Aminoglycosides (6 - 10)

1. Which statement about "once-daily" dosing with aminoglycosides is not accurate?

Dose adjustment is less important in renal dysfunction

It is convenient for outpatient treatment

Less nursing time is required for drug administration

Often fewer side effects than multiple (conventional) dosing regimens

Underdoing is less of a problem

In “once-daily dosing” with aminoglycosides, the selection of an appropriate dose is particularly critical in patients with renal insufficiency. The aminoglycosides are eliminated by the kidney in proportion to creatinine clearance. Knowledge of the degree of insufficiency, based on plasma creatinine (or BUN), is essential for estimation of the appropriate single daily dose of an aminoglycoside.

For more visit www.rimemcq.com

Explanation

In “once-daily dosing” with aminoglycosides, the selection of an appropriate dose is particularly critical in patients with renal insufficiency. The aminoglycosides are eliminated by the kidney in proportion to creatinine clearance. Knowledge of the degree of insufficiency, based on plasma creatinine (or BUN), is essential for estimation of the appropriate single daily dose of an aminoglycoside.

For more visit www.rimemcq.com

2. Regarding the toxicity of aminoglycosides which statement is accurate?

Gentamicin and tobramycin are the least likely to cause renal damage

Ototoxicity due to amikacin and gentamicin includes vestibular dysfunction, which is often irreversible

Ototoxicity is reduced if loop diuretics are used to facilitate the renal excretion of aminoglycoside antibiotics

Reduced blood creatinine is an early sign of aminoglycoside nephrotoxicity

Skin reactions are very rare following topical use of neomycin

Gentamicin and tobramycin are the most nephrotoxic aminoglycosides. The incidence of nephrotoxic effects with gentamicin is 2 to 3 times greater than the incidence of ototoxicity. With traditional dosage regimens, the first indication of potential nephrotoxicity is an increase in trough serum levels of aminoglycosides, which is followed by an increase in blood creatinine. Although aminoglycoside ototoxicity usually involves irreversible effects on vestibular function, hearing loss can also occur. Ototoxicity is enhanced by loop diuretics. Skin reactions are common with topical use of neomycin.

For more visit www.rimemcq.com

Explanation

Gentamicin and tobramycin are the most nephrotoxic aminoglycosides. The incidence of nephrotoxic effects with gentamicin is 2 to 3 times greater than the incidence of ototoxicity. With traditional dosage regimens, the first indication of potential nephrotoxicity is an increase in trough serum levels of aminoglycosides, which is followed by an increase in blood creatinine. Although aminoglycoside ototoxicity usually involves irreversible effects on vestibular function, hearing loss can also occur. Ototoxicity is enhanced by loop diuretics. Skin reactions are common with topical use of neomycin.

For more visit www.rimemcq.com

3. Your 23-year-old female patient is pregnant and has gonorrhea. The medical history includes anaphylaxis following exposure to amoxicillin. The most appropriate drug to use is

Azithromycin

Cefixime

Ceftriaxone

Ciprofloxacin

Doxycycline

All of the listed drugs have been used for the treatment of gonorrhea. Cephalosporins should be avoided in patients with a history of severe hypersensitivity to penicillins, and fluoroquinolones (see Chapter 46) should be avoided in pregnancy. Tetracyclines including doxycycline have been used in the past for gonorrhea, but not as single doses, and they too should be avoided in pregnancy.

For more visit www.rimemcq.com

Explanation

All of the listed drugs have been used for the treatment of gonorrhea. Cephalosporins should be avoided in patients with a history of severe hypersensitivity to penicillins, and fluoroquinolones (see Chapter 46) should be avoided in pregnancy. Tetracyclines including doxycycline have been used in the past for gonorrhea, but not as single doses, and they too should be avoided in pregnancy.

For more visit www.rimemcq.com

4. This drug has characteristics almost identical to those of gentamicin but has much weaker activity in combination with penicillin against enterococci.

Amikacin

Erythromycin

Netilmicin

Spectinomycin

Tobramycin

Tobramycin is almost identical to gentamicin in both its pharmacodynamic and pharmacokinetic properties. However, for reasons that are unclear, it is much less active than either gentamicin or streptomycin when used in combination with a penicillin in the treatment of enterococcal endocarditis.

For more visit www.rimemcq.com

Explanation

Tobramycin is almost identical to gentamicin in both its pharmacodynamic and pharmacokinetic properties. However, for reasons that are unclear, it is much less active than either gentamicin or streptomycin when used in combination with a penicillin in the treatment of enterococcal endocarditis.

For more visit www.rimemcq.com

5. A 76-year-old man is seen in a hospital emergency department complaining of pain in and behind the right ear. Physical examination shows edema of the external otic canal with purulent exudate and weakness of the muscles on the right side of the face. The patient informs the physician that he is a diabetic. Gram stain of the exudate from the ear shows many polymorphonucleocytes and gram-negative rods, and samples are sent to the microbiology laboratory for culture and drug susceptibility testing. A preliminary diagnosis is made of external otitis. At this point, which of the following is most appropriate?

Amikacin should be injected intramuscularly, and the patient should be sent home

Analgesics should be prescribed, but antibiotics should be withheld pending microbiological results

Oral cefaclor should be prescribed together with analgesics, and the patient should be sent home

The patient should be hospitalized, and treatment started with imipenem-cystatin

The patient should be hospitalized, and treatment started with gentamicin plus ticarcillin

The diabetic patient with external otitis is at special risk because of the danger of spread to the middle ear and possibly the meninges, so hospitalization is advisable, especially in the elderly. Likely pathogens include E coli and Pseudomonas aeruginosa, and coverage must be provided for these and possibly other gram-negative rods. The combination of an aminoglycoside plus a wider spectrum penicillin is most suitable in this case and is synergistic against many pseudomonas strains. Imipenem-cilastatin is also possible, but resistant strains of P aeruginosa have emerged during treatment. Cefaclor lacks antipseudomonal activity.

For more visit www.rimemcq.com

Explanation

The diabetic patient with external otitis is at special risk because of the danger of spread to the middle ear and possibly the meninges, so hospitalization is advisable, especially in the elderly. Likely pathogens include E coli and Pseudomonas aeruginosa, and coverage must be provided for these and possibly other gram-negative rods. The combination of an aminoglycoside plus a wider spectrum penicillin is most suitable in this case and is synergistic against many pseudomonas strains. Imipenem-cilastatin is also possible, but resistant strains of P aeruginosa have emerged during treatment. Cefaclor lacks antipseudomonal activity.

For more visit www.rimemcq.com