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required enzyme, dihydrofolate reductase. This binding is very much a Trimethoprim very medium-dependent.
PRIMSOL (trimethoprim hydrochloride oral solution) is a solution of the stronger for the bacterial enzyme than for the corresponding mam- b Range applicable only to tests performed by broth microdilution synthetic antibacterial trimethoprim in water prepared with the aid of malian enzyme. Thus, trimethoprim selectively interferes with bacterial method using Haemophilus Test Medium (HTM).1 hydrochloric acid. Each 5 mL for oral administration contains trimetho- biosynthesis of nucleic acids and proteins.
prim hydrochloride equivalent to 50 mg trimethoprim and the inactive Range applicable only to tests performed by broth microdilution Trimethoprim has been shown to be active against most strains of the ingredients bubble gum flavor, fructose, glycerin, methylparaben, method using cation-adjusted Mueller-Hinton broth with 2 to 5% following microorganisms, both in vitro and in clinical infections as monoammonium glycyrrhizinate, povidone, propylparaben, propylene described in the INDICATIONS AND USAGE section.
glycol, saccharin sodium, sodium benzoate, sorbitol, water and hydrochloric acid and/or sodium hydroxide to adjust pH to a range of Aerobic gram-positive microorganisms
Quantitative methods that require measurement of zone diameters also 3.0 - 5.0. Trimethoprim is 2,4-diamino-5-(3,4,5-trimethoxybenzyl) (coagulase-negative strains, including S. provide reproducible estimates of the susceptibility of bacteria to pyrimidine. Trimethoprim is a white to cream-colored, odorless, bitter antimicrobial compounds. One such standardized procedure2 requires compound with a molecular formula of C14H18N4O3 and a molecular Streptococcus pneumoniae (penicillin-susceptible strains) the use of standardized inoculum concentrations. This procedure uses weight of 290.32 and the following structural formula: paper disks impregnated with 5 mcg trimethoprim to test the suscepti- Aerobic gram-negative microorganisms
bility of microorganisms to trimethoprim.
Reports from the laboratory providing results of the standard single- (excluding beta-lactamase negative, ampicillin disk susceptibility test with a 5 mcg trimethoprima disk should be interpreted according to the following criteria: For testing aerobic microorganisms isolated from urinary tract infec- NOTE: Moraxella catarrhalis isolates were found consistently resistant Susceptibility Tests
CLINICAL PHARMACOLOGY
Trimethoprim is rapidly absorbed following oral administration. It exists For testing Haemophilus influenzae b: in the blood as unbound, protein-bound and metabolized forms. Ten to Quantitative methods are used to determine antimicrobial minimum twenty percent of trimethoprim is metabolized, primarily in the liver; inhibitory concentrations (MIC’s). These MIC’s provide estimates of the the remainder is excreted unchanged in the urine. The principal susceptibility of bacteria to antimicrobial compounds. The MIC’s should metabolites of trimethoprim are the 1- and 3-oxides and the 3′- and 4′- be determined using a standardized procedure. Standardized proce- hydroxy derivatives. The free form is considered to be the therapeuti- dures are based on a dilution method1 (broth or agar) or equivalent cally active form. Approximately 44% of trimethoprim is bound to plas- with standardized inoculum concentrations and standardized concen- trations of trimethoprim powder. The MIC values should be interpreted Blood-containing media (except for lysed horse blood) are generally not suitable for testing trimethoprim. Mueller-Hinton agar should be Mean peak plasma concentrations of approximately 1 mcg/mL occur 1 checked for excessive levels of thymidine. To determine whether to 4 hours after oral administration of a single 100 mg dose. A single For testing aerobic microorganisms isolated from urinary tract infec- Mueller-Hinton medium has sufficiently low levels of thymidine and 200 mg dose will result in plasma concentrations approximately twice thymine, an Enterococcus faecalis (ATCC 29212 or ATCC 33186) as high. The mean half-life of trimethoprim is approximately 9 hours.
may be tested with trimethoprim/sulfamethoxazole disks. A zone of However, patients with severely impaired renal function exhibit an inhibition ≥20 mm that is essentially free of fine colonies indicates a increase in the half-life of trimethoprim, which requires either dosage sufficiently low level of thymidine and thymine.
regimen adjustment or not using the drug in such patients (see Interpretive criteria applicable only to tests performed by disk DOSAGE AND ADMINISTRATION section). During a 13-week study of When testing Haemophilus influenzae a diffusion method using Haemophilus Test Medium (HTM).2 trimethoprim tablets administered at a dosage of 50 mg q.i.d., themean minimum steady-state concentration of the drug was 1.1 mcg/mL. Steady-state concentrations were achieved within two to three Diffusion techniques are not recommended for determining susceptibil- days of chronic administration and were maintained throughout the ity of Streptococcus pneumoniae to trimethoprim.
Interpretation should be as stated above for results using dilution tech- Excretion of trimethoprim is primarily by the kidneys through glomeru- When testing Streptococcus pneumoniae b niques. Interpretation involves correlation of the diameter obtained in lar filtration and tubular secretion. Urine concentrations of trimetho- the disk test with the MIC for trimethoprim.
prim are considerably higher than are the concentrations in the blood.
After a single oral dose of 100 mg, urine concentrations of trimetho- As with standardized dilution techniques, diffusion methods require the Dye-free, alcohol-free, flavored solution, prim ranged from 30 to 160 mcg/mL during the 0- to 4-hour period use of laboratory control microorganisms that are used to control the (trimethoprim hydrochloride oral solution technical aspects of the laboratory procedures. For the diffusion tech- Solution
and declined to approximately 18 to 91 mcg/mL during the 8- to 24- Interpretive criteria applicable only to tests performed by broth hour period. A 200 mg single oral dose will result in trimethoprim urine nique, the 5 mcg trimethoprima disk should provide the following zone microdilution method using Haemophilus Test Medium (HTM).1 concentrations approximately twice as high. After oral administration, diameters in this laboratory test quality control strain: 50% to 60% of trimethoprim is excreted in the urine within 24 hours, Interpretive criteria applicable only to tests performed by broth approximately 80% of this being unmetabolized trimethoprim.
microdilution method using cation-adjusted Mueller-Hinton brothwith 2 to 5% lysed horse blood.1 Trimethoprim half-life, clearance, and volume of distribution vary with Haemophilus influenzae b ATCC 49247 age. Excluding newborns, an apparent trend of increasing half-life, vol- A report of “Susceptible” indicates that the pathogen is likely to be ume of distribution, and decreasing clearance is observed with increas- inhibited if the antimicrobial compound in the blood reaches the con- centrations usually achievable. A report of “Intermediate” indicates that Blood-containing media (except for lysed horse blood) are generally the result should be considered equivocal, and, if the microorganism is not suitable for testing trimethoprim. Mueller-Hinton agar should be Since normal vaginal and fecal flora are the source of most pathogens not fully susceptible to alternative, clinically feasible drugs, the test checked for excessive levels of thymidine. To determine whether causing urinary tract infections, it is relevant to consider the distribu- should be repeated. This category implies possible clinical applicability Mueller-Hinton medium has sufficiently low levels of thymidine and tion of trimethoprim into these sites. Concentrations of trimethoprim in in body sites where the drug is physiologically concentrated or in situa- thymine, an Enterococcus faecalis (ATCC 29212 or ATCC 33186) vaginal secretions are consistently greater than those found simultane- tions where high dosage of drug can be used. This category also pro- may be tested with trimethoprim/sulfamethoxazole disks. A zone of ously in the serum, being typically 1.6 times the concentrations of vides a buffer zone which prevents small uncontrolled technical factors inhibition ≥20 mm that is essentially free of fine colonies indicates a simultaneously obtained serum samples. Sufficient trimethoprim is from causing major discrepancies in interpretation. A report of sufficiently low level of thymidine and thymine.
excreted in the feces to markedly reduce or eliminate trimethoprim- “Resistant” indicates that the pathogen is not likely to be inhibited if the susceptible organisms from the fecal flora. The dominant non- Range applicable only to tests performed by disk diffusion method antimicrobial compound in the blood reaches the concentrations usual- Enterobacteriaceae fecal organisms, Bacteroides spp. and Lactobacillus using Haemophilus Test Medium (HTM).2 ly achievable; other therapy should be selected.
spp., are not susceptible to trimethoprim concentrations obtained with Primsol® Solution
Standardized susceptibility test procedures require the use of laborato- Diffusion techniques are not recommended for determining susceptibil- (trimethoprim hydrochloride oral solution) ry control microorganisms to control the technical aspects of the labo- Trimethoprim also concentrates into middle ear fluid (MEF) very effi- ity of Streptococcus pneumoniae to trimethoprim.
Dye-free, alcohol-free, flavored solution, ratory procedures. Standard trimethoprima powder should provide the ciently. In a study in children aged 1 to 12 years, administration of a INDICATIONS AND USAGE
single 4 mg/kg dose resulted in a mean peak MEF concentration of 2.0 PRIMSOL Solution is indicated for the treatment of infections caused by susceptible strains of the designated microorganisms in the condi- Trimethoprim also passes the placental barrier and is excreted in breast Pediatric Patients:
Microbiology: Trimethoprim blocks the production of tetrahydrofolic
Streptococcus pneumoniae c ATCC 49619 acid from dihydrofolic acid by binding to and reversibly inhibiting the Acute Otitis Media: For the treatment of acute otitis media due to
susceptible strains of Streptococcus pneumoniae and Haemophilus Drug Interactions: PRIMSOL may inhibit the hepatic metabolism of
phenytoin. Trimethoprim, given at a common clinical dosage, increasedthe phenytoin half-life by 51% and decreased the phenytoin metabolic NOTE: Moraxella catarrhalis isolates were found consistently resistant
clearance rate by 30%. When administering these drugs concurrently, to trimethoprim in vitro. Therefore, when infection with Moraxella one should be alert for possible excessive phenytoin effect.
atric patients following treatment with PRIMSOL or sulfamethoxazole + catarrhalis is suspected, the use of alternative antimicrobial agents Drug/Laboratory Test Interactions: Trimethoprim can interfere with a
should be considered. PRIMSOL is not indicated for prophylactic or serum methotrexate assay as determined by the competitive binding Adverse Reactions Reported For Trimethoprim: REFERENCES
prolonged administration in otitis media at any age. protein technique (CBPA) when a bacterial dihydrofolate reductase is In addition to the adverse events listed above which have been National Committee for Clinical Laboratory Standards. Methods for Dilution Antimicrobial used as the binding protein. No interference occurs, however, if observed in pediatric patients receiving PRIMSOL, the following adverse Susceptibility Tests for Bacteria that Grow Aerobically --Third Edition. Approved Standard methotrexate is measured by a radioimmunoassay (RIA).
NCCLS Document M7-A3, Vol. 13, No. 25, NCCLS, Villanova, PA, December, 1993.
Urinary Tract Infections: For the treatment of initial episodes of uncom-
reactions and altered laboratory tests have been previously reported for National Committee for Clinical Laboratory Standards. Performance Standards for plicated urinary tract infections due to susceptible strains of the follow- The presence of trimethoprim may also interfere with the Jaffé alkaline trimethoprim and, therefore, may occur with PRIMSOL therapy: Antimicrobial Disk Susceptibility Tests - Fifth Edition. Approved Standard NCCLS ing organisms: Escherichia coli, Proteus mirabilis, Klebsiella pneumoni- picrate reaction assay for creatinine resulting in overestimations of Dermatologic reactions: pruritus and exfoliative dermatitis. At the rec- Document M2-A5, Vol. 13, No. 24, NCCLS, Villanova, PA, December, 1993.
ae, Enterobacter species and coagulase-negative Staphylococcus about 10% in the range of normal values.
ommended adult dosage regimens of 100 mg b.i.d., or 200 mg q.d., Brumfitt W, Pursell R: Trimethoprim/Sulfamethoxazole in the Treatment of Bacteriuria inWomen, J Infect Dis 128 (suppl): S657-S663, 1973.
species, including S. saprophyticus.
each for 10 days, the incidence of rash is 2.9% to 6.7%. In clinical Carcinogenesis, Mutagenesis, Impairment of Fertility: Long-term
Cultures and susceptibility tests should be performed to determine the studies which employed high doses of trimethoprim in adults, an elevat- studies in animals to evaluate carcinogenic potential have not been con- susceptibility of the bacteria to trimethoprim. Therapy may be initiated ed incidence of rash was noted. These rashes were maculopapular, ducted with trimethoprim. Trimethoprim was demonstrated to be non- prior to obtaining the results of these tests.
morbilliform, pruritic and generally mild to moderate, appearing 7 to 14 mutagenic in the Ames assay. No chromosomal damage was observed days after the initiation of therapy.
TaroPharma
in human leukocytes cultured in vitro with trimethoprim; the concentra- a division of Taro Pharmaceuticals U.S.A., Inc.
CLINICAL STUDIES
tion used exceeded blood levels following therapy with PRIMSOL. No Gastrointestinal reactions: Epigastric distress, nausea, and glossitis.
The results of one multicenter, 30-day, comparative, randomized clinical adverse effects on fertility or general reproductive performance were Hematologic reactions: Thrombocytopenia, leukopenia, neutropenia, trial without tympanocentesis in 262 pediatric patients with acute otitis by Lyne Laboratories, Inc., Brockton, MA 02301 observed in rats given trimethoprim in oral dosages as high as 70 megaloblastic anemia and methemoglobinemia. media (AOM) are shown below. In this clinical trial, strict evaluability mg/kg/day for males and 14 mg/kg/day for females.
Metabolic reactions: Hyperkalemia, hyponatremia.
criteria were used to determine clinical response.
Pregnancy:
Miscellaneous reactions: Fever, elevation of serum transaminase and Primsol® is a registered trademark of Ascent Pediatrics, Inc. used under license by Taro Pharmaceuticals U.S.A., Inc.
Teratogenic Effects: Pregnancy Category C. Trimethoprim has been bilirubin, and increases in BUN and serum creatinine levels.
shown to be teratogenic in the rat when given in doses 40 times the OVERDOSAGE
human dose. In some rabbit studies, the overall increase in fetal loss Acute: Signs of acute overdosage with trimethoprim may appear follow-
(dead and resorbed and malformed conceptuses) was associated with ing ingestion of 1 gram or more of the drug and include nausea, vomit- doses 6 times the human therapeutic dose.
ing, dizziness, headaches, mental depression, confusion and bone mar- While there are no large well-controlled studies on the use of trimetho- row depression (see OVERDOSAGE-Chronic).
prim in pregnant women, Brumfitt and Pursell,3 in a retrospective study, Treatment consists of gastric lavage and general supportive measures.
reported the outcome of 186 pregnancies during which the mother Acidification of the urine will increase renal elimination of trimethoprim.
received either placebo or trimethoprim in combination with sul- Peritoneal dialysis is not effective and hemodialysis only moderately famethoxazole. The incidence of congenital abnormalities was 4.5% (3 of 66) in those who received placebo and 3.3% (4 of 120) in those Chronic: Use of trimethoprim at high doses and/or for extended periods
receiving trimethoprim plus sulfamethoxazole. There were no abnormal- *sulfamethoxazole + trimethoprim oral suspension of time may cause bone marrow depression manifested as thrombocy- ities in the 10 children whose mothers received the drug during the first topenia, leukopenia and/or megaloblastic anemia. If signs of bone mar- The results of an uncontrolled 30-day trial with tympanocentesis in 120 trimester. In a separate survey, Brumfitt and Pursell also found no con- row depression occur, trimethoprim should be discontinued and the pediatric patients with AOM are shown below: genital abnormalities in 35 children whose mothers had received patient should be given leucovorin, 3 to 6 mg intramuscularly daily for trimethoprim plus sulfamethoxazole at the time of conception or shortly three days, or as required to restore normal hematopoiesis.
Because trimethoprim may interfere with folic acid metabolism, PRIM- DOSAGE AND ADMINISTRATION
SOL should be used during pregnancy only if the potential benefit justi- Acute Otitis Media in Pediatric Patients: The recommended dose for
fies the potential risk to the fetus.
pediatric patients with acute otitis media is 10 mg/kg trimethoprim per 24 hours, given in divided doses every 12 hours for 10 days. The fol- Nonteratogenic Effects: The oral administration of trimethoprim to rats lowing table is a guideline for the attainment of this dosage: at a dose of 70 mg/kg/day commencing with the last third of gestationand continuing through parturition and lactation caused no deleterious Pediatric patients 6 months of age or older: effects on gestation or pup growth and survival.
Nursing Mothers: Trimethoprim is excreted in human milk. Because
trimethoprim may interfere with folic acid metabolism, caution should be exercised when PRIMSOL is administered to a nursing woman.
Pediatric Use: The safety of trimethoprim has not been established in
pediatric patients below the age of 2 months. The effectiveness of Moraxella catarrhalis, isolated from five patients, was found consistently trimethoprim in the treatment of acute otitis media has not been estab- resistant to trimethoprim in vitro.
lished in patients below the age of 6 months.
CONTRAINDICATIONS
ADVERSE REACTIONS
PRIMSOL is contraindicated in individuals hypersensitive to trimetho- Adverse Events Reported During Pediatric Clinical Trials With PRIMSOL: prim and in those with documented megaloblastic anemia due to folate The following table lists those drug-related adverse events reported Uncomplicated Urinary Tract Infections: The usual oral adult dosage is
most frequently during the clinical trials in pediatric patients aged 6 100 mg (10 mL) every 12 hours or 200 mg (20 mL) every 24 hours, months to 12 years. Most of these events were determined to be mild.
WARNINGS
The incidence of drug-related adverse events was significantly lower for Patients with Impaired Renal Function: The use of trimethoprim in
Experience with trimethoprim alone is limited, but it has been reported PRIMSOL, which was most apparent for those events related to patients with a creatinine clearance of less than 15 mL/min is not rec- rarely to interfere with hematopoiesis, especially when administered in ommended. Patients with a creatinine clearance of 15 to 30 mL/min large doses and/or for prolonged periods.
should receive half the dose recommended for patients of the same age The presence of clinical signs such as sore throat, fever, pallor or pur- pura may be early indications of serious blood disorders.
HOW SUPPLIED
PRECAUTIONS
PRIMSOL (trimethoprim hydrochloride oral solution), dye-free, alcohol- General: Trimethoprim should be given with caution to patients with
free, bubble gum flavored, containing trimethoprim hydrochloride possible folate deficiency. Folates may be administered concomitantly equivalent to 50 mg of trimethoprim in each 5 mL: bottle of 473 mL without interfering with the antibacterial action of trimethoprim.
(1 pint). NDC 51672-5200-9. Store between 15˚-25˚C (59˚-77˚F).
Trimethoprim should also be given with caution to patients with Dispense in tight, light-resistant glass or PET plastic containers as impaired renal or hepatic function. If any clinical signs of a blood disor- der are noted in a patient receiving trimethoprim, a complete blood count should be obtained and the drug discontinued if a significantreduction in the count of any formed blood element is found.
*sulfamethoxazole + trimethoprim oral suspension An increase in lymphocytes and eosinophils was noted in some pedi-

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