Antibiotic therapy

Question 1

what is the mechanism of action of TMS

Answer 1

Sulfonomides interrupt bacterial synthesis of folic acid from para-aminobenzoic acid by acting as a competitive inhibitor of the enzyme dihydropteroate synthetase

Alone, sulfonamides and trimethoprim are bacteriostatic, but the combination of these drugs results in a bactericidal antibiotic

Question 2

Explain why folates is necessary to cellular mechanism

Answer 2

Folate (Vitamine B9) is necessary for the cell to manufacture thymidine (the “T” nucleotide in DNA), especially during cellular division

Folate is also essential in RBC production

Question 3

What is the mechanism of action of trimethoprim

Answer 3

Trimethoprim acts in a similar manner to sulfonomides but “down-stream”
- It interferes with dihydrofolate reductase, which prevents the conversion of dihydrolic acid to tetrahydrolic acid (folinic acid)

Question 4

What are the indications of use

Answer 4

They are now less used than they tend to be

They are used in combination with clindamycin and/or pyrimethamine for treatment of Toxoplasma gondii infections

Because enteric bacteria manufacture large amounts of dihydrofolate reductase, these drugs tend to be less effective against these organisms thus minimal disruption to the normal gut flora

Question 5

What are the main pharmacokinetics facts of TMS

Answer 5

They are rapidly absorbed from the gut and have a high bioavailability

They are widely distributed in tissues, including the eye and CNS

They are metabolized by liver and eliminated by renal glomerular filtrations and tubular excretion

Question 6

What are the toxic effects of TMS

Answer 6

TMS is quite safe at normal doses but cats may be quite susceptible to the toxic side effects including anorexia, vomiting, azotemia, anemia and leukopenia
- cats can develop severe ptyalism if liquid or uncoated tablets are used

Bone marrow suppression associated with chronic overdoses may be treaated with folinic acid if severe

Allergic immune complex reactions and keratoconjunctivitis sicca, reported relatively frequently in dogs, do not seem to be a problem in cats