after 11 days of subcutaneous injections of kanamycin. Birds were operantly conditioned to respond to pure-tones ranging in frequency from 0.25 kHz to 7 kHz using the method of constant stimuli and were tested daily for 141 days after the first injection of aminoglycoside. All four birds sustained hearing losses greater than 60 dB at frequencies from 4 kHz to 7 kHz by the end of the 11 day injection schedule. Two birds had a slight shift in threshold at 3 kHz. No change in threshold occurred for any of the birds at lower frequencies. Recovery of detection thresholds began soon after the injections ceased and continued for approximately 50 days. In all four birds there was some degree of permanent hearing loss: 5 dB to 15 dB at frequencies between 4 kHz and 6 kHz, and approximately 25 dB at 7 kHz. Scanning electron microscopy (SEM) was performed at 0 and 5 days post-injection in a separate group of starlings given the same injection schedule. Hair cell loss and damage was observed across the basal 34% to 36% of the basilar papilla. SEM in two behaviorally tested birds sacrificed 142 days after the first injection showed that there was regeneration of hair cells to populate the previously damaged region, but that disorientation of stereocilia bundles in the basal third of the basilar papilla was common. The other two behaviorally tested birds were treated with kanamycin again for 16 days beginning at 142 days after the first injection. Thresholds shifted again, but less than during the first dosing period. SEM of these birds' basilar papillae showed less hair cell loss than observed in the birds given only a single, 11 day dosing of kanamycin. This result suggests that birds may be less susceptible to the ototoxic effects of kanamycin in repeated treatments. In all four birds, the degree and position of damage observed with SEM corresponded with the extent and frequency of hearing loss.

Iron chelators protect from aminoglycoside-induced cochleo- and vestibulo-toxicity

The attenuation of gentamicin-induced hearing loss by iron chelators and radical scavengers has recently been demonstrated in guinea pig in vivo. The present study investigated whether this protective treatment is effective against hearing loss and vestibular damage caused by other aminoglycosides. In a direct comparison, dihydroxybenzoate was chosen over deferoxamine because of its more effective action against gentamicin-induced hearing loss. Guinea pigs received daily injections of kanamycin (250 mg/kg/d) or streptomycin (300 mg/kg/d) for 23 d to induce severe cochlear or vestibular toxicity, respectively. Kanamycin injections resulted in a progressive threshold shift of 60 to 80 dB at 18 kHz, while streptomycin injections induced only a small threshold shift. In contrast, streptomycin abolished almost all vestibular responses. Coinjection of aminoglycosides with a mixture of dihydroxybenzoate (100 mg/kg/d) and mannitol (30 mg/kg/d) significantly attenuated kanamycin-induced hearing loss and protected against streptomycin-induced vestibulotoxicity. DHB/mannitol did not affect serum levels or the antibacterial efficacy of either aminoglycoside. This study supports the idea that iron and free radicals play a critical role in the toxic side effects of aminoglycoside antibiotics. Furthermore, the previously proposed therapeutic protection is not limited to gentamicin but applicable to other aminoglycosides as well.

Comparative pharmacokinetics of BB-K8 and kanamycin in dogs and humans

Comparative studies in beagle dogs suggested that the pharmacokinetic profiles of BB-K8 and kanamycin are similar. After intravenous (iv) administration to dogs, BB-K8 and kanamycin were rapidly distributed in plasma and tissue fluids; their "apparent" volumes of distribution comprised approximately 23% of the total body volume. Like kanamycin, BB-K8 had a plasma half-life of about 0.8 h which paralleled the urinary excretion rate. Approximately 92% of the dose was excreted as unchanged drug within 6 h of dosing, and clearance appeared to be primarily by glomerular filtration. After intramuscular (im) administration to dogs, BB-K8 and kanamycin were totally and rapidly absorbed; peak concentrations in the plasma occurred 0.5 to 1.0 h after dosing. The kinetic parameters governing the distribution and elimination of BB-K8 and kanamycin after an im dose were similar to those obtained for iv dosing and indicate desirable dose-independent kinetics. A human pharmacokinetic study indicated that the kinetic profiles of BB-K8 and kanamycin are similar in man after im dosing. Like kanamycin, BB-K8 is rapidly absorbed, yielding peak serum concentrations of about 20 mug/ml at 1 h after a 500-mg im dose. The plasma half-life of these two drugs was approximately 2.3 h. Clearance in man was primarily by glomerular filtration, and the urinary excretion of BB-K8 and kanamycin accounted for 83% of the dose.

Single-dose therapy of gonococcal ophthalmia neonatorum with ceftriaxone

We conducted a randomized clinical trial comparing a single intramuscular dose of 125 mg of ceftriaxone with a single intramuscular dose of 75 mg of kanamycin followed by topical gentamicin for seven days, and with a single intramuscular dose of 75 mg of kanamycin followed by topical tetracycline for seven days, in the treatment of gonococcal ophthalmia neonatorum in Nairobi, Kenya. Of 122 newborns with culture-proved gonococcal ophthalmia neonatorum, 105 returned for follow-up. Sixty-one infants (54 percent) received ceftriaxone, 32 received kanamycin plus topical gentamicin, and 29 received kanamycin plus topical tetracycline. Sixty-six (54 percent) of the Neisseria gonorrhoeae isolates were penicillinase producing. All 55 newborns who received ceftriaxone and returned for follow-up were clinically and microbiologically cured. One of 26 returning newborns who received kanamycin plus tetracycline and 2 of 24 returning newborns who received kanamycin plus gentamicin had persistent or recurrent gonococcal conjunctivitis. Ceftriaxone also eradicated oropharyngeal gonococcal infection in 18 newborns, whereas oropharyngeal infection persisted in 2 of 8 newborns who had received kanamycin (P not significant). We conclude that 125 mg of ceftriaxone as a single intramuscular dose is very effective therapy for gonococcal ophthalmia neonatorum, with marked efficacy against extraocular infection and without the need for concomitant topical antimicrobial therapy.

Effects of kanamycin on the auditory evoked responses during postnatal development of the hearing of the rat

The ototoxic effects of kanamycin were studied in rats during the early postnatal period and at an adult age. Brain stem potentials as well as auditory cortical potentials were used for the estimating of ototoxic damage. The auditory potentials decreased promptly and markedly in the animals which were treated daily with 400 mg/kg body weight of kanamycin starting from the 11th day after birth. In these animals, the auditory potentials were almost completely abolished within 10 days after the beginning of the kanamycin treatment. However, when the same amount of kanamycin was applied earlier or later than that, i.e., avoiding the period of the initial appearance and the greatest development of auditory functions (from the 11th to the 15th day after birth in the rat), the auditory potentials were not apparently damaged. In light and scanning electronmicroscopy, marked ototoxic changes were observed which underlay the functional damage. The meaning of these findings is discussed.

Observation of click-evoked compound VIII nerve responses before, during, and over seven months after kanamycin treatment in the guinea pig

Compound VIII nerve action potential responses to clicks and filtered-clicks were recorded regularly over a period of 7 months following Kanamycin treatment (8 days, 400 mg/kg), in 3 awake guinea pigs each with an implanted electrode on the round window (left ear). From the end of the treatment the responses to the click became dissociated in various degrees within three major phases: (1) a rapid phase (8 to 10 days) where the responses were dramatically altered, (2) a recovery phase which lasted about 2 months, (3) a slow phase over the subsequent 5 months where the responses to the click decreased slowly but gradually while the N 1 component, as well as the responses to the 8 000 Hz filtered-click (which became recruiting at the end of the treatment), disappeared progressively. Responses to the low frequency filtered-clicks were less affected. Cochlear cytograms showed almost complete degeneration of the inner and outer hair cells of the first turn only.