Clinical pharmacokinetics of co-trimoxazole (trimethoprim-sulphamethoxazole)

Hyperkalemic effect of drug-drug interaction between esaxerenone and trimethoprim in patients with hypertension: a pilot study

BACKGROUND

We examined whether the pharmacodynamic drug-drug interaction between esaxerenone and trimethoprim enhances the hyperkalemic effect.

METHODS

A retrospective observational study was conducted to identify patients >18 years undertaking esaxerenone alone or esaxerenone plus trimethoprim at Mie University Hospital from May 2019 to December 2022. We performed propensity score-matching (1:1) to compare between-group differences in the maximum change in serum potassium levels (ΔK) using the Mann-Whitney U test. For esaxerenone plus trimethoprim, Spearman's correlation coefficients were used to examine correlations between ΔK and variables, including changes in blood urea nitrogen (ΔBUN), serum creatinine levels (ΔCr), and weekly trimethoprim cumulative dose.

RESULTS

Out of propensity score-matched groups (n=8 each), serum potassium levels significantly increased after administration of esaxerenone alone (4.4 [4.2 to 4.7] meq/L to 5.2 [4.7 to 5.4] meq/L, p=0.008) and esaxerenone plus trimethoprim (4.2 [4.0 to 5.1] meq/L to 5.4 [4.7 to 5.5] meq/L, p=0.023). ΔK did not significantly differ between the groups (esaxerenone alone; 0.6 [0.3 to 0.9] meq/L vs. esaxerenone plus trimethoprim; 1.0 [0.4 to 1.3] meq/L, p=0.342). ΔK positively correlated with ΔBUN (r=0.988, p<0.001) or ΔCr (r=0.800, p=0.017). There was a trend of correlation of ΔK with a weekly cumulative trimethoprim dose (r=0.607, p=0.110).

CONCLUSIONS

The hyperkalemic effect of the drug-drug interaction between esaxerenone and trimethoprim is not notable and related to renal function and trimethoprim dosage.

Sulfamethoxazole-induced crystal nephropathy: characterization and prognosis in a case series

Cotrimoxazole (Trimethoprim/Sulfamethoxazole-SMX) is frequently used in critically ill and immunocompromised patients. SMX is converted to N-acetyl-sulfamethoxazole (NASM) and excreted by the kidneys. NASM may form crystals in urine, especially in acid urine, that may induce a crystalline nephropathy. However, the imputability of crystals in acute kidney injury (AKI) has not been proven. We aimed to assess whether NASM crystals may promote AKI and to investigate risk factors associated with NASM crystalline nephropathy. Patients from Ile-de-France, France who developed AKI under SMX treatment introduced during hospitalization and had a crystalluria positive for NASM crystals were selected. Patients with excessive preanalytical delay for crystalluria or missing data regarding SMX treatment were excluded. We used the Naranjo score to assess the causal relationship between SMX and the development of AKI in patients with positive NASM crystalluria. Fourteen patients were included. SMX was the probable cause of AKI for 11 patients and a possible cause for 3 patients according to Naranjo score. Patients were exposed to high doses of SMX (but within recommended ranges), and most of them had a preexisting chronic kidney disease and were hypoalbuminemic. Urine pH was mildly acid (median 5.9). AKI occured more rapidly than expected after introduction of SMX (median 4 days) and recovered rapidly after drug discontinuation in most, but not all, cases. SMX is a probable cause of crystalline nephropathy. Monitoring of crystalluria in patients exposed to SMX may be of interest to prevent the development of crystalline nephropathy. Approval number of the study: BPD-2018-DIAG-008.

Effective Treatments of UTI—Is Intravesical Therapy the Future?

Urinary tract infection (UTI) afflicts millions of patients globally each year. While the majority of UTIs are successfully treated with orally administered antibiotics, the impact of oral antibiotics on the host microbiota is under close research scrutiny and the potential for dysbiosis is a cause for concern. Optimal treatment of UTI relies upon the selection of an agent which displays appropriate pharmacokinetic-pharmacodynamic (PK-PD) properties that will deliver appropriately high concentrations in the urinary tract after oral administration. Alternatively, high local concentrations of antibiotic at the urothelial surface can be achieved by direct instillation into the urinary tract. For antibiotics with the appropriate physicochemical properties, this can be of critical importance in cases for which an intracellular urothelial bacterial reservoir is suspected. In this review, we summarise the underpinning biopharmaceutical barriers to effective treatment of UTI and provide an overview of the evidence for the deployment of the intravesical administration route for antibiotics.

Quantification of Serum Sulfamethoxazole and Trimethoprim by Ultra-fast Solid-Phase Extraction-Tandem Mass Spectrometry

BACKGROUND

The combination of trimethoprim (TMP) and sulfamethoxazole (SMX) is used to treat a number of bacterial infections. TMP/SMX concentrations in serum are conventionally monitored using high-performance liquid chromatography (HPLC) or liquid chromatography tandem mass spectrometry. These methods require laborious manual extraction techniques and relatively long sample analysis times, necessitating the development of a simple, high-throughput method. A simple, high-throughput method to measure TMP/SMX using ultra-fast solid-phase extraction (SPE)-tandem mass spectrometry has been developed.

METHODS

Calibration standards, quality control materials, and patient samples were precipitated with acetonitrile containing isotopically labeled internal standards. Samples were vortexed, centrifuged for 5 minutes at 2053g, and the resulting supernatant was diluted in aqueous mobile phase and injected onto the C18 SPE cartridge. MS/MS analysis was performed by electrospray ionization in positive ion mode at a rate of <20 seconds per sample. A 5-point linear 1/x calibration curve was used to calculate sample concentrations.

RESULTS

The intra-assay precision coefficients of variation were <6% and <7% for SMX and TMP, respectively, and <10% for both interassay precision coefficients of variation. Comparison studies using 50 patient and spiked serum samples showed r values of 0.9890 and 0.9853 and y-intercept values of -1.918 and -1.357, respectively compared with the HPLC reference method. All data points were <±15% of the mean. Linearity [r = 0.9952 (SMX) and 0.9954 (TMP)] was established from 12 to 400 mcg/mL with a detection limit of 0.47 mcg/mL, and 1.2-40 mcg/mL with a detection limit of 0.06 mcg/mL, for SMX and TMP, respectively. For either drug, no significant carryover was observed after samples at the upper limit of quantification. No interference was observed from any of the 77 drugs and respective metabolites tested.

CONCLUSIONS

A high-throughput SPE-tandem mass spectrometry method for TMP/SMX quantification was developed. The <20 seconds analysis time is a significant improvement compared with traditional HPLC and liquid chromatography tandem mass spectrometry methods, without sacrificing analytical performance.

Bacteriological Profile and Antibiotic Resistance in Patients with Urinary Tract Infection in Tertiary Care Teaching Hospital in Western Rajasthan India

Urinary tract infection (UTI) is one of the most common bacterial infection with a significant economic burden on the health care system in developing countries like India. Rising antibiotic resistance is a matter of great concern. ; Aims: The aim of this study was to determine the bacteriological profile and antibiotic resistance pattern in patients with UTI in Tertiary Care Hospital in western Rajasthan India. ; Settings and Design: A cross-sectional, descriptive study was conducted from December 2017 to November 2018 at MDM hospital S.N. medical college, Jodhpur in Western Rajasthan. ; Materials and Methods: All the patients with symptoms of urinary tract infection presented in the outpatient unit or developed symptoms within 48 hr of hospitalisation were included in the study. Only those patients with significant bacteriuria (105 colony-forming units /ml) were included. ; Results: A total of 119 (55.34%) positive urine cultures were identified. The most common bacteria isolated in the urine sample was E. coli (37.2%) followed by Klebsiella pneumonia (10.2%), Enterococci spp. (3.3%), and Pseudomonas spp. (1.9%). Gram-negative bacteria represented 92.44% of the isolates. E. coli showed maximum resistance towards co-trimoxazole (78.75%) followed by cefuroxime (77.5%) and ciprofloxacin (72.5%). Klebsiella pneumoniae showed the highest resistance against co-trimoxazole (23.75%) and ciprofloxacin (23.75%). ; Conclusion: The present study gives an idea about the common trend of antibiotic resistance of uropathogens in this region. The findings in our study will help in the formulation of antibiotic policy and the determination of empirical treatment of UTI in this region.

Evaluating the risk of hyperkalaemia and acute kidney injury with cotrimoxazole: a retrospective observational study

OBJECTIVES

Increasing antimicrobial resistance has renewed interest in older, less used antimicrobials. Cotrimoxazole shows promise; however, hyperkalaemia and acute kidney injury (AKI) are potential complications. Identifying risk factors for and quantification of these events is required for safe use. This study aimed to evaluate predictors of cotrimoxazole-associated AKI and hyperkalaemia in a clinical setting.

METHODS

Patients prescribed cotrimoxazole were identified using electronic healthcare records over 3 years (1 April 2016 to 31 March 2019). Individual risk factors were recognized. Serum creatinine and potassium trends were analysed over the subsequent 21 days. AKI and patients with hyperkalaemia were classified using Kidney Disease Improving Global Outcomes (KDIGO) and laboratory criteria. Univariate and multiple logistic regression analyses were performed.

RESULTS

Among 214 patients prescribed cotrimoxazole, 42 (19.6%, 95% confidence interval (CI) 14.6-25.7) met AKI criteria and 33 (15.4%, 95% CI 11.0-21.1) developed hyperkalaemia. Low baseline estimated glomerular filtration rate (<60 mL/min/1.73 m², odds ratio (OR) 7.78, 95% CI 3.57-16.13, p < 0.0001) and cardiac disorders (OR 2.40, 95% CI 1.17-4.82, p 0.011) predicted AKI, while low baseline estimated glomerular filtration rate (<60 mL/min/1.73 m², OR 6.80, 95% CI 3.09-15.06, p < 0.0001) and higher baseline serum potassium (p 0.001) predicted hyperkalaemia. Low-dose cotrimoxazole (<1920 mg/d) was associated with lower AKI and hyperkalaemia risk (p 0.007 and 0.019 respectively). Early (within the first 2-4 days of therapy) serum creatinine changes predicted AKI (OR 3.65, 95% CI 1.73-7.41, p 0.001), and early serum potassium changes predicted hyperkalaemia (>0.6 mmol/L, OR 2.47, 95% CI 1.14-5.27, p 0.0236).

CONCLUSIONS

Cotrimoxazole-associated AKI and hyperkalaemia is frequent and dose dependent. Renal function, serum potassium and preexisting cardiac disorders should be evaluated before prescribing cotrimoxazole. Serum creatinine and potassium monitoring within first 2 to 4 days of treatment to identify susceptible patients is recommended, and the lowest effective dose ought to be prescribed.

Evaluation of treatment options for methicillin-resistant Staphylococcus aureus infections in the obese patient

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major cause of infection in both the hospital and community setting. Obesity is a risk factor for infection, and the prevalence of this disease has reached epidemic proportions worldwide. Treatment of infections in this special population is a challenge given the lack of data on the optimal antibiotic choice and dosing strategies, particularly for treatment of MRSA infections. Obesity is associated with various physiological changes that may lead to altered pharmacokinetic parameters. These changes include altered drug biodistribution, elimination, and absorption. This review provides clinicians with a summary of the literature pertaining to the pharmacokinetic and pharmacodynamic considerations when selecting antibiotic therapy for the treatment of MRSA infections in obese patients.

Suboptimal cotrimoxazole prophylactic concentrations in HIV-infected children according to the WHO guidelines

AIMS

A clinical study was conduct in HIV-infected children to evaluate the prophylactic doses of cotrimoxazole [sulfamethoxazole (SMX) and trimethoprim (TMP)] advised by the WHO.

METHODS

Children received lopinavir-based antiretroviral therapy with cotrimoxazole prophylaxis (200 mg of SMX/40 mg of TMP once daily). A nonlinear mixed effects modelling approach was used to analyse plasma concentrations. Factors that could impact the pharmacokinetic profile were investigated. The model was subsequently used to simulate individual exposure and evaluate different administration schemes.

RESULTS

The cohort comprised 136 children [average age: 1.9 years (range: [0.7-4]), average weight: 9.5 kg (range: [6-16.3])]. A dose per kg was justified by the significant influence of implementing an allometrically scaled body size covariate on SMX and TMP pharmacokinetics. SMX and TPM clearance were estimated at 0.49 l h^-1 /9.5 kg and 3.06 l h^-1 /9.5 kg, respectively. The simulated exposures obtained after administration of oral dosing recommended by the WHO for children from 10 to 15 kg were significantly lower than in adults for SMX and TMP. This could induce a reduction of effectiveness of cotrimoxazole. Simulations show that regimens of 30 mg kg^-1 of SMX and 6 mg kg^-1 of TMP in the 5-10 kg group and 25 mg kg^-1 of SMX and 5 mg kg^-1 of TMP in the 10-15 kg group are more suitable doses.

CONCLUSIONS

In this context of high prevalence of opportunistic infections, a lower exposure to cotrimoxazole in children than adults was noted. To achieve comparable exposure to adults, a dosing scheme per kg was proposed.

The effect of urine storage on antiviral and antibiotic compounds in the liquid phase of source-separated urine

The behaviour of pharmaceuticals related to the human immunodeficiency virus treatment was studied in the liquid phase of source-separated urine during six-month storage at 20°C. Six months is the recommended time for hygienization and use of urine as fertilizer. Compounds were spiked in urine as concentrations calculated to appear in urine. Assays were performed with separate compounds and as therapeutic groups of antivirals, antibiotics and anti-tuberculotics. In addition, urine was amended either with faeces or urease inhibitor. The pharmaceutical concentrations were monitored from filtered samples with solid phase extraction and liquid chromatography. The concentration reductions of the studied compounds as such or with amendments ranged from less than 1% to more than 99% after six-month storage. The reductions without amendments were 41.9-99% for anti-tuberculotics; <52% for antivirals (except with 3TC 75.6%) and <50% for antibiotics. In assays with amendments, the reductions were all <50%. Faeces amendment resulted in similar or lower reduction than without it even though bacterial activity should have increased. The urease inhibitor prevented ureolysis and pH rise but did not affect pharmaceutical removal. In conclusion, removal during storage might not be enough to reduce risks associated with the studied pharmaceuticals, in which case other feasible treatment practises or urine utilization means should be considered.

Rhabdomyolysis due to Trimethoprim-Sulfamethoxazole Administration following a Hematopoietic Stem Cell Transplant

Rhabdomyolysis, a syndrome of muscle necrosis, is a life-threatening event. Here we describe the case of a patient with chronic myeloid leukemia who underwent a haploidentical stem cell transplant and subsequently developed rhabdomyolysis after beginning trimethoprim-sulfamethoxazole (TMP/SMX) prophylaxis therapy. Rechallenge with TMP/SMX resulted in a repeat episode of rhabdomyolysis and confirmed the association. Withdrawal of TMP/SMX led to sustained normalization of creatine kinase levels in the patient. A high index of suspicion is necessary to identify TMP/SMX as the cause of rhabdomyolysis in immunocompromised patients.

Trimethoprim and sulfamethoxazole transmembrane clearance during modeled continuous renal replacement therapy

BACKGROUND/AIMS

There is limited data regarding trimethoprim (TMP)/sulfamethoxazole (SMX) continuous renal replacement therapy (CRRT) dosing. We aimed to estimate TMP/SMX transmembrane clearance (CLtm) during continuous hemofiltration (CH) and continuous hemodialysis (CD) to guide dosing.

METHODS

Using an in vitro model, TMP/SMX sieving coefficients (SC) and saturation coefficients (SA) were determined with high-flux polyarylethersulfone and polyacrylonitrile-sodium methallyl sulfonate copolymer hemodiafilters at ultrafiltration/dialysate rates of 1, 2, 3, and 6 l/h. TMP/SMX CLtm was calculated using measured SC and SA. TMP/SMX CRRT doses were modeled using CLtm and published TMP/SMX pharmacokinetic parameters.

RESULTS

TMP SC/SA during CH/CD were significantly higher than SMX SC/SA. During modeling, TMP 10 mg/kg/day and its corresponding SMX dose, 50 mg/kg/day, resulted in steady state TMP/SMX peak concentrations associated with efficacy against Pneumocystis jirovecii.

CONCLUSIONS

CRRT resulted in greater TMP CLtm than SMX. TMP 10 mg/kg/day divided q12h may be an appropriate initial dose to consider in patients undergoing CRRT.

Cotrimoxazole - optimal dosing in the critically ill

The optimum dosage regimen for cotrimoxazole in the treatment of life threatening infections due to susceptible organisms encountered in critically ill patients is unclear despite decades of the drug's use. Therapeutic drug monitoring to determine the appropriate dosing for successful infection eradication is not widely available. The clinician must utilize published pharmacokinetic, pharmacodynamic, and effective inhibitory concentration information to determine potential dosing regimens for individual patients when treating specific pathogens. Using minimum inhibitory concentrations known to successfully block growth for target pathogens, the pharmacokinetics of both trimethoprim and sulfamethoxazole can be utilized to establish empiric dosing regimens for critically ill patients while considering organ of clearance impairment. The author's recommendations for appropriate dosing regimens are forwarded based on these parameters.

Antibiograms from community-acquired uropathogens in Gulu, northern Uganda--a cross-sectional study

Background

Urinary tract infections (UTI) are common in clinical practice and empirical treatment is largely employed due to predictability of pathogens. However, variations in antibiotic sensitivity patterns do occur, and documentation is needed to inform local empirical therapy. The current edition of the Uganda Clinical Guidelines recommends amoxicillin or cotrimoxazole as choice drugs for empirical treatment of community-acquired UTI. From our clinical observations, we suspected that this recommendation was not effective in our setting. In order to examine validity, we sought to identify bacteria from community-acquired infections and determine their susceptibility against these antibiotics plus a range of potentially useful alternatives for treatment of UTI.

Methods

A cross-sectional study of mid-stream urine collected from 339 symptomatic patients over a three-month period at Gulu regional referral hospital. Qualitative culture and identification of bacteria and antibiotic sensitivity testing using the modified Kirby-Bauer disk diffusion method was done. Participants’ demographic and clinical characteristics were collected using a standard form. Results were analyzed by simple proportions among related variables and confidence intervals computed using binomial exact distribution.

Results

Eighty two cultures were positive for UTI. Staphylococcus spp (46.3%) and Escherichia coli (39%) were the most common pathogens. There was high resistance to cotrimoxazole (73.2%), nalidixic acid (52.4%) and amoxicillin (51.2%). The most favorable antibiograms were obtained with gentamicin, amoxicillin-clavulanate and levofloxacin where 85.4%, 72.0%, 67.1% of isolates respectively, were either sensitive or intermediate. Only 51% of isolates were sensitive to ciprofloxacin.

Conclusion

There was high resistance to most antibiotics tested in this study. The recommendations contained in the current edition of the Uganda Clinical Guidelines are not in tandem with antibiotic sensitivity pattern of uropathogens seen in our setting. Amoxicillin-clavulanate or gentamicin should be considered for replacement of amoxicillin and cotrimoxazole for empirical treatment of UTI in our setting.

Bacterial biofilms: development, dispersal, and therapeutic strategies in the dawn of the postantibiotic era

Biofilm formation constitutes an alternative lifestyle in which microorganisms adopt a multicellular behavior that facilitates and/or prolongs survival in diverse environmental niches. Biofilms form on biotic and abiotic surfaces both in the environment and in the healthcare setting. In hospital wards, the formation of biofilms on vents and medical equipment enables pathogens to persist as reservoirs that can readily spread to patients. Inside the host, biofilms allow pathogens to subvert innate immune defenses and are thus associated with long-term persistence. Here we provide a general review of the steps leading to biofilm formation on surfaces and within eukaryotic cells, highlighting several medically important pathogens, and discuss recent advances on novel strategies aimed at biofilm prevention and/or dissolution.

Treatment and prevention of urinary tract infection with orally active FimH inhibitors

Chronic and recurrent urinary tract infections pose a serious medical problem because there are few effective treatment options. Patients with chronic urinary tract infections are commonly treated with long-term prophylactic antibiotics that promote the development of antibiotic-resistant forms of uropathogenic Escherichia coli (UPEC), further complicating treatment. We developed small-molecular weight compounds termed mannosides that specifically inhibit the FimH type 1 pilus lectin of UPEC, which mediates bacterial colonization, invasion, and formation of recalcitrant intracellular bacterial communities in the bladder epithelium. Here, we optimized these compounds for oral bioavailability and demonstrated their fast-acting efficacy in treating chronic urinary tract infections in a preclinical murine model. These compounds also prevented infection in vivo when given prophylactically and strongly potentiated the activity of the current standard of care therapy, trimethoprim-sulfamethoxazole, against clinically resistant PBC-1 UPEC bacteria. These compounds have therapeutic efficacy after oral administration for the treatment of established urinary tract infections in vivo. Their unique mechanism of action-targeting the pilus tip adhesin FimH-circumvents the conventional requirement for drug penetration of the outer membrane, minimizing the potential for the development of resistance. The small-molecular weight compounds described herein promise to provide substantial benefit to women suffering from chronic and recurrent urinary tract infections.

Trimethoprim/Sulfamethoxazole pharmacokinetics in two patients undergoing continuous venovenous hemodiafiltration

OBJECTIVE

To determine the extent of elimination of trimethoprim (TMP) and sulfamethoxazole (SMX) via continuous venovenous hemodiafiltration (CVVHDF) in 2 critically ill patients with renal failure.

CASE SUMMARY

A 62-year-old woman with Pneumocystis jirovecii pneumonia (PCP) was admitted to our intensive care unit for severe acute respiratory distress syndrome. A 77-year-old man was admitted for aortic root replacement and developed septic shock and nosocomial pneumonia due to Stenotrophomonas maltophilia. Both patients developed acute renal failure, necessitating CVVHDF. They were treated with intravenous TMP/SMX adapted to renal function. The first patient received TMP 6.4 mg/kg/day and SMX 32 mg/kg/day, corresponding to 50% of the recommended high-dose TMP/SMX regimen in PCP patients. The second patient received TMP 1.7 mg/kg/day and SMX 8.6 mg/kg/day, corresponding to 50% of the usual dose in bacterial infections. We determined peak and trough serum TMP and SMX concentrations and the extent of TMP/SMX CVVHDF clearance at steady-state while the patients were still anuric and oliguric.

DISCUSSION

Data on TMP and SMX pharmacokinetics in CVVHDF are lacking and dosing recommendations are inconclusive. In both patients, CVVHDF clearance of TMP ranged from 21.5 to 28.9 mL/min, corresponding with normal renal clearance (20-80 mL/min). SMX clearance in CVVHDF showed high variability (18.7, 26.7, and 42.6 mL/min) and exceeded renal clearance values in normal renal function (1-5 mL/min). Accordingly, peak TMP serum concentrations were within the recommended range in the patient treated with a reduced TMP/SMX dose for PCP, whereas her SMX peak concentrations were only one third of recommended target concentrations.

CONCLUSIONS

Our data indicate that both TMP and SMX are removed by CVVHDF to a significant degree, and dose reduction of TMP/SMX in CVVHDF bears the risk of underdosing. Given variability in drug exposure in critically ill patients, therapeutic drug monitoring is advisable in anuric or oliguric patients undergoing continuous renal replacement therapy to ensure optimal TMP/SMX dosing.

Dosing regimens of cotrimoxazole (trimethoprim-sulfamethoxazole) for melioidosis

Melioidosis is an infectious disease with a propensity for relapse, despite prolonged antibiotic eradication therapy for 12 to 20 weeks. A pharmacokinetic (PK) simulation study was performed to determine the optimal dosing of cotrimoxazole (trimethoprim-sulfamethoxazole [TMP-SMX]) used in current eradication regimens in Thailand and Australia. Data for bioavailability, protein binding, and coefficients of absorption and elimination were taken from published literature. Apparent volumes of distribution were correlated with body mass and were estimated separately for Thai and Australian populations. In vitro experiments demonstrated concentration-dependent killing. In Australia, the currently used eradication regimen (320 [TMP]/1,600 [SMX] mg every 12 h [q12h]) was predicted to achieve the PK-pharmacodynamic (PD) target (an area under the concentration-time curve from 0 to 24 h/MIC ratio of >25 for both TMP and SMX) for strains with the MIC90 of Australian strains (< or = 1/19 mg/liter). In Thailand, the former regimen of 160/800 mg q12h would not be expected to attain the target for strains with an MIC of > or = 1/19 mg/liter, but the recently implemented weight-based regimen (<40 kg [body weight], 160/800 mg q12h; 40 to 60 kg, 240/1,200 mg q12h; >60 kg, 320/1,600 mg q12h) would be expected to achieve adequate concentrations for strains with an MIC of < or = 1/19 mg/liter. The results were sensitive to the variance of the PK parameters. Prospective PK-PD studies of Asian populations are needed to optimize TMP-SMX dosing in melioidosis.

Allergies to sulfonamide antibiotics and sulfur-containing drugs

OBJECTIVE

To provide a literature review and clinical summary of the evaluation and management of sulfonamide drug reactions.

DATA SOURCES

Published English-language medical literature.

STUDY SELECTION

Selected trials of drug desensitization protocols.

RESULTS

Obtaining a detailed history is invaluable in assessing a history of reactions to sulfonamide medications, because allergy to these drugs remains a clinical diagnosis at present. Numerous efficacious drug desensitization protocols for management have been published and are reviewed in detail.

CONCLUSIONS

The term sulfa allergy is imprecise and misleading and therefore should be discouraged. There are important distinctions between sulfonylarylamines (antimicrobial sulfonamides), nonarylamine (nonantimicrobial) sulfonamides, and sulfones, with regard to allergic and other adverse drug reactions. Most reactions to sulfonylarylamines probably result from multifactorial immunologic and toxic metabolic mechanisms, whereas less is known about the precise mechanisms of reactions to other sulfur-containing drugs.

Rapid and simultaneous determination of sulfamethoxazole and trimethoprim in human plasma by high-performance liquid chromatography

A simple and reproducible high-performance liquid chromatographic method was developed for simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) in human plasma. The method entailed injection of the samples after deproteination with perchloric acid and subsequent neutralizing. Primidone was used as internal standard. Chromatography was performed on a C(18) column (250 mm x 4.6 mm, 5 microm) under isocratic elution with 50 mM aqueous sodium dihydrogen phosphate-acetonitrile-triethylamine (100:25:0.5, v/v), pH 5.9. Detection was made at 240 nm and analyses were run at a flow-rate of 1.5 ml/min at a temperature of 35 degrees C. The recovery was 83.4, 88.5 and 98.2% for TMP, SMX and internal standard, respectively. The precision of the method was 2.6-9.8% over the concentration range of 0.125-2 microg/ml for TMP and 0.39-50 microg/ml for SMX. The limit of quantification (LOQ) in plasma was 0.125 and 0.39 microg/ml for TMP and SMX, respectively. The method was used for a bioequivalence study.

[Epidemiology and etiology of urinary tract infections in the community. Antimicrobial susceptibility of the main pathogens and clinical significance of resistance]

Urinary tract infections (UTI) are a frequent problem in primary care. They occur mainly in women without underlying diseases and with no functional or structural anomalies of the urinary tract; consequently most cases are considered uncomplicated UTI. Etiology is influenced by factors such as age, diabetes, spinal cord injury, urinary catheterization, and other factors. Escherichia coli causes 80-85% of acute episodes of uncomplicated cystitis. Staphylococcus saprophyticus, Proteus mirabilis, Streptococcus agalactiae and Klebsiella spp. are responsible for most of the remaining episodes. The spectrum of bacteria that causes complicated UTI is much broader. Rates of resistance have undergone considerable variations, and consequently the empirical treatment of UTI requires constant updating of the antibiotic sensitivity of the main uropathogens of the area, country or institution. To correctly interpret the global data on sensitivity, the type of UTI (uncomplicated versus complicated), sex, age and previous antibiotic therapy in each patient must be taken into account. Resistance in uncomplicated UTI has clinical significance (although less than in systemic infections such as bacteremia), which depends on whether the infection is cystitis or pyelonephritis.

Treatment of uncomplicated urinary tract infections in an era of increasing antimicrobial resistance

In the past few years, notable advances have occurred in our understanding of the epidemiology and clinical importance of drug resistance among uropathogens that cause uncomplicated urinary tract infections (UTIs) or cystitis. Guidelines recommend trimethoprim-sulfamethoxazole for empirical treatment of uncomplicated UTI unless trimethoprim-sulfamethoxazole resistance in a community exceeds 10% to 20%. The rationale for this 10% to 20% cutoff appears to be related to clinical and economical considerations and to concerns about the emergence of fluoroquinolone-resistant bacteria. In patients with uncomplicated UTIs caused by uropathogens resistant to trimethoprim-sulfamethoxazole who were treated with this drug combination, clinical outcomes were clarified recently and found to be suboptimal (<60% clinical cure). Following guidelines for empirical treatment of uncomplicated UTIs is problematic. Surveillance of antimicrobial resistance among uropathogens that cause uncomplicated UTIs is performed rarely. Hospital antibiograms provide data on resistance among bacteria that cause community-associated UTIs; however, antibiograms overestimate drug resistance among uropathogens that cause UTIs and may mislead clinicians about the prevalence of local resistance. We review options for management of uncomplicated UTIs in light of these considerations.

A reversed-phase high-performance liquid chromatography method for the determination of cotrimoxazole (trimethoprim/ sulphamethoxazole) in children treated for malaria

A high-performance liquid chromatography (HPLC) method was developed for the simultaneous analysis of trimethoprim (TMP), sulphamethoxazole (SMX), and acetylsulphamethoxazole (AcSMX) in small amounts of blood. The method involved precipitation with 50 microL trichloracetic acid (1M) to 125 microL plasma or serum sample. 60 microL supernatant was added to 60 microL mobile phase, modified with 50microL 1 M sodium hydroxide/mL. The mobile phase consisted of 20% acetonitrile and 80% phosphate buffer adjusted to pH 6.15. Using 125 microL of the sample, limits of quantitation were 0.1 microg/mL for TMP, 1.0 microg/mL for SMX, and 1.0 microg/mL for AcSMX. The precision of the method was 2% to 11% over the range of concentrations tested, 0.5-30 microg/mL for TMP, 5-300 microg/mL for SMX, and 2.5-150 microg/mL for AcSMX, respectively. No interference with other commonly used drugs was observed. The method is rapid, simple, specific, and sensitive enough for pharmacokinetic studies. The small amount of blood required makes it suitable for pediatric patients. The method was used to analyze samples from Tanzanian children aged 6-59 months participating in a cotrimoxazole (TMP/SMX)/chloroquine randomized trial for the treatment of uncomplicated malaria. Venous blood samples from 68 children were collected 2 hours after the first dose of TMP/SMX (4 mg/kg TMP/20 mg/kg SMX at two divided doses for 5 days) and again at treatment day 4. Individual variations in plasma concentrations of TMP, SMX, and AcSMX were considerable. The mean and SEM plasma concentrations (g/mL) of TMP, SMX, and AcSMX 2 hours after the first treatment dose were 2.0 +/- 1.0 (range 0.5-6), 53 +/- 22 (range 24-146), and 13.5 +/- 12 (range 0-65), respectively. On the fourth day the attained plasma concentrations were not significantly different from samples collected after the first dose.

Zidovudine, trimethoprim, and dapsone pharmacokinetic interactions in patients with human immunodeficiency virus infection

Zidovudine is widely prescribed for the treatment of human immunodeficiency virus (HIV) infection. Trimethoprim and dapsone are commonly used in the management of Pneumocystis carinii pneumonia in HIV-infected patients. To examine the pharmacokinetic interactions among these drugs, eight HIV-infected patients (26 to 43 years old) with a mean CD4 count of 524.4 +/- 405.7 cells per mm3 received zidovudine (200 mg), trimethoprim (200 mg), and dapsone (100 mg) as single agents and in two- and three-drug combinations. Blood and urine samples were collected at a specified time and analyzed for zidovudine, zidovudine-glucuronide, trimethoprim, dapsone, and monoacetyl-dapsone concentrations under single-dose and steady-state conditions. Zidovudine did not influence the pharmacokinetic disposition of dapsone or trimethoprim. Dapsone had no effect on the pharmacokinetic disposition of zidovudine. Trimethoprim significantly decreased the renal clearance of zidovudine by 58% (5.0 +/- 1.8 versus 2.1 +/- 0.5 ml/min/kg of body weight [P < 0.05]). There was a concurrent 54% decrease in the mean urinary recovery of zidovudine (11.7 +/- 3.5 versus 5.4 +/- 3.0 [P < 0.05]), and the metabolic ratio was decreased by 78% (0.32 +/- 0.4 versus 0.07 +/- 0.05 [P < 0.05]). The mean area under the concentration-time curve from 0 to 6 h of the zidovudine-glucuronide/ zidovudine ratio was unchanged. We conclude that zidovudine, trimethoprim, and dapsone can be coadministered to patients with AIDS without significant pharmacokinetic interaction. However, in AIDS patients with liver impairment and impaired glucuronidation, doses of zidovudine may need to be decreased.

A pharmacokinetic interaction study of didanosine coadministered with trimethoprim and/or sulphamethoxazole in HIV seropositive asymptomatic male patients

1. The pharmacokinetics of didanosine, trimethoprim, and sulphamethoxazole were evaluated in ten HIV seropositive asymptomatic patients as single agents and upon coadministration of single doses. 2. Using a randomized, balanced incomplete block crossover study with at least a 1-week washout period between successive treatments, each patient under fasting conditions received four of the following five treatments: 200 mg didanosine as a single agent; 200 mg trimethoprim + 1000 mg sulphamethoxazole; 200 mg trimethoprim + 200 mg didanosine; 1000 mg sulphamethoxazole + 200 mg of didanosine and; 200 mg trimethoprim + 1000 mg sulphamethoxazole + 200 mg didanosine. 3. Serial blood and urine samples were collected following the administration of each treatment. Plasma and urine samples were analyzed using high-pressure liquid chromatography (h.p.l.c.)/ultraviolet assays specific for unchanged didanosine, trimethoprim and/or sulphamethoxazole. 4. Percent urinary recovery (%UR) and renal clearance (CLR) emerged as consistently affected parameters, being decreased in the case of didanosine (35%, P = 0.016) and trimethoprim (32%, P = 0.019) and increased in the case of sulphamethoxazole (39%, P = 0.079), when all three agents were coadministered. The magnitude of the changes in didanosine CLR and %UR values was no greater when both trimethoprim and sulphamethoxazole were coadministered vs when each single agent was given with didanosine, suggesting that any effect was not additive. 5. Other key parameters such as Cmax, AUC, and t1/2 for didanosine (1309.9 ng ml-1, 1796.9 ng ml-1 h, and 1.61 h, respectively), trimethoprim (1.96 micrograms ml-1, 22.86 micrograms ml-1 h, and 9.03 h, respectively) or sulphamethoxazole (58.62 micrograms ml-1, 799.7 micrograms ml-1 h and 9.84 h, respectively) were not affected when didanosine was coadministered with either trimethoprim (didanosine: 1751.9 ng ml-1, 2158.0 ng ml-1 h, and 1.28 h; trimethoprim: 1.81 micrograms ml-1, 28.89 micrograms ml-1 h, and 11.4 h), sulphamethoxazole (didanosine: 1279.3 ng ml-1, 1793.2 ng ml-1 h, and 1.61 h; sulphamethoxazole: 53.57 micrograms ml-1, 732.1 micrograms ml-1 h, and 8.95 h), or the combination of trimethoprim and sulphamethoxazole (didanosine: 1283.7 ng ml-1, 1941.8 ng ml-1 h, and 1.38 h; trimethoprim: 1.59 micrograms ml-1, 26.68 micrograms ml-1 h, and 11.3 h; sulphamethoxazole: 59.48 micrograms ml-1, 760.9 micrograms ml-1 h, and 9.47 h). 6. Because the observed differences in CLR and %UR are small and not considered to be clinically relevant, it is not necessary to alter the dosing regimens of didanosine, trimethoprim or sulphamethoxazole when administered in combination to HIV seropositive patients.

Treatment of experimental endocarditis due to methicillin-susceptible or methicillin-resistant Staphylococcus aureus with trimethoprim-sulfamethoxazole and antibiotics that inhibit cell wall synthesis

Using two strains of Staphylococcus aureus, one susceptible and one heterogeneously resistant to methicillin, for which MICs and MBCs of trimethoprim-sulfamethoxazole (TMP-SMX) were 0.06 and 0.06 micrograms/ml and 0.06 and 0.25 microgram/ml, respectively (concentrations are those of TMP), we studied the efficacies of TMP-SMX and cloxacillin, teicoplanin, and vancomycin for treatment of experimental staphylococcal endocarditis. Rabbits were treated with dosages of TMP-SMX selected to achieve concentrations in serum equivalent to that obtained in humans treated for Pneumocystis carinii pneumonia. The overall mortality rate of rabbits treated with TMP-SMX was 84% at day 3, not different from that of the control groups (P > 0.1). No sterile vegetations were observed to be present in control groups or in animals treated with TMP-SMX. However, 26, 60, and 75% of rabbits treated with teicoplanin, cloxacillin, and vancomycin, respectively, showed sterile vegetations. For methicillin-susceptible S. aureus (MSSA), the mean vegetation counts were not significantly different between the control group and the group treated with TMP-SMX (P > 0.1). For methicillin-resistant S. aureus (MRSA), treatment with TMP-SMX was more effective than no therapy, decreasing the number of organisms in vegetations (P < 0.01). For both strains, therapy with cloxacillin and therapy with teicoplanin or vancomycin were significantly more effective than therapy with TMP-SMX. Despite high concentrations of teicoplanin in serum which exceeded MBCs for staphylococci more than 50 times at the peak and 10 times at the trough, therapy with cloxacillin or vancomycin was superior to therapy with teicoplanin against both MSSA and MRSA. These data do not support the use of TMP-SMX in treatment of endocarditis and other severe staphylococcal infections with high bacterial counts.

Pharmacokinetics of trimethoprim-sulfamethoxazole in critically ill and non-critically ill AIDS patients

Current dosage regimens of trimethoprim-sulfamethoxazole used to treat Pneumocystis carinii pneumonia in AIDS patients have been based on data from healthy subjects or patients without AIDS. The clearance and absorption characteristics of the drugs may potentially be different between patients with and without AIDS. This study was conducted to assess the pharmacokinetics of trimethoprim-sulfamethoxazole in critically ill and non-critically ill AIDS patients treated for P. carinii pneumonia. Patients received trimethoprim at 15 mg/kg of body weight and sulfamethoxazole at 75 mg/kg of body weight daily intravenously in three to four divided doses and were switched to the oral route when the regimen was tolerated. Serum samples for determination of drug concentrations were obtained over 12 h after intravenous and oral dosing. The pharmacokinetics of trimethoprim and sulfamethoxazole were compared in eight critically ill versus nine non-critically ill male patients and were as follows, respectively: clearance, 1.88 +/- 0.44 versus 1.73 +/- 0.64 ml/min/kg for trimethoprim and 0.40 +/- 0.12 versus 0.34 +/- 0.11 ml/min/kg for sulfamethoxazole; volume of distribution, 1.6 +/- 0.5 versus 1.5 +/- 0.5 liters/kg for trimethoprim and 0.5 +/- 0.3 versus 0.4 +/- 0.1 liters/kg for sulfamethoxazole; and half-life, 10.9 +/- 7.4 versus 11.3 +/- 4.0 h for trimethoprim, and 15.5 +/- 9.5 versus 14.3 +/- 4.7 h for sulfamethoxazole. No significant differences (P > 0.05) were observed between patient groups, although there was wide intersubject variability. Absorption appeared to be similar between the critically ill and non-critically patients: bioavailability was 97.5% +/- 22.4% versus 101.8% +/- 22.7% for trimethoprim and 86.2% +/- 17.9% versus 99.1% +/- 20.5% for sulfamethoxazole, respectively. Because of the similar pharmacokinetics of trimethoprim-sulfamethoxazole in critically ill and non-critically ill AIDS patients, the two groups of patients may receive similar dosages. Dosage adjustment does not appear to be required when switching from the intravenous to the oral route.

Analysis and bioequivalency study on two tablet formulations of co-trimoxazole

This paper describes an analytical procedure for simultaneous quantification of trimethoprim (TMP) and sulphamethoxazole (SMZ) in serum. Serum samples were rendered alkaline with glycine-sodium hydroxide buffer (pH 9.1) and extracted with ethyl acetate. The reconstituted sample was analysed using reversed-phase C-18 column high-performance chromatography. The mobile phase consisted of 75% triethyl ammonium acetate buffer, 20% methanol and 5% acetonitrile. The analytes were monitored at 289 nm and tetroxoprim was used as an internal standard. The maximum values for intra-day coefficients of variation (CV) for TMP-and SMZ were 5.7 and 2.1%, respectively. Interday CV values were 6.4 and 2.2%, respectively. The method was used to compare the bioavailability of two tablet formulations in terms of their pharmacokinetic parameters following oral administration of the tablets to 18 volunteers.

Trimethoprim-sulfamethoxazole

The antimicrobial combination of trimethoprim and sulfamethoxazole is active in vitro against various gram-positive and gram-negative bacteria. Clinically, it is useful for prophylaxis and treatment of selected infections of the genitourinary, respiratory, and gastrointestinal tracts. Trimethoprim-sulfamethoxazole by itself or in combination with other antimicrobial agents is indicated for most Nocardia asteroides infections and is the antimicrobial agent of choice for Pneumocystis carinii pneumonia. The drug is relatively nontoxic in patients who do not have the acquired immunodeficiency syndrome (AIDS) and is available in both oral and intravenous forms. The native compounds and the metabolites of trimethoprim and sulfamethoxazole are excreted primarily in the urine. When the creatinine clearance is less than 30 ml/min, the dosage of trimethoprim-sulfamethoxazole should be adjusted.

Clinical use of trimethoprim/sulfamethoxazole during renal dysfunction

This article reviews the pharmacokinetics, clinical use, and adverse effects of trimethoprim/sulfamethoxazole (TMP/SMX) in renally impaired patients. Renal dysfunction changes the pharmacokinetics of both component drugs. TMP and SMX disposition are not significantly altered until creatinine clearance is less than 30 mL/min, when SMX metabolites and TMP accumulate and may lead to toxicity. Renal dysfunction, however, does not preclude the use of TMP/SMX to treat susceptible infections, even when creatinine clearance is less than 15 mL/min. Adverse effects may occur more frequently in renally impaired patients but are not clearly related to increased serum concentrations of either drug. Guidelines for appropriate dosing and monitoring of TMP/SMX therapy in these patients are presented.

High-performance liquid chromatographic analysis of trimethoprim and sulfamethoxazole in microliter volumes of chinchilla middle ear effusion and serum

A reversed-phase high-performance liquid chromatographic procedure was developed to analyze 25-microliters volumes of chinchilla middle ear effusion and 50-microliters volumes of serum for trimethoprim and sulfamethoxazole. The small sample volumes were dictated by the chinchilla model of otitis media and our need to collect multiple samples over a 12-h drug dosing interval. The drugs were separated on a cyanopropylsilane column using acetonitrile-40 mM sodium phosphate, (16:84, v/v), pH 4.8. Trimethoprim and the internal standard were detected at 230 nm while sulfamethoxazole was detected at 250 nm. Middle ear effusion and serum samples were extracted with ethyl acetate-dichloromethane (25:75, v/v). The limit of quantitation was 0.5 micrograms/ml for sulfamethoxazole and 0.1 micrograms/ml for trimethoprim (coefficient of variation less than 20%), the limit of detection 0.25 and 0.05 micrograms/ml, respectively. Middle ear and serum samples of chinchilla with experimentally induced otitis media receiving 10 mg/kg trimethoprim and 50 mg/kg sulfamethoxazole intramuscularly were collected over a 12-h period and analyzed. All statistics that validate the analytic method are reported.

Clinical pharmacology of antibiotics and other drugs in cystic fibrosis

The disposition of many drugs in cystic fibrosis is abnormal. In general, changes in pharmacokinetics include: increased volume of distribution, decreased plasma concentration, and enhanced renal and sometimes non-renal elimination of drugs. Pathophysiology of the disease important for drug disposition includes: (a) hypersecretion of gastric acid and duodenal secretions which are of small volume, viscous and low in bicarbonate; (b) increased intestinal permeability to some sugars and probe substances; (c) hypergammaglobulinaemia and sometimes hypoalbuminaemia; (d) significant elevation of free fatty palmitoleic acid level and decreased low-density and high-density serum lipoproteins; (e) an average increase by 30 to 45% in plasma volume in patients with cystic fibrosis who have moderately severe pulmonary disease, right ventricle hypertrophy and dilatation, which occurs in 15 to 35% of patients with a Shwachman score of 81 to 100; (f) abnormal bile acid metabolism and enterohepatic recirculation; and (g) enlarged kidneys and glomerulomegaly with increased glomerular filtration rate, tubular clearance and urine flow rate in some patients with cystic fibrosis. Delayed absorption from the gastrointestinal tract has been reported in patients with cystic fibrosis for cloxacillin, epicillin, clindamycin, ciprofloxacin and probably for cephalexin, para-aminobenzoic acid and chloramphenicol. A possible increased absorption was reported for cimetidine. Of 7 drugs studied only theophylline had significantly decreased plasma protein binding. An increased volume of distribution and increased renal clearance reported for several drugs is caused mainly by increases in plasma volume and urine flow rate in many of these patients. Possible increased elimination of some drugs in bile (which probably results from bile acid malabsorption) and in bronchial secretions (which are abundant in some cystic fibrosis patients with acute pulmonary infection) may explain enhanced non-renal elimination of these drugs. The metabolism of cimetidine in cystic fibrosis was reported not to be changed significantly compared to control subjects.

Trimethoprim-sulfamethoxazole

The antimicrobial combination of trimethoprim and sulfamethoxazole is active in vitro against a variety of gram-positive and gram-negative bacteria. Clinically, it is useful for treatment and prophylaxis of various infections of the genitourinary tract and certain infections of the respiratory and gastrointestinal tracts. Trimethoprim-sulfamethoxazole by itself or in combination with other antimicrobial agents is indicated for most Nocardia asteroides infections. It is the antimicrobial agent of choice for Pneumocystis carinii pneumonia. The drug is relatively nontoxic in patients who do not have acquired immunodeficiency syndrome (AIDS), and it is available in oral and intravenous forms. The native compounds and the metabolites of trimethoprim and sulfamethoxazole are excreted primarily in the urine. When the creatinine clearance decreases to less than 30 ml/min, the dosage of trimethoprim-sulfamethoxazole should be adjusted.

Solubilities and intrinsic dissolution rates of sulphamethoxazole and trimethoprim

The influence of pH on the dissolution rates and solubilities of sulphamethoxazole and trimethoprim have been examined. Sulphamethoxazole was evaluated in buffers of ionic strength 0.5 mol dm-3 over the pH range 0.45-7.8 and at 25, 32 and 37 degrees C. The minimum solubility of sulphamethoxazole was 28.1 mg/100 mL at pH 3.22 and 25 degrees C. Solubilities increased significantly with both increased and decreased pH. Intrinsic dissolution rates demonstrated a linear relationship with the solubility data. Trimethoprim solubility was both buffer- and pH-dependent. In both water and hydrochloric acid solution at 32 degrees C the solubility of trimethoprim increased from 50 mg/100 mL in water at pH 8.54 to a maximum of 1550 mg/100 mL at pH 5.5. This maximum solubility was in excess of that predicted theoretically and may be due to supersaturation. Below pH 2 the solubility of protonated trimethoprim diminished from 1125 mg/100 mL with decreasing pH. This was due to the common ion effect. Intrinsic dissolution rates increased as pH was decreased with hydrochloric acid from 6.00 to 1.78, but decreased at pH 1.48 due to the common ion effect. Dissolution profiles of trimethoprim showed complex patterns dependent upon pH. The profile was zero-order at pH 6.00 and became distinctly stepwise at pH 5.5, this effect becoming less pronounced at lower pH values. This was reconciled in terms of the rate of formation of trimethoprim hydrochloride on the surface of the disc and the differing dissolution rates of this species and trimethoprim. A simple relationship between solubility and dissolution rate was not observed.

Trimethoprim used for selective decontamination of the digestive tract in rats: possible route of excretion

Selective elimination of Enterobacteriaceae species from the digestive tract of rats has been accomplished by oral treatment with trimethoprim (235 mg/kg body weight/day) within 6 days. In the present study it was investigated whether this elimination was mainly due to antimicrobial activity of trimethoprim excreted with the gastrointestinal mucus or mainly by non-absorbed trimethoprim in the lumen contents. By means of whole gut irrigation (WGI) the lumen contents were washed out, followed by mucosa-associated flora. The concentration of the mucosa-associated Enterobacteriaceae remained at least 10(1)/ml as measured in the last samples of rectal effluent during WGI in untreated rats. During trimethoprim treatment, however, the amount of mucosa-associated Enterobacteriaceae had decreased significantly more (p less than 0.05) compared with the Enterobacteriaceae present in the lumen contents of the gastrointestinal tract (photospectrometrically measured by the color of the rectal effluent). No difference was observed in the concentration of mucosa-associated enterococci in the rectal effluent of trimethoprim treated and untreated rats. It is concluded that orally administered trimethoprim may be predominantly active against Enterobacteriaceae associated with the mucous blanket.

Pharmacokinetics of the trimethoprim-sulphamethoxazole combination in the elderly

The pharmacokinetics of a co-trimoxazole preparation (Bactrim Forte) containing trimethoprim (TMP) 160 mg and sulphamethoxazole (SMZ) 800 mg were determined in six young adults (29.3 +/- 4.4 s.d. years) and six elderly people (78.6 +/- 6.6 s.d. years). Following oral administration of a single dose, the pharmacokinetic parameters of SMZ and its N4-acetylated metabolite (N4SMZ) were similar in both groups. However Cmax of TMP was greater (2.06 +/- 0.29 s.d. vs 1.57 +/- 0.32 s.d. mg l-1; P less than 0.01) and its area under the curve was larger (34.30 +/- 6.98 s.d. vs 23.87 +/- 3.82 s.d. mg l-1 h; P less than 0.001) in elderly people than in younger subjects. Total clearance (CL/F) of TMP normalized to body weight was not significantly different in the two groups. There was no significant difference in serum protein binding of TMP and SMZ between the two groups. Urinary excretion of TMP, SMZ and N4SMZ was reduced by about 50% in the elderly compared to the young subjects. Renal clearance of TMP was significantly lower in the elderly group (19 +/- 10 s.d. vs 55 +/- 14 s.d. ml h-1 kg-1; P less than 0.001). Renal clearance of SMZ was not significantly different in the two groups. A study of plasma concentrations of TMP, SMZ and N4SMZ during continuous dosing in seven elderly patients treated for urinary or respiratory infections showed that steady state was reached after 3 days of treatment and that plasma drug concentrations were about two to three times higher than those observed after a single dose.

Cotrimoxazole as an inhibitor of oxidative drug metabolism: effects of trimethoprim and sulphamethoxazole separately and combined on tolbutamide disposition

The effect of separate pretreatments with cotrimoxazole, sulphamethoxazole and trimethoprim on the disposition of tolbutamide was studied in seven healthy males. Tolbutamide 500 mg intravenously was administered on four separate occasions--as a control without pretreatment and on the seventh day of separate twice daily administration of cotrimoxazole (sulphamethoxazole 800 mg plus trimethoprim 160 mg) (ST phase), sulphamethoxazole 1 g (S phase) and trimethoprim 150 mg (T phase). Tolbutamide total and unbound plasma clearance (CL) were reduced following each of the individual pretreatments compared to the control phase (P less than 0.001). For unbound CL the reductions were 14% in the S and T phases and 25% in ST phase. Tolbutamide elimination half-life was prolonged following each pretreatment (P less than 0.001) by 20% in the S phase, 19% in the T phase and 30% in the ST phase. Tolbutamide total steady-state volume of distribution (VSS) was increased by 10% in the S and ST phases (P less than 0.01), the increase being accounted for by an increase in tolbutamide unbound fraction. There was no change in tolbutamide unbound VSS following any of the pretreatments. These results are consistent with inhibition of tolbutamide oxidation by cotrimoxazole, an additive effect of the two components sulphamethoxazole and trimethoprim. Sulphamethoxazole also reduces tolbutamide plasma protein binding.