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Pharmacology

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Antimicrobial Part-2

Question
64 out of 75
 

Which of the following is not a CYP inhibitor:



A Saquinavir
B Ritonavir

C Erythromycin
D Itraconazole

Ans. A Saquinavir (Ref. BG Katzung, Basic & Clinical Pharmacology,11th edition, pp-839-40, 2010)

1. Saquinavir

a. Of all the known inhibitors of protease in HIV, saquinavir is least potent inhibitor of CYP enzymes

b. Therefore, its potential of causing drug interactions is limiteD. It is extremely sensitive to inhibition by ritonavir.

c. Therefore, both of them are used together. Ritonavir will inhibit metabolism of the drug and this will boost the levels of saquinavir.

2. Ritonavir

a. Ritonavir is known to be one of the most potent inhibitors of CYP 3A4 enzymes; the most common enzyme system metabolizing the drugs

b. The drug should therefore be avoided with substrates of CYP 3A4; specially the ones with narrow therapeutic index.

3. Erythromycin

a. Both erythromycin and clarithromycin inhibit CYP 3A4 and therefore are involved in many clinically significant drug interactions.

b. Erythromycin inhibits metabolism of CECT (C=carbamazepine, coriticosteroids, e=ergot alkaloids, c=cyclosporine, t=theophylline).

4. Itraconazole

i. Itraconazole is metabolized in liver and is a substrate and potent inhibitor of CYP enzyme

ii. Itraconzole is the drug of choice for histoplasmosis, blastomycosis and Sporothrix.

iii. Many of the drug interactions with itraconazole can be of serious nature and can involve torsa de depointes when the drug is given with quinidine or cisapride.

iv. Although, the drug is less potent than ketoconazole in terms of its ability to inhibit liver enzymes.

v. Absorption of itraconazole is reduced when the drug is taken with rifamycins (e.g. rifampin, rifapubitin, rifapentine).

vi. The drug is not very effective against aspergillomA. Drug of choice for aspergilloma is voriconazole

Like ketoconazole, the absorption of the drug could be reduced by antacids or H2 blockers as absorption is dependent upon pH.

Antimicrobial Part-2 Flashcard List

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