Getting a 6 month old to take antibiotics...?

[ElphabaTheGreen]

6mo DS has a chest infection, giving him this horrific phlegmy cough which is going NOWHERE since I cannot stop him from spitting the antibiotics out! I think he's had a full dose maybe three times in the five days he's been taking them. The rest of the doses have been mostly or entirely spat out. He won't take it off a spoon so I'm using a syringe.

Any tips as to how to get the stuff down him??

You could try giving it to him in a spoon of jam or getting his teddy to do the honours. But if he still doesn't take it I think you just have to be firm.
Wrap him in a towel so he cannot move his arms, put the syringe right to the back of his mouth at the corner and squirt in one go. Then rub under his chin so he swallows.

Syringe into her cheek, slowly.

If he has a dummy then you can sneak the syringe down the side of the dummy.

No dummy, unfortunately.

The jam or the wrapping in the towel sound like potential options. Can the syringing into the cheek or into the corner of the mouth be done with jaws clamped shut?

Have you tried asking the GP for a different type of antibiotic? Our DD (10 months) had an infection and the GP prescribed flucloxacillin. DD would dribble it back out of her mouth and down her chin given the chance. When the infection hadn't cleared and we'd run out of antibiotic, we ended up in paedatric A&E and they were really surprised that the GP had prescribed flucloxacillin as it's an unpleasant tasting antibiotic. A&E then prescribed Coamoxiclav, which DD quite happily hoovered up. And the infection then cleared :)