Tetracyclines

Question 1

Classify the tetracyclines?

Answer 1

Short-acting: oxytetracycline, tetracycline
Intermediate-acting: Demeclocycline, Lymecycline
Long-acting: minocycline, doxycycline

Question 2

What is the MOA of tetracyclines?

Answer 2

Enter via passive diffusion/active transport. Binds reversibly to the 30s ribosomal subunit, inhibiting protein synthesis. Prevents binding of aminoacyl-tRNA into ribosomal aminoacyl acceptor site. Prevents codon-anticodon interactions

Question 3

List the mechanisms of resistance?

Answer 3

Decreased influx, increased efflux. Synthesis of proteins protecting ribosome. Enzyme inactivation

Question 4

What is absorption impaired by?

Answer 4

Food, divalent/trivalent cations, alkaline pH.

Question 5

What is special about the distribution of tetracyclines

Answer 5

Accumulate in bone, dentine and enamel of unerupted teeth.

Question 6

Other pharmacokinetic considerations?

Answer 6

Metabolism - most undergo hepatic metabolism and biliary excretion. When co-administered with liver enzyme inducers, decrease levels.
Majority are renally eliminated. 20%-60% excreted in urine in 24 hours.

Question 7

What are 4 adverse effects?

Answer 7

GIT effects (N,V,D), effects on bone and teeth (foetal teeth), renal toxicity (increase tetracyclines, vestibular reactions, photosensitivity reactions

Question 8

List the spectrum of activity

Answer 8

Gram +, gram - cocci, gram +, gram - rods, atypical bacteria, spirochetes.

Question 9

What are some clinical uses?

Answer 9

Effective for community-acquired pneumonia, vibrio cholerae, chlamydia trachomatis. Rickettsial, anthrax

Question 10

What is special about oral doxycycline administration?

Answer 10

Should be given with plenty of fluid, with the patient in an upright position

Question 11

What are some relative contraindications?

Answer 11

Children < 8 years of age.
Pregnancy
Breastfeeding
Allergic reaction
Renal insufficiency (except doxycyline)