A pharmaceutical composition comprising: (a) a semi-solid delivery vehicle comprising (i) a polyorthoester of formula where R* is a C 1-4 alkyl; n is an integer of at least 5; A is R 1, R 3 or R 4, where R 1 is: p is an integer of 1 to 20; R 5 is hydrogen or methyl; R 6 is s is an integer of 0 to 10; t is an integer of 2 to 30; R 7 is hydrogen or methyl; R 3 is x is an integer of 0 to 10 y is an integer of 2 to 30; R 8 is hydrogen or methyl; R 4 is the residue of a diol containing at least one functional group independently selected from amide, imide, urea, and urethane groups; in which at least 0.01 mol percent of the A units are of the formula R 1; and (ii) a pharmaceutically acceptable, polyorthoester-compatible liquid excipient selected from polyethylene glycol ether derivatives having a molecular weight between 200 and 4000; polyethylene glycol copolymers having a molecular weight between 400 and 4000, mono-, di-, or tri-glycerides of a C 2 -C 19 aliphatic carboxylic acid or a mixture of such acids, alkoxylated tetrahydrofurfuryl alcohols and their C 1 -C 4 alkyl ethers and C 2-19 aliphatic carboxylic acid esters, and biocompatible oils, and (b) granisetron. (a) a semi-solid delivery vehicle comprising (i) a polyorthoester of formula where R* is a C 1-4 alkyl; n is an integer of at least 5; A is R 1, R 3 or R 4, where R 1 is: p is an integer of 1 to 20; R 5 is hydrogen or methyl; R 6 is s is an integer of 0 to 10; t is an integer of 2 to 30; R 7 is hydrogen or methyl; R 3 is x is an integer of 0 to 10 y is an integer of 2 to 30; R 8 is hydrogen or methyl; R 4 is the residue of a diol containing at least one functional group independently selected from amide, imide, urea, and urethane groups; in which at least 0.01 mol percent of the A units are of the formula R 1; and (ii) a pharmaceutically acceptable, polyorthoester-compatible liquid excipient selected from polyethylene glycol ether derivatives having a molecular weight between 200 and 4000; polyethylene glycol copolymers having a molecular weight between 400 and 4000, mono-, di-, or tri-glycerides of a C 2 -C 19 aliphatic carboxylic acid or a mixture of such acids, alkoxylated tetrahydrofurfuryl alcohols and their C 1 -C 4 alkyl ethers and C 2-19 aliphatic carboxylic acid esters, and biocompatible oils, and (i) a polyorthoester of formula where R* is a C 1-4 alkyl; n is an integer of at least 5; A is R 1, R 3 or R 4, where R 1 is: p is an integer of 1 to 20; R 5 is hydrogen or methyl; R 6 is s is an integer of 0 to 10; t is an integer of 2 to 30; R 7 is hydrogen or methyl; R 3 is x is an integer of 0 to 10 y is an integer of 2 to 30; R 8 is hydrogen or methyl; R 4 is the residue of a diol containing at least one functional group independently selected from amide, imide, urea, and urethane groups; in which at least 0.01 mol percent of the A units are of the formula R 1; and R* is a C 1-4 alkyl; n is an integer of at least 5; A is R 1, R 3 or R 4, where R 1 is: p is an integer of 1 to 20; R 5 is hydrogen or methyl; R 6 is s is an integer of 0 to 10; t is an integer of 2 to 30; R 7 is hydrogen or methyl; R 3 is x is an integer of 0 to 10 y is an integer of 2 to 30; R 8 is hydrogen or methyl; R 4 is the residue of a diol containing at least one functional group independently selected from amide, imide, urea, and urethane groups; (ii) a pharmaceutically acceptable, polyorthoester-compatible liquid excipient selected from polyethylene glycol ether derivatives having a molecular weight between 200 and 4000; polyethylene glycol copolymers having a molecular weight between 400 and 4000, mono-, di-, or tri-glycerides of a C 2 -C 19 aliphatic carboxylic acid or a mixture of such acids, alkoxylated tetrahydrofurfuryl alcohols and their C 1 -C 4 alkyl ethers and C 2-19 aliphatic carboxylic acid esters, and biocompatible oils, and (b) granisetron.