Provided is a pharmaceutical composition comprising a solution comprised of synthetic peptide in a final concentration of not less than 70 mg/ml in admixture with a polyol; wherein the synthetic peptide is an HIV fusion inhibitor, and wherein the polyol is in a final concentration of no less than 5 weight % and no more than 75 weight % of the pharmaceutical composition. Also provided is a synthetic peptide-containing pharmaceutical composition as a unit dose comprising an aqueous formulation comprised of synthetic peptide in a final concentration of not less than 70 mg/ml in admixture with a polyol; wherein the synthetic peptide is an HIV fusion inhibitor, and wherein the polyol is in a final concentration of no less than 5 weight % and no more than 75 weight % of the pharmaceutical composition. Further provided is a method of treating HIV infection by administering to an HIV-infected individual a pharmaceutical composition according to the present invention.