How well are commonly used antibacterial agents actually absorbed from the GI tract?

Recent trend toward earlier transition from parenteral to oral antibacterials in many conditions, such as pneumonia and urinary tract infections, makes it imperative for clinicians to be familiar with the bioavailability of commonly used agents (1,2).

Agent                                                                                Absorption (%)

__________________________________________________________________________________________________________________________________________________________________________________

Amoxacillin                                                                         74-92

Amoxacillin/clavulanate (Augmentin®)                  60

Azithromycin (Zithromax®)                                         37

Cefpodoxime (Vantin®)                                                 30-50

Cefuroxime axetil (Ceftin®)                                         30-52

Cephalexin (Keflex®)                                                     90-100

Clindamycin (Cleocin®)                                                  90

Ciprofloxacin (Cipro) ®                                                   70

Doxycycline                                                                     >90 with food

Levofloxacin (Levaquin®)                                             >90

Metronidazole (Flagyl®)                                                 80

Moxifloxacin (Avelox®)                                                 88

Trimethoprim-sulfamethoxazole (Bactrim®)        70-90

 _________________________________________________________________________________________________________________________________________________________________________

It’s worth noting that the aborption of fluoroquinolones (e.g. ciprofloxacin, levofloxacin, and moxifloxacin) is reduced by concurrent administration with magnesium-aluminum antacids and sucralfate, and in decreasing order, iron, calcium and zinc (3). Spacing the doses of these agents from potential interacting agents is advised.

 

References

  1. Zhanel GG, Walkty A, Vercagine L, et al. The new fluoroquinolones: a critical review. Can J Infect Dis 1999;3:207-38.
  2. MacGregor RR, Graziani AL. Oral administration of antibiotics: a rational alternative to the parenteral route. Clin Infec Dis 1997;24:457-67. 
  3. Lomaestro BM, Bailie GR. Absorption interactions with fluoroquinolone:1995 update. Drug Safety 1995;12:314-33.

 

How well are commonly used antibacterial agents actually absorbed from the GI tract?

What is the clinical utility of neck stiffness, Kernig’s sign and Brudzinski’s sign in the evaluation of patients suspected of having meningitis?

The sensitivity of these signs for meningitis is poor: neck stiffness 30% and Kernig’s and Brudzinski’s signs 5% each (1).  Therefore, their absence does not exclude the possibility of meningitis. Although their specificities may be comparatively better (neck stiffness 68%, and Kernig’s and Brudzinski’s signs 95% each), the positive and negative predictive values of these signs generally leave a lot to be desired and their likelihood ratios (both positive and negative) are poor (near 1.0) (1).  

The poor sensitivities of Kernig’s and Brudzinski’s signs may be related to the fact that the original research papers published over 100 years ago involved primarily children with severe bacterial or tuberculous meningitis, a population that is quite different than today’s elderly or immunocompromised patients (2) who may present earlier during their course of disease. Thus, the decision to perform a lumbar puncture should be based primarily on factors other than these signs.

 References

  1. Thomas KE, Hasbun R, Jekel J, et al. The diagnostic accuracy of Kernig’s sign, Brudzinski’s sign, and nuchal rigidity in adults with suspected meningitis. Clin Infec Dis 2002;35:46-52.
  2. Mehndiratta M, Nayak R, Garg H, et al. Appraisal of Kernig’s and Brudzinski’s sign in meningitis. Ann Indian Acad Neurol. 2012 Oct-Dec; 15(4): 287–288.
What is the clinical utility of neck stiffness, Kernig’s sign and Brudzinski’s sign in the evaluation of patients suspected of having meningitis?