Source: FDA, National Drug Code (US) Revision Year: 2023
Sulfamethoxazole and trimethoprim injection is contraindicated in the following situations:
Some epidemiologic studies suggest that exposure to sulfamethoxazole and trimethoprim injection during pregnancy may be associated with an increased risk of congenital malformations, particularly neural tube defects, cardiovascular malformations, urinary tract defects, oral clefts, and club foot. If sulfamethoxazole and trimethoprim injection is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be advised of the potential hazards to the fetus [see Use in Specific Populations (8.1)].
Fatalities and serious adverse reactions including severe cutaneous adverse reactions (SCARs), including Stevens-Johnson Syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (DRESS), acute febrile neutrophilic dermatosis (AFND), acute generalized erythematous pustulosis (AGEP); fulminant hepatic necrosis; agranulocytosis, aplastic anemia and other blood dyscrasias; acute and delayed lung injury; anaphylaxis and circulatory shock have occurred with the administration of sulfamethoxazole and trimethoprim products, including sulfamethoxazole and trimethoprim injection [see Adverse Reactions (6.1)].
Cough, shortness of breath and pulmonary infiltrates potentially representing hypersensitivity reactions of the respiratory tract have been reported in association with sulfamethoxazole and trimethoprim treatment.
Other severe pulmonary adverse reactions occurring within days to week of sulfamethoxazole and trimethoprim injection initiation and resulting in prolonged respiratory failure requiring mechanical ventilation or extracorporeal membrane oxygenation (ECMO), lung transplantation or death have also been reported in patients and otherwise healthy individuals treated with sulfamethoxazole and trimethoprim products.
Circulatory shock with fever, severe hypotension, and confusion requiring intravenous fluid resuscitation and vasopressors has occurred within minutes to hours of rechallenge with sulfamethoxazole and trimethoprim products, including sulfamethoxazole and trimethoprim injection, in patients with history of recent (days to weeks) exposure to sulfamethoxazole and trimethoprim.
Sulfamethoxazole and trimethoprim injection should be discontinued at the first appearance of skin rash or any sign of a serious adverse reaction. A skin rash may be followed by more severe reactions, such as Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS, AFND, AGEP, hepatic necrosis or serious blood disorder. Clinical signs, such as rash, pharyngitis, fever, arthralgia, cough, chest pain, dyspnea, pallor, purpura or jaundice may be early indications of serious reactions.
Sulfamethoxazole and trimethoprim injection-induced thrombocytopenia may be an immune-mediated disorder. Severe cases of thrombocytopenia that are fatal or life threatening have been reported. Monitor patients for hematologic toxicity. Thrombocytopenia usually resolves within a week upon discontinuation of sulfamethoxazole and trimethoprim injection.
Avoid use of sulfamethoxazole and trimethoprim injection in the treatment of streptococcal pharyngitis. Clinical studies have documented that patients with group A ฮฒ-hemolytic streptococcal tonsillopharyngitis have a greater incidence of bacteriologic failure when treated with sulfamethoxazole and trimethoprim injection than do those patients treated with penicillin, as evidenced by failure to eradicate this organism from the tonsillopharyngeal area. Therefore, sulfamethoxazole and trimethoprim injection will not prevent sequelae such as rheumatic fever.
Clostridioides difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including sulfamethoxazole and trimethoprim injection, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of C. difficile.
C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibacterial use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.
If CDAD is suspected or confirmed, ongoing antibacterial use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibacterial treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated.
Sulfamethoxazole and trimethoprim injection contains sodium metabisulfite, a sulfite that may cause allergic-type reactions, including anaphylactic symptoms and life-threatening or less severe asthmatic episodes in certain susceptible people. The overall prevalence of sulfite sensitivity in the general population is unknown. Sulfite sensitivity is seen more frequently in asthmatic than in non-asthmatic people.
Sulfamethoxazole and trimethoprim injection contains benzyl alcohol as a preservative. Serious and fatal adverse reactions including “gasping syndrome” can occur in neonates and low birth weight infants treated with benzyl alcohol-preserved formulations in infusion solutions, including sulfamethoxazole and trimethoprim injection. The “gasping syndrome” is characterized by central nervous system depression, metabolic acidosis, and gasping respirations. Sulfamethoxazole and trimethoprim injection is contraindicated in pediatric patients less than two months of age [see Contraindications (4)].
When prescribing sulfamethoxazole and trimethoprim injection in pediatric patients (two months of age and older), consider the combined daily metabolic load of benzyl alcohol from all sources including sulfamethoxazole and trimethoprim injection (contains 10 mg of benzyl alcohol per mL) and other drugs containing benzyl alcohol. The minimum amount of benzyl alcohol at which serious adverse reactions may occur is not known [see Use in Specific Populations (8.4)].
Treatment failure and excess mortality were observed when sulfamethoxazole and trimethoprim injection was used concomitantly with leucovorin for the treatment of HIV positive patients with P. jirovecii pneumonia in a randomized placebo-controlled trial. Avoid coadministration of sulfamethoxazole and trimethoprim injection and leucovorin during treatment of P. jirovecii pneumonia.
Sulfamethoxazole and trimethoprim injection contains propylene glycol as a solvent (40% v/v). When administered at high doses as for the treatment of P. jirovecii pneumonia and concomitantly with other products that contain propylene glycol, hyperosmolarity with anion gap metabolic acidosis, including lactic acidosis can occur. Propylene glycol toxicity can lead to acute kidney injury, CNS toxicity, and multi-organ failure. Monitor for the total daily intake of propylene glycol from all sources and for acidbase disturbances. Discontinue sulfamethoxazole and trimethoprim injection if propylene glycol toxicity is suspected [see Adverse Reactions (6)].
Avoid use of sulfamethoxazole and trimethoprim injection in patients with impaired renal or hepatic function, in those with possible folate deficiency (e.g., the elderly, chronic alcoholics, patients receiving anticonvulsant therapy, patients with malabsorption syndrome, and patients in malnutrition states) and in those with severe allergies or bronchial asthma.
Hematologic changes indicative of folic acid deficiency may occur in elderly patients or in patients with preexisting folic acid deficiency or kidney failure. These effects are reversible by folinic acid therapy [see Use in Specific Populations (8.5)].
In glucose-6-phosphate dehydrogenase deficient individuals, hemolysis may occur. This reaction is frequently dose-related.
Local irritation and inflammation due to extravascular infiltration of the infusion have been observed with sulfamethoxazole and trimethoprim injection. If these occur the infusion should be discontinued and restarted at another site.
Cases of hypoglycemia in non-diabetic patients treated with sulfamethoxazole and trimethoprim injection have been seen, usually occurring after a few days of therapy. Patients with renal dysfunction, liver disease, malnutrition or those receiving high doses of sulfamethoxazole and trimethoprim injection are particularly at risk.
Trimethoprim, component of sulfamethoxazole and trimethoprim injection, has been noted to impair phenylalanine metabolism, but this is of no significance in phenylketonuric patients on appropriate dietary restriction.
Like other drugs containing sulfonamides, sulfamethoxazole and trimethoprim injection can precipitate porphyria crisis and hypothyroidism. Avoid use of sulfamethoxazole and trimethoprim injection in patients with porphyria or thyroid dysfunction.
AIDS patients may not tolerate or respond to sulfamethoxazole and trimethoprim injection in the same manner as non-AIDS patients. The incidence of adverse reactions, particularly rash, fever, leukopenia, and elevated aminotransferase (transaminase) values, with sulfamethoxazole and trimethoprim injection therapy in AIDS patients who are being treated for P. jirovecii pneumonia has been reported to be increased compared with the incidence normally associated with the use of sulfamethoxazole and trimethoprim injection in non-AIDS patients. If a patient develops skin rash, fever, leukopenia or any sign of an adverse reaction, reevaluate benefit-risk of continuing therapy or re-challenge with sulfamethoxazole and trimethoprim injection [see Warnings and Precautions (5.2)].
Avoid coadministration of sulfamethoxazole and trimethoprim injection and leucovorin during treatment of Pneumocystis jirovecii pneumonia [see Warnings and Precautions (5.8)]
High dosage of trimethoprim, as used in patients with P. jirovecii pneumonia, induces a progressive but reversible increase of serum potassium concentrations in a substantial number of patients. Even treatment with recommended doses may cause hyperkalemia when trimethoprim is administered to patients with underlying disorders of potassium metabolism, with renal insufficiency, or if drugs known to induce hyperkalemia are given concomitantly. Close monitoring of serum potassium is warranted in these patients.
Severe and symptomatic hyponatremia can occur in patients receiving sulfamethoxazole and trimethoprim injection, particularly for the treatment of P. jirovecii pneumonia. Evaluation for hyponatremia and appropriate correction is necessary in symptomatic patients to prevent life-threatening complications.
During treatment, ensure adequate fluid intake and urinary output to prevent crystalluria. Patients who are “slow acetylators” may be more prone to idiosyncratic reactions to sulfonamides.
Complete blood counts and clinical chemistry testing should be done frequently in patients receiving sulfamethoxazole and trimethoprim injection. Discontinue sulfamethoxazole and trimethoprim injection if a significant electrolyte abnormality, renal insufficiency or reduction in the count of any formed blood element is noted. Perform urinalyses with careful microscopic examination and renal function tests during therapy, particularly for those patients with impaired renal function.
Prescribing sulfamethoxazole and trimethoprim injection in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.
The following serious adverse reactions are described elsewhere in the labeling:
The following adverse reactions associated with the use of sulfamethoxazole and trimethoprim injection or sulfamethoxazole and trimethoprim were identified in clinical trials, postmarketing or published reports. Because some of these reactions were reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
The most common adverse reactions are gastrointestinal disturbances (nausea, vomiting, and anorexia) and allergic skin reactions (such as rash and urticaria).
Fatalities and serious adverse reactions, including severe cutaneous adverse reactions (SCARs), including Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (DRESS), acute febrile neutrophilic dermatosis (AFND), acute generalized erythematous pustulosis (AGEP); fulminant hepatic necrosis; agranulocytosis, aplastic anemia and other blood dyscrasias; acute and delayed lung injury; anaphylaxis and circulatory shock have occurred with the administration of sulfamethoxazole and trimethoprim products, including sulfamethoxazole and trimethoprim injection [see Warnings and Precautions (5.2)].
Local reaction, pain and slight irritation on intravenous (IV) administration are infrequent. Thrombophlebitis has been observed.
Table 3. Adverse Reactions Reported with Sulfamethoxazole and trimethoprim injection:
| Body System | Adverse Reactions |
|---|---|
| Hematologic | Agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, neutropenia, hemolytic anemia, megaloblastic anemia, hypoprothrombinemia, methemoglobinemia, eosinophilia, thrombotic thrombocytopenic purpura, idiopathic thrombocytopenic purpura. |
| Allergic Reactions | Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis, allergic myocarditis, erythema multiforme, exfoliative dermatitis, angioedema, drug fever, chills, Henoch- Schoenlein purpura, serum sickness-like syndrome, generalized allergic reactions, generalized skin eruptions, photosensitivity, conjunctival and scleral injection, pruritus, urticaria, rash, periarteritis nodosa, systemic lupus erythematosus, drug reaction with eosinophilia and systemic symptoms (DRESS), acute generalized erythematous pustulosis (AGEP), and acute febrile neutrophilic dermatosis (AFND) [see Warnings and Precautions (5.2)]. |
| Gastrointestinal | Hepatitis (including cholestatic jaundice and hepatic necrosis), elevation of serum transaminase and bilirubin, pseudomembranous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhea, anorexia. |
| Genitourinary | Renal failure, interstitial nephritis, BUN and serum creatinine elevation, renal insufficiency, oliguria and anuria, crystalluria and nephrotoxicity in association with cyclosporine. |
| Metabolic and Nutritional | Hyperkalemia, hyponatremia [see Warnings and Precautions (5.17)] , metabolic acidosis. |
| Neurologic | Aseptic meningitis, convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, headache. |
| Psychiatric | Hallucinations, depression, apathy, nervousness. |
| Endocrine | The sulfonamides bear certain chemical similarities to some goitrogens, diuretics (acetazolamide and the thiazides) and oral hypoglycemic agents. Cross-sensitivity may exist with these agents. Diuresis and hypoglycemia have occurred. |
| Musculoskeletal | Arthralgia, myalgia, rhabdomyolysis. |
| Respiratory | Cough, shortness of breath and pulmonary infiltrates, acute eosinophilic pneumonia, acute and delayed lung injury, interstitial lung disease, acute respiratory failure [see Warnings and Precautions (5.2)]. |
| Cardiovascular System | QT prolongation resulting in ventricular tachycardia and torsades de pointes, circulatory shock [see Warnings and Precautions (5.2)]. |
| Miscellaneous | Weakness, fatigue, insomnia. |
Trimethoprim is an inhibitor of CYP2C8 as well as OCT2 transporter. Sulfamethoxazole is an inhibitor of CYP2C9. Avoid coadministration of sulfamethoxazole and trimethoprim injection with drugs that are substrates of CYP2C8 and 2C9 or OCT2.
Table 4. Drug Interactions with Sulfamethoxazole and trimethoprim injection:
| Drug(s) | Recommendation | Comments |
|---|---|---|
| Diuretics | Avoid concurrent use | In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported. |
| Warfarin | Monitor prothrombin time and INR | It has been reported that sulfamethoxazole and trimethoprim injection may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin (a CYP2C9 substrate). This interaction should be kept in mind when sulfamethoxazole and trimethoprim injection is given to patients already on anticoagulant therapy, and the coagulation time should be reassessed. |
| Phenytoin | Monitor serum phenytoin levels | Sulfamethoxazole and trimethoprim injection may inhibit the hepatic metabolism of phenytoin (a CYP2C9 substrate). Sulfamethoxazole and trimethoprim injection, given at a common clinical dosage, increased the phenytoin half-life by 39% and decreased the phenytoin metabolic clearance rate by 27%. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect. |
| Methotrexate | Avoid concurrent use | Sulfonamides can also displace methotrexate from plasma protein binding sites and can compete with the renal transport of methotrexate, thus increasing free methotrexate concentrations. |
| Cyclosporine | Avoid concurrent use | There have been reports of marked but reversible nephrotoxicity with coadministration of sulfamethoxazole and trimethoprim injection and cyclosporine in renal transplant recipients. |
| Digoxin | Monitor serum digoxin levels | Increased digoxin blood levels can occur with concomitant sulfamethoxazole and trimethoprim injection therapy, especially in elderly patients |
| Indomethacin | Avoid concurrent use | Increased sulfamethoxazole blood levels may occur in patients who are also receiving indomethacin. |
| Pyrimethamine | Avoid concurrent use | Occasional reports suggest that patients receiving pyrimethamine as malaria prophylaxis in doses exceeding 25 mg weekly may develop megaloblastic anemia if sulfamethoxazole and trimethoprim injection is prescribed. |
| Tricyclic Antidepressants (TCAs) | Monitor therapeutic response and adjust dose of TCA accordingly | The efficacy of tricyclic antidepressants can decrease when coadministered with sulfamethoxazole and trimethoprim injection. |
| Oral hypoglycemics | Monitor blood glucose more frequently | Like other sulfonamide-containing drugs, sulfamethoxazole and trimethoprim injection potentiates the effect of oral hypoglycemic that are metabolized by CYP2C8 (e.g., pioglitazone, repaglinide, and rosiglitazone) or CYP2C9 (e.g., glipizide and glyburide) or eliminated renally via OCT2 (e.g., metformin). Additional monitoring of blood glucose may be warranted. |
| Amantadine | Avoid concurrent use | In the literature, a single case of toxic delirium has been reported after concomitant intake of sulfamethoxazole and trimethoprim injection and amantadine (an OCT2 substrate). Cases of interactions with other OCT2 substrates, memantine and metformin, have also been reported. |
| Angiotensin Converting Enzyme Inhibitors | Avoid concurrent use | In the literature, three cases of hyperkalemia in elderly patients have been reported after concomitant intake of sulfamethoxazole and trimethoprim injection and an angiotensin converting enzyme inhibitor.6,7 |
| Zidovudine | Monitor for hematologic toxicity | Zidovudine and sulfamethoxazole and trimethoprim injection are known to induce hematological abnormalities. Hence, there is potential for an additive myelotoxicity when coadministered.8 |
| Dofetilide | Concurrent administration is contraindicated | Elevated plasma concentrations of dofetilide have been reported following concurrent administration of trimethoprim and dofetilide. Increased plasma concentrations of dofetilide may cause serious ventricular arrhythmias associated with QT interval prolongation, including torsade de pointes.2,3 |
| Procainamide | Closely monitor for clinical and ECG signs of procainamide toxicity and/or procainamide plasma concentration if available | Trimethoprim increases the plasma concentrations of procainamide and its active N-acetyl metabolite (NAPA) when trimethoprim and procainamide are coadministered. The increased procainamide and NAPA plasma concentrations that resulted from the pharmacokinetic interaction with trimethoprim are associated with further prolongation of the QTc interval.9 |
Sulfamethoxazole and trimethoprim injection, specifically the trimethoprim component, can interfere with a serum methotrexate assay as determined by the competitive binding protein technique (CBPA) when a bacterial dihydrofolate reductase is used as the binding protein. No interference occurs, however, if methotrexate is measured by a radioimmunoassay (RIA).
The presence of sulfamethoxazole and trimethoprim injection may also interfere with the JaffยกSR alkaline picrate reaction assay for creatinine, resulting in overestimations of about 10% in the range of normal values.
Sulfamethoxazole and trimethoprim injection may cause fetal harm if administered to a pregnant woman. Some epidemiologic studies suggest that exposure to sulfamethoxazole and trimethoprim injection during pregnancy may be associated with an increased risk of congenital malformations, particularly neural tube defects, cardiovascular abnormalities, urinary tract defects, oral clefts, and club foot (see Human Data).
One of 3 rat studies showed cleft palate at doses approximately 5 times the recommended human dose on a body surface area basis; the other 2 studies did not show teratogenicity at similar doses. Studies in pregnant rabbits showed increased fetal loss at approximately 6 times the human dose on a body surface area basis (see Animal Data).
The estimated background risk of major birth defects and miscarriages for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively. Advise pregnant women of the potential harm of sulfamethoxazole and trimethoprim injection to the fetus (see Clinical Considerations).
Urinary tract infection in pregnancy is associated with adverse perinatal outcomes such as preterm birth, low birth weight, and pre-eclampsia, and increased mortality to the pregnant woman. P. jirovecii pneumonia in pregnancy is associated with preterm birth and increased morbidity and mortality for the pregnant woman. Sulfamethoxazole and trimethoprim injection should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
While there are no large, prospective, well-controlled studies in pregnant women and their babies, some retrospective epidemiologic studies suggest an association between first trimester exposure to sulfamethoxazole and trimethoprim injection with an increased risk of congenital malformations, particularly neural tube defects, cardiovascular abnormalities, urinary tract defects, oral clefts, and club foot. These studies, however, were limited by the small number of exposed cases and the lack of adjustment for multiple statistical comparisons and confounders. These studies are further limited by recall, selection, and information biases, and by limited generalizability of their findings. Lastly, outcome measures varied between studies, limiting cross-study comparisons.
Alternatively, other epidemiologic studies did not detect statistically significant associations between sulfamethoxazole and trimethoprim injection exposure and specific malformations. Brumfitt and Pursell, 10 in a retrospective study, reported the outcome of 186 pregnancies during which the mother received either placebo or oral trimethoprim and sulfamethoxazole. The incidence of congenital abnormalities was 4.5% (3 of 66) in those who received placebo and 3.3% (4 of 120) in those receiving trimethoprim and sulfamethoxazole. There were no abnormalities in the 10 children whose mothers received the drug during the first trimester. In a separate survey, Brumfitt and Pursell also found no congenital abnormalities in 35 children whose mothers had received oral trimethoprim and sulfamethoxazole at the time of conception or shortly thereafter.
In rats, oral doses of either 533 mg/kg sulfamethoxazole or 200 mg/kg trimethoprim produced teratologic effects manifested mainly as cleft palates. These doses are approximately 5 and 6 times the recommended human total daily dose on a body surface area basis. In two studies in rats, no teratology was observed when 512 mg/kg of sulfamethoxazole was used in combination with 128 mg/kg of trimethoprim. In some rabbit studies, an overall increase in fetal loss (dead and resorbed conceptuses) was associated with doses of trimethoprim 6 times the human therapeutic dose based on body surface area.
Levels of sulfamethoxazole and trimethoprim injection in breast milk are approximately 2 to 5% of the recommended daily dose for pediatric patients over two months of age. There is no information regarding the effect of sulfamethoxazole and trimethoprim injection on the breastfed infant or the effect on milk production. Because of the potential risk of bilirubin displacement and kernicterus on the breastfed child [see Contraindications (4)], advise women to avoid breastfeeding during treatment with sulfamethoxazole and trimethoprim injection.
Sulfamethoxazole and trimethoprim injection is contraindicated in pediatric patients younger than two months of age because of the potential risk of bilirubin displacement and kernicterus [see Contraindications (4)].
Serious adverse reactions including fatal reactions and the “gasping syndrome” occurred in premature neonates and low birth weight infants in the neonatal intensive care unit who received benzyl alcohol as a preservative in infusion solutions. In these cases, benzyl alcohol dosages of 99 to 234 mg/kg/day produced high levels of benzyl alcohol and its metabolites in the blood and urine (blood levels of benzyl alcohol were 0.61 to 1.378 mmol/L). Additional adverse reactions included gradual neurological deterioration, seizures, intracranial hemorrhage, hematologic abnormalities, skin breakdown, hepatic and renal failure, hypotension, bradycardia, and cardiovascular collapse. Preterm, low-birth weight infants may be more likely to develop these reactions because they may be less able to metabolize benzyl alcohol.
When prescribing sulfamethoxazole and trimethoprim injection in pediatric patients consider the combined daily metabolic load of benzyl alcohol from all sources including sulfamethoxazole and trimethoprim injection (Sulfamethoxazole and trimethoprim injection contains 10 mg of benzyl alcohol per mL) and other drugs containing benzyl alcohol. The minimum amount of benzyl alcohol at which serious adverse reactions may occur is not known [see Warnings and Precautions (5.7)].
Clinical studies of sulfamethoxazole and trimethoprim injection did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects.
There may be an increased risk of severe adverse reactions in elderly patients, particularly when complicating conditions exist, e.g., impaired kidney and/or liver function, or concomitant use of other drugs. Severe skin reactions, generalized bone marrow suppression [see Warnings and Precautions (5.10), Adverse Reactions (6.1)], a specific decrease in platelets (with or without purpura), and hyperkalemia are the most frequently reported severe adverse reactions in elderly patients.
In those concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported. Increased digoxin blood levels can occur with concomitant sulfamethoxazole and trimethoprim injection therapy, especially in elderly patients. Serum digoxin levels should be monitored [see Drug Interactions (7)].
Hematologic changes indicative of folic acid deficiency may occur in elderly patients. These effects are reversible by folinic acid therapy. Appropriate dosage adjustments should be made for patients with impaired kidney function and duration of use should be as short as possible to minimize risks of undesired reactions [see Dosage and Administration (2.2)].
The trimethoprim component of sulfamethoxazole and trimethoprim injection may cause hyperkalemia when administered to patients with underlying disorders of potassium metabolism, with renal insufficiency or when given concomitantly with drugs known to induce hyperkalemia, such as angiotensin converting enzyme inhibitors. Close monitoring of serum potassium is warranted in these patients. Discontinuation of sulfamethoxazole and trimethoprim injection treatment is recommended to help lower potassium serum levels.
Pharmacokinetics parameters for sulfamethoxazole were similar for geriatric subjects and younger adult subjects. The mean maximum serum trimethoprim concentration was higher and mean renal clearance of trimethoprim was lower in geriatric subjects compared with younger subjects [see Clinical Pharmacology (12.3)].
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