Sulfadiazine (sulfadiazine)

The usual adult dosage of sulfadiazine is 2-4 g initially, followed by 2-4 g daily administered in 3-6 equally divided doses.

When sulfadiazine is used in infants and children older than 2 months of age, the manufacturer recommends 75 mg/kg or 2 g/m2 initially, followed by 150 mg/kg or 4 g/m2 daily administered in 4-6 equally divided doses. For the treatment of mild, moderate, or severe infections, the American Academy of Pediatrics (AAP) recommends that children beyond the neonatal period receive a sulfadiazine dosage of 120-150 mg/kg daily given in 4-6 divided doses. Pediatric dosage should not exceed 6 g daily.

Sulfadiazine is administered orally.

Patients should be instructed to drink one full glass (250 mL) of water with each dose of sulfadiazine and at frequent intervals throughout the day while they are receiving the drug.

There is no enhanced messaging for this drug.

Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

Antibiotics/Fecal Microbiota

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Fecal microbiota is a suspension of live bacteria, which may be compromised by concurrent use of antibiotics.(1)

CLINICAL EFFECTS: Antibiotics may decrease the effectiveness of fecal microbiota.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Antibiotics should not be used concurrently with fecal microbiota. Antibacterial treatment should be completed for 24 to 72 hours before initiating treatment with fecal microbiota. Do not use antibiotics for up to 8 weeks after fecal microbiota.(1)

DISCUSSION: Antibiotics may compromise the effectiveness of fecal microbiota.

Antibiotics/Fecal Microbiota Spores

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Fecal microbiota spores is a suspension of live bacterial spores, which may be compromised by concurrent use of antibiotics.(1)

CLINICAL EFFECTS: Antibiotics may decrease the effectiveness of fecal microbiota spores.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Antibiotics should not be used concurrently with fecal microbiota spores. Antibacterial treatment should be completed for 2 to 4 days before initiating treatment with fecal microbiota spores.(1)

DISCUSSION: Antibiotics may compromise the effectiveness of fecal microbiota spores.

Antimicrobials/Live Typhoid Vaccine

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: The antimicrobial may be active against the organism in the live-vaccine. Antimicrobial therapy may prevent the vaccine organism from replicating enough to trigger an immune response.(1)

CLINICAL EFFECTS: Vaccination may be ineffective.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Do not give oral typhoid vaccine until 72 hours after the last dose of antimicrobial. If possible, to optimize vaccine effectiveness, do not start antibacterial drugs for 72 hours after the last dose of oral typhoid vaccine. A longer interval should be considered for long-acting antimicrobials, such as azithromycin.(3)

DISCUSSION: Because antimicrobial therapy may prevent sufficient vaccine-organism replication to generate an immune response, the manufacturer of live-attenuated typhoid vaccine and the Centers for Disease Control (CDC) state that the vaccine should not be administered to patients receiving antimicrobial therapy.(1-3)

Selected Photosensitizers/Tretinoin-Mequinol

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Tretinoin, anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides are all known photosensitizers.(1)

CLINICAL EFFECTS: Concurrent use of tretinoin in patients taking anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides may increase the risk of phototoxicity.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturer states that tretinoin-mequinol should not be administered to patients receiving photosensitizers including anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides.(1)

DISCUSSION: Because of the risk of increased photosensitivity, the US manufacturer states that tretinoin-mequinol should not be administered to patients receiving photosensitizers including anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), methotrexate, phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides.(1)

Sulfonamides/Methenamine

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Methenamine is hydrolyzed to formaldehyde in acidic urine. Sulfonamides may form an insoluble precipitate with formaldehyde in the urine.(1,2)

CLINICAL EFFECTS: The concurrent administration of methenamine and sulfamethizole or sulfathiazole is likely to form a precipitate in the urine.(1-3)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Methenamine should not be administered to patients receiving sulfonamides.(1-3)

DISCUSSION: Methenamine is hydrolyzed to formaldehyde in acidic urine. An in vitro study showed that addition of methenamine and mandelic acid to saturated solutions of sulfamethizole at pH 5.0 and 6.0 produced a precipitate in one hour.(4)

Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

Agents That Affect Iodide/Radioactive Iodide

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Many compounds can affect iodide protein binding and alter iodide pharmacokinetics and pharmacodynamics.(1)

CLINICAL EFFECTS: Compounds that affect iodide pharmacokinetics and pharmacodynamics may impact the effectiveness of radioactive iodide.(1)

PREDISPOSING FACTORS: Compounds that affect iodide pharmacokinetics and pharmacodynamics are expected to have the most impact during therapy using radioactive iodide. Diagnostic procedures would be expected to be impacted less.

PATIENT MANAGEMENT: Discuss the use of agents that affect iodide pharmacokinetics and pharmacodynamics with the patient's oncologist.(1) Because indocyanine green contains sodium iodide, the iodine-binding capacity of thyroid tissue may be reduced for at least one week following administration. Do not perform radioactive iodine uptake studies for at least one week following administration of indocyanine green.(2) The manufacturer of iopamidol states administration may interfere with thyroid uptake of radioactive iodine and decrease therapeutic and diagnostic efficacy. Avoid thyroid therapy or testing for up to 6 weeks post administration of iopamidol.(3)

DISCUSSION: Many agents interact with radioactive iodine. The average duration of effect is: anticoagulants - 1 week antihistamines - 1 week anti-thyroid drugs, e.g: carbimazole, methimazole, propylthiouracil - 3-5 days corticosteroids - 1 week iodide-containing medications, e.g: amiodarone - 1-6 months expectorants - 2 weeks Lugol solution - 3 weeks saturated solution of potassium iodine - 3 weeks vitamins - 10-14 days iodide-containing X-ray contrast agents - up to 1 year lithium - 4 weeks phenylbutazone - 1-2 weeks sulfonamides - 1 week thyroid hormones (natural or synthetic), e.g.: thyroxine - 4 weeks tri-iodothyronine - 2 weeks tolbutamide - 1 week topical iodide - 1-9 months (1)

Agents That Affect Iodide/Sodium Iodide I 131

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Many compounds can affect iodide protein binding and alter iodide pharmacokinetics and pharmacodynamics.(1,2)

CLINICAL EFFECTS: Compounds that affect iodide pharmacokinetics and pharmacodynamics may impact the effectiveness of radioactive iodide.(1,2)

PREDISPOSING FACTORS: Compounds that affect iodide pharmacokinetics and pharmacodynamics are expected to have the most impact during therapy using radioactive iodide. Diagnostic procedures would be expected to be impacted less.

PATIENT MANAGEMENT: Discuss the use of agents that affect iodide pharmacokinetics and pharmacodynamics with the patient's oncologist.(1,2) Because indocyanine green contains sodium iodide, the iodine-binding capacity of thyroid tissue may be reduced for at least one week following administration. Do not perform radioactive iodine uptake studies for at least one week following administration of indocyanine green.(3) The manufacturer of iopamidol states administration may interfere with thyroid uptake of radioactive iodine and decrease therapeutic and diagnostic efficacy. Avoid thyroid therapy or testing for up to 6 weeks post administration of iopamidol.(4)

DISCUSSION: Many agents interact with radioactive iodine. The average duration of effect is: anticoagulants - 1 week antihistamines - 1 week anti-thyroid drugs, e.g: carbimazole, methimazole, propylthiouracil - 3-5 days corticosteroids - 1 week iodide-containing medications, e.g: amiodarone - 1-6 months expectorants - 2 weeks Lugol solution - 3 weeks saturated solution of potassium iodine - 3 weeks vitamins - 10-14 days iodide-containing X-ray contrast agents - up to 1 year lithium - 4 weeks phenylbutazone - 1-2 weeks sulfonamides - 1 week thyroid hormones (natural or synthetic), e.g.: thyroxine - 4 weeks tri-iodothyronine - 2 weeks tolbutamide - 1 week topical iodide - 1-9 months (1,2)

Selected Photosensitizers/Aminolevulinic Acid

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Aminolevulinic acid, anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides are all known photosensitizers.(1)

CLINICAL EFFECTS: Concurrent use of aminolevulinic acid in patients taking anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides may increase the risk of phototoxicity.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturer states that aminolevulinic acid should be avoided in patients receiving photosensitizers including anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides for 24 hours before and after administration of aminolevulinic acid.(1)

DISCUSSION: Because of the risk of increased photosensitivity, the US manufacturer states that aminolevulinic acid should be avoided in patients receiving photosensitizers including anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides for 24 hours before and after administration of aminolevulinic acid.(1)

Selected Photosensitizers/Methoxsalen

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Methoxsalen causes photosensitivity due to residual drug which is present in all parts of the skin from photopheresis. Anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides are other known photosensitizers.(1)

CLINICAL EFFECTS: Concurrent use of methoxsalen in patients taking anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides may increase the risk of phototoxicity.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturer of methoxsalen states that concurrent use of methoxsalen with anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides should be avoided.(1)

DISCUSSION: All patients who have received methoxsalen become photosensitive. It is unknown what the risk of photosensitivity reactions is when methoxsalen is used concurrently with other photosensitizing agents.(1)

Selected Photosensitizers/Porfimer

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Porfimer causes photosensitivity due to residual drug which is present in all parts of the skin. Anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides are other known photosensitizers.(1)

CLINICAL EFFECTS: Concurrent use of porfimer in patients taking anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides may increase the risk of phototoxicity.(1)

PREDISPOSING FACTORS: Patients with any hepatic impairment and patients with severe renal impairment have reduced drug elimination and may remain photosensitive for 90 days or longer.(1)

PATIENT MANAGEMENT: The US manufacturer of porfimer states that concurrent use of porfimer with photosensitizers including anthralin, coal tar and derivatives, fluoroquinolones, griseofulvin, organic staining dyes (such as methylene blue, rose bengal, or toluidine blue), phenothiazines, selected NSAIDs (such as diclofenac, ketoprofen, nabumetone, naproxen, piroxicam, and tiaprofenic acid), methotrexate, St. John's wort, sulfonamides, sulfonylureas, tetracyclines, and thiazides should be avoided.(1) Since the photosensitive effect of porfimer may persist for at least 30 days (and for 90 days in some patients), it would be prudent to avoid other photosensitizing agents for at least 30 days after administration of porfimer.

DISCUSSION: All patients who have received porfimer become photosensitive. It is unknown what the risk of photosensitivity reactions is when porfimer is used concurrently with other photosensitizing agents. When porfimer was used in clinical trials, photosensitivity reactions occurred in about 20% of cancer patients and in 69% of high-grade dysplasia in Barretts esophagus patients. Most of the reactions were mild to moderate erythema, but they also included swelling, pruritus, burning sensation, feeling hot, or blisters. The majority of reactions occurred within 90 days of porfimer administration.(1)

Sulfonamide Antibac; Trimethoprim/Methotrexate; Pralatrexate

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Sulfonamide antibacterials and/or trimethoprim may decrease the renal clearance of methotrexate and pralatrexate or produce a synergistically-induced folate deficiency. Sulfonamide antibacterials and/or trimethoprim may decrease protein binding of methotrexate.

CLINICAL EFFECTS: Concurrent use of sulfonamide antibacterials and/or trimethoprim may increase levels of and toxicity from methotrexate and pralatrexate, leading to increased risk of severe neurotoxicity, stomatitis, and myelosuppression, including neutropenia.

PREDISPOSING FACTORS: Risk factors for methotrexate or pralatrexate toxicity include: - High-dose oncology regimens - Impaired renal function, ascites, or pleural effusions

PATIENT MANAGEMENT: Concurrent use of sulfonamide antibiotics or trimethoprim with methotrexate or pralatrexate should be avoided. If coadministration cannot be avoided, closely monitor patients who are receiving concurrent therapy or patients who have recently finished methotrexate or pralatrexate therapy and who are beginning sulfonamide therapy for signs of toxicity, including bone marrow suppression, pancytopenia, thrombocytopenia, and stomatitis.

DISCUSSION: In one study in pediatric leukemia patients, concurrent administration of methotrexate and trimethoprim-sulfamethoxazole resulted in an increase in free methotrexate and a decrease in free methotrexate clearance. These changes resulted in a 66% increase in systemic exposure to methotrexate, although there were no significant changes in total methotrexate clearance or methotrexate half-life. In another study in pediatric leukemia patients, concurrent therapy with methotrexate and trimethoprim-sulfamethoxazole did not alter the intestinal absorption, degree of plasma protein binding, or average concentration of methotrexate. Case reports have documented methotrexate toxicities such as bone marrow hypoplasia, pancytopenia, thrombocytopenia, and stomatitis during concurrent therapy and during therapy with trimethoprim-sulfamethoxazole following the conclusion of methotrexate therapy. Some of these reports involved patients receiving low-dose methotrexate for rheumatoid arthritis. Methotrexate plasma protein binding and renal clearance have been shown to be decreased by the concurrent administration of sulfisoxazole. In a retrospective cohort study of 3204 adults taking low-dose methotrexate, the risk of all-cause hospitalization (Risk Ratio (RR) 1.49 (95% Confidence Interval (CI) 1.13-1.97) and infection (RR 2.78 (95% CI 1.30 - 5.95)) was higher in adults treated with trimethoprim-sulfamethoxazole (n=1602) than those treated with cephalosporins (n=1602). This interaction has also been reported in patients receiving concurrent methotrexate and trimethoprim without concurrent sulfamethoxazole.

Sulfonamide Antibact/Selected Anticoagulants (Vit K Antag)

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: The mechanism may involve several processes. Some sulfonamides, e.g. cotrimoxazole, sulfamethizole, sulfaphenazole, inhibit the CYP2C9 mediated metabolism of warfarin. Sulfonamides have also been shown to displace plasma protein bound warfarin. The use of sulfonamides may decrease vitamin-K producing bacteria in the gastrointestinal tract. Disease related factors such as fever, decreased oral intake and acute illness may also play a role in bleeding risk.

CLINICAL EFFECTS: Concurrent use of anticoagulants and sulfonamides may increase the risk for bleeding.

PREDISPOSING FACTORS: The risk for bleeding episodes may be greater in patients with disease-associated factors (e.g. thrombocytopenia). Drug associated risk factors include concurrent use of multiple drugs which inhibit anticoagulant/antiplatelet metabolism and/or have an inherent risk for bleeding (e.g. NSAIDs). Patients with a CYP2C9 intermediate metabolizer genotype, and/or 1-2 copies of a reduced function VKORC1 gene are expected to be more susceptible to this interaction. Although patients with a pre-existing CYP2C9 poor metabolizer genotype are expected to be less susceptible to effects from this drug combination, their reduced function genotypes (e.g. CYP2C9 *1/*3, *2/*2, *2/*3, and *3/*3) result in an inherently higher warfarin half-life and risk for warfarin-associated bleeding. CYP2C9 poor metabolizers generally require lower anticoagulant doses and more time (>2 to 4 weeks) to achieve effective and safe anticoagulation than patients without these CYP2C9 variants.

PATIENT MANAGEMENT: If concurrent therapy is warranted, monitor patients receiving concurrent therapy for signs of blood loss, including decreased hemoglobin, hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. Perform agent-specific laboratory test (e.g. INR) to monitor efficacy and safety of anticoagulation. Discontinue anticoagulation in patients with active pathologic bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling. The time of highest risk for a coumarin-type drug interaction is when the precipitant drug is initiated or discontinued. Contact the prescriber before initiating, altering the dose or discontinuing either drug.

DISCUSSION: Numerous studies and case reports have documented an interaction between warfarin and sulfamethoxazole/trimethoprim. The effects are generally seen within two to six days and may or may not be accompanied by increased warfarin concentrations. Case reports also document an interaction between warfarin and sulfisoxazole and sulfamethizole resulting in increased bleeding, warfarin half-life and decreased warfarin clearance rates. Because of the proposed mechanism, it is prudent to expect similar results during the concurrent administration of warfarin and other sulfonamides. A large systematic review was performed on 72 warfarin drug-drug interactions studies that reported on bleeding, thromboembolic events, or death. Most studies were retrospective cohorts. A meta-analysis of 11 of those studies found a higher rate of clinically significant bleeding in patients on warfarin and antimicrobials (OR=1.63; 95% CI 1.45-1.83). Increased bleeding risk was also seen in subgroup analyses with sulfonamides (OR=2.41; 95% CI 1.42-4.10).

Sulfonamides/Cyclosporine

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Both cyclosporine and sulfonamides can cause serum creatinine and BUN elevations and nephrotoxicity.(1,2)

CLINICAL EFFECTS: Coadministration of sulfonamides and cyclosporine may produce additive nephrotoxicity.(1,2)

PREDISPOSING FACTORS: The risk of nephrotoxicity is higher with elderly patients and increasing doses of cyclosporine.

PATIENT MANAGEMENT: The manufacturer of trimethoprim/sulfamethoxazole states that concurrent use of cyclosporine should be avoided.(1) The manufacturer of cyclosporine states that concurrent use of drugs that may cause additive or synergistic renal impairment should be approached with caution. Renal function (especially serum creatinine) should be closely monitored. In all patients treated with cyclosporine, renal function should be assessed repeatedly by measurement of serum creatinine and BUN.(2)

DISCUSSION: It is not unusual for cyclosporine to cause elevations in serum creatinine and BUN.(2) There have been reports of marked but reversible nephrotoxicity with coadministration of trimethoprim/sulfamethoxazole (TMP/SMX) and cyclosporine in renal transplant patients.(1,3-4) A double-blind controlled trial of 132 renal transplant recipients on cyclosporine and randomized for prophylactic TMP/SMX therapy found that patients on TMP/SMX had 15% higher serum creatinine than control patients (p<0.01). However, the difference reflected trimethoprim inhibition of tubular excretion of creatinine and was reversible. There was no evidence that TMP/SMX augmented nephrotoxicity.(5)

Moderate Interaction: Assess the risk to the patient and take action as needed.

Selected Sulfonamide Antibacterials; Trimethoprim/Hydantoins

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Trimethoprim and selected sulfonamides may inhibit the CYP2C9 mediated metabolism of phenytoin and possibly other hydantoins.

CLINICAL EFFECTS: Concurrent use of trimethoprim or selected sulfonamides may result in elevated levels of and toxicity from the hydantoin. Phenytoin has a narrow therapeutic range. Early symptoms of phenytoin toxicity may include nystagmus, ataxia, dysarthria, tremor, hyperreflexia, lethargy, slurred speech, blurred vision, nausea, and vomiting. Severe toxicity may produce organ dysfunction (e.g. coma, irreversible cerebellar dysfunction and atrophy, hypotension, bradycardia, seizures, and cardiac arrest) and may be fatal.

PREDISPOSING FACTORS: Renal impairment, hepatic impairment, or hypoalbuminemia.

PATIENT MANAGEMENT: Monitor the patient for signs of hydantoin toxicity (e.g. nystagmus, ataxia, dysarthria, tremor, hyperreflexia, lethargy, slurred speech, blurred vision, nausea, and vomiting). If available, monitor hydantoin serum levels. Adjust the dose of hydantoins if needed.

DISCUSSION: In a case-control cohort study, elderly patients hospitalized due to phenytoin toxicity were more than twice as likely to have had concurrent use of trimethoprim-sulfamethoxazole in the previous 30 days (729 subjects) as compared to concurrent use of amoxicillin in the previous 30 days (3148 subjects). The adjusted odds ratio was 2.11 with a 95% CI of 1.24, 3.60. In another study, concurrent administration of phenytoin and trimethoprim as well as phenytoin and trimethoprim-sulfamethoxazole have been reported to increase the half-life of phenytoin by 50% and 39%, respectively. Concomitant administration of phenytoin with sulfamethoxazole alone produced small increases in the half-life of phenytoin. The severity of this interaction appears to vary with the different sulfonamides and is subject to large individual variability.

Sulfonamide Antibacterials/Paba

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Sulfonamide antibacterials are structurally similar to PABA (p-aminobenzoic acid). PABA is an essential precursor for synthesis of tetrahydrofolate. Sulfonamides competitively inhibit utilization of PABA and therefore disrupt tetrahydrofolate biosynthesis. Supplementation with PABA antagonizes sulfonamide antibacterials.

CLINICAL EFFECTS: Reduced antibacterial effectiveness of sulfonamides with concomitant use.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid concomitant administration of these drugs.

DISCUSSION: This interaction is well documented.

There is no enhanced messaging for this drug.

• Hemolytic anemia from pyruvate kinase and g6PD deficiencies
• Lactation
• Pregnancy- third trimester

• Blood dyscrasias
• Disease of liver
• Folic acid deficient megaloblastic anemia
• Porphyria

• Kidney disease with reduction in glomerular filtration rate (GFr)

There is no enhanced messaging for this drug.

More Frequent

• Drug fever
• Skin photosensitivity

Less Frequent

• Hepatitis

Rare or Very Rare

• Acidosis
• Acute generalized exanthematous pustulosis
• Acute respiratory failure
• Agranulocytosis
• Alveolitis
• Anaphylaxis
• Angioedema
• Anuria
• Aplastic anemia
• Behcet syndrome
• Cauda equina syndrome
• Clostridioides difficile infection
• Crystalluria
• Cyanosis
• DRESS syndrome
• Dyspnea
• Enterocolitis
• Eosinophilia
• Eosinophilic pneumonia
• Erythema multiforme
• Erythema nodosum
• Exfoliative dermatitis
• Gastrointestinal hemorrhage
• Glucose-6-phosphate dehydrogenase (g6Pd) deficiency anemia
• Goiter
• Granulocytopenic disorder
• Guillain-barre syndrome
• Hematuria
• Hemolytic anemia
• Hemolytic uremic syndrome
• Hemophagocytic lymphohistiocytosis
• Hepatic necrosis
• Hepatocellular damage
• Hypofibrinogenemia
• Hyponatremia
• Hypoprothrombinemia
• Hypothyroidism
• IgA vasculitis
• Interstitial lung disease
• Interstitial nephritis
• Intracranial hypertension
• Leukopenia
• Lupus-like syndrome
• Megaloblastic anemia
• Methemoglobinemia
• Myelodysplastic syndrome
• Myocarditis
• Neutropenic disorder
• Oliguria
• Pancreatitis
• Pericarditis
• Periorbital edema
• Pleuritis
• Polyarteritis nodosa
• Proteinuria
• Pulmonary infiltrates
• Renal tubular acidosis
• Renal tubular necrosis
• Seizure disorder
• Serum sickness
• Shock
• Stevens-johnson syndrome
• Sweet's syndrome
• Thrombocytopenic disorder
• Thrombotic thrombocytopenic purpura
• Toxic epidermal necrolysis
• Urolithiasis
• Vasculitis

More Frequent

• Anorexia
• Diarrhea
• Dizziness
• Headache disorder
• Lethargy
• Nausea
• Pruritus of skin
• Skin rash
• Vomiting

Rare or Very Rare

• Acute abdominal pain
• Acute cognitive impairment
• Alopecia
• Arthralgia
• Ataxia
• Black tarry stools
• Chills
• Cough
• Depression
• Drowsy
• Drug-induced psychosis
• Fatigue
• Flatulence
• Gastroenteritis
• General weakness
• Glossitis
• Hallucinations
• Hearing loss
• Hypoglycemic disorder
• Indifference
• Insomnia
• Nervousness
• Paresthesia
• Peripheral neuropathy
• Stomatitis
• Symptoms of anxiety
• Tinnitus
• Urticaria
• Uveitis
• Vertigo

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