▶Monoamine-oxidase A and B inhibitors, irreversibleare
predicted to decrease the antihypertensive effects of
guanethidine. Avoid and for 14 days after stopping the MAOI.
rTheoretical→Also seeTABLE 8p. 848
▶Phenothiazinesare predicted to decrease the antihypertensive
effects ofguanethidine.oTheoretical→Also seeTABLE 8
p. 848
▶Guanethidineis predicted to increase the effects of
sympathomimetics, inotropic(dopamine).rTheoretical
▶Guanethidineis predicted to increase the effects of
sympathomimetics, vasoconstrictor(adrenaline/epinephrine,
noradrenaline/norepinephrine).oStudy
▶Guanethidineincreases the effects ofsympathomimetics,
vasoconstrictor(metaraminol).rAnecdotal
▶Guanethidineincreases the effects ofsympathomimetics,
vasoconstrictor(phenylephrine).rStudy
▶Tricyclic antidepressantsare predicted to decrease the
antihypertensive effects ofguanethidine.oStudy→Also
seeTABLE 8p. 848
Guanfacine→seeTABLE 8p. 848 (hypotension),TABLE 11p. 849 (CNS
depressant effects)
▶Antiarrhythmics(dronedarone)are predicted to increase the
concentration ofguanfacine. Adjustguanfacinedose,p. 231.
oTheoretical
▶Antiepileptics(carbamazepine, fosphenytoin, phenobarbital,
phenytoin, primidone)are predicted to decrease the
concentration ofguanfacine. Adjustguanfacinedose,p. 231.
oStudy→Also seeTABLE 11p. 849
▶Antiepileptics(oxcarbazepine)are predicted to decrease the
concentration ofguanfacine. Monitor and adjustguanfacine
dose,p. 231.oTheoretical
▶Guanfacineincreases the concentration ofantiepileptics
(valproate). Monitor and adjust dose.oStudy
▶Antifungals, azoles(fluconazole, isavuconazole, posaconazole)
are predicted to increase the concentration ofguanfacine.
Adjustguanfacinedose,p. 231.oTheoretical
▶Antifungals, azoles(itraconazole, ketoconazole, voriconazole)are
predicted to increase the exposure toguanfacine. Adjust
guanfacinedose,p. 231.oStudy
▶Aprepitantis predicted to increase the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oTheoretical
▶Bosentanis predicted to decrease the concentration of
guanfacine. Adjust dose.oTheoretical
▶Calcium channel blockers(diltiazem, verapamil)are predicted to
increase the concentration ofguanfacine. Adjustguanfacine
dose,p. 231.oTheoretical→Also seeTABLE 8p. 848
▶Chloramphenicolis predicted to increase the exposure to
guanfacine. Adjustguanfacinedose,p. 231.oTheoretical
▶Cobicistatis predicted to increase the exposure toguanfacine.
Adjustguanfacinedose,p. 231.oStudy
▶Crizotinibis predicted to increase the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oTheoretical
▶Efavirenzis predicted to decrease the concentration of
guanfacine. Adjust dose.oTheoretical
▶Enzalutamideis predicted to decrease the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oStudy
▶Fosaprepitantis predicted to increase the concentration of
guanfacine.oTheoretical
▶Grapefruit juiceis predicted to increase the exposure to
guanfacine. Avoid.oTheoretical
▶HIV-protease inhibitorsare predicted to increase the exposure
toguanfacine. Adjustguanfacinedose,p. 231.oStudy
▶Idelalisibis predicted to increase the exposure toguanfacine.
Adjustguanfacinedose,p. 231.oStudy
▶Imatinibis predicted to increase the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oTheoretical
▶Macrolides(clarithromycin)are predicted to increase the
exposure toguanfacine. Adjustguanfacinedose,p. 231.
oStudy
▶Macrolides(erythromycin)are predicted to increase the
concentration ofguanfacine. Adjustguanfacinedose,p. 231.
oTheoretical
▶Mitotaneis predicted to decrease the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oStudy
▶Netupitantis predicted to increase the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oTheoretical
▶Nevirapineis predicted to decrease the concentration of
guanfacine. Adjust dose.oTheoretical
▶Nilotinibis predicted to increase the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oTheoretical
▶Rifampicinis predicted to decrease the concentration of
guanfacine. Adjustguanfacinedose,p. 231.oStudy
▶St John’sWortis predicted to decrease the concentration of
guanfacine. Adjust dose.oTheoretical
Guselkumab→see monoclonal antibodies
H 2 receptor antagonists
cimetidine.famotidine.nizatidine.ranitidine..
▶Cimetidinedecreases the clearance ofalbendazole.o
Study
▶Cimetidineincreases the concentration ofaminophylline.
Adjust dose.rStudy
▶Cimetidineslightly increases the exposure toanthracyclines
(epirubicin). Avoid.oStudy
▶Cimetidineincreases the exposure toantiarrhythmics
(amiodarone).oStudy
▶Cimetidineslightly increases the exposure toantiarrhythmics
(flecainide). Monitor and adjust dose.nStudy
▶Cimetidineincreases the exposure toantiarrhythmics
(lidocaine). Monitor and adjust dose.oStudy
▶Cimetidineis predicted to increase the exposure to
antiarrhythmics(propafenone). Monitor and adjust dose.
oTheoretical
▶Cimetidinetransiently increases the concentration of
antiepileptics(carbamazepine). Monitor concentration and
adjust dose.oStudy
▶Cimetidineincreases the concentration ofantiepileptics
(fosphenytoin, phenytoin). Monitor concentration and adjust
dose.rStudy
▶H 2 receptor antagonistsare predicted to decrease the
absorption ofantifungals, azoles(itraconazole). Administer
itraconazolecapsules with an acidic beverage.oStudy
▶H 2 receptor antagonistsare predicted to decrease the
absorption ofantifungals, azoles(ketoconazole). Administer
ketoconazolewith an acidic beverage.oStudy
▶H 2 receptor antagonistsare predicted to decrease the exposure
toantifungals, azoles(posaconazole). Avoid use of posaconazole
oral suspension.oStudy
▶Cimetidinedecreases the clearance ofantimalarials
(chloroquine).oStudy
▶Cimetidineslightly increases the exposure toantimalarials
(quinine).oStudy
▶H 2 receptor antagonistsare predicted to decrease the
absorption ofbosutinib.oTheoretical
▶Cimetidineslightly increases the exposure tocalcium channel
blockers(diltiazem, nimodipine). Monitor and adjust dose.
oStudy
▶Cimetidine(high-dose) is predicted to increase the exposure to
calcium channel blockers(lercanidipine).oTheoretical
▶Cimetidinemoderately increases the exposure tocalcium
channel blockers(nifedipine). Monitor and adjust dose.r
Study
▶Cimetidineincreases the exposure tocalcium channel blockers
(verapamil).oStudy
▶Cimetidineis predicted to slightly increase the exposure to
capecitabine.rTheoretical
▶H 2 receptor antagonistsare predicted to decrease the
absorption ofceritinib.oTheoretical
▶Cimetidineincreases the concentration ofciclosporin.n
Study
▶Cimetidineincreases the anticoagulant effect ofcoumarins.
rStudy
▶H 2 receptor antagonistsare predicted to decrease the exposure
todasatinib. Avoid.oStudy
▶H 2 receptor antagonistsare predicted to decrease the
absorption ofdipyridamole(immediate release tablets).
oTheoretical
▶Cimetidineslightly increases the exposure todopamine receptor
agonists(pramipexole). Adjust dose.oStudyBNFC 2018 – 2019 Guanethidine—H 2 receptor antagonists 927
Interactions|Appendix 1A1