A type 1 diabetic can take Metformin but not just Metformin. Metformin controls the release of glucose from the liver and therefore helps with basal fasting levels but a type 1 diabetic cannot produce their own insulin at all and must take insulin. At the very least, they should take basal insulin once or twice a day. Some type 1 diabetics may be prescribed a mix like Novolin 70/30 twice a day before breakfast and dinner and advised to be low carb for lunch but a type 1 diabetic should really be on a basal/bolus treatment with long lasting or intermediate insulin for basal levels ( half of their total daily dose ) and the remainder for their meal time doses calculated by counting the carbs in the meal, dividing that by their prescribed carb to insulin ration ( often 10-12 grams of carbs to 1 u of insulin ) and adding a correction dose based on a pre-meal glucose test of about 1u for every 3 mmol/L ( 50 mg/dl ) of correction to their target level which at a hospital would be 6.1 mmol/L ( 110 mg/dl ) but outside a hospital would usually be between 6.7-10.0 mmol/L ( 120-180 mg/dl ) depending on how prone to hypoglycemia they are. Basal only or mix only treatment are only common if the diabetic does not perform the carbohydrate counting properly or is sufficiently well controlled without it, often these will be patients adamant about a low carb high potein diet as the end all to their health problems and refuse to listen to reason about a balanced diet despite the ketoacidosis involved in a low carb diet.
When the levels are above 10.0 mmol/L ( 180 mg/dl ), he will be urinating a lot because his kidneys will start removing glucose when it's between 8.9-10.0 mmol/L ( 160-180 mg/dl ) and he will be thirsty. When it reaches 13.3 mmol/L ( 240 mg/dl ), you need to start testing for ketones, the high glucose levels above 8.6 mmol/L ( 154 mg/dl ) cause long term problems but it's the lack of insulin causing cells to use fats and proteins for energy thereby producing ketones that present the short term problems of abdominal pain, unconsciousness, coma and death. If ketone levels are detected twice in tests every four hours while the glucose remains high, you must call your Doctor or a medical professional, if they are moderate to high, you should go to ER but don't drive yourself.
You must not exercise if there are ketones.
A type 1 on a full basal/bolus treatment will have type R ( Novolog, Humalin R etc. ) insulin for their bolus shots ( meal time ) and can apply a correction dose of 1u for every 3 mmol/L ( 50 mg/dl ) of correction to their target ( best to aim a little high like 10.0 mmol/L, 180 mg/dl ) so if your husband hasn't recently taken insulin in the last two hours, he can apply a correction dose of about 1.5 u based on the 258 mg/dl reading and if it hasn't gone down to acceptable levels in two hours, another correction dose may be applied. He should not do this alone as there will be no one to call for help if he passes out from too much insulin. First thing to do is test for ketones, and test the glucose again in 15 minutes, if it's still high and or going up, apply a correction dose if type R is available, call for help if there are two positive ketone readings four hours apart or if they are moderate to high.
There are two glucose meters that also test for ketones but the test strips are expensive. You can buy urine test strips for $10 for a vial of 50 strips but as you should rarely be using them it's better to order the foil wrapped packages at the pharmacy, the foil wrapped packages have to be special ordered and cost more but since you should be throwing most out as they expired, they're a better deal. Use a disposable cup for the urine as the container must be clean.
Hot cider does very little to help with glucose despite what the homeopaths would say, Stevia herbal supplements are supposed to benefit the restoration of beta cells ( which of course will be then destroyed by a type 1's immune system ) and there are rumours that cinnamon and chromium helps but you cannot rely on homeopathic treatments no matter what someone might say.