Phenylpropanolamine Indinavir

SYMPATHOMIMETICS ANTIVIRALS-PROTEASE INHIBITORS 1. Risk of serotonin syndrome when dexamfetamine is administered with ritonavir 2. Indinavir may t phenylpropanolamine levels 1. Protease inhibitors inhibit CYP2D6-mediated metabolism 2. Likely inhibition of phenylpropanolamine metabolism 1. Avoid co-administration 2. Monitor BP closely watch for marked t BP... 

In one case the use of phenylpropanolamine with triple drug therapy for HIV prophylaxis led to a hypertensive crisis (44). As the patient had previously tolerated phenylpropanolamine well, one must suspect that one or more of the anti-HIV drugs (probably indinavir) had interfered with the metabolic breakdown of the phenylpropanolamine. 

It seems very likely that the protease inhibitor indinavir inhibited the metabolism of phenylpropanolamine by cytochrome P450 (predominantly CYP3A4), increasing circulating concentrations, and causing systemic and cerebral vasoconstriction. 

A report describes a hypertensive crisis when a patient taking indinavir was also given phenylpropanolamine. 

The patient had been taking phenylpropanolamine intermittently for several years without any adverse reaction and it was thought that the recent addition of the anti-HTV regimen potentiated the effect of the phenylpropanolamine. It seems likely that the indinavir was responsible for the interaction as it is a potent enzyme inhibitor. This is an isolated report and... 

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