Sinepin (doxepin)

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

Dry mouth

Drowsiness

Blurred vision

Constipation

Nausea

Difficulty in passing urine

Drop in blood pressure when going from lying or sitting to sitting or standing, causing dizziness and lightheadedness (postural hypotension)

Sweating

Involuntary muscle movements such as tremors or twitching

Rashes

Confusion or delirium

Headache

Sexual problems

Increased appetite and weight gain

Taste disturbances

Low blood pressure (hypotension)

Disturbances in the normal numbers of blood cells in the blood

Abnormal heart beats

Faster than normal heart beat (tachycardia)

Convulsions (fits)

The side effects listed above may not include all of the side effects reported by the drug's manufacturer. For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

Doxepin should not be taken in combination with a monoamine oxidase inhibitor antidepressant (MAOI), eg phenelzine, tranylcypromine, isocarboxazid, or moclobemide. Treatment with doxepin should not be started until at least two weeks after stopping an MAOI. Conversely, an MAOI should not be started until two weeks after stopping doxepin. Moclobemide should not be started until at least a week after stopping doxepin.

If doxepin is taken with other medicines that enhance serotonin activity in the brain, there may be an increased risk of side effects such as agitation, tremor, shivering, increased heart rate and diarrhoea, known collectively as the 'serotonin syndrome'. Other medicines that increase serotonin activity include the following:

lithium

rasagiline

selegiline

sibutramine

SSRI antidepressants, eg fluoxetine, paroxetine

SNRI antidepressants, eg duloxetine, venlafaxine

other tricyclic antidepressants.

There may be an increased risk of drowsiness if doxepin is taken in combination with other medicines that can cause drowsiness, such as the following:

benzodiazepines, eg diazepam, temazepam

sedating antihistamines, eg chlorphenamine, promethazine

sleeping tablets, eg zopiclone

strong opioid painkillers, such as morphine, codeine.

There may be an increased risk of side effects such as dry mouth, constipation, difficulty passing urine and blurred vision if doxepin is taken with other medicines that have anticholinergic effects, such as the following:

anticholinergics for urinary incontinence, eg tolterodine, oxybutynin

anticholinergics for Parkinson's disease, eg procyclidine, trihexyphenidyl

antihistamines, eg promethazine, chlorphenamine

antispasmodics, eg hyoscine, atropine

antipsychotics, eg chlorpromazine, clozapine (some antipsychotics may also increase the blood level of doxepin)

antiarrhythmics, eg disopyramide, propafenone

certain other antidepressants

muscle relaxants, eg baclofen

antisickness medicines, eg meclozine, cyclizine.

There may be an increased risk of side effects on the heart if doxepin is taken in combination with the following medicines; these medicines should be avoided in people taking doxepin:

atomoxetine

certain medicines to treat abnormal heart rhythms (antiarrhythmics), eg amiodarone, procainamide, quinidine, disopyramide, sotalol

the antihistamines astemizole, terfenadine or mizolastine

the antimalarials halofantrine, chloroquine or quinine

certain antipsychotics, eg thioridazine, haloperidol, pimozide

moxifloxacin

pentamidine.

Doxepin may alter the anti-blood-clotting effect of anticoagulant medicines such as warfarin. Your blood clotting time (INR) should be carefully monitored if you are taking these two medicines together.

Doxepin may antagonise the blood pressure lowering effect of clonidine and guanethidine.

There may be a sudden and marked increase in blood pressure and heart rate if adrenaline, noradrenaline or phenylephrine are given by injection to people taking doxepin. These medicines should be avoided in people taking doxepin.

The following medicines may increase the blood level of doxepin and could increase the risk of its side effects:

calcium channel blockers such as diltiazem or verapamil

cimetidine

methylphenidate

oestrogen-containing contraceptives (these may also decrease the antidepressant effect of doxepin)

ritonavir

SSRI antidepressants such as fluvoxamine and fluoxetine.

The level of doxepin in the blood may be decreased by the following medicines, and these could make it less effective:

barbiturates such as phenobarbital

rifampicin.

If you experience a dry mouth as a side effect of this medicine you may find that medicines that are designed to dissolve and be absorbed from under the tongue, eg sublingual glyceryl trinitrate (GTN) tablets for angina, become less effective. This is because the tablets do not dissolve properly in a dry mouth. To resolve this, drink a mouthful of water before taking sublingual tablets.

Other medicines containing the same active ingredient

There are currently no other antidepressants available in the UK that contain doxepin as the active ingredient.

Doxepin used to be marketed by Pfizer under the brand name Sinequan, but this has now been discontinued.

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