Theatre: Sylvia Apollo, London

Dogs have to carry an enormous symbolic burden - we live in a dog-eat-dog world, we hound people or bitch at them, we suffer from the black dog, we let the tail wag the dog, we look like a dog's breakfast and so on. No wonder they get dog-tired.

Sylvia, the heroine of AR Gurney's somewhat dog-eared comedy, is a dog with a particularly heavy load to bear. When she first introduces herself to Greg (Robin Ellis), literally jumping into his lap in Central Park, he's happy to welcome her as an heir to the "man's best friend" tradition, and she responds in kind - sitting at his feet in her jeans and spiky bleached crop, she gazes at him with a soupy expression and tells him: "I love you. I think you're God."

Soon, though, Greg is investing Sylvia with all kinds of significance - she becomes the focus of his mid-life crisis, connecting him with an earthy, physical reality that he's lost sight of, cocooned in his highly paid job. But as a philosophical fellow dog-owner warns him, dogs can ruin relationships - "Give a dog a woman's name, you might start to think of her as a woman." In his rhapsodies over Sylvia and her sensational "butt", and the paroxysms of jealousy he suffers when she goes on heat, Greg seems to be trespassing on JR Ackerley dog-fancying territory. Not surprisingly, Greg's wife Kate (Maria Aitken) loathes Sylvia, and not simply because she feels displaced sexually. She has a new career teaching Shakespeare to under-privileged children; and Sylvia is a living contradiction of her idealism.

The chief charm of Michael Blakemore's production is Zoe Wanamaker's perky interpretation of dog behaviour in human terms - skipping round the stage shouting "Hey hey hey" at moments of heightened excitement, snarling obscenities at cats, snuffling at lamp-posts - though you never feel that she's being stretched here. There are other incidental pleasures, mostly from Neil McCaul in three supporting roles.

The trouble is, all the pleasures are incidental. Gurney doesn't really know what he's saying: on the one hand, he wants to tell us that a dog is a dog is a dog, pure and simple; on the other, he wants Sylvia to be a way of teaching Kate and Greg about themselves. The tension between these two viewpoints is never resolved, with the result that the style veers wildly and too many of the jokes are annoyingly opportunistic. There's also a streak of treacly sentimentality - Greg and Sylvia's duet on "Every Time We Say Good-Bye" is one of the less stomach-settling experiences you can have in the West End, and the ending degenerates into pure schmaltz. Sylvia, you realise, is a sadly toothless dog.

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