L2 | Urinary Antiseptics

Question 1

What are the most common organisms causing UTIs?

Answer 1

Most to least:
1. E.coli
2. S.saprophyticus
3. K.pneumonae
4. Proteus Mirabilis

Question 2

What are some drugs within this class of medications?

Answer 2

1. Nitrofurantoin (synthetic antibiotic)
2. Methenamine
3. Nalidixic Acid (quinolone derivative, not used with Nitrofurantoin, can cause hemolysis in pts with G6PD)
4. Mandelic Acid (causes acidification of urine, used with methenamine)

Question 3

What are the pharmacokinetics of Nitrofurantoin?

Answer 3

1. It’s well absorbed after being taken orally
2. It’s concentrated in urine
3. It works best in acidic environments

Question 4

What are the classes of bacteria that Nitrofurantoin works against?

Answer 4

It works against a variety of organisms including:
1. E.coli
2. Gram positive organisms

• Gram negative organisms can be resistant to it except pseudomonas
• bacteria that are susceptible to it don’t usually develop resistance during therapy.

Question 5

What are the indications of Nitrofurantoin?

Answer 5

It’s used for the prophylaxis of lower UTI’s
- it’s safe to use during pregnancy except when it’s term, because it can cause neonatal hemolysis.

Question 6

What are the adverse effects of Nitrofurantoin?

Answer 6

1. GI Upset (nausea and vomiting: can be avoided by using macrocrystalline preparations.
2. Diarrhea
3. Peripheral neuritis
4. Allergic reactions (skin rash, urticaria, pulmonary infiltration)
5. Chronic use: interstitial pulmonary fibrosis esp. in elderly

Question 7

what are the contraindications of Nitrofurantoin?

Answer 7

1. Significant renal impairment: renders the drug more toxic and less useful.
2. Pregnancy: term ( > 38 weeks)
3. Hemolytic anemia in patients with G6PD.

Question 8

What are the pharmacokinetics of methenamine?

Answer 8

• it’s well absorbed after being administered orally
• it’s metabolized in the liver and excreted in urine
• it works best in acidic environments (5.5 or less in urine)
• after it’s metabolized, its active form — formaldehyde — which has antiseptic activity accumulates in urine and is toxic to bacteria
• bacteria can’t develop resistance to formaldehyde

Question 9

What are the type of organisms that methenamine works against?

Answer 9

It works best against E.coli although it can work against other organisms as well.

Urea-splitting organisms like proteus species can develop resistance to it

Question 10

What are the adverse effects of methenamine?

Answer 10

1. GI upset
2. Higher doses: albuminuria, hematuria and rash

Question 11

what are the contraindications of methenamine?

Answer 11

1. Hepatic insufficiency
2. Renal insufficiency (mandelic acid may precipitate)

Question 12

what are the drug interactions of methenamine?

Answer 12

1. Should not be taken with sodium bicarbonate antacids.
2. Should not be taken with sulfonamides since they react with formaldehyde which increases the risk of crystaluria