LHPG Comment: Note the difference between the European SPC (no dose adjustments) and the US Prescribing Information (caution). The charts reflect the more cautious option.

No dose adjustment is necessary with antacids, proton-pump inhibitors or histamine H2 receptor antagonists. Coadministration of ranitidine (300 mg single dose) and fosamprenavir (1400 mg single dose) decreased amprenavir Cmax and AUC by 51% and 30%, but had no effect on Cmin.
Telzir Summary of Product Characteristics, ViiV Healthcare UK Ltd, January 2021.

Use with caution. Fosamprenavir may be less effective due to decreased amprenavir plasma concentrations. Coadministration of a single dose of ranitidine (300 mg) administered 1 hour before a single dose of fosamprenavir (1400 mg) to 30 subjects decreased amprenavir Cmax and AUC by 51% and 30%, but had no effect on amprenavir Cmin. The interaction with fosamprenavir/ritonavir has not been evaluated.
Lexiva Prescribing Information, ViiV Healthcare, October 2020.

In a single dose study in healthy volunteers, when fosamprenavir (1400 mg) was administered 1 h after ranitidine (300 mg), amprenavir AUC and Cmin were decreased by 30% and 51% respectively; there was no siginificant effect on amprenavir Cmin. Caution is recommended when fosamprenavir is coadministered with H2 receptor antagonists or proton pump inhibitors.
Effect of antacids and ranitidine on the single-dose pharmacokinetics of fosamprenavir. Ford SL, Wire MB, Lou Y, Baker KL, Stein DS. Antimicrob Agents Chemother, 2005, 49: 467-469.