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Chapter 2The Pre-Travel Consultation

Interactions among Travel Vaccines & Drugs

Ilan Youngster, Elizabeth D. Barnett

Vaccines and medications are prescribed frequently in pre-travel consultations, and potential interactions between vaccines and medications, including those already taken by the traveler, must be considered. Although a comprehensive list of interactions is beyond the scope of this section, some of the more serious interactions of commonly used travel-related vaccines and medications are discussed here.


In general, concomitant administration of multiple vaccines, including live attenuated immunizations, is safe and effective. Administering a live-virus vaccine within 4 weeks after administration of another live-virus vaccine can decrease immunogenicity to the second administered vaccine. This observation has given rise to the recommendation that live-virus vaccines should be administered the same day or ≥4 weeks apart. If the 4-week span is not achievable, the second vaccine may be administered sooner to afford some protection, but it should be readministered ≥4 weeks later if the traveler is at continued risk. A recent study examining concurrent administration of the yellow fever vaccine with the measles-mumps-rubella (MMR) vaccine in 12-month-old children showed slightly reduced immunogenicity to yellow fever and mumps components, compared with responses following separate vaccination with MMR and yellow fever vaccine 30 days apart. The clinical significance of this finding is uncertain at present.

Chapter 4
Malaria Case Management Hotline

Health care providers needing assistance with the diagnosis or management of suspected cases of malaria, may call the CDC Malaria Hotline: 770-488-7788 or toll-free 1-855-856-4713 (M-F, 9am-5pm, Eastern Time). Clinicians needing emergency consultation after hours, call: 770-488-7100 and request to speak with a CDC Malaria Branch clinician.

Malaria Case Management Hotline

Health care providers needing assistance with the diagnosis or management of suspected cases of malaria, may call the CDC Malaria Hotline: 770-488-7788 or toll-free 1-855-856-4713 (M-F, 9am-5pm, Eastern Time). Clinicians needing emergency consultation after hours, call: 770-488-7100 and request to speak with a CDC Malaria Branch clinician.



Increase in the international normalized ratio has been reported when levofloxacin and warfarin are used concurrently. Concurrent administration of ciprofloxacin and antacids that contain magnesium or aluminum hydroxide may reduce bioavailability of ciprofloxacin. Ciprofloxacin decreases clearance of theophylline and caffeine; theophylline levels should be monitored when ciprofloxacin is used concurrently. Ciprofloxacin and other fluoroquinolones should not be used with tizanidine. Sildenafil should not be used in patients on ciprofloxacin, as concomitant use is associated with increased rates of adverse effects. Fluoroquinolones have no known interaction with antiretroviral agents, but concurrent use may increase levels of calcineurin inhibitors and fluoroquinolone levels, and use should reflect renal function.


Close monitoring for side effects of azithromycin is recommended when azithromycin is used with nelfinavir. Increased anticoagulant effects have been noted when azithromycin is used with warfarin; monitoring prothrombin time is recommended for people taking these drugs concomitantly. Additive QTc prolongation may occur when azithromycin is used with the antimalarial artemether, and concomitant therapy should be avoided. Drug interactions have been reported with macrolides and antiretroviral protease inhibitors, as well as efavirenz and nevirapine, and can increase risk of QTc prolongation. Concurrent use with macrolides may lead to increased levels of calcineurin inhibitors.


No clinically significant drug interactions have been reported to date with rifaximin. Although the drug induces CYP3A4 enzymes, studies of concurrent administration of rifaximin with midazolam, and with a single dose of the oral contraceptive ethinylestradiol and norgestimate, did not show changes in the pharmacokinetics of these drugs.



Acetazolamide produces alkaline urine that can increase the rate of excretion of barbiturates and salicylates and may potentiate salicylate toxicity, particularly if taking a high dose of aspirin. Decreased excretion of dextroamphetamine, anticholinergics, mecamylamine, ephedrine, mexiletine, or quinidine may also occur. Hypokalemia caused by corticosteroids may be potentiated by concurrent use of acetazolamide. Acetazolamide should not be given to patients taking the anticonvulsant topiramate, as concurrent use is associated with increased toxicity. Increased monitoring of cyclosporine, tacrolimus, and sirolimus is warranted if these drugs are given with acetazolamide. Concurrent administration of metformin and acetazolamide should be done with caution as there may be an additive risk for lactic acidosis.


Dexamethasone interacts with multiple classes of drugs. Using this drug to treat altitude illness may, however, be life-saving. Interactions may occur with dexamethasone and the following drugs and drug classes: macrolide antibiotics, anticholinesterases, anticoagulants, hypoglycemic agents, isoniazid, digitalis preparations, oral contraceptives, and phenytoin.


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  6. Kolawole JA, Mustapha A, Abdul-Aguye I, Ochekpe N, Taylor RB. Effects of cimetidine on the pharmacokinetics of proguanil in healthy subjects and in peptic ulcer patients. J Pharm Biomed Anal. 1999 Sep;20(5):737–43.
  7. Kollaritsch H, Que JU, Kunz C, Wiedermann G, Herzog C, Cryz SJ Jr. Safety and immunogenicity of live oral cholera and typhoid vaccines administered alone or in combination with antimalarial drugs, oral polio vaccine, or yellow fever vaccine. J Infect Dis. 1997 Apr;175(4):871–5.
  8. Nascimento Silva JR, Camacho LA, Siqueira MM, Freire Mde S, Castro YP, Maia Mde L, et al. Mutual interference on the immune response to yellow fever vaccine and a combined vaccine against measles, mumps and rubella. Vaccine. 2011 Aug 26;29(37):6327–34.
  9. Pappaioanou M, Fishbein DB, Dreesen DW, Schwartz IK, Campbell GH, Sumner JW, et al. Antibody response to preexposure human diploid-cell rabies vaccine given concurrently with chloroquine. N Engl J Med. 1986 Jan 30;314(5):280–4.
  10. Projean D, Baune B, Farinotti R, Flinois JP, Beaune P, Taburet AM, et al. In vitro metabolism of chloroquine: identification of CYP2C8, CYP3A4, and CYP2D6 as the main isoforms catalyzing N-desethylchloroquine formation. Drug Metab Dispos. 2003 Jun;31(6):748–54.
  11. Ridtitid W, Wongnawa M, Mahatthanatrakul W, Raungsri N, Sunbhanich M. Ketoconazole increases plasma concentrations of antimalarial mefloquine in healthy human volunteers. J Clin Pharm Ther. 2005 Jun;30(3):285–90.
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